Physics and Applications of High Brightness Beams

19 Jun 2023, 09:00 → 23 Jun 2023, 13:00 Europe/Madrid

James Rosenzweig, Massimo Ferrario (INFN-LNF)

The ICFA-supported workshop series on the Physics and Applications of High Brightness Beams is traditionally a meeting ground for discussion of high brightness beam production, manipulation, and acceleration in state-of-the-art systems ranging from cutting-edge RF accelerators, to very high-field plasma-based schemes. The resultant beams provide the underpinnings of new scientific instruments such as X-ray free-electron lasers (XFELs) and TeV-class linear colliders. The workshops also provide an essential opportunity to guide the full ecosystem of beam physicists along with the advanced user communities who utilize the newly emergent instruments arising from high brightness beam research. In the upcoming version of this workshop series, we will concentrate on a particularly compelling example of the burgeoning field of new instruments based on advanced, high-field accelerators and high brightness beams. This is the 5th generation light source, which seeks to merge two compelling new instruments – next-step, compact XFELs, and advanced, high-field accelerators. This merger has produced a hybrid field, which has by now many promising incarnations. The present workshop will concentrate on the physics of such systems, which are now proceeding towards realization using approaches ranging from cryogenic RF to wakefields in plasmas and structures. These initiatives are strongly motivated by synergistic application to the energy frontier, as 5th generation light sources may also be fruitfully seen as stepping stone projects which demonstrate beam physics feasibility issues needed to proceed to future linear colliders based on advanced concepts.

Such ambitions require a continuous re-examination of progress in the fields of high brightness beam physics, advanced acceleration, and their nexus in applications. This is precisely the mission accepted at this workshop, and we look forward to seeing you in this year’s meeting, taking place at the Kursaal venue in San Sebastian, Spain, June 19-23, 2023. This edition of the workshop will emphasize two emerging trends: first, the vital involvement in the development of the field through student and post-doctoral training through a dedicated half-day session sponsored by the NSF STC Center for Bright Beams); and the key involvement in the future user communities of 5th generation light sources.

We hope you will participate in this meeting, joining us for what is always a very stimulating and timely workshop.

Please refer to the main conference website https://conferences.pa.ucla.edu/PAHBB23/ for up-to-date information on the workshop. This Indico site will be mainly used to manage the scientific program. 

Monday, 19 June

09:30 → 11:00 5th generation light source

09:30 PAHBB

Speaker: Massimo Ferrario (INFN-LNF)

PAHBB 2023_2.pdf

PAHBB 2023_2.pptx

09:55 UCXFEL

Speaker: James Rosenzweig

10:20 Measuring the dynamics of quantum materials over different length scales with X-ray free electron lasers

Quantum materials exhibit complex interactions between electron, structural and spin degrees-of-freedom over a wide range of length scales, leading to exotic phenomenon that are challenging to study. Ultrafast excitation can disentangle these degrees-of-freedom, but resolving the different length scales remains challenging. Here I will present recent results using X-ray free electron lasers to resolve femtosecond electronic and structural dynamics in the quantum material vanadium dioxide from the picometer to micrometer length-scale. Hard X-ray total diffraction is used to study incoherent small polaron distortions which have been found to allow efficient seeding of light-induced phase transitions, while soft X-ray coherent imaging is used to measure nanoscale phase co-existence during the light-induced phase transition itself, shedding light on the nature of proposed out-of-equilibrium phases at the nanoscale [1].

[1] A.S. Johnson et al., Nature Physics 19 (2), 215-220 (2023)

Speaker: Allan Johnson (IMDEA Nanoscience)

Presentation_ASJ.pptx

11:00 → 11:30 Coffee break

11:30 → 13:00 5th generation light source

11:30 X-ray Regenerative Amplifier Free-Electron Laser

Despite tremendous progress in X-ray free-electron laser (XFEL) science over the last decade, future applications still demand fully coherent, stable X-rays that have not been demonstrated in existing X-ray FEL facilities. In this talk, we review the progress toward an X-ray regenerative amplifier FEL (XRAFEL) to produce both high-peak and high-average power FEL pulses with full temporal coherence. We discuss electron beam and cavity optics requirements, as well as various mechanisms to outcouple maximum amount of radiation power. Finally, we illustrate how an XRAFEL can be applied to a high-repetition rate XFEL and an ultra-compact XFEL to significantly increase the X-ray brightness or the spectral photon flux.

Speakers: Zhirong Huang (SLAC) , River Robles (Stanford University)

XRAFEL.pptx

11:55 Seeding at SwissFEL

SwissFEL at the Paul Scherrer Institute is a free-electron laser facility providing hard and soft X-rays, based on the SASE principle. In addition, the soft X-ray beamline Athos is currently extended for electron beam manipulation with external lasers, aiming to provide seeding capabilities based on the two-stage echo-enabled
harmonic generation (EEHG) scheme. Completion of the installation is foreseen in spring 2023. We present the initial results on the single-stage operation for ESASE and mode-locked lasing and give an outlook on the expected performance for seeding down to 1 nm.

Speaker: Dr Sven Reiche (Paul Scherrer Institut)

12:20 High brilliance Free-Electron Laser Oscillator operating at multi-MegaHertz repetition rate in the short-TeraHertz emission range

We present the design study of an innovative scheme to generate high repetition rate
(multi-MHz-class) THz and X synchronized radiation pulses
by using an Energy Recovered Super Conducting Linac operating in Continuous Wave
mode driving a Free-Electron Laser Oscillator.
The FEL and X rays performances are illustrated for one and two color operation.
Start-to-end simulations are presented to assess the capability of this scheme for
typical values of wavelengths of interest
in the 10-50 um (6-30 THz) and 3-0.05 A.

Speaker: Dr Andrea Renato Rossi (INFN-MIlano)

13:00 → 15:00 Lunch

15:00 → 16:30 FEL and coherent radiation

15:00 EUPRAXIA

Speaker: Massimo Ferrario

15:25 Terawatt-Scale Attosecond X-ray Pulses from a Free Electron Laser Cascade

High intensity, sub-femtosecond XFEL pulses are key to taking full advantage of nonlinear x-ray spectroscopies and advanced imaging methods. The X-ray Laser-Enhanced Attosecond Pulses (XLEAP) collaboration is an ongoing project for the development of attosecond x-ray modes at the Linac Coherent Light Source (LCLS). Here we report development of a high power attosecond mode via cascaded amplification in two undulator stages. In the first stage, a sub-femtosecond x-ray pulse is produced by enhanced self-amplified spontaneous emission (ESASE) by a femtosecond, high-current spike within the electron beam. A magnetic chicane delays the electron beam, allowing the x-ray pulse to slip onto a fresh slice of the bunch in the second undulator stage, where it undergoes further amplification. We experimentally demonstrate generation of sub-femtosecond duration soft x-ray free electron laser pulses with hundreds of microjoules of energy, and use angular streaking to characterize the pulse durations.
This work was supported by US Department of Energy Contracts No. DE-AC02-76SF00515

Speaker: Paris Franz (Stanford University)

PAHBB_2023_Franz.pptx

15:50 Radiation detection and coherent harmonic generation for the PAX Experiment at FACET-II

The ongoing Plasma-driven Attosecond X-ray source experiment (PAX) at FACET-II aims to produce coherent soft X-ray pulses of attosecond duration using a Plasma Wakefield Accelerator [1]. These kinds of X-ray pulses can be used to study chemical processes where attosecond-scale electron motion is important. For this first stage of the experiment, PAX plans to demonstrate that <100 nm bunch length electron beams can be generated using the 10 GeV beam accelerated in the FACET-II linac and using the plasma cell to give it a percent-per-micron chirp. The strongly chirped beam is then compressed in a weak chicane to sub-100nm length, producing CSR in the final chicane magnet at wavelengths as low as 10s of nm. In this contribution we describe the results expected from this initial setup, as well as future iterations of the experiment in which we plan to use short undulators to drive coherent harmonic generation to produce attosecond, gigawatt X-ray pulses down to 1-2 nm.

[1] C. Emma, X.Xu et al APL Photonics 6, 076107 (2021)

Speaker: Rafi Hessami (SLAC National Accelerator Laboratory)

Rafi_Hessami_PAHBB_2023_Presentation.pptx

16:30 → 17:00 Coffee break

17:00 → 18:30 FEL and coherent radiation

17:05 Ponderomotive Microbunching for a Superradiant Thomson Source

Compact sources offering high-brightness radiation in the extreme ultraviolet to X-ray regime are highly desired. Thomson scattering, in which an electron beam colliding with a laser pulse produces radiation, is a source of X-rays of increasing prevalence in modern labs, complementing large scale facilities like synchrotrons and X-ray free electron lasers. By imposing a density modulation on the electron beam the brilliance of a Thomson source can be enhanced by orders of magnitude via superradiant emission. However, microbunching at the electron beam energy relevant to Thomson sources is a challenge that has yet to be met. Here, we
show under which conditions sufficient density modulation is attained by the ponderomotive force from the copropagating beat wave formed by two laser pulses at different frequencies. In addition, we propose a coherent soft X-ray Thomson source based on ponderomotive bunching.

Speaker: Brian Schaap (University of Technology Eindhoven)

17:30 First Light at the Israeli THz Superradiant Free Electron Laser

We report first observation of terahertz super radiant emission from the Israeli Free Electron Laser. This is first demonstration of a THz FEL source based on the scheme of coherent spontaneous superradiant (SR) emission by an ultra-short e-beam bunch. The first measured radiation signal corresponds to a 3.5THz beam output of 180 nanoJ.
The Israeli superradiant FEL operates in the FEL center of Ariel and Tel-Aviv universities. It is based upon the ORGAD RF-LINAC at the Schlesinger Accelerator Center in Ariel. The accelerator is a compact RF gun of accelerating energies 3.5 to 8.5 MeV. The gun is 64 cm long. It produces an electron bunch of about 100 femto-seconds. Since the frequency of the emitted radiation is 3.5 Tera Hertz, the bunch duration is shorter than half a period of the radiation (290 ftSec), satisfying the condition for SR emission. In this case all electrons in the bunch emit in phase with each other, and the total emitted radiation energy is proportional to the square of the number of the electrons N2 and not to the number of electrons N as in conventional spontaneous emission. Based on a modal excitation theory we will estimates the short wavelength limits of SR.

Speaker: Avraham Gover (Tel Aviv University)

17:50 An open source platform for integrated design and control of compact radiation sources

The international collaboration towards a 5th-generation lightsource should adopt an open source platform to enable a) instantaneous collaboration between distributed design teams; b) code benchmarking, multiphysics and code chaining for end-to-end simulation; c) multi-level user support for all relevant codes, from GUI to supercomputer; d) applicability to all subsystems individually, including support for surrogate model development; and e) automatic integration with control systems for testing, commissioning and operation. Sirepo is a framework for cloud computing, which partially or fully satisfies many of these demanding requirements today and has been openly developed on GitHub since its inception in 2015. Sirepo.com is a free scientific gateway for the worldwide community. The recently deployed Sirepo-Omega app demonstrates the integration of OPAL, elegant and GENESIS for end-to-end FEL modeling. Sirepo-Bluesky is an open source integration that is actively used for X-ray beamline controls at NSLS-II. Additional support for accelerator controls is planned. Recent work on relevant subsystems will be discussed: laser-plasma channels; LLRF for C-band linacs; thermal effects in high-rep-rate Ti:Sapphire laser amplifiers; beam loading in high-current linacs; radiation transport and shielding; as well as surrogate models for photoinjectors.

Speaker: David Bruhwiler (RadiaSoft LLC)

Bruhwiler_et_al_PAHBB_20230619_v3.pdf

Tuesday, 20 June

09:30 → 11:00 High brightness electron sources

09:30 Advancements in Sub-GV/m X-Band Photocathode Gun at the Argonne Wakefield Accelerator Facility

The Argonne Wakefield Accelerator (AWA) supports an extensive research portfolio along three themes: electron beam production, electron beam manipulation, and electron beam-driven wakefield acceleration. Currently, AWA is developing a sub-GV/m X-band photocathode gun (Xgun) driven by ultra-short radiofrequency (rf) pulses. With a demonstrated gradient of 400 MV/m on the photocathode surface, the Xgun exhibits low dark current and breakdown rates. The Xgun is powered by high-power rf (300 MW) and short rf pulses (9-ns FWHM) from AWA's power and transfer structure based on two-beam acceleration (TBA). This development has several significant applications. In the short term, the Xgun will be employed to investigate photocathode emission physics in ultra-high-field environments (see E. Frame's presentation). In the medium term, it will be utilized as an injector for compact X-ray free electron lasers (X-FELs). Lastly, in the long term, it will serve as AWA's 500 MeV TBA demonstrator. This talk will highlight the recent progress and outline our research and development roadmap for the coming years.

Speaker: John Power

John-Power_PAHBB_Xgun.pdf

09:55 A Versatile High Brightness Travelling-Wave Radio-Frequency Photogun

S-band Standing-wave RF Photoguns represent the current state of the art for high brightness electron sources. These devices significantly contributed to the development of high brightness accelerators. However, the push for even brighter electron sources presents a significant technological challenge. Aiming to continue to push the boundaries of high brightness electron beams, a travelling-wave (TW) C-band RF photogun is under development as part of the IFAST programme. This TW photogun offers the ability to significantly increase peak cathode fields up to 200 MV/m through the use of very short RF pulses and higher operational frequencies. These short pulses also open up the possibility of RF pulse repetition rates up to 1 kHz. Finally, the TW gun presents a path to higher frequency RF photoguns without the need for RF circulators which are notoriously complex to fabricate at high frequencies. This presentation will detail the RF and mechanical design of the TW RF Photogun along with its application to an FEL injector demonstrating its ability to increase the SwissFEL 5D brightness by a factor of 5.

Speaker: Thomas Geoffrey Lucas (Paul Scherrer Institut)

10:20 CsSb atomically smooth thin films as novel visible light photocathodes

The so-called “green photocathodes”, based on alkali antimonide compounds, are characterized by high efficiency at green light wavelengths (1-10% at 500-550 nm) and excellent charge lifetime, but are easily poisoned in poor vacuum and are usually grown in form of disordered polycrystalline layers. Surface disorder is an extrinsic factor significantly contributing to enhance the MTE at the photocathode. State-of-the art deposition techniques have been successfully employed to create smooth and ordered alkali antimonides; for example, epitaxial Cs3Sb photocathodes have been grown by electron diffraction monitored molecular beam epitaxy. By focusing on structure rather than efficiency, we discovered that atomically smooth films of CsSb can be reproducibly grown on selected substrates. While the quantum efficiency at 505 nm is significantly lower than the Cs3Sb counterpart, this material is still a visible light photocathode (with QE~0.5-1% at 405 nm) and appears to be more robust against contamination. We report a detailed characterization of this phase via x-ray and UV photoemission spectroscopy, angle resolved photoemission spectroscopy and scanning tunneling microscopy.

Speaker: Alice Galdi

PAHBB_Alice.pptx

11:00 → 11:30 Coffee Break

11:30 → 13:00 High brightness electron sources

11:30 High Efficiency FEL

Strongly tapered free-electron lasers (FELs) offer a promising avenue towards achieving higher peak and average power radiation sources. Through the strong seeding of an input laser or microbunched electron beam, larger efficiencies can be achieved by adapting the undulator parameters to maintain resonance with the decelerated electrons. Additionally, the use of an oscillator cavity driven by a high repetition rate electron beam could enable power amplification from a weaker seed. In this context, we discuss ongoing research efforts and recent progress in developing high efficiency FELs, as well as the tools used to study these systems.

Speaker: Andrew Fisher (UCLA)

11:55 Status of high gradient C-band RF photoinjector project at LANL

This talk will report on the status Cathodes And Radio-frequency Interactions in Extremes (CARIE) high gradient C-band RF photoinjector project at Los Alamos. Modern applications such as X-ray sources require electron beams with ultra-low emittance and very high brightness that may be achieved by accelerating the electron beam produced in an RF photoinjector with electric field higher than 100 MV/m. At LANL we are putting together the high gradient photoinjector test stand capable of producing electric fields at the cathodes as high as 250 MV/m. The photoinjector will be powered by a 50 MW, 5.712 GHz Canon klystron. Adding capability to operate the photoinjector at cryogenic temperatures is considered. The construction of CARIE began in October of 2022. A concrete vault was renovated, capable to provide radiation protection for electron beams with beam power up to 20 kW. The klystron will be delivered in summer of 2023. All waveguide and vacuum components have been ordered. The all-copper photoinjector was designed and is currently in fabrication. The second version of the photoinjector will operate with replaceable high quantum-efficiency cathodes and produce an ultra-bright 250 pC electron beam accelerated to the energy of 8 MeV. The status of the facility, the designs of the photoinjector and the beamline, and plans for photocathode testing will be presented.

Speaker: Evgenya Simakov (LANL)

HighBrightnessSimakov.pptx

12:20 Effect of molybdenum coatings on the accelerating cavity quality factor: a numerical study

Methods for realizing resonant cavities with high field gradients have been studied in the last years. Cavities are often made of copper, which however has too low work function (WF) (thus eventually leading to dark currents) and tends to produce uncontrolled discharges (breakdowns) which might damage the copper surface, finally degrading the cavity performance. For this reason, the idea of lining the copper cavity with a layer of molybdenum/molybdenum oxides, characterized by a higher WF and greater resistance to stress than copper, has been being pursued for some years.
In this paper, we analyze the effect of the molybdenum coating on the cavity quality factor. To do this, an electromagnetic simulation is performed to evaluate the effect of a coating on the effective surface impedance of the cavity surfaces as a function of the thickness and resistivity of the coating. Since the quality factor is related to the impedance of the walls, the estimate of the impedance provides useful information on the possible variation of the cavity quality factor.

Speaker: Dr Pablo Vidal Garcia (Roma Tre University)

20230620_PhAHBB_MoO3_coating_cavity.pdf

12:40 Status of the high-brightness photoinjector accelerator R&D and applications

The Photo Injector Test facility at DESY in Zeuthen (PITZ) develops high brightness photocathode RF guns, advanced diagnostics and applications of the high brightness electron beams, which currently can be accelerated up to 22 MeV. In this talk, we will present the latest development at the L-band normal conducting photoinjector (e.g., new prototype RF gun Gun5.1, photocathode laser shaping and green cathode) and two applications: the worldwide first high-power THz SASE free-electron laser (FEL) and a new R&D platform (FLASHlab@PITZ) for FLASH radiation therapy and radiation biology.
The Gun5.1 was designed for the operation with an RF pulse length of 1 ms at a cathode gradient of 60 MV/m. It has been installed at PITZ since late 2021. The results from gun conditioning and its current performance will be discussed.
The THz SASE FEL aims at producing high power tunable narrow band THz pulses with an energy of hundreds of µJ per pulse. This can be realized by transporting and matching an electron beam with a bunch charge of 2 to 4 nC and a peak current up to 200 A into an undulator. Methods have been developed at PITZ for the beam envelop and trajectory optimization of the strongly space charge dominated electron beam. Results from the electron beam matching, THz lasing and seeding at 3 THz will be presented.
The R&D platform FLASHlab@PITZ for radiation therapy and radiation biology is being prepared at PITZ. PITZ can provide a uniquely wide parameter range for studying this newest modality of radiation treatment against cancer. A startup beamline has been installed, first successful experiments have been done and an upgrade plan for exploiting the full capability of PITZ has been developed. All these will be summarized in the talk.

Speaker: Xiangkun Li (DESY)

PAHBB 23 workshop_XKL.pptx

13:00 → 15:00 Lunch

15:00 → 16:30 CBB-sponsored student session

15:00 Spectrotemporal shaping of attosecond x-ray free-electron laser pulses

The development of attosecond methods at free-electron lasers has led to new possibilities in the probing and control of electronic dynamics in molecules. Beyond simple observation of ultrafast processes, one of the longstanding goals of atomic and molecular physics is control of the electronic wavefunction on attosecond timescales. This implies a need to go beyond impulsive excitation with isolated pulses: more general spectrotemporal pulse shaping is demanded. We present a method to shape the spectrotemporal characteristics of attosecond XFEL pulses in a two-stage scheme. First, an isolated attosecond pulse is generated using now-state of the art methods. That pulse then interacts with a fresh part of the electron beam in a second stage where control of the undulator taper leads to direct shaping of the output pulse. We highlight several example shaping options: pulse pairs with controllable time and color separation, isolated fs-scale pulses with controllable linear chirp, and trains of attosecond pulses with tunable spacing. We highlight one atomic physics application – to use pulse pairs to control and probe the decay of core-excited electronic wavepackets.

Speaker: River Robles (Stanford University)

MAXIMUS.pptx

15:20 Detailed Phase Space Reconstruction from a Limited Number of Beam Measurements Using Neural Networks and Differentiable Simulations

Characterizing the phase space distribution of particle beams is essential in the study of accelerator systems. As the accelerator community keeps pushing the brightness frontier, resolving fine details in the 6D beam phase space density has become important in the optimization and control of next-generation beamlines. However, conventional reconstruction-based techniques either use simplifying assumptions, reducing the level of detail, or require specialized diagnostics to infer high dimensional (>2D) beam properties. In this work, we introduce a general-purpose algorithm that combines neural networks with differentiable particle tracking to reconstruct high-dimensional phase space distributions without using specialized beam diagnostics or beam manipulations. We demonstrate that our algorithm reconstructs detailed 4D phase space distributions with corresponding confidence intervals in both simulation and experiment using a single focusing quadrupole and a limited number of measurements on a diagnostic screen. This technique allows for the simultaneous measurement of multiple correlated phase spaces, enabling simplified 6D phase space reconstruction diagnostics in the future.

Speaker: Juan Pablo Gonzalez-Aguilera (University of Chicago)

PAHBB 23.pdf

15:40 The Ion Channel Laser: Physics Advances and Experimental Plans

The ion channel laser (ICL) is an alternative to the free electron laser (FEL) that uses the electric fields in an ion channel rather than the magnetic fields in an undulator to transversely oscillate a relativistic electron beam and produce coherent radiation. The strong focusing force of the ion channel leads to a Pierce parameter more than an order of magnitude larger than the typical values associated with FELs. This allows the ICL to lase in an extremely short distance while using electron beams with an energy spread of up to a few percent. The ICL may thus be able to accommodate beams that can be produced by laser wakefield accelerators today. ICLs have several practical challenges, however, including stringent constraints on the beam’s transverse phase space and unique physics in the high K regime. We discuss recent advances in the physics of the ion channel laser as well as experimental plans at SLAC’s FACET-II facility and the potential for future plasma plasma based light sources.

The authors would like to acknowledge the OSIRIS Consortium, consisting of UCLA and IST (Lisbon, Portugal) for providing access to the OSIRIS 4.0 framework. Work supported by NSF ACI-1339893. Work supported by the National Science Foundation through grant NSF-2047083 and the US Department of Energy through grant DE-SC0017906.

Speaker: Claire Hansel (University of Colorado Boulder)

16:00 Transverse stability in an alternating gradient planar-symmetric dielectric wakefield structure

In this work we present the result of a Dielectric Wakefield Acceleration (DWA) design that uses a longitudinally varying alternating gradient configuration of a planar-symmetric DWA structure to exploit the inherent quadrupole-mode transverse wakes to achieve second-order stability. We have designed and fabricated a new apparatus for positioning the DWA components in our setup. This allows us to precisely and independently control the gap in both transverse dimensions and consequently the strength of the respective destabilizing fields. We present the effect of various structure configurations on the transverse beam distribution and compare those results to simulation. Our results show that the use of alternating gradient structures in DWA can significantly improve its performance, offering a promising path forward for high-gradient particle acceleration.

Speaker: Walter Lynn (UCLA)

HBBADWASlides.pptx

16:30 → 17:00 Coffee Break

17:00 → 19:00 Poster

Wednesday, 21 June

09:30 → 11:00 Ultrafast electron probes

09:30 Few-electron correlations after ultrafast photoemission from nanometric needle tips

Free electrons are central to such diverse applications as electron microscopes, accelerators, and photo-emission spectroscopy. However, space charge effects of many electrons are often problematic and, when confined to extremely small space-time dimensions, already two electrons can interact strongly. Here, we demonstrate that the resulting Coulomb repulsion can also be advantageous, as it leads to strong electron-electron correlations. We show that femtosecond laser-emitted electrons from nanometric needle tips are highly anti-correlated in energy because of dynamic Coulomb repulsion, with a visibility of 56%. We extract a mean energy splitting of 3.3 eV and a correlation decay time of 82 fs. The energy-filtered electrons display a sub-Poissonian number distribution with a second order correlation function as small as g(2) = 0.34, implying that shot noise-reduced pulsed electron beams can be realized based on simple energy filtering. We also reach the strong-field regime of laser-driven electron emission and gain insights into how the electron correlations of the different electron classes (direct or rescattered) are influenced by the strong laser fields. Furthermore, we will also briefly show very recent results of coherent electron acceleration with laser light on a nanophotonic chip, with significant energy gain.

Speaker: Peter Hommelhoff (FAU Erlangen)

09:55 Resolving structural dynamics at multiple length and time scales with the Cornell high-brightness, ultrafast electron microdiffraction apparatus

The out-of-equilibrium dynamics of engineered nanoscale systems, such as moiré materials, is an important domain for ultrafast science. Ultrafast electron diffraction (with high-angular magnification) is especially suited to investigating spatially coherent normal modes of oscillation in these systems, collective motion that could hold the key to novel device functionality. Nanometer and longer periodicities can appear as fine details in reciprocal space, only resolvable by a highly coherent (low momentum spread) probe. In the conjugate dimension, small probe spots are needed to obtain data from micron-sized material samples. To satisfy these two requirements simultaneously --- high coherence and small probe size --- requires a high-brightness electron beam. I describe early results of the kiloelectron-volt ultrafast electron diffraction apparatus at Cornell, and show with reference to an experimental case study in moiré materials that this machine meets demanding size and coherence requirements, thanks to a low emittance semiconductor photocathode source.

Speaker: Cameron Duncan

10:20 Sub-picosecond ultracold electron bunches

The Ultra Cold Electron Source (UCES) being developed at Eindhoven University of Technology is based on near-threshold, femtosecond photoionization of a laser-cooled rubidium gas in a magneto-optical trap. The UCES accelerates bunches containing ~1000 electrons in a DC field up to energies of ~10 keV with a normalized emittance of ~1 nm·rad.
Recently, bunch lengths as short as 735±7 fs (rms) have been measured in the self-compression point of the DC source by means of ponderomotive scattering of the electrons by a 25 fs, 800 nm laser pulse. This is an improvement by more than an order of magnitude compared to the previous bunch length record. The observed temporal structure of the electron bunch depends on the central wavelength of the ionization laser pulse, in agreement with detailed simulations of the atomic photoionization process. This shows that the bunch length limit imposed by the atomic photoionization process has been reached.
To increase the range of applications of the UCES, the ultracold bunches have recently been accelerated in a standing wave RF cavity up to energies of 35 keV. During acceleration the transverse bunch quality was preserved as measured by diffraction on a single crystal gold foil. Transverse coherence lengths as high as 20 nm were obtained in a spot a few tens of microns across, paving the way towards applications such as ultrafast protein crystallography.

Speaker: Tim De Raadt (Eindhoven University of Technology)

HBB confrence - Tim de Raadt - V6.pptx

10:40 Novel approaches and innovative modalities in ultrafast electron scattering applications with accelerators

Ultrafast electron probing modalities offer unique experimental tools to access the structural dynamics of ultrafast photoinduced processes in materials and molecules, in liquid, gas, and condensed phase systems. Here we propose to capitalize on the exceptional and versatile electron beam parameters of the SEALAB Superconducting RF (SRF) photoinjector to develop a world-wide unique facility for ultrafast electron diffraction and imaging (UED and UEI), dedicated to experiments with high sensitivity in space, energy, and time. These applications highly demand not only extreme beam quality in 6-D phase space such as a few nanometer transverse emittances and femtosecond duration but also equivalent beam stability at MHz repetition rate. The talk with rationalize on beam dynamics driven design studies for different modlaities and discuss first results from preparatory measurements.

Speaker: Benat Alberdi-Esuain (Helmholtz-Zentrum Berlin)

Presentation_PAHBB.pdf

11:00 → 11:30 Coffee Break

11:30 → 13:00 Ultrafast electron probes

11:30 Imaging gas-phase molecules with high temporal resolution by coherent electron diffraction

Imaging time-resolved molecular dynamics demands atto- to few-femtosecond temporal and picometer spatial resolution. Laser-induced electron diffraction (LIED) is a strong-field method based on coherent laser-driven scattering with one of the target's own electrons after photoionization. In this way, LIED differs from conventional ultrafast electron diffraction (UED) with external electron beams, in which the electron pulse is scattered by many target molecules, causing incoherent scattering of hundreds (to tens of thousands) of electrons. LIED has demonstrated its ability to image the three-dimensional structure of a single gas-phase molecule in full kinematic coincidence with combined sub-atomic picometre and femtosecond spatiotemporal resolution. However, retrieving complex molecular systems becomes progressively difficult with increasing molecular structure and is a challenge for any diffraction-based imaging technique.
In my talk, I will present our state-of-the-art technical achievements on the LIED and their consequent experimental results to overcome the limitations of imaging complex molecules for highly time-resolved investigation.

Speaker: Katharina Chirvi (ICFO)

11:55 Shaping the collective interaction of relativistic electrons with matter

In this talk, I will discuss how the collective field of a relativistic electron beam can be used to instigate novel quantum dynamics and allow us to study ultrafast physics beyond typical laser-excited systems. At LCLS, the beam-supported fields can be shaped into strong (V/A), broadband (0-10 eV), and/or microbunched pulses that are intrinsically synchronized and mutually coherent with a soft x-ray laser. Preliminary experience commissioning a photon-electron pump-probe experiment (PEPPEx) illustrates the opportunities and challenges associated with using a space-charge field for ultrafast science.

Speaker: David Cesar

Cesar_PAHBB_June_2023.pdf

12:15 Establishing a Relativistic Ultrafast Electron Diffraction & Imaging Facility in the UK

RUEDI (Relativistic Ultrafast Electron Diffraction & Imaging) is a proposed UK national facility in the which will deliver single-shot, time-resolved, imaging with MeV electrons, and ultrafast electron diffraction down to 10 fs timescales. RUEDI is being designed to enable the following science themes: dynamics of chemical change; materials in ex-treme conditions; quantum materials; energy generation, storage, and conversion; and in vivo biosciences. RUEDI is proposed to be built at STFC’s Daresbury Laboratory in the UK. The Conceptual Design Review and Outline Instrument Design reports were published in November 2022 and summarised here, with a Technical Design Review report to follow in November 2023.

Speaker: Julian McKenzie (STFC Daresbury Laboratory)

2023,06,21 Julian McKenzie - RUEDI - PAHBB.pptx

12:35 Application of Low-Emittance Electron Beams for MeV UED

Mega-electronvolt ultrafast electron diffraction (MeV-UED) is a complementary tool to X-ray based instruments that has enabled ground-breaking studies in condensed matter physics and chemical science. A significant opportunity exists for MeV-UED beyond current instrument capabilities in quantum materials, microelectronics and photo-chemical research. Further improvement in MeV-UED transverse emittance would allow access to longer-range electron correlations in quantum materials and to probe micron-sized homogeneous regions within complex heterogeneous materials. To broaden the scientific opportunities, improved instrument performance of MeV UED has been heavily requested. We discuss plans at the SLAC MeV-UED facility to enable substantial near-term improvements in beam brightness, data acquisition rate, and temporal and momentum-space resolution.

Speaker: Dr Joel England (SLAC)

England_UED_PAHBB_2023.pdf

13:00 → 19:00 Free Half Day

Thursday, 22 June

09:30 → 11:00 Plasma acceleration

09:30 Density downramp injection in plasma-based acceleration and its applicaitons in XFELs

Generation of high-quality electron beams in plasma-based acceleration is a critical and active topic in the past decade. By conducting full-scale particle-in-cell simulations, we have shown that electron beams with ultra-high brightness (10^20 ~10^21 A/m^2/rad^2) and 0.1~1 MeV energy spread can be produced in density downramp injection in the three-dimensional blowout regime of plasma-based acceleration. Two underlying physical mechanisms that lead to the generation of high-quality electrons are uncovered: transverse deceleration and longitudinal mapping. Recently, we pointed out the injection in a slowly expanding bubble caused by the evolution of a laser pulse driver or an electron beam driver in a uniform plasma shares the same dynamics as downramp injection, thus can indeed produce high quality self-injected electron beams. Furthermore, we proposed to generate a high-quality electron beam with nanometer-scale current modulation in a density modulated downramp. These high-quality beams have many potential applications in X-ray free-electron lasers, such as drive a fully coherent XFEL in a short undulator.

Speaker: Xinlu Xu (Peking University)

09:55 Towards PWFA-X-FEL

We present a blueprint for an ultra-compact X-ray free-electron laser (X-FEL) powered by plasma wakefield acceleration (PWFA). The study shows in a high-fidelity S2E simulation how to produce and preserve ultra-high 6D brightness electron beams in a plasma photocathode PWFA stage. Then, a post-plasma beam transport line captures, isolates and refocuses these electron beams into an undulator without charge and quality loss. Inside the undulator, these electron beams emit attosecond duration coherent X-ray pulses down to the sub-Angstrom wavelength after 10 m of the undulator section [1]. We conclude with ongoing efforts of the experimental ecosystem and discuss novel scientific avenues arising from ultra-compact PWFA-X-FELs.

[1] Habib, A.F. et al. Attosecond-Angstrom free-electron-laser towards the cold beam limit. Nat Commun 14, 1054 (2023).

Speaker: A. Fahim Habib (University of Strathclyde, Glasgow, UK, Department of Physics,)

10:20 High-Brightness tuneable attosecond bunches with the Resonant Multi Pulse Ionization injection

Recent advances with the Resonant Multi Pulse Ionization Injection scheme [1,2], which was already proven by simulations to be able to generate few femtosecond long 5GeV beams [3] with beam quality large enough to efficiently drive a FEL [4], move toward the generation of high-brigthness beams with duration of a few hudreds of attoseconds. At the same time, with the aid of an advanced model for the tunnel ionization process in the saturation regime [5], the optimization of the scheme lead to a reduction of the needed number of sub-pulses in the driving train from eight [3] down to two pulses, making the implementation of the scheme more simple and improving its robustness against laser/target imperfections. By just tuning the delay between the wakefield driving train and the ionization injection, it's possible to shape the longitudinal profile of the e-beam, thus adjusting its time duration down to a few hundreds of attoseconds, or even down to 100as if a post-compression technique is employed onto the ionization pulse.
Our test-case FB-PIC q-3D simulations with the simplified two-pulses driving scheme, show that >1GeV e-beam with about 10pC charge, projected energy spread <0.8% and length of about 500as can be generated with a single 200TW Ti:Sa laser system, the e-beam having 5D brightness exceeding 2x10^17 A/m^2 and 6D brightness exceeding 2x10^16 A/m^2/0.1%. The effect of a passive plasma lens placed right after the plasma downramp is also discussed. Finally, the potentiality of the simplified scheme with the usage of 1PW pulses with the aim of generating >1GeV e-beams will be discussed.

[1] P. Tomassini et al., "The resonant multi-pulse ionization injection", PoP 24, 103120 (2017); https://doi.org/10.1063/1.5000696

[2] P. Tomassini et al., "High quality electron bunches for a multistage GeV accelerator with resonant multipulse ionization injection", Phys. Rev. Accel. Beams 22, 111302 (2019)

[3] P. Tomassini et al., "High-quality 5 GeV electron bunches with resonant multi-pulse ionization injection", PPCF 62 014010
DOI 10.1088/1361-6587/ab45c5 (2020)

[4] P. Tomassini et al., "Brilliant X-ray Free Electron Laser driven by Resonant Multi-Pulse injection accelerator", proc. FEL22 conference (Trieste, I)

[5] P. Tomassini et al., "Accurate electron beam phase-space theory for ionization-injection schemes driven by laser pulses", High Power Laser Science and Engineering, (2022), Vol. 10, e15, doi: 10.1017/hpl.2021.56

Speaker: Paolo Tomassini (ELI-NP)

10:40 Developing a reliable test bed for laser plasma accelerator driven compact light sources

The Hundred Terawatt Undulator (HTU) beamline at the BELLA Center is being used as a test bed for the development of compact laser plasma accelerator (LPA)-driven light sources, with a particular focus on developing a reliable LPA-driven FEL. While LPA technology is well established, hurdles remain to make it usable for practical light source applications. Stability and reliability are primary concerns. The laser plasma interaction that results in the trapping and accelerating of electrons involves various nonlinear physical processes making it sensitive to subtle variations. Furthermore, there is a basic requirement that the transverse jitter of an electron beam in an undulator should be a small fraction of its transverse beam size for an efficient FEL. This requirement imposes an onerous condition on the transverse stability of the high power lasers used to generate the electron beams.

I will discuss recent efforts undertaken at the BELLA Center to address some of these challenges. In particular, I will focus on recent results that demonstrated substantial improvement in the transverse stability of LPA generated electron beams as well as ongoing efforts to make stability improvements to our laser system that will improve shot-to-shot variation in e-beam charge. Progress on LPA-driven FEL lasing using the 4m VISA undulator will be also be presented.

This work was supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, and through a Strategic Partnership Program with TAU Systems Inc.

Speaker: Sam Barber (LBNL)

Barber PAHBB 2023.pptx

11:00 → 11:30 Coffee Break

11:30 → 13:00 Plasma acceleration

11:30 Stable operation of SASE and Seeded FEL driven by a plasma accelerator

The breakthrough provided by plasma-based accelerators enabled unprecedented accelerating fields by boosting electron beams to GeV energies within few cm.
This enables the realization of table-top accelerators able to drive a Free-Electron Laser (FEL), a formidable tool to investigate matter at sub-atomic level by generating X-UV coherent light pulses with fs and sub-fs durations.
So far, short wavelength FELs had to rely on the use of conventional large-size radio-frequency (RF) accelerators due to the limited accelerating fields provided by such a technology.
Here we report the experimental evidence of a FEL driven by a compact (3 cm) plasma accelerator. The accelerated beams are characterized in the six-dimensional phase-space and have a quality, comparable with state-of-the-art accelerators. This allowed the observation of amplified SASE radiation in the infrared range with typical pulse energy exponential growth, reaching tens of nJ over six consecutive undulators.
On the basis of these first amplification results starting from spontaneous emission (SASE), we upgraded the setup by seeding the amplifier with an external laser. Compared to SASE, the seeded FEL pulses are characterized by a higher pulse energy, two orders of magnitude larger (up to about 1 uJ) and an enhanced reproducibility (up to about 90%) resulting in a higher shot-to-shot stability.

Speaker: Mario Galletti (Tor Vergata University - INFN)

11:55 First laser plasma accelerator based seeded FEL

Free Electron Lasers (FELs) are traditionally operated on Radio-Frequency Accelerators (RFAs). But the use of Laser Plasma Accelerators (LPAs), exhibiting much higher accelerating gradients, could enable to reduce the footprint of the FEL facilities, especially in the case of FELs operated in the X-ray range.
We report the first lasing of a seeded FEL fully driven by an LPA. The experiment was performed at HZDR (Germany), coupling the high quality electron beams of the HZDR's LPA with the versatile COXINEL beam manipulation beamline. Our results substantiate the continuous progress of LPA technology to enable FEL operation and finally bring temporal coherence to those compact promising sources.

Speaker: Marie Labat

12:20 Direct probing of fields inside an LWFA using a relativistic electron beam probe

Laser wakefield accelerators (LWFA) have produced electron beams with up to ~10 GeV of energy in tens of centimeters. In addition to producing high accelerating gradients, theory predicts the existence of linear focusing forces when an LWFA is driven in the blowout regime, where all electrons behind the laser are expelled. Such linear fields are essential for maintaining an electron beam’s emittance during acceleration. Here, we present a method for direct characterization of these fields within an LWFA driven in the blowout regime. The experiments leverage the unique terawatt CO$_2$ laser system ($\lambda \sim 9.2 \mu$m) and the 55 MeV linac-driven electron beam at the Accelerator Test Facility (ATF) of Brookhaven National Laboratory. Transmission Electron Microscopy (TEM) grids were used to create electron “beamlets”, which allowed for selective transverse illumination of the different portions of the wake. The resulting deflection and the location of the focal point of the probe beamlets can then be used to characterize the electric field strength within the wake. The analytical evaluation of the approach, supporting simulation results, and recent experimental progress will be presented and discussed.

Speaker: Navid Vafaei-Najafabadi (Stony Brook University, Brookhaven National Laboratory)

230622_Vafaei-PAHBB-v2.pptx

13:00 → 15:00 Lunch

15:00 → 16:30 Beam dynamics and controls

15:00 Energy spread increase by intrabeam scattering and microbunching in FEL injectors

The energy spread is one of the properties that determine the brightness of electron beams and a fundamental parameter in X-ray free-electron lasers (FELs). In the last couple of years, measurements at different FEL injectors have shown energy spread values much larger than predicted by simulations. This talk will present high-resolution energy spread measurements at the SwissFEL injector as a function of the electron peak current, the optics, and the longitudinal dispersion of the lattice. The measured dependences indicate that the energy spread increase is caused by intrabeam scattering and microbunching instability, effects not covered in the conventional modeling of FEL injectors. We will also show numerical calculations that reproduce the experimental data and a recipe to mitigate the energy spread deterioration. The work underlines the importance of considering the energy spread in the optimization and design of high-brightness electron beam sources and the need to develop new models to adequately understand and simulate the observed physics effects.

Speaker: Eduard Prat (Paul Scherrer Institut)

espread_IBS.pptx

15:25 Photoinjector transverse phase space linearization with sacrificial charge

Compensating the emittance growth due to linear and nonlinear space charge effects in photoinjectors is critical for high-brightness electron beam applications ranging from XFELs to various ultrafast electron probes. While linear emittance compensation is extremely robust, nonlinear emittance compensation depends on the detailed nature of the charge distribution, and in general, producing simultaneous compensation of linear and nonlinear space charge effects is an ongoing challenge. This challenge will grow in importance as intrinsic emittance from photocathodes is further improved.

In this work, we will show results discovered via multiobjective optimization of various high-brightness photoinjectors equipped with scraping apertures. We find a new class of robust nonlinear emittance compensation that uses the space charge field of the sacrificial component of the beam to linearize the transverse slice phase space of the surviving component. We study this effect analytically and show excellent agreement with space charge simulation and extremely low emittance for charges relevant for XFEL injectors.

Speaker: Jared Maxson

PAHBB_Maxson_2023_SanSebastian.pptx

15:45 Update on Electron Beam Manipulation at the Argonne Wakefield Accelerator Facility

The Argonne Wakefield Accelerator (AWA) supports an extensive research portfolio along three themes: electron beam production, electron beam manipulation, and electron beam-driven wakefield acceleration. Current research activities focus on longitudinal distribution shaping and cross-plane manipulations for emittance redistribution between two and three degrees of freedom, such as one-dimensional manipulation based on photoemission laser-pulse shaping, selective transverse collimation combined with emittance exchange technique, and local cross-plane "bump" combining transverse-deflecting cavities with transverse collimation. Likewise, transverse phase-space control focuses on the generation and transport of magnetized beams for electron cooling of hadron beams and the production of flat beams for wakefield excitation in asymmetric structures. Finally, an experiment on emittance repartitioning between the three degrees of freedom is under planning with the ultimate goal of circumventing the need for an electron-damping ring in future linear colliders. In this presentation, we present recent research progress on bunch manipulation and discuss future research directions at the AWA.

Speaker: Seongyeol Kim (Argonne National Laboratory)

2023_06_22_PAHBB2023_Seongyeol_Kim.pdf

16:05 C-band vs S-band: Minimizing Emittance in a High Charge TopGun Photoinjector

The space charge emittance compensation in the C-band TopGun design has been demonstrated with 100 pC bunch charge. It has shown that a minimum emittance is limited by the intrinsic emittance at the cathode. Scaling this approach to higher bunch charges, however, requires a larger transverse size and a longer pulse duration. The rf emittance dilution due to the iris kick scales quadratically with the transverse size and linearly with the pulse duration. This effect becomes a determinant factor for the minimum emittance in the TopGun designs. The study of S-band TopGun will show the ease of the constraint imposed by the rf emittance. We will show if an intrinsic emittance will become a limiting factor for 250 pC case.

Speaker: Petr Anisimov (Los Alamos National Laboratory)

Anisimov.pdf

16:30 → 17:00 Coffee Break

17:00 → 18:30 Beam dynamics and controls

17:00 Predicting the transverse emittance of space charge dominated beams using the phase advance scan technique and a neural network

The transverse emittance of a charged particle beam is an important figure of merit for many accelerator applications. One of the easiest to implement methods to determine the transverse emittance is the phase advance scan method using a focusing element and a screen. This method has been shown to work well in the thermal regime. In the space charge dominated laminar flow regime, however, the scheme becomes difficult to apply because of the lack of a closed description of the beam envelope including space charge effects. Furthermore, certain mathematical, as well as beamline design criteria must be met in order to ensure accurate results. This work shows that it is possible to analyze phase advance scan data using a neural network (NN), even in setups, which do not meet these criteria.

Speaker: Dr Frank Mayet (DESY, Hamburg, Germany)

PAHBB_SanSebastian_2023_FrankMayet_v2.pdf

17:25 Virtual Diagnostics for High Brightness Accelerators

Diagnostic methods that are enhanced with machine learning are improving the speed and detail with which beam behavior can be characterized on-the-fly in real accelerator systems. Detailed characterization can in turn improve both high-precision modeling of accelerator systems and high-precision optimization/control for high brightness beams. This talk will outline the state-of-the-art in machine learning enhanced diagnostics for accelerators, ranging from fast data-driven approaches for shot-to-shot prediction to methods that tightly couple machine learning and physics simulations for unprecedented fidelity in beam phase space reconstruction.

Speaker: Auralee Edelen (SLAC)

20230621_PAHBB_Edelen_vf.pdf

Virtual Diagnostics for High Brightness Accelerators

17:50 Physics-Informed Priors for Sample Efficient Models of Beam Transport with Intense Space Charge

Highly accurate simulation tools have become a staple in the design and operation of high-brightness particle accelerators. These tools are not without limitations, however. They are often computationally expensive. Many codes are incompatible with automatic differentiation (for machine learning). It can also be unclear how to include real-world measurements in a way that improves the model. Many of these problems are solved with a data-driven approach. Surrogate models are fast to evaluate, differentiable, and treat data from simulations and particle accelerators uniformly. Unfortunately, surrogate models often require a large amount of (possibly expensive) training data for their creation. In this work, we bridge the gap between purely data-driven models and physics-based simulation tools by introducing physics-informed priors for accelerator surrogate modeling. By coaxing our models to obey the physical laws that govern charged particles in an accelerator, we can improve sample efficiency while maintaining the benefits of surrogate models. We present our initial results that directly compare the accuracy of conventional and physics-informed models trained with few samples.

Speaker: Christopher Pierce

chris-pierce-physics-informed-priors.pptx

Friday, 23 June

09:30 → 11:00 Advanced concepts and Conclusions

09:30 EuPRAXIA Advanced Photon Sources (EuAPS): a plasma-based betatron source

The EuPRAXIA Advanced Photon Sources (EuAPS) project, led by INFN in collaboration with the CNR and the University of Tor Vergata, involves the construction of a laser-driven “betatron” X-ray user facility at the SPARC_LAB laboratory of the LNF. EuAPS also includes the development of high power (up to 1 PW at LNS) and high repetition frequency (up to 100 Hz at CNR Pisa) laser drives for EuPRAXIA.
In this talk we first examine the physics behind the dynamics of accelerated electron betatrons in plasma accelerator cavities: the betatron oscillations of relativistic electrons at very short scale lengths are responsible for the emission of ultrashort X-ray bursts.
Next, we present the current status of the experimental activity at the LNF, finally discussing the relevant results for the EuAPS project, highlighting the expected performance of the source for user applications.

Speaker: Dr Alessandro Curcio (INFN LNF)

09:55 Beam dynamics studies for a stable, reliable and reproducible plasma-based accelerator

Plasma accelerators are emerging as formidable and innovative technology thanks to their compactness and reduced costs to drive of user facilities being able to sustain several GV/m accelerating gradients at normal conducting temperature.
The EuPRAXIA@SPARC_LAB collaboration is preparing a technical design report for a multi-GeV plasma-based accelerator with outstanding electron beam quality to pilot an X-ray FEL, the most demanding in terms of beam brightness. The beam dynamics has been studied aiming to a reliable operation of the RF injector to generate a so-called comb-beam with 500 MeV energy suitable as driver of the Beam-driven Plasma Wakefield Accelerator. A case of interest is the generation of a trailing bunch with 1 GeV energy, less than 1 mm-mrad transverse emittance and up to 2 kA peak current at the undulator entrance. The comb-beam is generated through the velocity bunching technique, an RF compression tool that enables high brightness beams within relatively compact machine. Since it is based on a rotation of the beam phase space inside the external RF fields, it could be particularly sensitive to amplitude and phase jitters in the RF injector. The electron beam dynamics and the machine sensitivity to the possible jitters are presented in terms of effect on the beam quality so to provide the basis for the alignment procedure and jitter tolerances. Numerical studies have been consolidated with experimental results obtained at SPARC_LAB, a test facility currently oriented to plasma acceleration physics where the velocity bunching scheme is routinely applied.

Speaker: Anna Giribono (INFN - LNF)

10:20 The Munich Compact Light Source (MuCLS) – a laboratory-size laser-undulator X-ray source for biomedical applications

The Munich Compact Light Source (MuCLS) is a tuneable, brilliant and compact hard X-ray synchrotron source. Electrons are accelerated in a classical RF-accelerator and injected into a small storage ring (4.6 m circumference). X-rays are generated via a laser-undulator, realised as a short laser pulse circulating in an enhancement cavity. Thus, the MuCLS provides incoherently-produced brilliant quasi-monochromatic X-rays in the energy range 15 keV – 35 keV. The MuCLS`s radiation has been exploited for biomedical research focussing on this source’s particular advantages: partial spatial coherence, quasi-monochromaticity, milli-radian divergence angle and availability for longitudinal studies.
First, we present the MuCLS and its recent upgrades [1] before we highlight the value of compact synchrotron sources for biomedical applications, e.g. [2]. Results from phase-contrast imaging are shown, like improved detection of tumorous lesions in mammography and in vivo lung imaging in mice for the assessment of airway health or drug development. Furthermore, we demonstrate the benefit of K-edge subtraction imaging, e.g., for angiography and display the performance of the MuCLS for X-ray absorption spectroscopy.
[1] Günther, PhD-Thesis, Springer Cham, DOI: 10.1007/978-3-031-17742-2 (2023)
[2] Günther et al., J. Synch. Rad. 27, 1395-1414 (2020)

Speaker: Dr Benedikt Günther (Technical University of Munich)

2023_MuCLS_PAHBB.pptx

10:40 Underdense Passive Plasma Lens Experiments at FACET-II

The underdense passive plasma lens (UPPL) has several features that make it uniquely attractive for the focusing high-energy electron beams. Nominally formed via laser ionization of gas in the outflow of a supersonic jet, it is a simple, ultra-compact, and easily tunable device. Because it operates in the nonlinear blowout regime, the focusing strength scales with the plasma density and lens thickness, which can be controlled via the gas jet backing pressure and the focal properties of the laser, respectively. In contrast to active plasma lenses, the UPPL always acts as a linear focusing optic, preserving emittance even for the most intense beams. Potential use cases include matching and staging for plasma accelerators, as well as the final focus for a future collider or for HED physics. By introducing a modest transverse density gradient, the UPPL can even behave like a “micro-dipole” or “micro-sextupole”. We will present theoretical descriptions of the UPPL under various conditions, along with a summary of early commissioning data from FACET-II and future experimental plans.

Speaker: Michael Litos (University of Colorado Boulder)

11:00 → 11:30 Coffee Break

11:30 → 13:00 Advanced concepts and Conclusions

11:30 Enhancing XFEL Performance Through Laser-Based Manipulation

While XFEL electron bunches can be manipulated for tailored x-ray generation via laser-electron interactions in select locations along the accelerator, such as laser heaters, XFEL performance is dominantly impacted by the electron bunch parameters directly after generation in the photoinjector. Optimal performance of the photoinjector requires excitation laser pulses, typically in the ultraviolet (UV), with non-Gaussian temporal intensity profiles and durations on the order of 10s of ps. We demonstrate a photoinjector laser shaping method with a numerical and experimental implementation to generate ~25 ps flat-top pulses in the ultraviolet designed for MHz-rate photoinjectors which have been shown in simulation to reduce transverse emittance by upwards of 25%. We achieve upwards of 30% conversion efficiency during the nonlinear shaping stage allowing for applications of this method beyond XFELs to ones with higher bunch charge requirements. In supplement to the demonstrated experimental method, we show a machine learning extension aimed at kHz-level adaptive laser shaping for XFEL experiential multiplexing and fast-response machine performance optimization.

Speaker: Randy Lemons

11:55 Applications of laser-driven anti-resonant waveguides to electron beams

Large-core anti-resonant fibers have recently found key applications in non-linear optics. Here we report on their applications to charged beams. We show that large energy modulations can be applied via a TM01-like mode, which can be further exploited to produce attosecond microbunches. We also report on the dipole HE11-like mode, to support high-power streaking resolutions for diagnostics purposes. Limitations, opportunities, and future plans are also discussed.

Speaker: Francois Lemery (DESY)

HBB2023-Fibers-Lemery.pptx

12:20 Prospective methods for generating sub-picosecond long-wave infrared lasers for advanced accelerators

The $\lambda^2$ scaling of the ponderomotive force underpinning laser-based particle accelerators encourages the use of long wavelengths in regimes such as laser wakefield acceleration of electrons at low plasma densities. High pressure $\mathrm{CO_2}$ amplifiers are the workhorse source of such lasers, able to achieve multi-TW peak powers and picosecond pulse lengths. We are developing wavelength conversion techniques utilizing stimulated Raman scattering, where the energy of a photon is modified by inelastically scattering with a coherent excited state of a material, employing calcite to generate the 9.2 $\mathrm{\mu m}$ seed, and ionic liquids, artificial salts that are liquid at room temperature, for the 4.3 $\mathrm{\mu m}$ pump. Additionally, we are examining the use of self phase modulation to broaden the spectrum after the amplifier, followed by chirp compensation/compression. Together, we anticipate that these techniques will generate 25 TW, 100 fs LWIR pulses, which have been shown in simulation to enable new regimes in laser wakefield acceleration, such as the blowout regime of laser wakefield accelerators with millimeter-scale plasma structures.

Speaker: William Li (Brookhaven National Laboratory)

pahbb_2023_LWIR_LI.pptx

12:40 Pathways & progress to ultrabright pulses from plasmas

Hybrid combinations of lasers and electron beams allow LWFA->PWFA and plasma photocathodes to be realized. This is a pathway to ultrabright electron and photon pulses. Experimental progress on hybrid LWFA->PWFA, and on plasma photocathodes driven by linac-PWFA, and now also by the hybrid LWFA->PWFA approach, will be presented. Intrinsically synchronized, ultrabright electron and photon pulses e.g. via X-FEL from compact, all-optical setups then enable unique experimental constellations and applications of ultraintense IR--e-beam--X-ray interaction.

[1] Kurz, Heinemann et al., Demonstration of a compact plasma accelerator powered by laser-accelerated electron beams, Nat. Comm. 2021
[2] Deng, Karger et al., Generation and acceleration of electron bunches from a plasma photocathode, Nat. Phys. 2021
[3] Habib et al., Attosecond-Angstrom free-electron-laser towards the cold beam limit, Nat. Comm. 2023

Speaker: Bernhard Hidding (Heinrich Heine University Düsseldorf)