20th Advanced Accelerator Concepts Workshop

Nov 6, 2022, 3:00 PM → Nov 11, 2022, 5:10 PM America/New_York

Hyatt Regency Long Island

Mark Palmer (Brookhaven National Laboratory), Navid Vafaei-Najafabadi (Stony Brook University)

The AAC’22 workshop is the 20th in a series of by-invitation biennial fora for intensive discussions on long-term research in advanced accelerator physics and technology. This research supports the development of capabilities for the basic sciences, from photon science to high energy physics, as well as the development of compact accelerators for industrial, medical and security applications.

AAC'22 will be organized into eight working groups covering the following topical areas:

1. Laser-Plasma Wakefield Acceleration 
2. Computation for Accelerator Physics
3. Laser and High-Gradient Structure-Based Acceleration
4. Beam-Driven Acceleration
5. Beam Sources, Monitoring, and Control
6. Laser-Plasma Acceleration of Ions
7. Radiation Generation and Advanced Concepts
8. Advanced Laser and Beam Technology and Facilities

Conference Home:  https://www.aac2022.org/

 

Sunday, November 6

6:00 PM → 7:30 PM Welcome Reception

Monday, November 7

10:20 AM → 10:40 AM Coffee Break

12:10 PM → 1:30 PM Lunch

3:00 PM → 3:30 PM Coffee Break

Tuesday, November 8

10:00 AM → 10:30 AM Coffee Break

12:00 PM → 1:20 PM Lunch

3:00 PM → 3:30 PM Coffee Break/Exhibits

3:30 PM → 5:00 PM WG6: Laser-Plasma Acceleration of Ions: Session 4

Conveners: Dr Lieselotte Obst-Huebl (Lawrence Berkeley National Lab), Dr Igor Pogorelsky (BNL), Mamiko Nishiuchi (QST)

3:30 PM Generation of focused high-energy ion beams via hole-boring radiation pressure acceleration of curved-surface low-density targets

Relativistic ion beams have wide applications ranging from proton therapy, neutron beam/warm dense matter generation, and fast ignition of fusion pellets. In particular, generating a monoenergetic high energy flux ion beam is of great interest, since fast-ignition scheme of fusion targets require energy fluxes of ~GJ/cm^2. We show that a foam-based target with parabolically shaped front surface can be accelerated and focused to a micron-scale spot using available laser systems and targets. The focal length is controlled by the target front surface shape, and the ion energy: by laser intensity and target mass density. An analytic model based on Hole-Boring Radiation Pressure Acceleration mechanism is developed to explain the result. This scheme is scalable and can be used for a wide range of laser power and target densities to focus monoenergetic ions with different energy to variable focal lengths and can generate fs-scale ultrahigh energy density/flux beams. The mechanism is robust and can be implemented using realistic transverse laser profiles, multi-species targets, or targets with finite longitudinal step-like boundaries.

Speaker: Jihoon Kim (Cornell University)

3:50 PM Ultra-short pulse laser acceleration of protons from cryogenic hydrogen jets tailored to near-critical density

Laser plasma-based particle accelerators attract great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. However, despite the fact that first principles simulations have predicted several advantageous ion acceleration schemes, laser accelerators have not yet reached their full potential in producing simultaneous high-radiation doses at high particle energies. The most stringent limitation is the lack of a suitable high-repetition rate target that also provides a high degree of control of the plasma conditions which is required to access these advanced regimes.
Here, we demonstrate that the interaction of petawatt-class laser pulses with a micrometer-sized cryogenic hydrogen jet plasma overcomes these limitations. Controlled pre-expansion of the initially solid target by low intensity pre-pulses allowed for tailored density scans from the overdense to the underdense regime. Our experiment demonstrates that the near-critical plasma density profile produces proton energies of 80 MeV. This energy presents more than a factor of two increase compared to the solid hydrogen target. Our three-dimensional particle in cell simulations show the transition between different acceleration mechanisms and suggest enhanced proton acceleration at the relativistic transparency front for the optimal case.

Speaker: Martin Rehwald (HZDR)

4:10 PM Effects of Laser Polarization on Target Focusing and Acceleration in a Laser-Ion Lens and Accelerator

Recently, a novel concept of Laser-Ion Lensing and Acceleration (LILA) [1] has been introduced for highly-efficient generation of monoenergetic low-emittance ion beams. The LILA scheme is based on the illumination of a solid-density target with radially-dependent thickness by an intense circularly polarized (CP) laser pulse, resulting in simultaneous acceleration and focusing of proton beams to a micron-sized spot. We extend the LILA concept to include elliptically polarized (EP) laser pulses. While it is well-known that elliptically polarized (EP) laser pulses cannot be used for radiation pressure acceleration (RPA) of planar targets because of strong electron heating [2], we find that the situation is qualitatively different for non-planar rapidly-converging targets. Three-dimensional PIC simulations, backed up by simple theoretical estimates, are used to optimize the target thickness and shape to realize the LILA scheme with EP laser pulses. Unexpectedly, even linearly polarized laser pulses can efficiently generate low-emittance focused ion beams when non-uniform thickness targets are used, with overall laser-to-ions energy conversion comparable to those achievable with CP laser pulses.

Speaker: Roopendra Singh Rajawat (Cornell University)

Wednesday, November 9

10:00 AM → 10:30 AM Coffee Break/Exhibits

12:00 PM → 1:20 PM Lunch

1:30 PM → 3:00 PM WG6: Laser-Plasma Acceleration of Ions: Session 5

Conveners: Dr Lieselotte Obst-Huebl (Lawrence Berkeley National Lab), Dr Igor Pogorelsky (BNL), Mamiko Nishiuchi (QST)

1:30 PM Ion acceleration and neutron generation with few-cycle, relativistic intensity laser pulses

Most of the ion acceleration experiments have been carried out with multi-cycle, Joule-class lasers in the TNSA and RPA regime. The recent developments of few-cycle laser systems with 100 W average power created the technological basis for the generation of ion current of tens of microA consisting of ultrashort particle bunches– something that many applications dream of. Here we present an experimental study of proton and deuteron acceleration in both forward and backward directions with ~30mJ, 12 fs laser pulses. With the use of adaptive mirror, the focused intensity of such laser pulses reaches ~10^19W/cm^2 intensity on target.
Protons were accelerated on thin foils made of various materials, with thicknesses ranging from 5 nm to 9 microns. The highest cut-off energy and conversion efficiency was 1.5 MeV, and 1.5 %, respectively, with a beam emittance as small as 0.00032 π-mm-mrad.
Deuterons were accelerated close to MeV by irradiating homemade 200 nm thin deuterated polyethylene foils on a rotating wheel target system. The laser was run at 1 Hz repetition rate in bursts of 75 shots. With a systematic change of the dispersion of the laser pulse, we have revealed that the optimum conditions for achieving the highest cut-off energy particles and the highest conversion efficiency of a particle bunch are significantly different.
The accelerated deuterons hit a 0.1 mm thick deuterated polyethylene disk and induced neutrons with a mean energy of 2.45 MeV. From the ToF signals of four plastic scintillators at various angles around the chamber, we have concluded that an average of ~4000 fast neutrons were generated in a shot. With the development of high repetition rate primary-target systems including thickness optimization, the yield of neutrons in a second may exceed what can be achieved with state-of-the-art PW class lasers.

Speaker: Karoly Osvay (National Laser-Initiated Transmutation Laboratory, University of Szeged, Hungary)

Osvay_AAC_221109_distr.pdf

1:50 PM New capabilities of the iP2 beamline for laser-solid interaction studies at the BELLA PW facility

The newly commissioned short focal length, high intensity beamline, named iP2, at the BELLA Center enables frontier experiments in high energy density science. This 1 Hz system provides a focused beam profile of <3 micron in FWHM, resulting in an on-target peak intensity greater than 5e21 W/cm^2 , and a pointing fluctuation on the order of 1 micron. A temporal contrast ratio of <1e-14 on the nanosecond timescale is expected with the addition of an on-demand double plasma mirror setup in the near future. This beamline is well suited for studies requiring ultra-high intensity and substantial control over the temporal contrast, such as investigation of novel regimes of advanced ion acceleration and their applications. The recent results from iP2 commissioning experiments will be presented as well as the outlook for in vivo radiobiological studies at ultra-high dose rates. In preparation for an experimental campaign to investigate the magnetic vortex acceleration regime, a series of 3D simulations using the WarpX code were performed to optimize the target design and guide the development of diagnostics. We studied the acceleration performance with different laser temporal contrast conditions at normal and oblique laser incidence angles. The simulation results will be presented along with an overview of the planned experimental setup at iP2.

Speaker: Sahel Hakimi (Lawrence Berkeley National Laboratory)

2:10 PM Proton acceleration with a CO2 laser at the Accelerator Test Facility

Long-wave infra-red lasers, like the TW CO2 laser at the Accelerator Test Facility (ATF), offer a number of benefits in studying laser-driven ion acceleration, including favorable scaling of the critical density, and the ability to access relativistic regimes at lower intensities. We present recent work studying hole-boring radiation pressure acceleration (HB-RPA) and collisionless shock acceleration at near-critical densities with a0~1. We demonstrate spectrally peaked, MeV level protons for shaped, near-critical density hydrogen gas targets, showing good agreement with the predicted HB-RPA energy scaling. We also report on decreasing proton energy spreads with increasing target density, down to 5%. Finally, we report on the new opportunity for shock imaging via a 100fs Ti:sapphire probe capability available now at the ATF.

Speaker: Igor Pogorelsky (BNL)

WG6 ICL -Igor.pptx

Thursday, November 10

10:00 AM → 10:30 AM Coffee Break/Exhibits

10:30 AM → 12:00 PM WG6: Laser-Plasma Acceleration of Ions: Session 7

Conveners: Dr Igor Pogorelsky (BNL), Dr Lieselotte Obst-Huebl (Lawrence Berkeley National Lab), Mamiko Nishiuchi (QST)

10:30 AM Exploring potential of 3D printed structures in PW laser driven ion acceleration experiments

Laser-produced ion beams from 1 um laser-plasma interactions have been a focus of high-energy density physics studies for several decades. Traditionally, these beams have been accelerated via the target normal sheath acceleration (TNSA) mechanism, which has a rootlike scaling of the maximum kinetic energy of protons Ep∞√I, where I is the laser intensity. To enhance TNSA via increase in coupling efficiency of radiation into hot electrons, beyond the ponderomotive potential of the laser, the current trend is to utilize very thin ~100-200 nm foils. Here, as was shown experimentally in a PW laser-plasma interactions, a relativistic induced transparency and associated flux of super-thermal electrons can result in increase in proton energy to near-100 MeV with a particle yield of ~10e9 (MeVxSr)-1. However, survival of such an ultrathin target irradiated by picosecond prepulse becomes a true limiting factor in wide usage of this approach. To develop a robust platform for ion acceleration in PW laser-solid target interactions, we explore a novel target design, laser-printed 2PP structures with and without regular organization of elements. Use of a relatively thick low-density target (~10-50l, where l is the laser wavelength) can improve the absorption of the laser energy, substantially drop requirements for the pulse contrast and facilitate generation of a relativistic plasma with electron temperature, Te≥1MeV in which different mechanisms of ion acceleration both in the bulk and boundary parts may play a role.
In the experiments, a 0.7 PW OMEGA EP laser beam was focused to an average intensity of ~5x1020 W/cm2 onto a 3D printed log-pile or stochastic target made of ~1 m size wires. We tested both 10 and 50 m thick structures with and without foils at the exit side. For a shorter log-pile target, protons with energies up to ~80 MeV were measured by the RCF stack and that correlated well with the Thomson spectrometer data, which detected both protons and C6+ ions. 2D PIC modeling revealed that the laser interacts with a family of microstructured overdense plasmas and sheath acceleration is the dominant mechanism. The results and future activities will be discussed.

Speaker: Sergei Tochitsky (UCLA)

Tochitsky AAC2022 LDIA.pptx

10:50 AM Theoretical and numerical investigation of ion acceleration in the interaction of high intensity attosecond pulses with solid proton-Boron targets

Several setups have recently been proposed to generate ultra-short laser pulses in the 10-100 as range with high energies (0.1-10 J) and a wavelength in the EUV-X range (1-100 nm), either by broadening the spectrum of near-infrared laser pulses to obtain single-cycle pulses that can be converted to single cycle attosecond pulses by a plasma mirror, or by directly using Doppler-boosted petawatt-class lasers. The corresponding photon energy range is from 10 eV to 1 keV. Such high energy photons are able to propagate even inside solid density targets and will allow to study the propagation of such pulses in matter, and to explore new regimes of laser-matter interaction with strong application potential as the laser energy involved will be limited and the repetition rate will be high. Another unique feature of this regime will be the ultra-high intensities that will be reached thanks to the very short duration of the pulse itself, and to the small focal spots reachable at these wavelengths.
These new unexplored regimes of interaction have the potential to achieve considerable breakthroughs in high efficiency laser particle acceleration, high efficiency and high energy radiation sources, ultra-high amplitude magnetic field generation and ultra-high pressures. Applications in fundamental physics and extreme laboratory astrophysics will therefore arise linked to high field quantum electrodynamics, nuclear physics and general relativity. We have investigated the interaction of high energy attosecond pulses with solid proton–Boron targets and the associated electron acceleration, ion acceleration, and radiation generation supported by Particle-In-Cell simulations. We demonstrate the efficiency of single–cycle attosecond pulses in comparison to multi–cycle attosecond pulses for transverse ion acceleration and magnetic field generation, making this regime of interaction promising for proton–Boron fusion. We also discuss the influence of the laser and target parameters to optimize longitudinal ion acceleration and high energy radiation generation.

Speaker: Emmanuel d'Humieres (CELIA, Univ. Bordeaux)

Talk_AAC22_dHumieres.pdf

11:10 AM OPPORTUNITIES FOR ADVANCED ACCELERATOR RESEARCH WITH FEMTOSECOND LONG-WAVELENGTH LASERS

Ultra-intense lasers are the driving force of the advanced accelerator research (AAR). Extension of their spectral reach from the presently achievable near-IR into the long-wave IR (LWIR) domain opens opportunities to explore new regimes of particle acceleration, gaining deeper insight into laser-plasma interactions, and improve laser accelerator parameters. Longer laser wavelength facilitates low density regimes of laser plasma accelerators where bigger plasma bubbles are created for laser wake field electron acceleration or gas jets can be used for monoenergetic shock-wave ion acceleration.
BNL Accelerator Test Facility (ATF) traditionally offers users an access to a terawatt class picosecond CO2 laser operating at 9 m. The present-day ATF’s state-of-art laser system features the most advanced configuration that includes a solid-state, femtosecond, optical parametric amplifier front end, a chirped pulse amplification (CPA), and the use of multiple CO2 isotopes in a chain of laser amplifiers. This laser is capable to deliver 5 TW peak power in a single 2 ps pulse. However, realization of the LWFA bubble regime requires reduction in the laser pulse duration down to 500 fs or shorter and an increase in peak power over the present ATF laser system. Such upgrade is the target of the ATF’s two-year modernization program that includes two parallel approaches: The first thrust is the nonlinear post-compression where spectrum of the laser pulse is broadened by a self-phase modulation in a nonlinear optical material. The resulting chirped pulse can be compressed to 500 fs at 10 TW by a dispersive optical element. Another approach includes developing a source for the 500 fs, 10 mJ, 9 m seed pulse that should allow to reach 20 TW in the CPA regime. A combination of these two approaches holds the promise of achieving 100 TW at 100 fs. The combination of such LWIR laser with also available at ATF electron linac and near-IR lasers will empower a unique state-of-the-art science program at the forefront of AAR.

Speaker: Igor Pogorelsky (BNL)

12:00 PM → 1:20 PM Lunch

3:00 PM → 6:00 PM Afternoon at Leisure

Friday, November 11

10:00 AM → 10:30 AM Coffee Break

12:00 PM → 1:00 PM Lunch

2:40 PM → 3:00 PM Coffee Break