# International Workshop on Energy Recovery Linacs (ERL 22)

America/New_York
Cornell University

#### Cornell University

Hosted by Cornell University Ithaca, NY 14853 United States
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Description

### Hosted by Cornell University

ERL 22 will be held in person at Cornell University October 3 - 6.  The meeting is the 66th Advanced Beam Dynamics Workshop (ABDW) held by the International Committee for Future Accelerators (ICFA).  Cornell is proud to be hosting this meeting for the second time.  The workshop will be held in Clark Hall on the Cornell campus and is jointly organized by Cornell University, Brookhaven National Lab, and Thomas Jefferson National Accelerator Facility (JLab).

Further information is available at the website for the workshop:

ERL 22 Website

Registration
ERL 22 Registration
Participants
• Alex Bogacz
• Alexei Fedotov
• Alice Galdi
• Andrew Hutton
• Andriy Ushakov
• Anjali Kavar
• Anna Petway
• Axel Neumann
• Carmelo Barbagallo
• Chang-Ki Min
• Colwyn Gulliford
• Daniel Capostagno
• David Douglas
• David Sagan
• Dejan Trbojevic
• Dmitry Kayran
• Donald Hartill
• Erdong Wang
• Ezgi Ergenlik
• Felix Glöckner
• Felix Schliessmann
• Georg Hoffstaetter
• Gustavo Pérez Segurana
• Heung-Sik Kang
• Hiroshi Sakai
• Hisato Yamaguchi
• Igor Pinayev
• Irina Petrushina
• Ivan Konoplev
• J. Scott Berg
• James Crittenden
• Jens Knobloch
• Jiyuan Zhai
• John Skaritka
• JOSEPH GRAMES
• Julius Kuehn
• K Aulenbacher
• Karl Smolenski
• Lee Jones
• Levi Schachter
• Liana Shpani
• Luca Cultrera
• luca serafini
• Maria Chamizo-Llatas
• Matthew Andorf
• Matthias Liepe
• Maud Baylac
• maury tigner
• maxwell nyarko
• Meghan McAteer
• Mengjia Gaowei
• Michaela Arnold
• Nicholas Shipman
• Nilanjan Banerjee
• Ningdong Wang
• Norio Nakamura
• Oliver Bruning
• Oliver Kugeler
• Omer Rahman
• Peter McIntosh
• Peter Quigley
• Peter Walter
• Peter Williams
• Pragya Nama
• Quantang Zhao
• Rick van den Berg
• Rob Michnoff
• Robert Apsimon
• Rong Xiang
• Sebastian Diego Walter Taubert
• Simone Di Mitri
• Stephen Benson
• Stephen Brooks
• Sunil Pokharel
• Taro Konomi
• Thorsten Kamps
• Udo Friman-Gayer
• Val Kostroun
• Wencan Xu
• Xiaofeng Gu
• Xin Yang
• Yasaman Yousefi
• yingchao du
• Monday, 3 October
• 08:00 09:00
Coffe and Breakfast Treats 1h
• 09:00 10:20
Welcome and Introduction
Convener: Karl Smolenski
• 09:00
Director's Welcome 10m

A welcome to Cornell and the ERL 22 workshop by the laboratory director

Speaker: Prof. Donald Hartill (Cornell University)
• 09:10
Workshop Welcome 10m

A welcome to the workshop

Speakers: Georg Hoffstaetter (Cornell University (US)) , Stephen Benson (Thomas Jefferson National Accelerator La b)
• 09:20
ERL Introductory Talk 20m
• 09:40

Speaker: Andrew Hutton (Jefferson Lab)
• 10:20 10:40
Coffee Break 20m
• 10:40 12:20
Facility Reports: Session I
• 10:40
CEBAF 5-pass 20m

The 5-pass energy recovery project at CEBAF (ER@CEBAF) would become the first facility to have the energy reach to demonstrate ERL performance in the multi-GeV range. This increment in peak energy from the $1\,\textrm{GeV}$ CEBAF-ER demonstration to the target $\sim7\,\textrm{GeV}$ brings incoherent synchrotron radiation-induced energy loss, presents an invaluable opportunity for multi-pass beam break-up studies, and enables the experimental exploration of multi-pass, multi-GeV energy recovery. We update the current project status, studies on RF optics optimization, longitudinal match, and modifications to CEBAF.

Speaker: Gustavo Pérez Segurana (CERN)
• 11:00
Facility Report MESA 20m
Speaker: Florian Hug (Mainz University)
• 11:20
Facility report of Compact ERL (cERL) at KEK 20m

Compact ERL (cERL) is a test facility, which was constructed on the ERL Test Facility in KEK. Its aim was to demonstrate energy recovery concept with low emittance, high-current CW beams of more than 10 mA for future multi-GeV ERL. In 2016 and 2018, we successfully operate the CW 1 mA beam in the energy recovery condition. Recently, this cERL was operated to promote a variety of the industrial applications such as SASE-IR-FEL operation for future ERL based EUV-FEL production, THz operation and Rare Isotope (RI) production for medical application. In this presentation, we will present the status of the studies to realize the stable high-current, low-emittance CW beam and report some industrial and medical applications with this beam in cERL.

Speaker: Hiroshi Sakai (KEK)
• 11:40
STATUS AND PERSPECTIVE OF THE ENERGY RECOVERY LINAC AT HZB 20m

Since end of the year 2020 the energy recovery linac (ERL) project bERLinPro of Helmholtz-Zentrum Berlin (HZB) has been officially completed. But what is the status of this facility, the next scientific goals in the framework of accelerator physics at HZB, what are the perspectives? To reflect the continuation of this endeavor and the broadening of applications of this machine from high current SRF based energy recovery concept up to an ultrafast electron diffraction (UED) facility producing shortest electron pulses, the facility is now named Sealab, Superconducting RF Electron Accelerator Laboratory. In this contribution, an overview of lessons learned so far, the status of the machine, the coming set up and commissioning steps with an outlook to midterm and future applications will be given. In summary, Sealab will expand, including the ERL application, and become a general accelerator physics and technology test machine to employ injector parameter space and UED as a first application study case. It will also be an ideal testbed to investigate new control schemes and contribute by studies to the European ERL Roadmap for high energy physics programme.

Speaker: Axel Neumann (Helmholtz Zentrum Berlin)
• 12:00
ERL Operation of the Superconducting Darmstadt Electron Linear Accelerator S-DALINAC – a Facility Report* 20m

Institut für Kernphysik, Fachbereich Physik, Technische Universität Darmstadt

The superconducting Darmstadt linear accelerator S-DALINAC [1] is a thrice-recirculating accelerator for electrons at TU Darmstadt. Since its establishment in 1991, the S-DALINAC was mainly developed and operated by students. Besides the conventional acceleration scheme serving various nuclear-physics experiments, the accelerator can also be operated as an energy-recovery linac (ERL). Following the first operation as a once recirculating ERL [2], the S DALINAC achieved high-transmission multi-turn energy recovery in August 2021 [3]. Dedicated beam dynamics simulations, as well as beam diagnostic devices designed for ERL operation, are essential to operate an accelerator as an ERL. This contribution will give an overview of the facility with a focus on the ERL activities. Options for a successor ERL will be discussed.

*Work supported by DFG (GRK 2128, project ID 264883531), BMBF (05H21RDRB1), the State of Hesse within the Research Cluster ELEMENTS (Project ID 500/10.006) and the LOEWE Research Group Nuclear Photonics.

[1] N. Pietralla, Nuclear Physics News, Vol. 28, No. 2, 4 (2018).
[2] M. Arnold et al., Phys. Rev. Accel. Beams 23, 020101 (2020).
[3] F. Schließmann, Contribution to this conference

Speaker: Dr Michaela Arnold (TU Darmstadt)
• 12:20 13:20
Lunch 1h
• 13:20 15:00
Facility Reports: Session II
Convener: Dejan Trbojevic
• 13:20
BriXSinO high-flux dual X-ray and THz radiation source based on Energy Recovery Linacs 15m

We present the detailed design of a compact light source named BriXSinO. BriXsinO is a dual high flux radiation source Inverse Compton Source (ICS) of X-ray and Free-Electron Laser of THz spectral range radiation conceived for medical applications and general applied research. The accelerator is a push-pull CW-SC Energy Recovery Linac (ERL) based on superconducting cavities technology and allows to sustain MW-class beam power with just one hundred kW active power dissipation/consumption. Moreover, the BriXSinO layout allows performing two pass beam acceleration experiments.

ICS line produces 33 keV monochromatic X-Rays via Compton scattering of the electron beam with a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz. The THz FEL oscillator is based on an undulator imbedded in optical cavity and generates THz wavelengths from 15 to 50 micron.

Speaker: Dr Dario Giove (INFN Milano - LASA)
• 13:35
Facility Report CBETA 20m
Speaker: Georg Hoffstaetter (Cornell University (US))
• 13:55
TRIUMF e-Linac facility and ERL upgrade 15m

Speaker: Ms Aveen Mahon (TRIUMF | UVic)
• 14:10
Facility Report PERLE 20m
Speaker: Walid Kaabi (IJC Lab)
• 15:00 15:30
Coffee Break 30m
• 15:30 17:30
CBETA Tour
• 18:00 20:00
Welcome Reception 2h

Hors d'oeuvres and drinks at the Hilton Garden Inn Hotel

• Tuesday, 4 October
• 08:00 08:30
Coffe and Breakfast Treats 30m
• 08:30 10:05
Beam Dynamics and Instrumentation: Session I
Convener: Alex Bogacz (JLab)
• 08:30
Evidence of intrabeam scattering in high brightness electron linacs 15m

So far, IBS has not been observed in single pass electron accelerators because charge density orders of magnitude higher than in storage rings would be needed. We show that such density is now available at high brightness electron linacs for free-electron lasers (FELs).We report measurements of the beam energy spread in the FERMI linac in the presence of the microbunching instability, which are consistent with a revisited IBS model for single pass systems. We criticaly review experimental and numerical results in the literature in the light of most recent understanding of IBS-dominated dynamics, including a systematic characterization of the FERMI seeded FEL brilliance vs. electron beam optics, benchmarked with an IBS-MBI semi-analytical model. We also show that neglecting the hereby demonstrated effect of IBS in the parameter range typical of seeded VUV and soft x-ray FELs, results in too conservative a facility design, or failure to realise the accessible potential performance.

Speaker: Simone Di Mitri (Elettra Sincrotrone Trieste)
• 08:45
Multi-pass ERL Driven FELs and Light Sources 20m

Any proposal for an accelerator facility based upon a multipass energy recovery linac (ERL) must possess a self-consistent match in longitudinal phase space, not just transverse phase space. We therefore present a semianalytic method to determine self-consistent longitudinal matches in any multipass ERL. We apply this method in collider scenarios (embodying an energy spread minimizing match) and FEL scenarios (embodying a compressive match), and discuss the consequences of each. As an example of the utility of the method, we prove that the choice of common or separate recirculation transport determines the feasibility of longitudinal matches in cases where disruption, such as synchrotron radiation loss, exists. We show that any high energy multipass ERL collider based upon common recirculation transport will require special care to produce a self-consistent longitudinal match, but that one based upon separate transport is readily available. Furthermore, we show that any high energy multipass ERL FEL driver based upon common recirculation transport requires a larger resultant rf beam load than the one based on separate transport, favoring the separate transport designs.

Speaker: Gustavo Pérez Segurana (CERN)
• 09:05
Proposed Test of the Two Beam BPM at RHIC 20m

The essence of the ERL operation implies that at least two beams (accelerated and decelerated) are co-propagating in the same vacuum vessel and each beam has its own trajectory. The existing beam position monitors measure only “average” trajectory but not that of an individual beam, unless the time separation between bunches is so large that one can resolve individual bunches.
It was proposed to use phase information of the pick-up signal to extract information on the orbit “difference”. We are planning to conduct experiments at RHIC to test the proposed idea. The approach and experiment set-up are described in the paper.

Speaker: Igor Pinayev (Brookhaven National Laboratory)
• 09:25
Challenges of a Twice-Recirculating ERL Mode 20m

In a multi-recirculating energy-recovery LINAC (ERL), electrons are accelerated several times in the same LINAC and are decelerated afterwards in the very same LINAC just as often. Even in the case of a twice-recirculating ERL, there are challenges compared to a single-recirculating ERL: When low injector energies are used, phase slippage leads to significantly different energy gains per LINAC pass for the beam to be accelerated for the first time and the beam to be accelerated for the second time. If the cost-efficient sharing model is used, the once-accelerated and the once-decelerated beam share the same recirculation beamline. This case poses a particular challenge for finding a transverse confinement due to the lack of degrees of freedom for the once-decelerated beam: the beam optics adjusted to the once-accelerated beam must also ensure the guidance of the once-decelerated beam. The presence of phase slippage and the low number of degrees of freedom requires a sophisticated setup of the machine, which had to be determined in advance via beam dynamics simulations. We address challenges of a twice-recirculating ERL mode in the sharing model by presenting experiences and measured data obtained during the successful realization of that mode at S-DALINAC in 2021.

• 09:45
Beam Dynamics Challenges of a Far-Future ERL-Based Collider - The Ghost Collider 20m

In a recent paper, Valery Telnov proposed a linear collider based on twin axis cavities [1]. In a subsequent presentation, Erk Jensen proposed a modification with intra-bucket energy recovery [2], which eliminates higher order mode excitation. Interestingly, this means that there is no need for large aperture SRF cavities and high-power HOM couplers. The Ghost Collider adopts these ideas, and adds the concept of four-beam collisions (initially proposed by Joel LeDuff [3]) to remove beam-beam interactions and disruption. This concept brings up a series of new beam dynamics problems which make optimization of the parameters difficult. The presentation will describe the concept, which has a series of beam-dynamics challenges to be solved before the concept can advance.
[1] V.I. Telnov, JINST 16 (2021) no.12, P12025
[2] E. Jensen https://indico.cern.ch/event/1040671/?view=nicecompact
[3] Status Report on D. C. I, The Orsay Storage Ring Group, IEEE Transactions on Nuclear Science, Vol. NS-26, No.3, June 1979

Speaker: Andrew Hutton (Jefferson Lab)
• 10:05 10:25
Coffee Break 20m
• 10:25 12:25
Beam Dynamics and Instrumentation: Session II
Convener: Meghan McAteer (Helmholtz-Zentrum Berlin)
• 10:25
CBETA Instrumentation: From Beam Diagnostics to Machine Protection 20m
Speaker: Robert Michnoff (Brookhaven National LAb)
• 10:45
Using Polynomial Chaos Expansion to determine solenoid misalignment during bERLinPro commissioning 20m
Speaker: Bettina Kuske (HZB)
• 11:05
Beam Dynamics and Performance Studies of PERLE 20m
Speaker: Kevin Andre (CERN)
• 11:25
High Bunch Charge Operation with Small Emittance 20m
• 11:45
Multi-Turn Performance Studies and Beam Dynamics Issues 20m
Speaker: Steven Brooks (BNL)
• 12:05
Implications of beam filling patterns on the design of recirculating energy recovery linacs 20m
Speaker: Rob Apsimom (Cockroft Institute)
• 12:25 13:30
Industry Session: Introductions

During Lunch Industrial Participants will give brief introductions of their capabilities

Convener: Stephen Benson (Thomas Jefferson National Accelerator La b)
• 12:25 13:30
Lunch 1h 5m
• 13:30 15:10
SRF: Session I

Convener: Peter McIntosh (STFC)
• 13:30
SRF performance on the Compact ERL at KEK 20m

A superconducting Compact Energy Recovery Linac (cERL) was constructed in 2013 at KEK to demonstrate energy recovery concept with low emittance, high-current CW beams of more than 10 mA for future multi-GeV ERL. cERL consists of 500 kV DC photocathode gun, the injector cavities, the main linac cavity, which made energy recovery, recirculation loop and the beam dump.Under long-term beam operation, we met several SRF performance degradation like field emission and thermal breakdown. In this presentation, we will present how to keep SRF performance and overcome these issues to give the stable beam operation and show the long-term performance of SRF cavites of injector and main linac cryomodule until now.

Speaker: Hiroshi Sakai (KEK)
• 13:50
High gradient "turn key" SRF systems for small scale ERLs like MESA 20m
Speaker: Prof. Florian Hug (JGU Mainz, Institut für Kernphysik)
• 14:10
SRF photo-injector and Booster modules at bERLinPro: Assembly and commissioning status 20m

The energy recovery linac (ERL) at Helmholtz-Zentrum Berlin (HZB) is in the final stage of assembly and follow-up commissioning of the injector beam line. This injector consists of a 1.4\lamba/2 cell SRF photo-injector and a three two cell Booster cryomodule, the latter based on a modified design of the Cornell injector cavity shape. The injector was designed for a final beam current of 100 mA and an injection energy of 6.5 MeV into the 50 MeV recirculator. Currently, we are working on assembling and commissioning of the first cryo-module, being the SRF photo-injector, which already ran in 2018 [1], received a major overhaul of mainly the SRF cavities between 2019 to 2021, so that first beam is expected towards early 2023. In parallel, preparations to assemble the Booster cryo-module are on-going as well as final preparation of the injector beam vacuum system, which receives upgrades to also serve as an ultrafast electron diffraction (UED) beam line in addition to the foreseen accelerator research program and ERL studies at HZB. In this contribution, the development and current work on the SRF photo-injector will be presented in addition to latest results of the high power conditioning of the 120 kW Booster couplers.

Speaker: Axel Neumann (Helmholtz Zentrum Berlin)
• 14:30
Achieving stable cw operation in vector sum 20m
Speaker: Ramona Leewe (Triumf)
• 14:50
Design of the 9-cell superconducting cavity for EUV light source accelerator 20m

KEK has been designing the 10 mA class ERL-EUV light source accelerator. The main linac uses 9-cell superconducting cavities with beamline HOM damper. The target accelerating gradient is 12.5 MV/m. The 9-cell cavity is designed from experience of the KEK compact ERL (cERL) main linac. The cERL main linac was designed to suppress the HOM-BBU with beam current of 100mA by enlarging the iris diameter to 80mm. This resulted into the high ratio of the peak surface electric field and the accelerating field (Ep/Eacc) of 3. The accelerating gradient is limited from 8.5 to 10 MV/m during the CW beam operation due to field emission. The EUV can accept lower BBU limit than cERL because the target beam current of the EUV is 10 mA. The iris diameter is set to 70mm to lower Ep/Eacc around 2. The target accelerating gradient can be achieved if the surface peak electric field is equal to cERL. EUV end cells were designed to minimize HOM Q factor in the above condition. The optimal shape was designed by matching HOM frequencies of the two end cells and center cells calculated individually. The absorption heat of HOM damper is estimated to about 10 W. The AlN is known as high damping efficiency at cryogenic temperature. The HOM damper was designed using complex permittivity data measured at 80 K for AlN. The performance of the HOM damper combined with the cavity is capable of operating the beam at 10 mA. In this presentation, we will describe the EUV cavity and HOM damper design.

Speaker: Taro Konomi (FRIB)
• 15:10 15:40
Coffee Break 30m
• 15:40 17:00
Electron Sources: Session I

Electron Source (Guns) Technology and Developments

Convener: Luca Cultrera
• 15:40
Progress on 2D protective coating for photocathodes 20m
Speaker: Hisato Yamaguchi (LANL)
• 16:00
Progress on spin polarized electron beam sources for high current 20m
Speaker: Joe Grames (JLab)
• 16:20
Single-crystal alkali antimonide photocathode: High efficiency in the ultra-thin limit 20m
Speaker: Alice Galdi
• 16:40
Photocathodes for high average current electron beam: state-of-the-art and new perspective 20m
Speaker: Mengjia Gaowei (BNL)
• Wednesday, 5 October
• 08:00 08:30
Coffe and Breakfast Treats 30m
• 08:30 10:10
Uses and Applications: Session I

Applications of ERL accelerators

Convener: Dr Peter Williams (STFC, AsTeC)
• 08:30
ERL based EUV-FEL light source for lithography 20m

In extreme ultraviolet (EUV) lithography, high volume manufacturing recently started using a laser-produced plasma (LPP) source of 250-W power at 13.5 nm. However, development of a high-power EUV light source is still very important to overcome stochastic effects with a high throughput. The required EUV power to realize the 3-nm node and beyond with a high speed of future scanners is estimated to be more than 1 kW [1]. We have designed and studied an ERL-based EUV-FEL for future lithography [2-6] and showed that it can provide EUV power of more than 1 kW for ten scanners simultaneously. It is also upgradable to a “Beyond EUV” FEL light source that performs much finer pattering with shorter wavelength light (~6.7 nm). In addition, it can variably control the polarization of the EUV light, which might be utilized for high-NA lithography. Switching to the EUV-FEL light source from the LPP source can greatly reduce electric power consumption per scanner or 1-kW EUV power and it is suitable for sustainable semiconductor technologies and systems [7]. In this talk, I will present the ERL-based EUV-FEL light source for future lithography and the related activities.

[1] S. Inoue, Proc. of 4th EUV-FEL Workshop, Akihabara, Tokyo, Japan (2019).
[2] N. Nakamura et al., Proc. of ERL2015, Stony Brook, New York, USA, pp.4-9 (2015).
[3] N. Nakamura, R. Kato, T. Miyajima, M. Shimada, T. Hotei and R. Hajima, Journal of Physics: Conf. Series 874 (2017) 012013.
[4] H. Sakai et al., Proc. of SRF2017, pp.13-18 (2017).
[5] R. Kato, Proc. of 4th EUV FEL Workshop, Akihabara, Tokyo, Japan (2019).
[6] H. Kawata, N. Nakamura, H. Sakai, R. Kato and R. Hajima, J. Micro/Nanopattern. Mater. Metrol. 21(2), 021210 (2022).

Speaker: Norio Nakamura (High Energy Accelerator Organization (KEK))
• 08:50
ERL for Photonuclear Reactions 20m

The electromagnetic interaction of atomic nuclei with photons is a well-understood process that provides model-independent access to their properties. Consequently, photonuclear-reaction studies below and above the particle separation threshold have been a driving force in the study of the nuclear force for decades. Around the turn of the century, the field experienced a renaissance with the availability of intense, quasi-monochromatic, polarized photon sources in the MeV energy range based on the laser-Compton backscattering (LCB) process. Next-generation LCB facilities based on Energy Recovery Linacs (ERLs) have the potential to greatly enhance the reach of fundamental nuclear physics research. In addition, they are an important step towards technological applications of photonuclear processes.

This contribution will introduce the important reaction mechanisms of photons with atomic nuclei, in particular nuclear resonance fluorescence$^1$. After discussing the advantages and disadvantages of contemporary photon sources, the potential of ERL-based facilities will be discussed based on current research efforts.

$^1$ A. Zilges $\textit{et al.}$, Prog. Part. Nucl. Phys. $\textbf{122}$, 103903 (2019)

Speaker: Udo Friman-Gayer (Department of Physics, Duke University, and Triangle Universities Nuclear Laboratory, Durham, NC-27708, USA)
• 09:10
Strong Hadron Cooling in EIC with an ERL 20m

IntraBeam Scattering (IBS) and other diffusion mechanisms in the EIC Hadron Storage Ring (HSR) degrade the beam emittances during a store, with growth times of about 2 hours at the two nominal proton energies of 275 GeV and 100 GeV. Strong Hadron Cooling (SHC) maintains good beam quality and high luminosity during long collision stores. A novel cooling method – Coherent electron Cooling (CeC) – is chosen as the baseline SHC method, due to its high cooling rates. An Energy Recovery Linac (ERL) is used to deliver an intense high-quality electron beam for the cooling. In this talk, we discuss the beam requirements for SHC-CeC in HSR and describe the current status of the ERL design, as well as the challenges and the R&D topics that are being pursued.

Speaker: Erdong Wang
• 09:30
Energy Recovery Linac Design and Studies for Electron Cooling of EIC Hadron Beams 20m

The baseline scheme for hadron beam cooling in the Electron Ion Collider (EIC) calls for Coherent electron Cooling (CeC) of the hadrons with non-magnetized electrons at high energy (150 MeV electrons), and additional cooling via conventional bunched beam cooling using a precooler system. The electron beam parameters for these concepts are at or beyond the current state of the art, with electron bunch charges of the order of 1 nC and average currents on the order of 100 mA and require an Energy Recovery Linac (ERL)-based accelerator to produce such beams. Using specifications provided by BNL and Jefferson Lab, physicists and engineers at Xelera Research are working on a complete design of an ERL system capable of satisfying such a cooler. This work includes designs for the injector, merger, multi-pass Linac, merger into the cooling section, demerger into the return line (which includes 180-degree arcs), and final extraction of the energy-recovered beam, beam breakup simulations, tolerance studies, start-to-end simulations, and beam halo studies.

Speaker: Colwyn Gulliford (Xelera Research)
• 09:50
Novel Nuclear experiments at MESA 20m
Speaker: Kurt Aulenbacker (Mainz University)
• 10:20 10:40
Coffee Break 20m
• 10:40 12:20
Uses and Applications: Session II

Applications of ERL accelerators

Convener: Erdong Wang
• 10:40
Circular-Linear energy recovery accelerator to probe the energy-frontier 20m

Energy-frontier particle accelerators are among the most exciting, complex, challenging, and expensive research instruments performing high precision measurements confirming the fundamentals of the physics and broadening new research horizons. Currently the highest energy machines, from multi-GeV to several TeV, (ILC, FCC, CLIC) capable of searching for the most basic building blocks of matter are either driven by circular or linear accelerators. The circular machines, having the centre-of-mass (CM) energy values reaching 200 GeV (for leptons) and above, experience beam energy loss and quality dilution, for example, due to synchrotron radiation, limiting the overall CM energy achievable and requiring a constant energy top-up to compensate the loss and the beam quality dilution. Linear colliders overcome these limitations, while the finite capabilities of generating high average current beams limits the luminosity. This is partially compensated by the quality of the colliding beams. Most of the accepted state-of-the-art designs, while reaching the energies required, have very large footprint and show the same signs of limitations and drawbacks and in this work, we suggest a novel design of circular-linear accelerator based on the merging of the weakly emitting, low-energy storage rings and energy recovery linear accelerators. To enable the operation of such a system and in particular the energy recovery from spent, high-intensity beams the use of the dual-axis asymmetric cavities is suggested. The merging of circular and linear systems, and applications of dual axes cavities, aim to maintain high beam quality, high luminosity, and high energy efficiency, while simultaneously offering a flexible energy management. The concept presented can be potentially used to reach ultimate energy frontiers in high-energy physics as well as to drive next generation light sources combining tools for fundamental and applied studies. The numbers which will be presented are for illustration purpose and can be improved further.

Speaker: Dr I.V. Konoplev (1. JAI, University of Oxford, Oxford, UK. 2.Department of Physics, Sevastopol State University, Russia)
• 11:00
High-energy high-luminosity e+e− collider using ERL 20m
Speaker: Vladimir Litvinenko (Stony Brook University)
• 11:20
GeV muon beams with picometer-class emittance from electron-photon collisions 20m
Speaker: Luca serafini (INFN)
• 11:40
ion collisions in gas-jet targets of the dark-light type 20m
Speaker: Richard Milner (MIT)
• 12:00
Compton Backscattering sources 20m
Speaker: Dmitry Kayran (Brookhaven National Laboratory)
• 12:20 13:20
Lunch 1h
• 13:20 14:40
Electron Sources: Session II

Electron Source (Guns) Technology and Developments

Convener: Dmitry Kayran (Brookhaven National Laboratory)
• 13:20
PERLE electron source status and requirement for LHeC 20m
Speaker: Maude Balac (IJCLab)
• 13:40
High voltage DC gun for high intensity polarized electron source 20m
Speaker: Omer Rahman (BNL)
• 14:00
DC gun for Low Energy RHIC cooler (LEReC) project 20m
Speaker: Xiaofeng Gu (BNL)
• 14:20
The high repetition rate thermionic injector 20m

At Eindhoven university a high repetition rate thermionic injector is being built. The injector is capable of supplying electron bunches at a repetition rate of 1.5 GHz, which can be used for x-ray generation.
The electron source generates a continuous beam with a high current and low emittance through thermionic emission. The continuous electron beam is then chopped into a pulsed beam by a combination of a dual mode elliptical RF cavity and a knife-edge. The dual mode cavity uses both the fundamental mode (1.5 GHz) and its second harmonic (3.0 GHz) to increase the duty cycle of the chopping process to approximately 30% with a minimal loss of beam quality. Finally, a second dual mode elliptical RF cavity compresses the pulse length of the bunches, preparing the beam for injection into an X-band linear accelerator.
The first part of the injector is capable of operating at an emission current of 10 mA with a sub-50 nm rad transverse rms emittance. Construction of the elliptical chopper cavity has completed and is currently being implemented, after which the properties of the electron bunches after chopping will be measured.

Speaker: Rick van den Berg (Technische Universiteit Eindhoven)
• 14:40 15:00
Coffee Break 20m
• 15:00 16:00
SRF: Session II

Convener: Nilanjan Banerjee
• 15:00
High power coupler conditioning for the ERL injector Booster module 20m
Speaker: Axel Neumann (Helmholtz Zentrum Berlin)
• 15:20
Overview Nb3Sn cavity progress (for CW machine) 20m
Speaker: Liana Shpani
• 15:40
SRF systems for the EIC hadron cooling 20m
Speaker: Robert Rimmer (JLab)
• 16:00 20:00
Workshop Picnic 4h

Tour bus to Treman State Park for hiking and BBQ dinner, then return rides to the hotels

• Thursday, 6 October
• 08:00 09:00
Coffe and Breakfast Treats 1h
• 09:00 10:40
SRF: Session III

Convener: Hiroshi Sakai (KEK)
• 09:00
Speaker: Ramona Leewe (Triumf)
• 09:20
SRF Operations, microphonic control at CBETA 20m
Speaker: Nilanjan Banerjee
• 09:40
HOM-Damping Studies in a Multi-Cell Elliptical Superconducting RF Cavity for the Multi-Turn Energy Recovery Linac PERLE 20m

Higher order modes (HOMs) damping is a crucial issue for the next generation of high-current accelerators. Beam-induced HOMs can store sufficient energy in the superconducting RF (SRF) cavities giving rise to beam instabilities and increasing the heat load at cryogenic temperature. To limit these effects, the use of HOM couplers on the cutoff tubes of SRF cavities becomes crucial to absorb beam-induced wakefields, consisting of all cavity eigenmodes. These couplers feature probe or loop antennas designed to couple ERL optics-related dipole cavity modes and to reject the fundamental mode sufficiently. The study presented here focuses on a 5-cell 801.6 MHz elliptical SRF cavity designed for PERLE (Powerful Energy Recovery Linac for Experiments), a multi-turn ERL currently under study and to be hosted at IJCLab in Orsay. Several coaxial coupler designs are firstly analyzed by means of equivalent circuit models. A subsequent coupler optimization is made on a 3D geometry of the coupler to enhance the damping of dipole HOMs of the 5-cell cavity. The broadband performance of HOM damping and power deposition is also confirmed by the time-domain wakefield and the frequency-domain simulations. In addition, the thermal behavior of the HOM couplers is investigated. A comparison between various HOM-damping schemes is carried out to guarantee an efficient HOM power extraction from the cavity.

Speaker: Mr Carmelo Barbagallo (IJCLab - Université Paris-Saclay)
• 10:00
Horizontal test of Superconducting RF gun #2 at KEK 20m

Superconducting radio-frequency (SRF) electron guns are attractive for delivery of beams at a high bunch repetition rate with a high accelerating field. KEK has been developing the SRF gun to demonstrate basic performance. The SRF gun consists of 1.3 GHz and 1.5 cell SRF gun cavity and K2CsSb photocathode coated on 2K cathode plug. In the vertical test, the surface peak electric field and the surface peak electric field reached to 75 MV/m and 170 mT respectively. The SRF gun was installed to horizontal multipurpose cryostat equipped with a superconducting solenoid, photocathode preparation chamber and beam diagnostic line. Unfortunately, the peak surface gradient dropped to 42 MV/m. This was probably due to particulate issued that entered the cavity during assembly. We suspect that it was caused particulate are come into the cavity during assembly. In this presentation, we will describe the high gradient performance in vertical and horizontal test and individual test for each beam line components.

Speaker: Taro Konomi (FRIB)
• 10:20
Fast Reactive Tuner developments at CERN 20m
Speaker: Nik Shipman (CERN)
• 10:40 11:00
Coffee Break 20m
• 11:00 12:00
Electron Sources: Session III

Electron Source (Guns) Technology and Developments

• 11:00
Long term operational experience of running Cs2Te cathodes in HZDRs SRF gun 20m
Speaker: Rong Xiang (Helmholtz-Zentrum Dresden-Rossendorf)
• 11:20
Low frequency 113MHz SRF gun with room temperature photocathode for Coherent electron cooling experiment (CeC-X) 20m
Speaker: Irinia Petrushina (BNL)
• 11:40
Commissioning of the SLAC Linac Coherent Light Source II electron source 20m
Speaker: Feng Zhou (SLAC)
• 12:00 13:00
Lunch 1h