EWPAA 2024In-Person Event

17 Sept 2024, 08:00 → 19 Sept 2024, 15:00 Europe/Berlin

106/255 - Hörsaal / Lecture Hall (HZDR)

Anton Ryzhov (HZDR), Rong Xiang (Helmholtz Zentrum Dresden Rossendorf)

Dear Colleagues,

We are pleased to announce the next European Workshop on Photocathodes for Particle Accelerator Applications (EWPAA 2024) which will be held on September 17-19, 2024. This in-person workshop will be hosted by Helmholtz-Zentrum Dresden-Rossendorf in Dresden, Germany.

Following the successful experience of previous EWPAAs, our goal is to create a communication platform for photocathode enthusiasts worldwide. This will be achieved through a scientific program that includes both oral presentations as well as poster sessions to facilitate face-to-face interactions between participants.

The workshop is supported by Helmholtz Center Dresden-Rossendorf (HZDR) and German Research Foundation (DFG project No. 545151564). There is no registration fee for the workshop.

We cordially invite you to participate in the workshop and present your research. The program will cover a variety of areas, including operational experience, preparation, materials, instrumentation, analytical methods, theoretical modelling, industrial applications, and novel concepts.

The sessions will be mostly composed of invited talks, and few remaining time slots may be filled with proposed contributions. Abstract submission for both, invited talks and posters, will open on April 1 – we are eager to see your contributions!

 

Scientific Program Committee 
Maud Baylac (CNRS-LPSC)  
Caterina Cocchi (Universitat Oldenburg)  
Romain Ganter (PSI)  
Lee Jones (UKRI STFC)
Julius Kühn (HZB)  
Tim Noakes (UKRI STFC)  
Daniele Sertore (INFN Milano - LASA)  
Rong Xiang (HZDR)

Local Commitee 
Rong Xiang (HZDR)  
Anton Ryzhov (HZDR)

Conference Poster

EWPAA_Proceedings_Template.docx

Group_photo_DSCF8994_ed2.png

Tuesday 17 September

08:00 Bus Dresden > HZDR

08:45 Registration

Welcome and Overview of Photocathode Research

Rong Xiang

1 Welcome

Speaker: Prof. Sebastian Schmidt (HZDR)

2 European cathode activities

Activities on photocathodes are constantly evolving. In Europe, in particular, new experiments/accelerators are emerging alongside the historical players in this field. This presentation aims to update the status of activities in Europe from the state made at EWPAA2022, with a focus on new initiatives and topics that are emerging in this field.

Speaker: Dr Daniele Sertore (INFN)

EWPAA2024_Europe.pptx

3 Summary PPP 2023 workshop

Speaker: Dr Luca Cultrera (BNL)

EWPPA2024-P3 summary- FINAL.pdf

4 Cathode activities in Asia

Speaker: Dr Masao Kuriki (Hiroshima University)

1709_1_4_MKuriki.pdf

11:00 Coffee break

Photocathode performance in accelerator applications

Lee Jones

5 Cathode for LCLS

Speaker: Dr Theo Vecchione (LCLS)

1709_2_1_Vecchione_Cathode_for_LCLS.pdf

6 Na-K-Sb photocathodes for high brilliant electron beams

The goal of the Sealab/bERLinPro project is to build a new generation superconducting RF electron accelerator at HZB. Na-K-Sb photocathode deposited on Mo plug is chosen for this application for its high QE at green laser, long dark lifetime and high thermal stability.
Currently, Na-K-Sb photocathodes are produced in UHV preparation chamber at photocathode lab. In the contribution, we will share our experience for film growth (2 recipes), as well as the QE, dark lifetime and thermal stability on Na-K-Sb photocathodes. Besides, we would also like to give an introduction of the update of preparation system at photocathode lab.

Speaker: Mr Chen Wang (HZB)

2024-09-18-EWPAA2024-Chen.pptx

7 Cathode for mA high current

High-brightness electron sources are crucial for applications like X-ray free electron lasers (XFEL), ultrafast electron diffraction (UED), and electron ion colliders (EIC), etc. At Peking University, the DC-SRF gun operates reliably at a low emittance mode of 0.54 mm·mrad(normalized) with 100 pC bunch charge at 1 MHz repetition rate, and a high current mode of 37 pC at 81.25 MHz (3 mA). The K2CsSb photocathode is illuminated by a 515 nm green laser, achieving a quantum efficiency (QE) of 6-8%, which drops to around 1% in the cold gun electrode at ~30 K. The photocathode maintains its efficacy for up to a month during experiments, delivering 0.1~3 mA during a 16-hour continuous-wave (CW) test. Additionally, the response time and intrinsic emittance of the bialkali photocathode were also evaluated.

Speaker: Dr Huamu Xie

EWPAA2024.pptx

8 Boosting Photocathode Performance through Plasmonic Effects and In-situ Rejuvenation Techniques

Semiconductor Cs-Te photocathodes are essential components in high-brightness electron sources, playing a pivotal role in the operation of large-scale accelerators. However, their operational lifetime and efficiency remain critical challenges. To address these challenges, we explore two complementary approaches to enhance photocathode performance and longevity: First, we analyze the systematic production and rejuvenation of Cs-Te photocathodes, and second, we introduce a novel method to overcome the limitations of conventional photocathodes by utilizing direct-laser nanostructuring techniques on copper substrates. This nanoengineering approach excites localized surface plasmons, generating hot electrons that contribute to a substantial increase in quantum efficiency (QE).

Speaker: Eduardo Granados (CERN)

EWPAA_2024_Granados_compact.pdf

EWPAA_2024_Granados_compact.pptx

13:00 Lunch

Novel concepts and lasers

Laura Monaco

9 Overview of the SwissFEL photocathode lasers and cathode R&D

SwissFEL, the Swiss Free Electron Laser facility in user operation since 2019 is a 700m long X-ray FEL delivering femtosecond soft and hard X-ray photons in two parallel beamlines, respectively Athos and Aramis. In order to achieve low emittance and short electron bunches, SwissFEL uses a photo-injector. In that context, the photocathode lasers facility is a crucial subsystem that must seed the photo-electron gun with high-end performance, shaping capabilities as well as long term stability and reliability. In parallel, we produced and use CsTe cathode with high QE and long lifetime. The talk will lead you through the key steps as well as the state of the art technological and optical solutions that have been developed and implemented to build the photocathode lasers facility and the cathode.

Speaker: Alexandre Trisorio (Paul Scherrer Institute)

2024_09_17_ Talk EWPPA_Trisorio.pptx

10 Laser-plasma based electron sources for FEL applications

Speaker: Arie Irman (HZDR)

EWPAA2024_ArieIrman_vf.pptx

11 Novel Integrated Photonics and Plasmonic Photocathodes

Next-generation electron sources, including novel plasmonic and photonics-integrated cathodes, are poised to revolutionize applications ranging from low bunch charge stroboscopic ultrafast electron diffraction and microscopy to beam-driven wakefield accelerators requiring transversely shaped electron bunches. In this study, we report the generation of a record low root mean square (RMS) normalized transverse electron emittance of less than 40 pm-rad from a plasmonic photocathode—a reduction of at least an order of magnitude from previous benchmarks. This was achieved through plasmonic light focusing using Archimedean spiral structures, resulting in an RMS electron emission spot size of approximately 50 nm. Additionally, we demonstrate the feasibility of photonics-integrated photocathodes by utilizing nanofabricated waveguides and thin alkali antimonide photoemissive films to produce transversely shaped electron beams. These findings underscore the potential of these advanced cathodes in developing next-generation high-brightness electron sources for a wide range of accelerator applications.

Speaker: Alimohammed Kachwala (Arizona State University)

Kachwala_V1.pdf

Poster session

12 1-slide-1-minute teaser talks

1-slide-1-minute.pdf

13 A Novel Method for TiN Thin Film Deposition for Next-Generation Electron Source Photocathodes

Titanium Nitride (TiN) has recently garnered much interest as a potential photocathodic material with superior properties to conventional materials [1]. TiN thin films can be grown on various substrates using magnetron sputtering or vapour deposition techniques. However, these require an existing sputter target or powder of high-quality TiN. This study presents a molecular beam epitaxy approach to TiN thin film growth, developing a method of TiN deposition via reactive ion beam sputtering. Ti and TiN thin films were grown on Cu, SiO2 and Si substrates and are characterised using AFM, XPS and low magnification light microscopy. The geometry of the deposition chamber and its effect on uniformity and quality of the growth product is also discussed. XPS analysis confirms the presence of TiN on the surface via the shifted N 1s peak. This crystalline thin-film of TiN shows promise as a protective over-layer for next-generation photocathodic materials which are more sensitive to atmospheric poisoning than the previous generation.

Speaker: Dominic Sterland (University of Warwick)

EWPAA teaser slide.pptx

Poster EWPAA 2024.pdf

14 Adaptive Automated Activation Procedure for GaAs Photocathodes*

Photo-electron sources utilizing GaAs-based photocathodes are used to provide high-brightness and high-current beams of possibly spin-polarized electrons for accelerator applications such as free-electron lasers (FELs) and energy recovery linacs (ERLs). These cathodes require a thin surface layer consisting of cesium and an oxidant in order to achieve negative electron affinity (NEA) for efficient photoemission. The layer is deposited during the so-called activation procedure, whose behavior greatly influences the resulting quantum efficiency of the photocathode and robustness of said layer. It is therefore of great interest to optimize and standardize this process to provide easily reproducable, high-performance GaAs-photocathodes. An automatization of the activation procedure can streamline this process, making it independent from expert input for operational use in an accelerator. At the Institute for Nuclear Physics at Technische Universität Darmstadt, a dedicated test stand for Photo-Cathode Activation, Test and Cleaning using atomic-Hydrogen (Photo-CATCH) is available for GaAs photocathode research. The components of its activation chamber are remote-controlled using a combination of EPICS and python. This contribution will present recent studies of an adaptive automated activation procedure at Photo-CATCH. Following the co-deposition scheme with Cs and O2, several automated activations have been performed. A good reproducibility of quantum efficiency has been observed, comparable to manual activations.

*Work supported by DFG (GRK 2128 “AccelencE”, project number 264883531)

Speaker: Markus Rainer Engart (TU Darmstadt)

Teaser-Slide_Engart.pdf

15 Energetic and electronic properties of K-Sb and Na-Sb binary crystals from high-throughput ab initio calculations

Alkali-based photocathode materials have come into the limelight as novel semiconducting materials for electron sources. However, the study of the fundamental properties of alkali antimonide photocathodes is currently hindered by the limited purity of the samples and the complexity of the growth process.
First-principles studies can effectively complement experiments to gain insight into the stability and the electronic structure of these compounds. In this work, we investigate K-Sb and Na-Sb binary crystals taking input structures available from computational databases. Adopting automatized routines for density functional theory as implemented in the in-house developed library aim2dat [1], we evaluate the energetic stability of the scrutinized materials by generating a convex hull of stable crystals as a function of the relative ratio between the involved species. The absolute minimum of the convex hull for the Na-Sb compounds corresponds to the 3:1 stoichiometry extensively predicted and characterized experimentally. On the other hand, among the K-Sb compounds, the convex hull forms a plateau of stable structures between 1:1 and 3:1 ratios. We analyze the electronic properties of the stable crystals focusing on the correlation between band-gaps and material composition. The analysis of the electronic properties of representative stable compounds for both sets of structures highlights similarities, especially for the known cubic phases Na3Sb and K3Sb, but also remarkable differences. K-based semiconductors span a smaller range of band gap values up to 1.3 eV, while Na-containing crystals have larger band gaps up to 2.5 eV. For the Na-Sb binaries, there is a clear trend relating the size of the band gap with the relative Na content: indirect low-band-gap semiconductors are found among Na-poor phases while large, direct semiconductors appear with 3:1 Na-Sb ratio. In both sets of compounds, metallic phases appear.
Our results [2] provide useful indications to predict and characterize binary phases forming during the growth of multi-alkali antimonide photocathodes. Additionally, the analysis of the electronic structure of the stable compounds gives insight into the fundamental properties of stable compounds. This information is essential to complement the experimental characterization of alkali antimonide samples grown via evaporation techniques that often exhibit metastable or polycrystalline structures.
[1] https://github.com/aim2dat/aim2dat
[2] R. Schier, D. Guo, H.-D. Saßnick, and C. Cocchi, Stability and electronic properties of K-Sb and Na-Sb binary crystals from high-throughput ab initio calculations, submitted (2024).

Speaker: Richard Schier

introductory_slide.pdf

introductory_slide.pptx

16 High current photogun and photocathode preparation for the PERLE project

In an Energy Recovery Linac (ERL), the beam, after acceleration and interaction, is recirculated and decelerated in the accelerating cavities of the linac. In such a scheme, the energy of the beam is recovered, leading to substantial savings in electrical power. Moreover, the beam is dumped at injection energy, considerably simplifying the radioprotection of the facility. The PERLE project aims at developing a multi-turn high power ERL in Orsay. The high intensity electron beam (20 mA) will be generated by a photoinjector, based on a DC photogun. Photocathodes of bi-alkali material will be produced by preparation facility connected to the photogun under vacuum for a fast transfer. This R&D is pursued within the framework of a collaboration agreement with RI Research Instruments.

Speaker: Maud Baylac (CNRS - LPSC)

teaser-PERLE-EWPAA24.pptx

17 High-Precision Measurements of Asymmetry and Quantum Efficiency in Photocathodes for Polarised Electron Beam Experiments

At the new, energy-recovering superconducting accelerator MESA in Mainz, spin-polarised electrons are required in the P2 experiment. Here the requirements increase considerably compared to the experiments at the micotron MAMI in Mainz.

A very sensitive part of the photocathodes lies in the specially prepared surface, characterised by its negative electron affinity. This surface is highly sensitive to residual gases in vacuum and subjected to ion back bombardment.
Traditionally, this negative electron affinity is achieved through a preparation involving caesium and oxygen. Beam current losses induce a degradation of quantum efficiency and, in addition, the spin polarisation undergoes significant change.
The exploration of the intricate relationship between asymmetry and quantum efficiency bears considerable importance, especially for the P2 experiment.

Our aim is to clarify this connection and its implications, offering insights into managing spin polarisation and quantum efficiency in photocathodes.

Speaker: Mr Kurt Aulenbacher (Institut für Kernphysik der JGU Mainz)

EWPAA_Contribution_Aulenbacher,Kurt_Figure.pdf

EWPAA_Contribution_Aulenbacher,Kurt.tex

EWPAA_Trieb_pitch.pdf

18 Photoemission and Bright Beams Lab at ASU

The Photoemission and Bright Beams Lab at ASU performs experimental and theoretical research to develop a fundamental understanding of light-matter interactions as relevant to the photoemission process with the goal of developing advanced electron sources for electron microscopy, ultrafast science, and nuclear and high energy physics. We employ the smoothest of atomically ordered surfaces at cryogenic temperatures under extraordinarily high electric fields along with the intense femtosecond pulsed lasers to obtain the brightest photoemission electron sources. The lab houses state-of-the-art surface preparation and characterization facilities connected in ultrahigh- vacuum to unique photoemission characterization techniques and a 200kV cryogenic DC electron gun to demonstrate the generation of the brightest possible beams. The DC electron gun can be used to generate bright femto-second scale electron bunches to study the ultrafast dynamics of materials.

Speaker: Alimohammed Kachwala (Arizona State University)

Ali_EWPAA24_VFinal.pdf

Teaser.pdf

19 Spectral response and quantum efficiency of rejuvenated Cesium Telluride photocathodes for high average current photoinjectors

Cesium telluride (Cs-Te) photocathodes are widely used as an electron source in photoinjectors due to their high quantum efficiency (QE) and reliable performance. Unfortunately, they are chemically highly reactive, which limits their operational lifetime and require frequent interventions for Cs-Te film replacement or rejuvenation. The precise control of the Cs-Te deposition stoichiometry ratio during the photocathode fabrication process is essential to optimise the resulting QE and emittance of electron sources. For example, an excess of Cs or the formation of another CsxTe phase can lead to a sub-optimal electron bunch energy spread or a decrease in overall quantum yield. In this study, we analyse the photoemissive characteristics of Cs-Te photocathodes rejuvenated by co-depositing a Cs-Te layer over a degraded one. The QE of the photocathodes was measured using a 10 Hz 5 ns pulsed OPO in the wavelength range from 240 to 430 nm. This experiment allows to estimate the photoemission threshold and corresponding energy distribution of emitted electrons, and to compare with the expected spectral response.
Our results contribute to a deeper understanding of Cs-Te photocathodes and provide practical insights for optimising production to improve performance and reliability.

Speaker: Palma Klara Katona (CERN)

EWPAA2024_poster_Katona.pdf

EWPAA_Teaser_slide.pptx

20 Thermodynamic Stability and Vibrational Properties of Multi-Alkali Antimonides

Modern advances in generating ultrabright electron beams have enabled significant experimental progress using synchrotron radiation. Current challenges include improving the quality of electron sources with novel photocathode materials such as alkali-based semiconductors. To fully harness their potential, a detailed characterization and prediction of their fundamental properties are essential. In this work, we employ density functional theory combined with machine learning techniques, integrated into the hiphive package, to probe the thermodynamic stability of various alkali antimonide crystals, emphasizing the role of the approximations taken for the exchange-correlation potential. Our results reveal that the SCAN functional offers an optimal trade-off between accuracy and computational cost in describing the vibrational properties of these materials. Furthermore, we find that systems with a higher concentration of Cs atoms exhibit enhanced anharmonicities, which are accurately predicted and characterized using our methodology.

Speaker: Julia Santana Andreo (Carl von Ossietzky Universität Oldenburg)

Flash_Julia_Santana.pdf

17:00 Bus from HZDR to Dresden

Wednesday 18 September

08:30 Bus Dresden > HZDR

Low emittance applications

Romain Ganter

21 Photocathode options for low emittance injectors

Speaker: John Smedley (SLAC)

EWPAA talk short.pptx

22 The Relativistic Ultrafast Electron Diffraction And Imaging (RUEDI) Facility

The Relativistic Ultrafast Electron Diffraction and Imaging (RUEDI) facility has been recently approved by the UKRI Infrastructure Fund to be a new ultrafast science capability for the UK based at Daresbury Laboratory. It 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 extreme conditions; quantum materials; energy generation, storage, and conversion; and biosciences. The evolution of the design of the facility will be outlined along with the remaining challenges to deliver a world leading capability. Particular reference to the photoinjector and photocathode options chosen will be made.

Speaker: Tim Noakes (STFC Daresbury Laboratory)

4_2_Noakes.pptx

23 Pulsed laser deposition assisted epitaxial growth of cesium telluride photocathode for high brightness electron source

Photocathodes play an integral role in the development of electron accelerators and photon detectors. In spite of having an ultrasmooth photocathode developed by a co-deposition process [Gaowei et al (2019)], there are still limitations on emitted beam brightness by the surface and bulk disorder of the polycrystalline photocathode material. Epitaxial growth of photocathodes has the potential to overcome this problem and achieve high-brightness electron beams [Parzyck et al (2022)]. This work demonstrates the epitaxial growth of Cs2Te photocathodes on a variety of single-crystal substrates. In our study, the growth of an epitaxial layer with a flat surface and high crystallinity is confirmed by reflection high energy electron diffraction (RHEED) for the Cs2Te thin film. In situ x-ray characterization is used to confirm the film stoichiometry, surface roughness, and crystallinity. Spectral responses are observed, where Cs2Te thin film photocathodes with a Quantum Efficiency (QE) of about 17 % of peak value at 270 nm are obtained from epitaxially grown Cs2Te with a film thickness ~ 20 nm and with a surface roughness of less than 1 nm.

Speaker: Kali Prasanna Mondal (Collider-Accelerator Department, Brookhaven National Laboratory)

Cs2Te_Epitaxial_growth_KPMondal.pdf

24 Status of the Photoemission and Mean Transverse Energy Experiment – PhoTEx

At Helmholtz-Zentrum Berlin photocathodes are developed as electron source for the SRF-photoinjector of the superconducting RF electron accelerator laboratory (SEALab). Sodium-Potassium-Antimonide (Na-K-Sb) photocathodes are grown and characterized by spectral response and X-ray photoelectron spectroscopy in the photocathode lab, but until now there was no device to analyze the mean transverse energy (MTE) of the photocathodes at HZB, which is also an important figure of merit.

Therefore the Photoemission and Transverse Energy Experiment ‘PhoTEx’ was developed to to study the MTE, quantum efficiency (QE) and lifetime of these photocathodes independent from the preparation chamber. The device was build as a stand-alone drift tube spectrometer. A tunable light source allows the illumination of the cathode in the full visible regime. Simulations showed that the instrument will be able to measure the MTE in the range of 40 meV up to 5 eV with a relative uncertainty of 10 %.
PhoTEx is fully assembled and ready to measure the first Na-K-Sb photocathode. In this talk the PhoTEx system is presented in detail.

Speaker: Jonas Dube

EWPAA_2024_Dube_final.pptx

11:00 Coffee break

„Green“ photocathodes development

Julius Kühn

25 Promoting epitaxy in alkali antimonides

Speaker: Jared Maxson (Cornell)

EWPAA-Maxson-2024.pptx

26 Atomically smooth films of CsSb: a chemically robust visible light photocathode

Cs3Sb and related alkali antimonide compounds are high efficiency semiconductor photocathodes that can be operated with visible light and possess quantum efficiency of the order of 1-10% at green light wavelength. Use of these photocathodes in modern linear accelerators is desirable thanks to their potential to generate high brightness electron beams. However, the ultimate brightness of a photocathode is limited by surface disorder of the usually polycrystalline and inhomogeneous films. We used state-of-the-art molecular beam epitaxy to achieve epitaxy of the Cs3Sb phase for the first time, thus realizing ordered, homogeneous surfaces. Furthermore, using in-situ electron diffraction as a structural probe during growth, instead of quantum efficiency, we were able to stabilize atomically flat films with composition Cs:Sb~1:1, a phase characterized by higher photoemission threshold than Cs3Sb, having ~1% quantum efficiency at 405 nm and higher resistance to oxygen poisoning.

Speaker: Dr Alice Galdi (Università degli Studi di Salerno)

EWPAA22_AGaldi_CsSb.pptx

27 Development of Multialkali antimonides photocathodes for high-brightness photoinjectors

Speaker: Mr Sandeep Mohanty (DESY)

EWPAA 2024_Green cathode.pptx

28 High QE photocathode preparations and tests at SHINE

Speaker: Xudong Li (Shanghai Advanced Research Institute, Chinese Academy of Sciences, China)

EWPAA_2024_Xudong_final.pdf

13:00 Lunch

Photocathode theory and characterization

Tim Noakes

29 Machine Learning-Assisted Design of Cesium-Based Photocathodes from First Principles

Cesium-based photocathodes, such as cesium-telluride, are commonly used as electron sources in particle accelerators. Yet, precise control over these materials is hindered by challenges in regulating their crystal structure and stoichiometry during synthesis. While ab initio methods such as density functional theory (DFT) can successfully complement experimental efforts, they also require structural information as an input. Hence, the lack of reliable experimental data in this regard limits the potential of computational research and thus their contribution to unveil the fundamental properties of the photocathode materials. To overcome these limitations, we propose a novel approach combining high-throughput DFT calculations with machine learning. Our method predicts stable crystal structures within binary and ternary systems by systematically evaluating various structural descriptors and machine learning algorithms. We demonstrate the superiority of models based on atomic coordination environments, with transfer-learned graph neural networks emerging as a particularly promising technique. By validating our approach on well-characterized Cs-Te materials, we showcase its potential to enhance traditional computational methods and accelerate the development of advanced photocathode materials.

Speaker: Holger-Dietrich Saßnick (Institute of Physics, Carl-von-Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany)

ewpaa_24_pres_holger.pdf

30 Comparing theory with experimental data

Speaker: Dr Felix Mildner (Imperial College)

1809_6_2_FMildner_EWPAA_Dresden_2024.pptx

31 An Overview of MTE Measurement Techniques and Photocathode R&D at Daresbury Laboratory

In this presentation, I will give a brief overview of some of the established and productive methods for measuring the transverse and longitudinal energy spreads from photocathode electron sources (Mean Longitudinal Energy and Mean Transverse Energy, or MLE and MTE respectively). These quantities represent the intrinsic emittance of the photocathode electron source. The generation of a high-brightness electron beam can be achieved through the operation of a photocathode with a low intrinsic emittance. Measurement of the intrinsic emittance can be challenging as the electron energies are frequently small, as are the MLE and MTE themselves. Over recent decades, several different systems have been developed which are capable of successfully measuring these performance characteristics, some of which go further to characterise spectral response too, for example.
The motivation for this aspect of accelerator science is frequently linked to the operation of an X-ray Free-Electron Laser (X-FEL), and this is the justification for the work being carried out in this field at the STFC Daresbury Laboratory.
In the second half of this presentation, I will review the work currently being undertaken by the Daresbury Photocathode R&D team and link this to various accelerator projects, focussing on the progress made since the last meeting.

Speaker: Dr Lee Jones (UKRI STFC)

1809_6_3_EWPAA '24 - Lee Jones - Photocathode R&D at Daresbury Laboratory.pptx

32 Photocathode characterization using a UV-tunable ultrashort pulse radiation source

See attached file.

Speaker: Walter Schroeder (University of Illinois at Chicago)

EWPAA2024_slides_white.pptx

EWPPA2024abstract.pdf

Lab Tour

15:40 Lab tour

17:30 Getting-together Dinner

19:00 Bus transfer from HZDR to Dresden

Thursday 19 September

08:30 Bus Dresden > HZDR

Cathodes for polarized electron sources

Maud Baylac

33 Activation studies for GaAs photocathodes at Photo-CATCH

The institute for nuclear physics at TU Darmstadt houses a test stand for Photo-Cathode Activation, Testing and Cleaning using atomic-Hydrogen (Photo-CATCH). It enables dedicated research on, e.g., quantum efficiency and lifetimes of GaAs photocathodes as well as DC photo-gun design for future use at the in-house Superconducting Darmstadt Linear Accelerator S-DALINAC. This contribution will give an overview of recent, ongoing and planned activation studies at Photo-CATCH.

*Work supported by DFG (GRK 2128 “AccelencE”, project number 264883531)

Speaker: Maximilian Herbert (Institut für Kernphysik, Technische Universität Darmstadt)

2024_EWPAA_Vortrag_mherbert.pdf

2024_EWPAA_Vortrag_mherbert.pptx

34 High intensity polarized beam photogun to drive a positron source

A photogun to generate high intensity, high polarization electron beam with unprecedented kC lifetime is being envisioned at JLab for the proposed Ce+BAF polarized positron source. The positron source will require > 1 milliampere CW with > 90% polarization electron beam at 120 MeV. To be practical for a user program, a photogun operating at 1 milliampere should deliver ~2 kC high polarization beam for a month without intervention. The limiting factor is ion-back bombardment of the delicate strained super lattice photocathode. The number of ions can only be
reduced by improving vacuum in the accelerating anode-cathode gap and biasing the anode.
Additionally, the ion induced damage can be spread out by illuminating the photocathode with larger laser spot sizes. Earlier tests of this approach resulted in improved lifetime, but was limited by the photogun electrode size. The envisioned photogun design will incorporate large electrodes to accommodate unprecedented large laser spot sizes shifted as far as possible from the photocathode electrostatic center, and large conical insulators to operate at > 300 kV for beam capture into a SRF booster.

Speaker: Dr Carlos Hernandez-Garcia (Jefferson Lab)

High intensity polarized beam photogun to drive a positron source EWPAA CHG abstract.pdf

High intensity polarized beam photogun to drive a positron source EWPAA FINAL.pptx

35 Cathodes with optimized quantum efficiency for driving a spin polarized positron source

Polarized positron beams generated from MeV-class accelerators may become useful for applied physics. We first discuss how existing facilities – e.g. the low emittance positron beamline at the MAMI accelerator in Mainz - can be extended towards spin-polarized operation. In the end, however, it is the intensity of the driving polarized electron source which is one of the most important limiting factors for the positron intensity that could be expected. We discuss important factors that need to be optimized from the cathode point of view, such as quantum efficiency and heat transfer.

Speaker: Kurt Aulenbacher (Institut für Kernphysik der JGU Mainz)

Abstract EWPAA 2024.pdf

EWPAA_Photcathodes with optimized QE for spin polarzed positrons2.pdf

36 DBR Photocathodes for EIC polarized electron source

The future Electron Ion Collider (EIC) will use photocathode based DC electron guns for both polarized and unpolarized electron beam generation. In this talk, the current status and recent progress of polarized photocathode research and applications at Brookhaven National Lab (BNL) will be presented. We will describe the experimental results from 300 a kV DC electron gun with DBR-SSL-GaAs photocathodes, including surface charge limit and lifetime studies.

Speaker: Omer Rahman (Brookhaven National Lab)

DBR photocathodes for EIC polarized electron source_Rahman_EWPAA_2024.pdf

11:00 Coffee break

Summary and discussion

37 Summary from sessions 1-7

13:00 Lunch

14:00 Bus transfer from HZDR to Dresden