| Paper | Title | Page |
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TUXX01 |
Review of High Brightness Photoinjectors | |
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| High brightness photoinjectors have become the enabling technology in accelerator based light sources, ultrafast electron microscopy, energy recovery linac for ion cooling and many other advanced accelerator concepts. To match the frontiers of these scientific applications, photoinjectors continue to develop for both higher peak and higher average beam brightness. In this review, state of the art photoinjector performances and developments are presented. | ||
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| TUPAB034 | Development of Multi-Alkali Antimonides Photocathodes for High-Brightness RF Photoinjectors | 1416 |
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| Multi-alkali antimonide-based photocathodes are suitable candidate for the electron sources of next-generation high brightness RF photoinjectors due to their excellent photoemissive properties especially, like low thermal emittances and high sensitivity to visible light. The former stands out, paving the way towards CW operations. Based on the previous successful development of Cesium Telluride photocathodes, we are now channelling our efforts toward an R&D activity focused on KCsSb and NaKSb(Cs) photocathodes. Parallel to that R&D activity, we have installed a new dedicated photocathode production system at the INFN-LASA to start the preparation of these photocathodes for their test in the PITZ photoinjector at DESY in Zeuthen. In this paper, detailed experimental results obtained from the KCsSb, along with a preliminary result from the NaKSb(Cs) photocathode material as well as the status of the overall project are presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB034 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 31 August 2021 | |
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| TUPAB387 | Superconducting Solenoid Field Measurement and Optimization | 2425 |
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| The solenoid is a significant part of an electron injector to provide a proper focusing, and preserve the beam projected emittance. A superconducting solenoid is applied for the SRF photoinjector at HZDR. The solenoid itself can degrade electron beam quality due to magnetic field imperfections like multipole components. In order to determine the field aberrations in the solenoid, we measured the superconducting solenoid magnetic field in the cryomodule. A simple and effective method is used to analyze the multipole field components, which will be presented in this paper. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB387 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 20 August 2021 | |
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| WEPAB040 | Characterization of Low Emittance Electron Beams Generated by Transverse Laser Beam Shaping | 2690 |
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| Linac based X-ray free electron laser demand a high beam quality from the electron source, therefore RF photoinjectors are used to generate the electron bunches for state of the art beam brightness. One important figure of merit for these injectors is the transverse emittance of the generated electron beam, which can be minimized by shaping the photocathode laser pulses. Best performance can be achieved with ellipsoidal laser pulses, but 3D shaping is technically challenging. Typically, a quasi-uniform transverse laser profile is truncated from the Gaussian profile generated by the laser with an aperture to reduce the transverse nonlinear space charge forces. This is investigated in detail by optimizing the laser transverse profile at the Photoinjector Test facility at DESY in Zeuthen (PITZ), where photoinjector R&D is conducted for the E-XFEL and FLASH free electron lasers at DESY in Hamburg. In this contribution we present experimental results at high acceleration gradients (up to 60 MV/m) for both 250 pC and 500 pC. For a bunch charge of 500 pC an emittance reduction of about 30% compared to the commonly used transverse flat-top laser distribution was achieved. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB040 | |
| About • | paper received ※ 17 May 2021 paper accepted ※ 02 June 2021 issue date ※ 19 August 2021 | |
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| WEPAB115 | Beam Preparation with Temporally Modulated Photocathode Laser Pulses for a Seeded THz FEL | 2866 |
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| The need for carrier-envelope-phase (CEP) stable THz pump pulses is recognized at many pump-probe experiments at the European XFEL. At the Photo Injector Test Facility at DESY in Zeuthen (PITZ), a proof-of-principle experiment of an accelerator-based THz FEL source is in preparation. Since the CEP stability of FEL pulses is not guaranteed in the SASE regime, a seeding scheme is needed. A common scheme for seeding is to drive the microbunching process with external laser pulses, which are power-limited in the THz range. Alternatively, a pre-bunched beam, generated for example by applying a temporally modulated photocathode laser pulse, can be used to drive the FEL. The beam dynamics with such a seeding method are studied with ASTRA tracking code simulations with space-charge forces as well as experimentally. The results of these studies are shown and discussed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB115 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 26 August 2021 | |
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| WEPAB257 | Matching of a Space-Charge Dominated Beam into the Undulator of the THz SASE FEL at PITZ | 3244 |
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| The Photo Injector Test facility at DESY in Zeuthen (PITZ) is developing a THz SASE FEL as a prototype high repetition rate accelerator-based source for the THz-pumped, X-ray-probed experiments at the European XFEL. For the generation of THz pulses of mJ-level energy from SASE, an electron beam with a high charge (up to 4 nC) and high peak current (~200 A) will be injected into an LCLS-I undulator, which is currently being installed at the end of the photo-injector. The narrow vacuum chamber (11x5 mm) between the magnetic poles and the strong vertical focusing from the undulator, as well as the lack of beam diagnostics, have made it a challenge to match the space-charge dominated beam into the undulator without beam loss during the following transport. In this paper, boundary conditions of a matched electron beam will be discussed and the simulation and experimental study on our matching strategy will be presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB257 | |
| About • | paper received ※ 08 May 2021 paper accepted ※ 02 July 2021 issue date ※ 13 August 2021 | |
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| WEPAB274 | Numerical Study of Beam Dynamics in PITZ Bunch Compressor | 3285 |
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| A magnetic bunch compressor has been recently designed for an accelerator-based THz source which is under development at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The THz source is assumed to be a prototype for an accelerator-based THz source for pump-probe experiments at the European XFEL. As an electron bunch is compressed to achieve higher bunch currents for the THz source, we investigate the beam dynamics in the bunch compressor by numerical simulations. A start-to-end simulation optimizer has been developed by combining the use of ASTRA, IMPACT-T, and OCELOT to support the design of the THz source prototype. Coherent synchrotron radiation effects degrade the compression performance for our study cases with bunch charges up to 4 nC and beam energy of 17 MeV at a bending angle of 19 degrees. Simulation and preliminary beam characteristic results will be presented in this paper. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB274 | |
| About • | paper received ※ 11 May 2021 paper accepted ※ 06 July 2021 issue date ※ 23 August 2021 | |
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FRXB06 |
Direct response time measurements on semiconductor photocathodes | |
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| Semiconductor photocathodes like Cs2Te enable stable electron sources with high photon to electron conversion rate (quantum efficiency, QE) for high brightness photoinjectors. Besides QE, work function and vacuum stability, bunch lengthening is a key figure of merit for these sources, resulting from UV photon penetration into the semiconductor and scattering of excited electrons before emission. These processes and their statistical variation lead to a delay, as well as to lengthening of the extracted electron bunch w.r.t. the incident laser pulse, often referred to as "response time". Thus far, no direct measurement of the response time of Cs2Te, one of the most widely used cathode materials, has been reported. As such a measurement is crucial for photocathode laser based bunch shaping, short bunch applications, emission modeling and for evaluating new cathode materials like CsKSb, a measurement procedure has been established at the photoinjector test facility at DESY in Zeuthen (PITZ) to measure longitudinal bunch shape variation due to cathode emission effects. Here, we introduce the method and show first results on direct cathode response measurements of Cs2Te cathodes. | ||
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