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TUXB02 |
Precision Control of Plasma Wakefields for Highly Efficient and Energy-Spread-Preserving Electron Acceleration | |
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Plasma-wakefield accelerators driven by intense particle beams promise to significantly reduce the size of future high-energy facilities. These applications require an energy-efficient acceleration process with a well-controlled energy spectrum, both of which can be achieved simultaneously by tailoring the plasma wakefield. A prerequisite for such control of the wakefield is its precise measurement. Here we discuss a new measurement technique that enables femtosecond-level sampling of the longitudinal electric fields and that is particularly powerful due to its operational simplicity*. Using this method, we experimentally demonstrated optimal beam loading in a nonlinear electron-driven plasma accelerator by wakefield flattening at the few-percent level**. Bunches were accelerated at a gradient of 1.3 GV/m and with an energy-transfer efficiency of (42±4)% while preserving per-mille energy spreads with full charge coupling. These results open the door to the high-quality operation of future plasma accelerators through precise control of the acceleration process.
* S. Schröder, et al. Nat Commun 11, 5984 (2020) ** C.A. Lindstrøm, et al. Phys. Rev. Lett. 126, 014801 (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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| WEPAB113 | Stripline Kickers for Injection Into PETRA IV | 2863 |
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| PETRA IV is the planned ultralow-emittance upgrade of the PETRA III synchrotron light source at DESY, Hamburg. The current design includes an on-axis beam injection scheme using fast stripline kickers. These kickers have to fulfill the requirements on kick-strength, field quality, pulse rise-rate and a matched beam impedance. 3D finite element simulations in conjunction with Bayesian optimisation are used to meet these requirements simultaneously. Here, we will discuss the requirements on the PETRA IV injection kickers and the current design status. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB113 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 15 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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