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WEVIR02 |
Effect of Long Response Time Photocathode Materials on Microbunching Instability in Free Electron Laser Facilities | |
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| Microbunching instability may be initiated by any intensity modulation on the bunch at low energy or by shot-noise along the machine. This instability may also be very detrimental in Free Electron Laser (FEL) facilities, because the resulting distortion of the beam phase space can strongly deteriorate the FEL intensity. The Laser Heater, which induces an increase of the beam energy in a controlled way, is used to mitigate this instability. In this paper we propose an alternative or complementary way to reduce the induced energy spread by using a long response time material as photocathode. By choosing a photocathode material with a response time larger than the value corresponding to the maximum amplification of the microbunching instability, the photocathode acts as a low pass filter of the laser profile, reducing in this way one of the possible sources of microbunching instability. The present experience shows that with this approach SwissFEL, the FEL facility in user operation at the Paul Scherrer Institute, efficiently lases without or with a very limited use of the laser heater. | ||
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WEVIR15 |
The PolariX TDS: Experimental Verification of a Next-Generation of Transverse Deflection Structure Working in the X-Band Frequency Regime | |
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The PolariX TDS (Polarizable X-Band Transverse Deflection Structure) is an innovative TDS-design operating in the X-band frequency-range invented at CERN*. The design gives full control of the streaking plane, which can be tuned in order to characterize the projections of the beam distribution in arbitrary transverse axes. This novel feature opens new opportunities for complete characterization of the electron beam including also the 3D reconstruction of the charge-density distribution of the bunch**. A collaboration of three research institutes (DESY, CERN and PSI) was formed to realize the prototype structure in view of future in-series production***. This new RF-cavity design requires very high manufacturing precision. The prototype was assembled using the high-precision-tuning-free assembly procedure developed at PSI****. Late 2019 the first PolariX TDS was installed in the FLASHForward beamline at DESY, where the expected performance of the structure has been validated during the first commissioning with electron beam. The experimental results open the path for novel and more extended beam characterization in the direction of multi-dimensional-beam-phase-space reconstruction.
*Grudiev A.,CLIC-Note-1067(2016). **Marx D. et al.,J.Phys.:Conf. Ser.874 012077(2017). ***Marchetti B.et al.,IPAC 2017, MOPAB044(2017). ****Craievich P. et al.,FEL 2019, WEP036(2019). |
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