Tohoku University, School of Scinece, Sendai
Generation of high brilliance beam using an RF gun is very attractive for advanced use of electron linacs. Beam dynamics in the RF gun has been studied theoretically so far, and many simulation codes have been developed. The stage in which the beam is extracted and accelerated to relativistic momentum is crucial for understanding of space charge dominated beams. In this sense, actual measurement of the beam phase space is highly desired to examine the validity of the simulation codes. However, for the low energy electrons, such measurement is difficult because the phase space is easily distorted due to space charge effect during travel through drift space. Accordingly, we have considered employing the energy dependent angular distribution of Cherenkov radiation. Though the emission angle of Cherenkov radiation decreases rapidly with increasing beam energy, it is still 25 deg/MeV at an energy around 2 MeV when we use a radiator that has a refractive index of 1.035. Thus the energy distribution can be measured by observing the Cherenkov ring with sufficient angular resolution. Since this method needs only a thin radiator, the drift space length can be minimized.
DESY, Hamburg
TEMF, TU Darmstadt, Darmstadt
DESY Zeuthen, Zeuthen
INRNE, Sofia
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
INFN/LASA, Segrate (MI)
RAS/INR, Moscow
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
Uni HH, Hamburg
FNRF, Chiang Mai
MBI, Berlin
The Photo Injector Test facility at DESY Zeuthen site (PITZ) is dedicated to developing and optimizing high brightness electron sources for short wavelength Free-Electron Lasers (FELs) like FLASH and the European XFEL, both in Hamburg (Germany). Since October 2009 a major upgrade has been ongoing with the goal of improving the accelerating components, the photocathode drive laser system, and the beam diagnostics. The previously operated and fully characterized gun was brought to FLASH and will go into operation soon. A gun of the same type is installed now in PITZ. The conditioning has started and the gun will be characterized throughout 2010. A new booster cavity, Cut Disk Structure (CDS), was developed and will be mounted at PITZ in spring 2010. The booster cavity will be able to accelerate electrons above 20 MeV/c and will be suitable for long RF pulses. The most important upgrade of the diagnostics system will be the implementation of a phase space tomography module (PST) consisting of three FODO cells each surrounded by two screen stations. The results of commissioning, gun and booster conditioning and the very first measurements will be reported.
DESY, Hamburg
DESY Zeuthen, Zeuthen
The stability of the photo injector is a key issue for the successful operation of linac based free electron lasers. Several types of jitter can impact the stability of a laser driven RF gun. Fluctuations of the RF launch phase and the cathode laser energy have significant influence on the performance of a high brightness electron source. Bunch charge measurements are used to monitor the stability of the rf gun phase and the cathode laser energy. A basic measurement is the so called phase scan: the accelerated charge downstream of the gun is measured as a function of the launch phase, the relative phase of the laser pulses with respect to the RF. We describe a method which provides simultaneous information on rms jitters from phase scans at different cathode laser energies. Fluctuations of the rf gun phase together with cathode laser energy jitter have been measured at the Photo Injector test facility at DESY in Zeuthen (PITZ). Obtained results will be presented in comparison with direct independent measurements of corresponding instability factors. Dedicated beam dynamics simulations have been done in order to optimize the method performance.
