Author: Pedrozzi, M.
Paper Title Page
MOPSO77 Timing Jitter Measurements of the SwissFEL Test Injector 140
 
  • C. Vicario, B. Beutner, M.C. Divall, C.P. Hauri, S. Hunziker, M.G. Kaiser, M. Luethi, M. Pedrozzi, T. Schietinger
    PSI, Villigen PSI, Switzerland
  • C.P. Hauri
    EPFL, Lausanne, Switzerland
 
  To reach nominal bunch compression and FEL performance of SwissFEL with stable beam conditions for the users, less than 40fs relative rms jitter is required from the injector. Phase noise measurement of the gun laser oscillator shows an exceptional 30fs integrated rms jitter. We present these measurements and analyze the contribution to the timing jitter and drift from the rest of the laser chain. These studies were performed at the SwissFEL injector test facility, using the rising edge of the Schottky-scan curve and on the laser system using fast digital signal analyzer and photodiode, revealing a residual jitter of 150fs at the cathode from the pulsed laser amplifier and beam transport, measured at 10Hz. Spectrally resolved cross-correlation technique will also be reviewed here as a future solution of measuring timing jitter at 100Hz directly against the pulsed optical timing link with an expected resolution in the order of 50fs. This device will provide the signal for feedback systems compensating for long term timing drift of the laser for the gun as well as for the pulsed lasers at the experimental stations.  
 
TUPSO03 Dark Current Transport and Collimation Studies for SwissFEL 209
 
  • S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche, L. Stingelin
    PSI, Villigen PSI, Switzerland
 
  In all accelerating cavities a non negligible background of electrons can be generated by field emission (dark current), transported and further accelerated. A careful estimate of the transport of the dark current is crucial in order to minimize radiation damage to the components and activation of the machine. This paper describes the generation and the transport of dark current from the SwissFEL photo injector downstream of the accelerator. The analysis is based on numerical simulations and experimental measurements performed at the SwissFEL Injector Test Facility (SITF). In the simulations the charge distribution is generated by an emission model based on the Fowler-Nordheim equation taking into account the filling time of the cavity and then tracked through the machine. This model has been used to analyze the impact of a low energy collimation system upstream of the first travelling wave accelerating structure on the dark current transport. A slit with several apertures has been installed in the SITF to benchmark the simulations and to verify the impact of the wakefields on the nominal beam.  
 
TUPSO04 Simulations of a Corrugated Beam Pipe for the Chirp Compensation in SwissFEL 214
 
  • S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche
    PSI, Villigen PSI, Switzerland
 
  In short wavelength FEL designs, bunch compression is obtained by making the beam passing through a magnetic chicane with an energy chirp typically of a percent level. At SwissFEL, before injection into the undulator it is foreseen to remove the residual chirp using the wakes in the C-band accelerating structures of the linac. This scheme works well for the hard X-ray undulator line, which includes the largest accumulation of wakefields, but it leaves a residual chirp in the other undulator line for the soft X-ray beam line, midway in the main linac. Another possibility to remove the residual chirp consists in using the longitudinal wakefields generated by a corrugated beam pipe, as recently proposed by G. Stupakov et al. Before planning a dechirper section in a FEL, an experimental verification of the analytical formulae describing the wakefields is crucial. The SwissFEL injector test facility (SITF) fulfils all the necessary criteria to perform such a proof of principle. We are investigating the technical implementation to perform an experiment in SITF in the second half of 2014. In this paper we present the tracking studies performed to optimize the experiment layout.  
 
TUPSO07 SwissFEL Injector Design: An Automatic Procedure 219
 
  • S. Bettoni, M. Pedrozzi, S. Reiche
    PSI, Villigen PSI, Switzerland
 
  The first section of photo-injectors are dominated by space charge effects due to the low beam energy and the high charge density. An optimization of several parameters such as the emittance and the mismatch along the bunch has to be carried out in order to optimize the final performances of the machine. We focus on the performances of the gun developed at PSI, planned to be installed in the mid of this year in the SwissFEL Injector Test Facility (SITF). Due to the number of variables and constraints we developed a code to automatically perform such an optimization. We used this code to optimize the 200 pC operating point of SwissFEL and to fine tune other charges configurations from 10 pC, obtaining considerably reduction of the slice emittance as compared to the CTF gun, presently installed in the SITF and on which the old lattice optimization was based. The same code with minor modifications has been successfully applied to the facility.  
 
TUPSO21 SwissFEL Cathode Load-lock System 259
 
  • R. Ganter, M. Bopp, N. Gaiffi, T. Le Quang, M. Pedrozzi, M. Schaer, T. Schietinger, L. Schulz, L. Stingelin, A. Trisorio
    PSI, Villigen PSI, Switzerland
 
  The SwissFEL electron source is an RF photo-injector in which the photo-cathode plug can be exchanged. Without load-lock, the cathode exchange takes about one week and cathode surface gets contaminated in the atmosphere during installation, leading to unpredictable quantum efficiency (QE) fluctuations. This motivated the construction of a load lock system to prepare and insert cathodes in the photo-injector. This load lock system consists of three parts: the preparation chamber, the transportable vacuum suitcase and the gun load lock chamber. This three parts system gives the possibility to prepare the cathode surface with methods like vacuum firing and plasma cleaning. The QE can be checked and the plug can be inserted in the gun without breaking vacuum. This will allow establishing an optimized a reproducible cathode preparation procedure. Since several cathodes can be loaded in advance, the exchange procedure reduces the machine shutdown to a few hours (shorter RF conditioning). The system is described and first experience with its use is reported.