PSI, Villigen
INFN/LNF, Frascati (Roma)
RF deflectors are crucial diagnostic tools for bunch length and slice emittance measurements with sub-picosecond resolution. Their use is essential in commissioning and operation of VUV and X-ray FELs. The 250MeV FEL injector, under construction at PSI, will use two of them. The first one will be installed after the gun at low energy (~7MeV), the second one at the end of the Linac at high energy (250MeV). The first RF deflector consists of a single cell standing wave cavity working on the TM110 deflecting mode, and tuned at 2997.912 MHz (frequency of the linac structures). In this note we report the motivation of this measurement, beam dynamics and beam diagnostics considerations and the RF design and simulations of this cavity.
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
Istituto Nazionale di Fisica Nucleare, Milano
INFN-Roma II, Roma
ENEA C.R. Frascati, Frascati (Roma)
University of Tehran, Tehran
INFN-Roma, Roma
One of the main goals of the SPARC high brightness photoinjector is the experimental demonstration of the emittance compensation process while compressing the beam with the velocity bunching technique, also named RF compressor. For this reason, the first two S-band travelling wave accelerating structures downstream of the RF gun are embedded in a long solenoid, in order to control the space charge induced emittace oscillations during the compression process. An RF deflecting cavity placed at the exit of the third accelerating structure allows bunch length measurements with a resolution of 50 μm. During the current SPARC run a parametric experimental study of the velocity bunching technique has been performed. The beam bunch length and projected emittance have been measured at 120 MeV as a function of the injection phase in the first linac, and for different solenoid field values. In this paper we describe the experimental layout and the results obtained thus far. Comparisons with simulations are also reported.
Rome University La Sapienza, Roma
INFN/LNF, Frascati (Roma)
We discuss the use of non resonant bead pull technique for measuring fields in standing wave accelerating structures. From the Steele perturbation theory, one can derive the relation between the magnitude and phase of the field in the cavity and the complex reflection coefficient. The effect of the bead size, the calibration of the bead and the comparison with the more common resonant techniques are addressed. As an example, we discuss the measurement on a X-band bi-periodic cavity proposed for linearizing emittance at the Frascati photo-injector SPARC.
UCLA, Los Angeles, California
INFN/LNF, Frascati (Roma)
Rome University La Sapienza, Roma
A hybrid photoinjector, which we present here, consists of a 6-cell traveling wave structure with a standard 1.6-cell RF gun attached to the one end and a 3-m long linac following for further acceleration. With this structure, no reflection observed at the input port. This enables to build the accelerator without a circulator which limits the power and the frequency of RF. From the beam dynamics point of view, the beam is produced as the normal RF guns and gets short by velocity bunching in the traveling wave section right after the gun. The peak current can reach more than 1 kA, with about 2 mm.mrad of the emittance at 20 MeV. We discuss more details about the beam dynamics as well as the RF structure.
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
CEA, Gif-sur-Yvette
INFN-Roma II, Roma
ENEA C.R. Frascati, Frascati (Roma)
SOLEIL, Gif-sur-Yvette
INFN-Roma, Roma
University of Tehran, Tehran
UCLA, Los Angeles, California
The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive 500 nm FEL experiments in SASE, Seeding and Single Spike configurations. The SPARC photoinjector is also the test facility for the recently approved VUV FEL project named SPARX. The second stage of the commissioning, that is currently underway, foresees a detailed analysis of the beam matching with the linac in order to confirm the theoretically prediction of emittance compensation based on the “invariant envelope” matching , the demonstration of the “velocity bunching” technique in the linac and the characterisation of the spontaneous and stimulated radiation in the SPARC undulators. In this paper we report the experimental results obtained so far. The possible future energy upgrade of the SPARC facility to produce UV radiation and its possible applications will also be discussed.
Università di Roma II Tor Vergata, Roma
INFN/LNF, Frascati (Roma)
Rome University La Sapienza, Roma
INFN-Roma II, Roma
ENEA C.R. Frascati, Frascati (Roma)
The SPARC photoinjector drives a SASE FEL to perform several experiments both for the production of high brightness electron beam and for testing new scheme of SASE radiation generation. The control of the beam properties, in particular at the level of the slice dimension, is crucial in order to optimize the FEL process. We report the different measurements performed in order to characterize the slice properties of the electron beam.