[en] The present state of the art in photoinjector designs will be presented in this review. The authors discuss both proposed and operational photoinjectors with operating frequencies from L-band (1.424 GHz) to X-band (11.424 GHz). Also a novel pulsed DC gun will be presented. All the RF photoinjector discussed here use an emittance compensation scheme to align the different slices of the electron beam to decrease the beams normalized rms emittance

No abstract available

[en] Photocathode rf guns depend on mode locked laser systems to produce an electron beam at a given phase of the rf. In general, the laser pulse is less than σ_z = 10^o of rf phase in length and the required stability is on the order of Δφ = 1^o. At 90 GHz (W-band), these requirements correspond to σ_z = 333 fsec and Δφ = 33 fsec. Laser system with pulse lengths in the fsec regime are commercially available, the timing stability is a major concern. We propose a multi-cell W-band photoinjector that does not require a mode locked laser system. Thereby eliminating the stability requirements at W-band. The laser pulse is allowed to be many rf periods long. In principle, the photoinjector can now be considered as a thermionic rf gun. Instead of using an alpha magnet to compress the electron bunch, which would have a detrimental effect on the transverse phase space quality due to longitudinal phase space mixing, we propose to use long pulse laser system and a pair of undulators to produce a low emittance, high current, ultra-short electron bunch for beam dynamics experiments in the 90 GHz regime

[en] The Linac Coherent Light Source (LCLS) will use the last portion of the SLAC accelerator as a driver for a short wavelength FEL. The injector must produce 1-nC, 3-ps rms electron bunches at a repetition rate of up to 120 Hz with a normalized rms emittance of about 1 mm-mrad. The injector design takes advantage of the photocathode rf gun technology developed since its conception in the mid 1980's, in particular the S-band rf gun developed by the SLAC/BNL/UCLA collaboration, and emittance compensation techniques developed in the last decade. The injector beamline has been designed using the SUPERFISH, POISSON, PARMELA, and TRANSPORT codes in a consistent way to simulate the beam from the gun up to the entrance of the main accelerator linac where the beam energy is 150 MeV. PARMELA simulations indicate that at 150 MeV, space charge effects are negligible

[en] The transverse emittance from optimized RF photoinjectors is limited by the thermal emittance. The thermal emittance can be lowered by a factor >2 by using a semiconductor photocathode

[en] The present state of the art in photoinjector designs will be presented in this review. We will discuss both proposed and operational photoinjectors with operating frequencies from L-band (1.424 GHz) to X-band (11.424 GHz). Also a novel pulsed DC gun will be presented. All the RF photoinjector discussed here use an emittance compensation scheme to align the different slices of the electron beam to decrease the beams normalized rms emittance. copyright 1997 American Institute of Physics

[en] Emittance compensation using the static axial magnetic field from a solenoid surrounding an rf photoinjector has been used to reduce the rms emittance of the electron beam by up to an order of magnitude, for photoinjectors ranging from 433 MHz to 8 GHz. The residual emittance after standard solenoidal compensation depends primarily on how linear the space-charge force is along the electron bunch in terms of an axial Taylor expansion, and is typically a strong function of both solenoid position and focusing strength. In this paper, the authors investigate the concept of second-order emittance compensation using the combination of a solenoid and radial rf focusing. They numerically demonstrate that (1) lower residual emittances are possible if second-order compensation is introduced by adding radially focusing rf forces in the first photoinjector cavity near the cathode, (2) the residual emittance is less sensitive to solenoid position, (3) the residual emittance is less sensitive to solenoid strength, and (4) the optimal solenoid position is further from the photoinjector cathode, leading to less stringent design requirements, especially at high frequencies

[en] The symmetrized 1.6 cell S-band photocathode gun developed by the BNL/SLAC/UCLA collaboration is in operation at the Brookhaven Accelerator Test Facility (ATF). A novel emittance compensation solenoid magnet has also been designed, built and is in operation at the ATF. These two subsystems form an emittance compensated photoinjector used for beam dynamics, advanced acceleration and free electron laser experiments at the ATF. The highest acceleration field achieved on the copper cathode is 150 MV/m, and the guns normal operating field is 130 MV/m. The maximum rf pulse length is 3 micros. The transverse emittance of the photoelectron beam were measured for various injection parameters. The 1 nC emittance results are presented along with electron bunch length measurements that indicated that at above the 400 pC, space charge bunch lengthening is occurring. The thermal emittance, ε_o, of the copper cathode has been measured

[en] A 1.6 cell photocathode S-Band gun developed by the BNL/SLAC/UCLA collaboration is now in operation at the Brookhaven Accelerator Test Facility (ATF). One of the main features of this RF gun is the symmetrization of the RF coupling iris with an identical vacuum pumping port located in the full cell. The effects of the asymmetry caused by the RF coupling iris were experimentally investigated by positioning a metallic plunger at the back wall of the vacuum port iris. The higher order modes produced were studied using electron beamlets with 8-fold symmetry. The 8-fold beamlets were produced by masking the laser beam. These experimental results indicate that the integrated electrical center and the geometrical center of the gun are within 175 microm. Which is within the laser alignment tolerance of 250 microm

[en] The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center. Comparisons between measurements and the predictions of design codes are made