Photocathode RF Gun Research Articles

Performance of the Brookhaven photocathode rf gun

Abstract The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser acceleration experiments. The rf gun consists of 1 1 2 cells driven at 2856 MHz in π-mode with a maximum cathode field of 100 MV/m. To achieve long lifetimes, our photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10 ps, frequency-quadrupled Nd: YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. These results are compared to models.

Proposed UV-FEL user facility at BNL

The NSLS at Brookhaven National Laboratory is proposing the construction of a UV-FEL operating in the wavelength range from visible to 750 Å. Nanocoulomb electron pulses will be generated at a laser photocathode rf gun at a repetition rate of 10 kHz. The 6 ps pulses will be accelerated to 250 MeV in a superconducting linac. The FEL output will serve four stations with independent wavelength tuning, using two wigglers and two rotating mirror beam switches. Seed radiation for the FEL amplifiers will be provided by conventional tunable lasers, and the final frequency multiplication from the visible or near UV to the VUV will be carried out in the FEL itself. Each FEL will be comprised of an initial wiggler resonant to the seed wavelength, a dispersion section, and a second wiggler resonant to the output wavelength. The facility will provide pump-probe capability, FEL on FEL, and FEL on synchrotron light from an insertion device on the NSLS X-ray ring.

Proposed UV FEL user facility at BNL

The NSLS at Brookhaven National Laboratory is proposing the construction of an UV FEL operating in the wavelength range from visible to 1000 Å. Nanocoulomb electron pulses will be generated at a laser photocathode rf gun at a repetition rate of 10 kHz. The 6 ps pulses will be accelerated to 250 MeV in a superconducting linac. The FEL consists of an exponential growth section followed by a tapered section. The amplifier input is a harmonic of a tunable visible laser generated either by nonlinear optical material or the nonlinearity of the FEL itself. The FEL output in 10 −4 bandwidth is 1 mJ per pulse, resulting in an average power of 10 W. The availability of radiation with these characteristics would open up new opportunities in photochemistry, biology and nonlinear optics, as discussed in a recent workshop held at BNL.

4881033 Noise-reduced synthetic T2 weighted images

Photocathode RF guns have been developed in many laboratories for generating high quality electron beams for free-electron lasers based on linear accelerators. Such guns can generate electron beams with an exceptionally high peak current as well as a small transverse emittance. Their applications have been recently expanded for ultrafast electron diffraction, coherent terahertz radiation, and X-ray or γ‐ray radiation by Compton scattering. In this paper, we design an S-band normal-conducting gun with capabilities of high quality beam generation and high repetition rate operation. The RF design and thermal analysis of the gun cavity and coupler are introduced. Optimal position of the gun focusing solenoid for low emittance beam generation is found by performing particle tracking simulations. Then, the gun system is designed to be able to afford the optimal solenoid position. The cooling-water channel surrounding the gun cavity and coupler is designed and analyzed numerically. The pressure in the gun is simulated with a vacuum model containing the detailed inner structure of the gun. An injector for a free-electron laser application is designed by using this gun and the beam dynamics simulation is shown. A cold test with a prototype gun for confirmation of the RF design is reported.

Simulations of high-brightness rf photocathode guns for LLNL-SLAC-LBL 1 GeV test experiment

An ideal rf photocathode gun in a π-mode configuration supporting only a single mode with no nonlinear rf field is studied numerically by using the simulation code PARMELA. For a given electron bunch, the normalized emittance can be minimized. Both the minimum normalized emittance and the optimized accelerating field are proportional to the square root of the peak current. Three possible rf photocathode guns for LLNL-SLAC-LBL 1 GeV test are simulated. It is found that both a 2 ps half-width bunch and a 6 ps half-width bunch with the transverse emittance roughly 8–17 mmm mrad and 1 nC charge per bunch can be generated by guns with (1) ƒ = 1269 MHz , E 0 = 30 MV/m; (2) ƒ = 1269 MHz , E 0 = 60 MV/m; and (3) ƒ = 2856 MHz , E 0 = 60 MV/m. Here, ƒ is the rf frequency, and E 0 is the peak accelerating field.