J. Sheehan

Emittance studies of the BNL/SLAC/UCLA 1.6 cell photocathode RF gun

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 /spl mu/s. 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, /spl epsiv//sub 0/, of the copper cathode has been measured.

Experimental characterization of the high-brightness electron photoinjector

Abstract Operational experience of the emittance compensated photoinjector at the Brookhaven Accelerator Test Facility (ATF) is presented in this paper. The photoinjector has demonstrated the stability and reliability required for UV and X-ray FEL applications. The RF gun has been routinely running at more than 100 MV/m peak acceleration field; the laser system of the photoinjector has achieved 2% peak to peak energy stability, 0,5% point stability and better than 2 ps timing jitter. The highest measured quantum efficiency of the Cu cathode is 0.05%. The electron beam bunch length was measured to be 10 ps using a linac RF phase scan. The normalized rms emittance for 0.5 nC charge was measured, to be from 1 to 2 mm rad, which agrees with PARMELA simulations.

Design and construction a full copper photocathode RF gun

The design and construction of an all copper S-band one-and-half cell photocathode electron gun without a choke joint is described. The methods utilized to determine the field balance at the operational frequency without usage of the bead pulling perturbation measurement is given together with the computational data.<<ETX>>

A modified feed-forward control system at the Accelerator Test Facility

A modified feed-forward control system has been operated at the Brookhaven Accelerator Test Facility to control the phase and amplitude of two high power klystron rf systems used to power a photocathode rf gun and a traveling wave electron linac. The changes to the control algorithm include an improved handling of cross coupling between the amplitude and the phase channels, an improved calibration routine that allows for changes in the matrix elements due to the variable base-line and improved filtering. The modifications to the software include modularity, portability, and user-friendliness. Improvements to the hardware include a linearized phase and amplitude controller with dc biasing for an improved dynamic range. The feed-forward system can handle nonlinear and noninstantaneous systems. With simultaneous regulation of two channels, the phase and the amplitude fluctuations over a time span of more than 3 μS were reduced to less than ±0.2° and ±0.2%, from the initial ±2.7° and ±1.8%, respectively.

Experimental results of the ATF in-line injection system

The initial experimental results of the Brookhaven accelerator test facility (ATF) in-line injector is presented. The ATF in-line injector employed a full copper RF gun with a pair of solenoid magnets for emittance compensation. The maximum acceleration field of the RF gun was measured to be 130 MV/m. The electron yield from the copper cathode was maximized using p-polarized laser and the Schottky effect. The quantum efficiency under optimum conditions was measured to be 0.04%. The measured electron bunch length was less than 11 ps, which agreed with the laser pulse length measurement using a streak camera. The normalized RMS emittance for 0.25 nC charge is 0.9/spl plusmn/0.1 mm-mrad, which is almost four times smaller than the emittance predicted by the space-charge effect for a non-emittance compensation photocathode RF gun. The normalized RMS emittance for 0.6 nC charge was measured range from 1 to 3 mm-mrad. This measurement was first experimental demonstration of emittance compensation in a high-gradient, S-band photocathode RF gun.

A superconducting short period undulator for a harmonic generation FEL experiment

A three stage superconducting (SC) undulator for a high gain harmonic generation (HGE) FEL experiment in the infrared is under construction at the NSLS in collaboration with Grumman Corporation. A novel undulator technology suitable for short period (6-40 mm) undulators will be employed for all three stages, the modulator, the dispersive section and the radiator. The undulator triples the frequency of a 10.4 /spl mu/m CO/sub 2/ seed laser. So far a 27 period (one third of the final radiator) prototype radiator has been designed, built and tested.<<ETX>>

Initial commissioning results of the next generation photoinjector

The BNL/SLAC/UCLA symmetrized 1.6 Cell S-band emittance-compensated photoinjector has been installed at the Brookhaven Accelerator Test Facility (ATF). The commissioning results and performance of the photocathode injector are presented. This emittance-compensated photoinjector consists of the symmetrized BNL/SLAC/UCLA 1.6 cell S-band photocathode radio-frequency (rf) gun and a single solenoidal magnet for transverse emittance compensation 1. The highest acceleration field achieved on the cathode is 150 MV/m, and the normal operating field is 130 MV/m. The quantum efficiency of the copper cathode was measured to be 4.5×10−5. The transverse emittance and bunch length of the photoelectron beam were measured. The optimized rms normalized emittance for a charge of 300 pC is 0.7 π mm-mrad. The bunch length dependency of photoelectron beam on the rf gun phase and acceleration fields were experimentally investigated.

Commissioning results of the BNL/SLAC/UCLA symmetrized 1.6-cell S-band emittance-compensated photoinjector

The BNL/SLAC/UCLA symmetrized 1.6 cell S-band emittance- compensated photoinjector has been installed at the Brookhaven Accelerator Test Facility (ATF). The commissioning results and performance of the photocathode injector are presented. This photoinjector consists of the symmetrized BNL/SLAC/UCLA 1.6 cell S-band photocathode radio frequency gun and a single solenoidal magnet for transverse emittance compensation. The highest acceleration field achieved on the cathode is 150 MV/m, and the normal operating field is 125 MV/m. The quantum efficiency of the copper cathode was measured to be 4.5 multiplied by 10-5. The measured quantum efficiency of the magnesium cathode is a factor of ten greater than that of copper after using both laser and laser assisted explosive electron emission cleaning. The transverse emittance and bunch length of the photoelectron beam were measured. The optimized rms normalized emittance for a charge of 329 plus or minus 12 pC is 2.0 plus or minus 0.3 pi mm-mrad. The bunch length dependency of photoelectron beam on the rf gun phase and acceleration fields were experimentally investigated. Electric and magnetic field asymmetries studies are presented.

Upgrade of NSLS timing system

We report on the progress of the new NSLS timing system. There are three types of requirements for NSLS timing system: clocks, synchronization and trigger circuits. All ring revolution frequency clocks are generated using ECL and high speed TTL logic. The synchronization circuits allows to fill both storage rings with any bunch pattern. The triggers are generated by using commercially available digital delay generators. The delay units outputs are ultrastable, with a resolution of 5 ps, and are programmed by computer via IEEE 488 interface. The block diagrams, description of all major timing components and the present status are provided in this paper.

Superconducting short-period undulator for a harmonic generation FEL experiment in the infrared

A three stage superconducting undulator (modulator, dispersive section, and radiator) is under construction at the National Synchrotron Light Source--Accelerator Test Facility at Brookhaven National Laboratory in collaboration with Grumman Corporation. A novel undulator technology suitable for short period undulators (6 - 40 mm) is employed that offers (1) high magnetic fields on axis at short periods, (2) as easily varied field, (3) a variable dispersion, (4) a variable magnetic field taper to ensure optimum resonance between the electrons and the radiation field, (5) transverse focusing to prevent electron beam emittance growth, and (6) low random field errors (below 0.3% rms) as machined and assembled, without shimming or trimming.