High-power, high-brightness electron beams are of interest for many applications, especially as drivers for free electron lasers and energy recovery linac light sources. For these particular applications, photoemission injectors are used in most cases, and the initial beam brightness from the injector sets a limit on the quality of the light generated at the end of the accelerator. At Cornell University, we have built such a high-power injector using a DC photoemission gun followed by a superconducting accelerating module. Recent results will be presented demonstrating record setting performance up to 65 mA average current with beam energies of 4-5 MeV. V

In this Letter we report the first experiments aimed at the simultaneous demonstration of the emittance compensation process and velocity bunching in a high brightness electron source, the SPARC photoinjector in INFN-LNF. While a maximum compression ratio up to a factor 14 has been observed, in a particular case of interest a compression factor of 3, yielding a slice current of 120 A with less than 2 microm slice emittance, has been measured. This technique may be crucial in achieving high brightness beams in photoinjectors aiming at optimized performance of short wavelength single-pass free electron lasers or other advanced applications in laser-plasma accelerators.

We present a detailed study of the six-dimensional phase space of the electron beam produced by the Cornell Energy Recovery Linac Photoinjector, a high-brightness, high repetition rate (1.3 GHz) DC photoemission source designed to drive a hard x-ray energy recovery linac (ERL). A complete simulation model of the injector has been constructed, verified by measurement, and optimized. Both the horizontal and vertical 2D transverse phase spaces, as well as the time-resolved (sliced) horizontal phase space, were simulated and directly measured at the end of the injector for 19 and 77 pC bunches at roughly 8 MeV. These bunch charges were chosen because they correspond to 25 and 100 mA average current if operating at the full 1.3 GHz repetition rate. The resulting 90% normalized transverse emittances for 19 ð77Þ pC=bunch were 0:23 AE 0:02 ð0:51 AE 0:04Þ m in the horizontal plane, and 0:14 AE 0:01 ð0:29 AE 0:02Þ m in the vertical plane, respectively. These emittances were measured with a corresponding bunch length of 2:1 AE 0:1 ð3:0 AE 0:2Þ ps, respectively. In each case the rms momentum spread was determined to be on the order of 10 À3 . Excellent overall agreement between measurement and simulation has been demonstrated. Using the emittances and bunch length measured at 19 pC=bunch, we estimate the electron beam quality in a 1.3 GHz, 5 GeV hard x-ray ERL to be at least a factor of 20 times better than that of existing storage rings when the rms energy spread of each device is considered. These results represent a milestone for the field of high-brightness, highcurrent photoinjectors.

Thermal emittance measurements of a CsK 2 Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56 ± 0.03 mm mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 microJ, 800 nm pulse focused to a 140 mum rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.