An Ultra Low Emittance DC/RF Photoelectron Gun

70868 The radio frequency (rf) photoinjector is one of the great accelerator inventions in recent years. Unfortunately, its performance is limited by space charge effects, particularly at the cathode where electrons are first created at thermal energies. The lowest emittance achieved so far is on the order of a few mm-mrad. However, future linear colliders and 4th generation light sources require the emittance to be much lower. This project will develop technology for accelerating electrons upon creation with a short pulse (<1ns), high voltage (~MV), small (~mm) dc gap to nearly relativistic energies with very high accelerating gradient (~GV/m), and then immediately injecting the electron beam into an integrated, emittance compensating, rf cavity for subsequent acceleration. An order of magnitude improvement in emittance is expected with this integrated dc/rf photoinjector. Phase I will design a short-pulse dc gap using a new type of high voltage, fast ionization, solid state switch; and develop methods to integrate the dc gap into rf cavities. The new pulser will be potentially capable of high rep rate up to 10 kHz. A 70 kV dc gap will be fabricated and tested, and numerical simulations will be performed to assess the performance of several integrated dc/rf gun designs. In Phase II an integrated, dc (250-500 kV) and rf (10-20 MeV) gun will be tested at an rf gun test facility in a national laboratory. Commercial Applications and Other Benefits as described by the awardee: An ultra-low emittance dc/rf gun would simplify the design and/or increase the luminosity of future linear colliders for high energy physics research. Also, the dc/rf gun should increase the brightness of 4th generation light sources that produce ultrafast x-rays for time resolved materials research, protein crystallography, and advanced medical and industrial applications.