A 2.5 MV subnanosecond pulser with laser triggered gap for the generation of high brightness electron bunches

High-intensity, low-emittance, short electron bunches are needed to attain self-amplified spontaneous emission (SASE) in X-ray free electron lasers (X-FEL) and for injection in future laser-Wakefield accelerators (LWFA). At such a high density, conventional techniques using magnetic compression of long bunches suffer from collective effects such as coherent synchrotron radiation, limiting the brightness achievable. On the other hand, when creating very short electron bunches using a high intensity femtosecond laser the internal space charge forces rapidly decrease the brightness of the bunch. However, these space charge forces become negligibly small at relativistic energies due to the Lorentz force and contraction. Simulations have shown that acceleration to relativistic energies in a field of 1 GV/m would preserve enough of the phase-space density to meet the requirements for SASE and bunch length sufficiently small for injection into a LWFA. Conventional (RF) accelerators have maximum fields of approximately 100 MV/m and are usually operated in the 10-30 MV/m range. A novel approach was proposed by Srinivasan-Rao et al. [T. Srinivasan-Rao and J. Smedley, 1996] in which a short high-voltage pulse is applied to a simple diode configuration to generate a GV/m electric field.