A Fast, Electromagnetically Driven Supersonic Gas Jet Target For Laser Wakefield Acceleration

Laser-Wakefield acceleration (LWFA) promises electron accelerators with unprecedented electric field gradients. Gas jets and gas-filled capillary discharge waveguides are two primary targets of choice for LWFA. Present gas jets have lengths of only 2-4 mm at densities of 1-4x10(19) /cm(3), sufficient for self-trapping and acceleration to energies up to similar to 150 MeV. While 3 cm capillary structures have been used to accelerate beams up to I GeV, gas jets require a well-collimated beam that is >= 10 mm in length and <500 mu m in width, with a tunable gas density profile to optimize the LWFA process. This paper describes the design of an electromagnetically driven, fast supersonic gas valve that opens in <100 mu s, closes in <500 mu s and can operate at pressures beyond 1000psia. The motion of the valve seat (flyer plate) is measured using a laser probe and compared with predictions of a model. The valve design is based on an optimization of many parameters: flyer plate mass and durability, driver bank speed and stored energy for high rep-rate (>10Hz) operation, return spring non-linearity and materials selection for various components. Optimization of the valve dynamics and preliminary designs of the supersonic flow patterns are described.