COMPARISON OF 2 CATHODE GEOMETRIES FOR HIGH CURRENT (2 KA) DIODES

AIRIX (FRANCE) and DARHT axis-1 (USA) facilities are two high current accelerators especially designed for X-ray flash radiography. The produced electron beam (2 kA, 60 ns, 3.5 to 3.8 MeV at the diode output) is extracted from a velvet cold cathode. Specific calculations have demonstrated the influence of the cathode geometry on the emitted beam profiles [1]. In order to check this assumption two different experiments (DARHT march 2003 – AIRIX march 2004) have been performed. The beam characteristics with two different geometries have been compared both theoretically and experimentally. The beam simulations have been done with 3 codes: a homemade one (M2V) and 2 commercial ones (PBGUNS and MAGIC). The extracted beam current and transverse profiles, for the first experiment, have been measured and compared to simulations results. In the second one, we have mainly compared the primary current intensity that can be drawn with the two different K-designs for a given energy.