Optimization of a Mega-Ampere DPF with Monolithic Beryllium Electrodes for High Neutron Yield

Abstract

The dense plasma focus FF-2B machine with 1.2 MA peak current is designed as a low-impurity fusion device for a high neutron yield. Using for the first time monolithic beryllium electrodes, FF-2B has achieved a forty-fold reduction of impurities by mass with a dramatic reduction in electrode erosion as compared with previous copper1 and tungsten2 electrodes. We observed evenly-spaced filaments initially in the sheath, but the leading portion of the current sheath becomes disordered during run-down, limiting compression and fusion yield. Oscillations in the initial 200 ns of the current pulse are a possible cause of this disordering and we discuss possible mitigations. The impedance of the FF-1 and FF-2B devices at the pinch for both the 10cm and 14cm electrodes was correlated with the fusion yield. To obtain improved neutron yield with beryllium electrodes, we are reducing the inductance of the machine with a doubling of the number of switches.