  This presentation focuses on the optimization of the trigger unit of a
six-rod TVS. The different configurations of the trigger pin and of the trigger
electrode have been considered to study the electric field distribution at the
triple points of the unit embedded in the cathode. To optimize the field
enhancement, electric field simulations with a planar and a circular heads of
the trigger pin in combinations with a convex and a concave shaped trigger
electrodes have been done. The simulations were done with an applied trigger
pulse voltage of Utrigger = 5 kV and with a discharge voltage the main switch
of Uswitch = 20 kV. The experimental values had been Utrigger = 40 kV and
Uswitch = 5 kV. The simulation results show that the combination of a circular
trigger pin head and a concave trigger electrode yields the highest electric
field of 9.6 .106 V/m at the triple point. In-parallel experiments have been
performed with those four trigger configurations. The results of the
experiments however cannot yet clearly confirm the trend in the results of the
field simulations.
