Reply To: JPL Employees File Suit to End Background Investigations

[asymmetric_implosion]

Capacitors at the level required for a large plasma focus typically have short lifetimes. Over specification of caps is the only solution. Repetition rate operation further stresses the caps due to effective series resistance in the capacitor which leads to heating. Typically, you need caps that are specifically designed to operate a repetition rate. Caps like the ones used on FF-1, Z and other large pulse power systems are not agreeable to high repetition rate operation. The pulse power solution being worked on at Sandia and other labs is called the linear transformer driver (LTD). The LTD is a transformer based high current driver. Currently, 1 MA modules are the norm but 2 MA modules have been designed. There isn’t a theoretical limit on the current output of an LTD. It is practically limited by the size of the transformer core.

The LTD is different because it is a step down transformer. It uses a large number of small capacitors (small caps are easier to build at high voltage levels to allow derating. Check out the General Atomics website as an example) coupled together with a transformer core. The 1 MA modules are already demonstrated at 1 Hz for hours on end in a test load. Sandia has designs for a 100 MA z-pinch driver that operates at 0.1 Hz. The downside to the LTD is the number of capacitors and switches. In a typical module, you have 40-80 caps with 20-40 switches. In the 100 MA design you have 500,000 switches. One of the biggest weaknesses of a pulse power system is the switches. You can’t use switches like Thyratrons or solid state switching for current reasons (Thyratron) and cost (solid state). This is a huge engineering challenge for any pulse power fusion system.