Upgrades To LLNL's MJOLNIR Dense Plasma Focus (DPF) Power Flow Region and Mounting Structure*

There is an updated design for the Lawrence Livermore National Laboratory’s Megajoule Neutron Imaging Radiography (MJOLNIR) Dense Plasma Focus (DPF) machine.

The first feature is clamp convolutes within the power flow region that provide both high compression and high voltage stand-off (~100kV) required to prevent plate separation due to the J × B force (3.7 MA with 5 microsecond rise time) present during high current operations. The clamping mechanism being planted in the cathode transmission plate and penetrating the anode transmission plate requiring a complex series of nested high strength steel bars and insulation that can withstand the pinch voltage (300 kV for 100 ns).

 

There is a programmatic need to quickly change DPF hardware to decrease down-time and increase the ease of these hardware swaps by firstly incorporating a removable slide rail system which allowed for faster mounting and unmounting of the docked load and secondly by fielding an assembly stand that allowed the load to securely rotate during the assembly and disassembly process.  

 

The previous design showed signs of current joint failure in several locations. Literature search results guided an improved joint design where minimum contact forces could be calculated for given metal parameters and current action. Therefore, all current joints have been redesigned by switching to a method allowing higher than typical metal-metal contact methods can support. 

 

For measuring gun current, a novel vacuum embedded, triple shielded Rogowski probe was constructed and operated.