Effect of Rod Material on the Impedance Behavior of Small Aspect Ratio Rod Pinches

A series of experiments on small aspect ratio rod pinches using solid tungsten, solid graphite, and thin-wall tantalum anode rods driven by a nominally 375-kV linear transformer driver, powered inductive voltage adder has characterized the impedance behavior over a range of aspect ratios and materials. For the tungsten and tantalum anodes, the impedance behavior is well described by the pinched current for self-magnetically insulated flow in a cylindrical geometry with ions present and gap closure velocities of 1-2 cm/μs. The graphite anodes always exhibited strong localized pinching of the electron beam onto the anode rod, with substantially higher operating impedance, as well as a delay in the formation of the plasma at the anode. The graphite anodes also had a longer radiation delay time, consistent with the longer anode plasma formation time.