Effect of rod material on the impedance behavior of small aspect ratio rod pinches

Summary form only given. A series of experiments on small aspect ratio rod pinches¹ using solid tungsten, solid graphite, and thin wall tantalum anode rods driven by a nominally 375 kV linear transformer driver (LTD) powered inductive voltage adder² 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 present³ 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 ion plasma at the anode.