Optimisation of the power coupling in the MAGPIE 4-way junction using a 1/6th scale model

A Mega-Ampere Generator for Plasma Implosion Experiments (MAGPIE) is currently under construction in the Plasma Physics group at Imperial College, London. The generator is specifically designed to carry out radiative collapse experiments in hydrogen fibre Z-pinches [1]. In order to achieve this goal, MAGPIE must be capable of delivering in excess of 1.5MA into a 150nH load in under 200ns. An artist´s impression of MAGPIE is shown in fig. 1. In the final generator, four 2.4MV Marx banks charge four 5 ohm, coaxial, 100ns single transit, water filled pulse forming lines (PFLs). The four PFLs are connected to a single coaxial vertical transfer line via four synchronously triggered trigatron switches. The vertical transfer line has an impedence of 1.25 ohm and therefore represents a matched load to the four PFLs. At the top of the transfer line a graded insulator stack makes up the vacuum-water interface. A magnetically insulated transmission line section then feeds the load. The total energy stored in the banks is 336kJ making MAGPIE a multi terrawatt, long pulse generator. A necessary feature of the generator is the junction of the four horizontal PFLs to the single vertical transfer line. This paper reports on work being carried out to characterize the power flow through this juncion using a 1/6th size scale model.