Design and simulation of a 3 MV compact generator for radiographic applications

As a possible driver to its future needs on flash X-rays radiography, the CEA is working on linear transformer driver (LTD) generator. The studies on this original concept invented and developed by the High Current Electronic Institute (HCEI) are done in collaboration with the company International Technology for High Pulse Power (ITHPP). The LTD can be described as an inductive voltage adder (IVA) with the storage elements directly linked to each feed gap. For each cell, the geometry of this direct connection (several branches in parallels) and the use of low inductance capacitor and switches yield to a very compact and simple driver. To understand the operation of this kind of generator and insure the electric specifications (pulse length of 75 ns FWHM), the efforts followed two approaches. First, a classic circuit model can be established. This part permits to rapidly survey the effect of each parameter. The temporal effects due to the electron density flowing along the MIT Line require a specific model to be implemented in the circuit code. The other approach uses a PIC code to completely simulate the generator. This description includes the driver - diode interface and takes into account the diode behaviour. In this paper, a design of a 3 MV LTD machine is presented. The analytic modelling is described on the second section. This modelling includes a Creedon approach to choose the spatial dimension of the MIT Line. The results obtained are checked with circuit simulation on the third section. Finally, particles simulations follow the charge density along the line down to the diode region and predict the electric pulse delivered to the diode