Cascades of Secondary Particles in High Voltage Accelerators

M. Cavenago[1], P. Antonini[1][3], P. Veltri[2], N. Pilan[2], V. Antoni[2], and G. Serianni[2]
[1]INFN-LNL, Legnaro, Padova, Italy
[2]Consorzio RFX, Padova, Italy
[3]Centro Ric. E. Fermi, Roma, Italy

A very simplified system for high voltage test is studied, considering reason for voltage holding failures which are not covered by conventional and local design criteria. A first understanding of the problem is obtained by solving the electrostatic potential in a 2D axis symmetric geometry, considering in detail the electrode shapes, and following a cascade of particle between opposite electrodes. Very specific attractors were found for the impact points; physical reason is that the highly non uniform electric field may focus, defocus or move the discharge. A second analysis takes into account the spread of the reemitted particle velocity and a consequent 3D motion. Solution of a Fokker Planck style equation for the impact point confirms the existence of hot spots.

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