Measurements of energy spectra and spatial profile of large-area diode RITS-6 electron beam

The RITS-6 induction voltage adder (IVA) electron accelerator has an output voltage of 7-12 MV and beam currents from about 10 kA to 170 kA depending on the diode employed and the two options impedance of the magnetically insulated transmission line (MITL). The determination of the diode voltage has traditionally be done by a combination of parapotential flow theory in the MITL and translating the voltage pulse to the diode or solving radiographers equations for the x-ray dose rate. However the time-integrated voltage can also be inferred from the electron beam energy spectrum unfolded from measurements of the absorbed dose as a function of depth in the anode material. Depth dose measurements using radiochromic film sandwiched in an aluminum anode were performed on RITS in the high voltage mode. Results are presented for the unfolded electron spectrum using a modified least-squares optimization method with Monte Carlo radiation transport code-generated mono-energetic depth-dose profiles. Variations in the beam spatial profile are observed. Time-resolved measurements of the beam current density profile were performed using gated CCD cameras which observed the beam-generated Cherenkov light pattern inside electron range-thin fused silica. These measurements were made at similar beam current but lower voltage than the depth-dose shots. Various cathode surface treatments were used to see if beam profile depended strongly on the electron source.