High-Impedance Coaxial Autoaccelerator

Experimentation of a single-stage, 100 coaxial autoaccelerator was carried out on a 3 MeV, 9 kA, and solid (non-annular) electron beam and achieved a maximum energy gain of about 900 keV. This method provides an alternative to multiple-stage, lower-impedance cavity designs in achieving higher energy gain. Upper and lower bounds for the transmission line length exists which depend on the total pulse width and the rise time of the pulse if one were to maximize the cavity voltage. Experimental measurements of the highest energy electrons included aluminum foil transmission, bremsstrahlung photon absorbed dose using a PIN diode dosimeter, depth-dose profiles in aluminum, and direct cavity voltage measurements using a capacitive voltage probe. Simulations were also performed using a particle-in-cell (PIC) plasma code to model coupling of the beam to the cavity to calculate voltages. Calculation results of the experimental structure suggested that the autoaccelerator gap is magnetically insulated against breakdown while the beam is passing the gap due to the combined effect of the applied axial magnetic field and the azimuthal magnetic field of the electron beam.