Measurements of the divergence of a 10-MA relativistic electron beam transported in a gas cell

The increase in time-integrated divergence of a 1.7-MeV, 10-MA relativistic electron beam due to transport over 10 cm in a gas cell filled with 1 and 6 Torr of nitrogen was measured. The divergence was characterized by a multiple-pinhole beam sampling technique involving an aperture plate, an expansion region, and an attenuator plate followed by nylon radiochromic film. The divergence is determined by a fit of the measured deposition profile to response functions calculated using Monte Carlo coupled electronphoton transport codes. The initial value of 6.9° after the entrance foil is observed to increase to 12°. The errors in the measurement are quantified with Monte Carlo techniques. The response function fit gives a significantly better estimate of the divergence than a Gaussian fit.