Development of a pulsed, 0.1 to 1.0 MeV electron accelerator for High Precision Characterization*

A mini- electron accelerator is being developed at the Triangle Universities Nuclear Laboratory (TUNL) for high precision characterization of detectors in the energy range for neutron beta decay, 0.1 to 1.0 MeV. The accelerator uses a pelletron charging system, and is designed to deliver up to about 10^7 electrons/second with an energy resolution of roughly 0.1%. The pulsing experiment is under development and utilizes a fiber-coupled, pulsed UV LED light source that attaches to a vacuum-designed optical assembly. Measurements of the timing uncertainties of the electrons are estimated to be roughly around one nanosecond. The optical assembly was modelled using Inventor Software to design a vacuum-safe flange and tube system for the fiber-coupled LED pulse. An off-axis parabolic mirror reflects the pulsed light from the fiber and directs it towards another parabolic mirror clamped to the first electrode which focuses the light onto the photo-cathode. To ensure the optical systems functioned to expectations, systematic studies of the optical transmission through this system were performed.

Simulations of the accelerator were conducted on the Kassiopeia 3.6.1 software to assess the impact of ambient magnetic fields and weak magnetic field guiding geometries within and around the accelerator. The electron transport model included all thirty electrodes within the accelerator tube, the photoemitter with a designed electric field-shaping plate, and a parabolic mirror with the associated clamps and containers. Magnetic field steerers and collimation are also incorporated into the model. We hope to characterize the expected performance of the system using the results of optical and accelerator column tests from these simulations.