Beam-induced Back-streaming Electron Suppression Analysis for Accelerator Type Neutron Generators

TL;DR

This paper analyzes methods to suppress electron backstreaming in a high-flux neutron generator, demonstrating that an electrostatic shroud effectively reduces secondary electrons, enabling higher beam currents for neutron production.

Contribution

It introduces and experimentally verifies an electrostatic shroud method for suppressing electron backstreaming in neutron generators, improving beam current capabilities.

Findings

Electrostatic shroud with -800 V effectively suppresses backstreaming electrons.

Simulation results aligned with experimental verification.

Suppression method enables higher neutron flux output.

Abstract

A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator design produces near monoenergetic 2.45 MeV neutrons at outputs of 10^8 n/s. Calculations provided show that future conditioning at higher currents and voltages will allow for a production rate over 10^10 n/s. A significant problem encountered was beam-induced electron backstreaming, that needed to be resolved to achieve meaningful beam currents. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics. Experimental tests verified these simulation results. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of -800 V relative to the target.