Nonuniform electron distributions in a solenoidal ioniser

Abstract Solenoidal ionisers are a new class of highly efficient helium detectors that increasingly important for high resolution atom scattering, molecular scattering and scanning microscopy. They operate via electron ionisation, where the electrons trapped by magnetic field solenoid additional electrostatic potentials. Their ionisation efficiency scales with population they contain, motivating large devices emission currents. However, these typically become unstable at densities, constraining their performance improvement. Through imaging exit ioniser, we demonstrate instabilities arise from non-uniformities in distribution. Considering ioniser as non-neutral plasma leads to proposal formation virtual cathode instability origins non-uniformity.