Progress in MHSP electron multiplier operation

The microhole and strip plate (MHSP) gas electron multiplier was studied as a stand-alone device or in combination with a cascade of gas electron multipliers (GEMs), for X-ray and UV-photon detection. An MHSP operating in Ar/5%Xe yielded gains above 10⁴ and energy resolutions of about 14% FWHM for 5.9-keV X-rays. Gains as high as 10⁷ were reached in a 3-GEM/MHSP gaseous photomultiplier operating in an Ar/5%CH₄; the ion back-flow ratio to the top of the first GEM could be reduced to ∼2%. Two-dimensional (2-D) imaging was performed using signals induced by avalanche ions on a wedge and strip (W&S) readout cathode, placed at close proximity to the anode strips; position resolution of 200-250 μm FWHM for 5.9-keV X-rays was measured.