First results of spherical GEMs

TL;DR

This paper introduces a novel spherical GEM detector design that reduces parallax error in radiation detection, featuring new manufacturing methods, curved spacers, and a conical field cage, with promising initial test results.

Contribution

It presents the first method to produce spherical GEM foils and a complete spherical detector prototype with improved spatial resolution and rate capability.

Findings

Successful development of spherical GEM foils and components

Initial tests show promising detector performance

Plans for a spherical 2D readout structure are underway

Abstract

We developed a method to make GEM foils with a spherical geometry. Tests of this procedure and with the resulting spherical GEMs are presented. Together with a spherical drift electrode, a spherical conversion gap can be formed. This eliminates the parallax error for detection of x-rays, neutrons or UV photons when a gaseous converter is used. This parallax error limits the spatial resolution at wide scattering angles. Besides spherical GEMs, we have developed curved spacers to maintain accurate spacing, and a conical field cage to prevent edge distortion of the radial drift field up to the limit of the angular acceptance of the detector. With these components first tests are done in a setup with a spherical entrance window but a planar readout structure; results will be presented and discussed. A flat readout structure poses difficulties, however. Therefore we will show advanced plans to make a prototype of an entirely spherical double-GEM detector, including a spherical 2D readout structure. This detector will have a superior position resolution, also at wide angles, and a high rate capability.