UTA GEM updates J Li A White J

UTA GEM updates J. Li, A. White, J. Yu 5/9/02

Preparations for prototype construction èTest GEM “chamber” designed at UTA - allows varying layer configurations - straightforward gas, HV etc. èMain issue is acquisition of GEM foils - contact with GEM inventor, F. Sauli, CERN

GEM test chamber J. Li, UTA

- Most foils made in CERN printed circuit workshop - Approximately 1, 000 foils made - Big project for COMPASS expt. 31 x 31 cm 2 foils - Most difficult step is kapton etching – Sauli has offered to reveal “trade secrets” in context of formal collaboration. - Fastest route – buy a few foils from Sauli: 10 x 10 cm 2 foils 70 m holes 140 m pitch ~$300 - Foils HV tested/verified at CERN.

- Sauli - procure a fully assembled, dismountable detector for us…but prefer our design - Also… Edik Tsyganov at UT Southwestern Med. has working multi-gem detector -Ultimately we want to able to make our own foils. - Some interesting GEM details:

CERN GDD Group – electron-micrograph of GEM foil

CERN GDD Group – electron-micrograph of GEM foil hole

GEM Issues è Gain uniformity ( ~15%) – should not be a big issue for digital mode operation è Discharges: single/double GEM’s: - single GEMS – OK for G 1500 - double GEM’s: “double detectors obtained cascading a Gas Electron Multiplier (GEM) as preamplification, and a second GEM, a MSGC or other devices as second amplifier permit to reach gains above 10000 before discharge under very high rates and exposure to heavily ionizing tracks. ” GDD group Web site

Single GEM gain/discharge probability A. Bressan et al NIM A 424 (1998) 321

-> We need to determine particle flux vs. particle type (MIP, neutral, heavily ionizing) from detailed simulation. -> Variations of hole sizes, shapes affect the discharge probability and hence operating region.

CONCLUSIONS P Learning more about GEM’s P Source(s) of GEM foils identified P Test Chamber designed P Need studies of particle fluxes in calorimeter P Need $$$ !