UTA Digital hadron Calorimetry using the GEM concept J.Li, A.White, J.Yu 5/30/02

Requirements for DHCAL (A) General -Thin sensitive/readout layer for compact calorimeter design -Simple 1- or 2-level “hit” recording for energy flow algorithm use -On-board amplification/digitization/discrimination for digital readout – noise/cross-talk minimization -Flexible design for easy implementation of arbitrary “cell” size -Minimal intrusions for “crackless” design -Ease of construction/cost minimization

(B) Gas Amplification Specific - Sufficient gain for good S/N for MIPs - Minimized cross-talk between “cells” - Readout path isolated from active volume - Modular design with ease module-to-module continuity for supplies, readout path - Digital readout from each cell - Pad design (to avoid x-y strip complications) - Keep HV low for safe/reliable use - Keep electronics simple = cheap/reliable

GEM (Gas Electron Multiplier) Approach GEM developed by F. Sauli (CERN) for use as pre- amplification stage for MSGC’s. GEM also can be used with printed circuit readout – allows very flexible approach to geometrical design. GEM’s with gains above 10 4 have been developed and spark probabilities per incident  less than Fast operation -> Ar CO 2 40 ns drift for 3mm gap. Relatively low HV (~ few x100V per GEM layer) (cf kV for RPC!)

From CERN-open , A. Sharma

Initial design concept for gas amplification DHCAL

Preparations for prototype construction  Test GEM “chamber” designed at UTA - allows varying layer configurations - straightforward gas, HV etc.  Main 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. 31x31 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: 10x10 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  Gain uniformity ( ~15%) – should not be a big issue for digital mode operation  Discharges: single/double GEM’s: - single GEMS – OK for G  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 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 A424 (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  Learning more about GEM’s  Source(s) of GEM foils identified  Test Chamber designed  Need studies of particle fluxes in calorimeter  Need $$$ !