GEM DETECTORS 1 Fabio Sauli CERN Title DEVELOPMENT

GEM DETECTORS 1 Fabio Sauli - CERN Title DEVELOPMENT AND APPLICATIONS OF GEM DETECTORS Fabio SAULI CERN, GENEVA, SWITZERLAND Symposium on Radiation Measurements and Applications SORMA 2002 University of Michigan, Ann Arbor - May 21 -23, 2002

Fabio Sauli - CERN GEM DETECTORS 2 GEM Gas Electron Multiplier Typical geometry: 5 µm Cu on 50 µm Kapton 70 µm holes at 140 mm pitch F. Sauli, Nucl. Instrum. Methods A 386(1997)531

GEM DETECTORS 3 Fabio Sauli - CERN GEM detector Gain and readout functions on separate electrodes Fast electron charge collected on patterned anode Energy signal detected on lower GEM electrode Cartesian Small angle Pads A. Bressan et al, Nucl. Instr. and Meth. A 425(1999)254

GEM DETECTORS 4 Fabio Sauli - CERN Multiple GEM Structures Cascaded GEMs permit to obtain larger gains Double GEM Triple GEM C. Buttner et al, Nucl. Instr. and Meth. A 409(1998)79 S. Bachmann et al, Nucl. Instr. and Meth. A 443(1999)464

Fabio Sauli - CERN GEM DETECTORS 5 Single-Double-Triple GEM Gain and Discharge Multiple structures provide equal gain at lower voltage The discharge probability on exposure to a particles is strongly reduced For a gain of 8000 (required for full efficiency on minimum ionizing tracks) in the TGEM the discharge probability is not measurable. S. Bachmann et al, Nucl. Instr. and Meth. A 479 (2002) 294

Fabio Sauli - CERN GEM DETECTORS 6 COMPASS Triple-GEM Detector • Active Area 30. 7 x 30. 7 cm 2 • 2 -Dimensional Read-out with 2 x 768 Strips @ 400 µm pitch • 12+1 sectors GEM foils (to reduce discharge energy) • Central Beam Killer 5 cm Ø (remotely controlled) • Total Thickness: 15 mm • Low mass honeycomb support plates B. Ketzer et al, IEEE Trans. Nucl. Sci. NS-48(2001)1065 C. Altumbas et al, CERN-EP/2002 -008

GEM DETECTORS 7 Fabio Sauli - CERN 2 -Dimensional Read-out Board Two orthogonal sets of parallel strips at 400 µm pitch engraved on 50 µm Kapton 80 µm wide on upper side, 350 µm wide on lower side (for equal charge sharing) 400 µm 80 µm 350 µm 400 µm

Fabio Sauli - CERN GEM DETECTORS 8 Beam killer A central sector on each GEM, 5 cm in diameter, is independently powered. Application of a lower potential (by ~ 200 V) on the sector completely kills detection of the main beam.

Fabio Sauli - CERN GEM DETECTORS 9 Quality control Before mounting, and at each assembly step, all GEM foils are HV tested in a N 2 gas box (requirement: less than 5 n. A at 550 V)

COMPASS Triple-GEM Chamber 30. 7 x 30. 7 cm 2 active 2 -D readout Readout Electronics Lower mass cut HV distribution

GEM DETECTORS 11 Fabio Sauli - CERN Pulse height spectra Minimum ionizing particles Gain 8000 Y-coordinate X-coordinate

Fabio Sauli - CERN GEM DETECTORS 12 Cluster charge correlation Very good correlation, used for multi-track ambiguity resolution s ~ 10% X-Y Cluster charge correlation:

GEM DETECTORS 13 Fabio Sauli - CERN Beam killer The central beam area can be remotely activated for calibrations and alignments. Disabled during high intensity runs. Beam disabled Beam activated APRIL 2002: 16 CHAMBERS INSTALLED AND OPERATIONAL

GEM DETECTORS 14 Fabio Sauli - CERN X-ray imaging Using the lower GEM signal, the readout can be selftriggered with energy discrimination: A. Bressan et al, Nucl. Instr. and Meth. A 425(1999)254 F. Sauli, Nucl. Instr. and Meth. A 461(2001)47 9 ke. V absorption radiography of a small mammal (image size ~ 60 x 30 mm 2)

Fabio Sauli - CERN GEM DETECTORS 15 High pressure operation Neutron detection in He 3? A. Bondar, A. Buzulutskov, L. Shekhtman, V. Snopkov and A. Vasiljev, Subm. Nucl. Instr. and Meth. (2002)

GEM DETECTORS 16 Fabio Sauli - CERN X-ray polarimeter Charge asymmetry: E. Costa et al, Nature 411(2001)662 R. Bellazzini et al Nucl. Instr. and Meth. A 478(2002)13 GEM chamber with pad readout to detect the direction of the photoelectron produced by X-rays 5. 9 Ke. V unpolarized source 5. 4 Ke. V polarized source

GEM DETECTORS 17 Fabio Sauli - CERN Multi-GEM for photon detection Multiple GEM detectors permit to achieve very large gains (106) in photocathode-friendly pure noble gases or poorly quenched mixtures. Reduced transparency strongly suppresses photon and ion feedback A. Buzulutskov et al, Nucl. Instrum. Methods A 443(2000)164 Large area position-sensitive photomultipliers R. Chechik et al, Nucl. Instr. and Meth. A 419(1998)423

Fabio Sauli - CERN GEM DETECTORS 18 GEM operation in CF 4 Photoelectron extraction from Cs. I: A. Breskin, A. Buzulutskov, R. Chechik Nucl. Instr. and Meth. A 483(2002)658

Fabio Sauli - CERN GEM DETECTORS 19 Sealed GEM Photomultiplier Semi-transparent Cs. I photocathode Single photo-electron signals: A. Breskin et al, Nucl. Instr. and Meth. A 478(2002)225

Fabio Sauli - CERN GEM: Reflective photocathode Cs. I Photocathode deposited on GEM upper side: • No photon feedback • High Quantum Efficiency D. Mörmann et al, Nucl. Instr. and Meth. A 471(2001)333 Nucl. Instr. and Meth. A 478(2002)230 GEM DETECTORS 20

Fabio Sauli - CERN GEM DETECTORS 21 GEM optical imager Scintillation light in a multiple GEM detector recorded by a CCD camera - particle tracks Proton and Triton tracks by neutrons in 3 He F. A. F. Fraga et al, Nucl. Instr. and Meth. A 478 (2002) 357

Fabio Sauli - CERN 2 D-dosimetry in radiation therapy J. H. Timmer et al, Nucl. Instr. and Meth. A 478(2002)98 GEM DETECTORS 22

GEM DETECTORS 23 Fabio Sauli - CERN Ultrafast X-ray plasma diagnostics (EURATOM-ENEA Frascati, Italy) Single GEM with fast pixel readout RATE CAPABILITY: Counts/50 µs Readout: 32 2 mm 2 pixels TIME-RESOLVED PLASMA ACTIVITY: D. Pacella et al, Rev. Scient. Instrum. 72 (2001) 1372 R. Bellazzini et al, Nucl. Instr. and Meth. A 478(2002)13 Time (ms)

Fabio Sauli - CERN Plasma diagnostics with GEM detector Plasma emission (~ 1. 5 ke. V) sampled at 10 k. Hz First observation of plasma rotation Courtesy D. Pacella, Princeton Plasma Physics Laboratory GEM DETECTORS 24

Fabio Sauli - CERN The End GEM DETECTORS 25