HBD CDR Gas System and Monitoring Craig Woody BNL DC Upgrades/EC Meeting March 9, 2005

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/052 Requirements  Must deliver very high purity gas to the HBD More stringent demands than any other PHENIX gas system (O 2, H 2 O at the few ppm level) No leaks (  stainless steel, welded gas lines wherever possible) CF 4 is expensive (  recovery system)  Operates reliably with CF 4 CF 4 is a highly reactive and corrosive gas (reaction with water produces HF acid, dissociation produces F - ions)  Special concern about compatibility of materials  Must continuously monitor gas Absorbance due to H 2 O and O 2 can cause loss of photoelectrons

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/053 Proposed HBD Gas System CF 4 output gas collected, compressed, purified and reused L.Kotchenda

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/054 Gas System Costs Company Name Purchases Cost Dwyer Instruments $ Tescom $ Ashcroft Aprx.$ ADI $ RXI $ Omega Engineering, Inc $ Peter Paul Electronics Co $ Khan $ Miller Energy Inc $ Asco $ Swagelok $ Newark $ Matheson Aprx.$ Hastings Instruments Aprx.$ Agilent $ National Instruments Aprx.$ Total $ Two Racks -~$1500 Computer -~$ L buffer cost - $ The labor cost is $ Total: ~ $60K (without pipes, => + $20K) L.Kotchenda Needs update with some CF 4 compatible components

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/055 Affects of Impurities on VUV Transmission Must maintain careful control of oxygen and water levels O 2  5 ppm H 2 O  10 ppm B.Azmoun

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/056 Transmission vs ppm’s of O 2 and H 2 O B.Azmoun

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/057 ( i = 1120, 1130,…,2000) Calculation of N pe vs ppm’s of Gas Impurities (H 2 O, O 2 ) B.Azmoun (n -1) =

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/058 N pe vs ppm’s of H 2 O and O 2 Parameters of Calc. * Length of CF 4 radiator= 50cm * (CF 4 )= *  =1 (energy of incident e- ) * Integrated over Wavelength Range: nm { eV (CF 4 cut-off)} * Corrected for mesh+GEM trans (0.885 x 0.83) * Extrapolated N pe down to 108nm assuming 100% trans. between 112 and 108nm (CsI QE also extrapolated over same range) * Using WIS QE plot: makes insignificant difference compared with BNL measuement B.Azmoun

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/059 Gas Transmission Monitoring  Measure UV transmission of input gas and output gas of each detector half separately  Movable mirror directs beam down four separate optical paths  Maximize beam intensity so can use CsI vacuum photodiodes for readout (gain stability with nanoamps of photocurrent)  Built mainly from commercial parts (McPherson) D 2 Lamp Monochromator Focusing elements Input gas Output gas HBD East Output gas HBD West Reference CsI Photodiodes MgF 2 WindowsGas Cells MgF 2 Windows Movable Mirror

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/0510 CsI QE Monitoring  Install UV lamp(s) inside detector  Run detector in reverse bias mode and measure DC current (special calibration mode)  QE monitoring only done rather infrequently (every few weeks ?)

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/0511 Additional Slides

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/0512 HBD in PHENIX  34 cm R min = 4.5 cm w/o VTX R min = 72 cm w/VTX R max = 55 cm w/o VTX R max = 22 cm w/VTX Weight ~ 6 kg (< 15 kg total) 84 SHV cables 1 gas inlet (1/2”) 1 gas outlet (1”) per side

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/0513 Test of a Triple GEM Detector in PHENIX 55 Fe spectrum with Ar/CO 2 in Lab Triple GEM detector installed close to beam pipe ( R ~ 50 cm) Detector was sensitive to soft background (thin window) Tested using using both Ar/CO 2 (70/30) and CF 4 Exhibited no sparking or excessive gain instabilities.

C.Woody, HBD CDR, DC Upgrades/EC Meeting, 3/9/0514 Test of a Triple GEM Detector in PHENIX 55 Fe specta with CF 4 with full luminosity Au-Au collisions at RHIC Detector gain and resolution was stable Observed some low level background (< 50 e’s) during part of one run - depended strongly on beam conditions. - mostly out of time with beam-beam collisions Conclusion: There appears to be no fundamental problem with operating a GEM detector close to the beam pipe at RHIC