A Prototype Diamond Detector for the Compton Polarimeter in Jefferson lab, Hall C Medium Energy Physics GroupAmrendra Narayan Mississippi State University JLab, Hall C, Compton Polarimeter Collaboration Outline The Compton Polarimeter Diamond as a Detector Electronic Setup Preliminary Results Future Tasks Thanks: Few Slides adapted from the talk of Roger Carlini The Compton Polarimeter Compton Scattering e-e- e-e- A high precision Compton Polarimeter is under construction at Hall-C for a non-destructive continuous monitoring of the e - beam polarization during the Qweak experiment and all other polarized e - scattering experiments to follow after the upgrade to 12 GeV capacity. Beam Current I 180 A PropertySiliconDiamond Band Gap (eV) Electron/Hole mobility (cm 2 /Vs)1450/ /1600 Saturation velocity (cm/s)0.8x10 7 2x10 7 Breakdown field (V/m)3x x10 7 Dielectric Constant Displacement energy (eV) e-h creation energy (eV)3.613 Av. e-h pairs per MIP per micron8936 Charge collection distance (micron)full~250 Low leakage current, short noise Fast signal collection Low capacitance, noise Radiation hardness Smaller signal Thanks: Dr. R. Wallny (UCLA) Diamond: A Closer look Advantages: lower leakage current, faster, lower noise and rad. hard Disadvantages: smaller signal ~ 40% smaller Recall that the Compton edge is 2cm from beam for recoil e - Silicon is a typical choice for a multi-strip position sensitive electron detector The Diamond Detector Diamond is known for its radiation hardness We chose Diamond (artificially grown by Chemical Vapor Deposition) for the detector How does it work? Operation of Diamond Detectors Bias voltage ~ 1000 V, Charge collection distance ~ 250 A Prototype Diamond Detector Metallization, Lithography & wire bonding done in High Energy Physics Lab at Ohio State University. Thanks Prof. Harris Kagan and his group at OSU. 10x10 mm m thick 15 strips ~450 m wide Schematic of the Electronic Setup The raw signal, a charge pulse Charge pulse converted to a voltage signal and amplified Timing signal created only for signals > V_ threshold Timing Filter Amp Electron detector Pre- amp Discriminator Shaping Amp Linear Gate MCA MPR - 16 STM 16+ Signals accepted only in co-incidence with the signal from timing filter amp Analog to Digital Converter Histograming of the digital signal Visual display Channel number counts The signal is shaped (tail truncated) to avoid overlapping of signals coming one after the other. Ortec 928 Ortec 926 A typical display Threshold Voltage was low ~50 mV Spectrum obtained by the Diamond detector Shaping gain pedestal suppressed spectra from diamond threshold set to 150 mV to suppress the background Triggering with a Scintillator Measuring only the minimum ionizing particles. Only those beta particles would be detected which pass the detector and reach the Scintillator. Electron Source Silicon detector Photomultiplier + Scintillator DAQ HV Bias Schematic of the Electronic Setup The raw signal, a charge pulse Charge pulse converted to a voltage signal and amplified Electron detector Pre- amp Discriminator Shaping Amp Linear Gate MCA MPR - 16 Signals accepted only in co-incidence with the signal from Scintillator Analog to Digital Converter Histograming of the digital signal Visual display Channel number counts The signal is shaped (tail truncated) to avoid overlapping of signals coming one after the other. Ortec 928 Ortec 926 A typical display Scintillator + PMT Instead of Self-trigger, we are now triggering with the Scintillator Channel Number counts Mean : Sr spectrum in Si Detector with Gain 200 *For Silicon: dE/dx = MeV/(g/cm 2 ); = 2.33 g/cm 3 ; Energy per e-h pair = 3.6 eV Thickness of the Si detector = 300 m e-h pairs Calibrating MCA The mean Energy deposited then comes out to be keV Corresponds to * From particle physics data book Triggering with a Scintillator Measuring only the minimum ionizing particles. Only those beta particles would be detected which pass the detector and reach the Scintillator. Electron Source Diamond detector Photomultiplier + Scintillator DAQ HV Bias *For Diamond: = 3.5 g/cm 3 ; Z/A = 0.499; Energy per unit e-h pair = 13 eV Mean : Sr spectrum in Diamond Detector; Gain = 1000 The Mean of 852 MeV With the calibration by Si Corresponds to 4742 e-h pairs (expect 9000 e - for 220 m CCD) * x effec = m Response of the Diamond Detector * A 220 m CCD was measured for this diamond with a metalized dot Negative bias Positive bias Mean : 708 Channel # Counts Repeat the measurements in a real electron beam (Detector has been shipped to TRIUMF, tests scheduled for mid-June) & Build the full size Diamond Detector (4 planes, 21 x 21 mm 2, 200 m pitch) An order for 4 planes placed with E6, delivery expected in 2 weeks. Quotes obtained from an E6 Spin-off to do metallization, the same company has expressed interest in making the carrier plates and doing the wire-bonding (turn key detector). Build the read-out electronics Build the DAQ Mississippi State Univ., Univ. of Winnipeg, Univ. of Manitoba, TRIUMF Next Steps THANK YOU