slide 1 Diamonds in Flash Steve Schnetzer Rd42 Collaboration Meeting May 14

slide 2 The Flash Experiment Measure to ~10% the fluorescence response of the atmosphere to the energy loss of particles in EM shower Needed for calibrating energy response of cosmic ray fluorescence detectors SLAC 28 GeV beam into alumina target measure fluorescent yield after 2X 0, 6X 0, 10X 0 and 14X 0 14 day run in June plus shorter run in July

slide 3 Purpose of Diamonds Total particle yield Particle spectrum Lateral particle distribution Use GEANT to get downstream of target Use diamond detectors to verify GEANT calculation lateral distribution of energy deposit absolute measurement of energy deposit relatively easy relatively hard calibration

slide 4 10 Hz pulse duration 1 ps Measure shower at 2X 0, 6X 0, 10X 0 and 14X 0 Beam: 28 GeV electrons 10 7 e  /pulse Use four 1 cm x 1cm CD 100 series diamonds Diamonds centered at x = 0cm, 5cm, 10cm, 15cm perpendicular to beam Parameters

slide 5 Diamond Segmentation pixel: 2.6 mm x 2.6 mm 3 x 3 pixel array outer ring for defining fiducial region segmented to help assure full beam flux hits 3x3 region during calibration active area 8 mm x 8 mm

slide 6 Ganging at x = 5 cm ganged to 3 strips at x = 10 cm & 15 cm ganged to 1 pad

slide 7 GEANT Simulations 2X 0 6X 0 energy deposited x= 0 cm

slide 8 GEANT Simulations 10X 0 14X 0 energy deposited x= 0 cm

slide 9 Charge Deposited assumes: 13 eV per e-h pair DepthCharge 2X x 10  7 C 6X x 10  7 C 10X x 10  8 C 14X x 10  9 C charge deposited in central pixel this charge deposited in 1 ps charge for 1 mip = 2.0 x 10  15 C

slide 10 Calibration  Calibrate linearity of response of diamond to large total charge deposition high ionization density  Use  = 1 mm beam with target out 10 7 to 10 8 ppp to map out linearity of response beam toroid provides precision intensity measurement  Decrease beam density by factor of 2 (  = 2 mm) to see how diamond response depends on ionization density

slide 11 Energy Deposit charge on central pixel (C) peak density (C/mm  2 ) 10 7 on thick target 1 mm beam (target out) 2 mm beam (target out) CERN BCM test in ~30 ns 14x 0 10x 0 6x 0 2x 0 Compared to CERN ~ 5 x higher peak density ~ 2 x more charge ~ 10 4 x faster deposit 10  8 10  7 10  8 10  9

slide 12 Readout Scheme VbVb RbRb CbCb CdCd I 50  CsCs RsRs diamond ADC one for each pixel V b C b >> 10  6 C Q/C s << V b R s C s = 100 ns R b C b << 0.1 s C s = 20 nF R s = 5  C b = 400 nF R b = 2.5 k   100 ns shaping

slide 13 Inductive Voltage Drop 2 x 10  7 C charge deposited charge in diamond is collected in about 10 ns  20 A over 10 ns  PC board has to be designed to minimize inductance this current wants to turn on in ~ 1ps the bunch length of the beam large inductive voltage drop  voltage on diamond sags

slide 14 Inductance VbVb RbRb CbCb CdCd I CsCs RsRs diamond inductance a problem here wire bond wire and PCB trace about 1 nH per mm use multiple wire bonds and traces should be able to keep inductance less than 5 nH causes voltage across diamond to sag

slide 15 Spice Simulation 10 nH 5 nH 1 nH voltage sags about 400 V for 1 to 2 ns input rise time 1 ps voltage on diamond

slide 16 PC Board caps as close to diamond as possible bias line can have 1 cm  hole here signals routed by flat cable to ganging board VbVb RbRb CbCb CdCd I CsCs RsRs on ganging board C b on backside on board

slide 17 X/Y Stage ~ 40 cm arm to keep stages out from behind optical box backscattering 29.5 cm

slide 18 Readout Diamond PC Board bias coax flat signal cable Ganging Board from control room coax signal lines to control room one for each diamond shaping resistors ganging of signals a few feet

slide 19 Issues absolute calibration of energy deposit  calibrate with direct electron beam effect of ionization density  vary density and intensity of electron beam low energy and stopping electrons  need precise GEANT calculation neutron background current build up inductive effects  minimize inductance 5 nH  400 V sag over 1 ns radiation damage on average 2 x e  cm  2 hr  1 in central pixel we’ll measure it

slide 20 Challenges 2 times more charge per pulse than anything previous 5 times greater ionization density than anything previous First attempt at a few % measurement (10% is the standard) Very rapid 1 ps energy deposit