Triplet polarimeter update

Transcription

1 Triplet polarimeter update M. Dugger, February

2 Plan Set up a polarimeter test bench in the Experimental Equipment Laboratory (EEL) Further test the silicon strip detector using fadc and sources Install and test the positioning system Once device is tested, it will be put into permanent home (collimator cave) 2

3 Future home Polarimeter location (red box) 3

4 Polarimeter stand in collimator cave 4

5 Upstream of polarimeter stand Secondary collimator Secondary sweep magnet Polarimeter stand 5

6 Further upstream of polarimeter stand Primary sweep magnet Secondary collimator 6

7 Construction 7

8 Vacuum system When the polarimeter is installed in the collimator cave, the vacuum will come from the beam line In the test bench, the vacuum has to be provided by a temporary system Using a rotary vane pump for the vacuum system of the test bench Rotary vane pumps will back-stream oil and this issue must be addressed 8

9 VisiTrap VisiTrap will catch any backstreaming before it hits the vacuum hose 9

10 Molecular Sieve and Stinger Molecular sieve will catch stray contaminates Loaded sieve with zeolite and heated for two hours 10

11 Vacuum system attached to chamber (view 1) Cleaned chamber with: Acetone Methonal DI water Attached the vacuum system 11

12 Leakage and outgassing tests Procedure: Pump down chamber Close butterfly valve between vacuum system and chamber Record the pressure as a function of time Slope = mtorr/min cycle 1 12

13 Vacuum leakage test results (empty chamber) For area and volume calculations of the chamber I included all of the flanges Volume ~ 29.5 liters. Surface area ~ 6500 cm 2 Outgassing rate = (Volume/Area)*dP/dt Tim Whitlatch said steel will outgas at a rate of 2E-09 Torr*l/(cc*s) Cycle dp/dt (mtorr/min) dp/dt (Torr/s) V/A*dP/dt (Torr*l/cc*s) * 10^ E * 10^ E * 10^ E * 10^ E-10 It looks like the test is consistent with the dp/dt of the chamber being from the outgassing of steel: No big obvious leaks 13

14 Vacuum test results (detector in chamber) Five hour pump down to ~20 mtorr dp/dt found to be 6.12x10-6 Torr*liter/s A turbo pump on the chamber with a flow rate of 100 liters/s should be sufficient to maintain a vacuum of 10-5 Torr 14

15 Detector upstream view with source stand and Po210 source Teflon fasteners connect detector to supports 15

16 Detector downstream view 16

17 Preamps Decided to have a parallel development of the preamps: Glasgow is building a pre-amplification system based off of the Rutherford Appleton Laboratory RAL-108 pramps and custom motherboards ASU is using a pre-amplification system from Swan research ( Box16 preamps ) 17

18 Swan preamps The STARS detector uses Micron S2 with swan research preamps Preamp hybrid Stars detector Input view Output view 16 channel box 18

19 Preamp to feedthrough cable assembly The Micron S3 detector uses special ribbon cable connectors Could not find suitable ribbon cables. Instead used Kapton wires that were individually placed in the cable connector 40 Wires attached to connector in picture shown 19

20 Detector, cable and source 20

21 Ring side cable Only enough preamps to instrument the sectors but made the ring side cables first 21

22 Preamps wired up and ground connections Sector side cables Ring side set to ground 22

23 Distribution box connected to preamp enclosure Original distribution box 23

24 New distribution box (view 1) While Kei was at ASU getting trained to be a polarimeter expert he was able to help assemble to new distribution box Signal plate 24

25 New distribution box (view 2) Power plate 25

26 Copper preamp-box grounding (slide 1) Preamp supports made out of anodized aluminum Decided to help ground the preamp boxes by using copper foil on the preamp supports 26

27 Copper preamp-box grounding (slide 2) Lined three sides of the preamp enclosure with the copper foil View: looking into the preamp enclosure through the opening for the vacuum chamber feedthrough flange Ground connector to ring side of detector 27

28 Copper preamp-box grounding (slide 3) View: looking into the preamp enclosure from the top Can see the EMshielding copper mesh for the fan inlet/outlet grounded to the copper foil 28

29 Signal plate grounding Cutting copper foil for the signal plate grounding Also grounded to the input voltages (power plate) 29

30 Signal plate and power plate grounding 30

31 Fan leads Routed the fan leads through the preamp enclosure towards the distribution box 31

32 View of polarimeter with original distribution box completely removed 32

33 Noise reduction Wrapping signal wire around toroidal core reduces noise Putting AC Power Entry Module (with inline filter and earth-line choke) into LV supply also helped with the noise 33

34 The silicon detector The detector is very much like a diode operated in reverse bias mode As the voltage is increased across the detector, the depletion region gets larger The larger the depletion region, the smaller the capacitance of the detector For each 3.6 ev of energy deposited in the depletion region there is one electron-hole pair that is created and then swept out of the detector 34

35 Noise of preamps versus input capacitance Preamp noise has a linear relationship with the detector capacitance Typical noise versus detector capacitance plot 35

36 High voltage For the test bench we are using a temporary power supply that is rather old Tennelec TC 952 The permanent power supply will be provided by JLab and will be of higher quality The temporary power supply has a ripple of about +/- 5 mv at 60 Hz 36

37 Ripple and other noise as function of HV (slide 1) 10 mv/div 10 ms/div HV = 0V Using Po210 source HV = 20V HV = 40V HV = 60V 37

38 Ripple and other noise as function of HV (slide 2) 10 mv/div 10 ms/div HV = 80V HV = 100V HV = 120V HV = 140V 38

39 Ripple and other noise as function of HV (slide 3) 10 mv/div 10 ms/div HV = 160V HV = 180V α HV = 200V HV = 200V 200 mv/div & 1 µs/div 39

40 Alpha o-scope picture Polonium 210 source Alpha energy = 5.3 MeV Signal about 500 mv 40

41 Electron o-scope picture Cesium 137 source Signal about 25 mv for this shot Finer time scale for this shot (50 ns/div) 41

42 Data acquisition system at ASU Using a Tektronix logging oscilloscope as a slow ADC Acquisition rate ~ 1 Hz LabView signal express GUI 42

43 Voltage Fit to signal Assume voltage has same form V = [Γ r V m /(Γ r - Γ f )][exp(γ r t) exp(γ r t)] Po210 signal time (μs) 43

44 Counts Calibration (sector 3) Po210 alpha source Center = mv E k = kev One hour of data Calculated sensitivity = 95mV/MeV mv 44

45 Alpha-test widths Looked at all 32 sectors Looks good except for a single channel (sector 32, lower preamp-box channel 10) 45

46 Voltage Typical fit to signal for Ba133 source time (μs) 46

47 Ba133 MC compared to data (sector 3) MC Data MC Generated photon energies: 223, 276, 302, 356, 383 kev Smeared energy deposited by standard deviation of 12 kev Fit: Centers locked to same photon energies that were generated in MC Standard deviation was the same for each Gaussian and allowed to vary Standard deviation from fit found to be 11+/- 1 kev Therefore, resolution of detector plus electronics is about 12 kev for this sector 47

48 Work still to be done at ASU Need to complete the positioning system Need to machine one side of preamp enclosure to allow for JLab ground feedthrough 48

49 Convertor tray Top of converter tray Bottom of converter tray 49

50 Positioning system Still need to clean parts and install limit switches I expect the positioning system to be ready to ship by the end of February 50

51 Chamber crated up 51

52 Crate counterbalance Undergraduate cratecounterbalance (Brianna) Brianna is also my machine-shop buddy and she helped build the polarimeter 52

53 Shipping Shipped the chamber, silicon strip detector and preamps on Monday February the 16 th Shipped the stepper motor and vacuum related items on Tuesday the 17 th of February Expect to ship everything by the end of February 53

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56 B-field study Study performed in April 2012 Applied magnetic field in vertical direction 56

57 Effect of B-field on δ-rays y (cm) y (cm) No field x (cm) 350 gauss field x (cm) M. Dugger, April

58 Azimuthal distribution with applied B-field 350 gauss field applied A[1+Bcos(2φ)] A[1+Bcos(2φ)+Ccos(φ)] φ 58

59 Analyzing power (B) Analyzing power vs. B-field Small field Small systematic effect Field strength (gauss) 59

60 Pile-up study Threw 10 million photon events Only 469 events seen on detector Assume 10 8 Hz in photon range between 8.4 and 9 GeV Timing window of preamp pulse to be 18 μs For a single sector we expect 0.7% of events to have more than one signal in the timing window Pile-up should not be much of an issue 2.1% of total 60

61 Pump to Visitrap to Molecular Sieve 61

62 Counts MC of Cesium 137 E dep (MeV) Smeared E dep by 40 kev Included only single sector hits 62

63 Counts Counts Quick comparison of data to MC for Cesium 137 Data MC σ/mean = σ/mean = Int (mv) E dep (MeV) 63

64 Triplet production Pair production off a nucleon: γ nucleon nucleon e + e -. For polarized photons σ = σ 0 [1 + PΣ cos(2φ)], where σ 0 is the unpolarized cross section, P is the photon beam polarization and Σ is the beam asymmetry Triplet production off an electron: γ e - e R - e + e -, where e R represents the recoil electron Any residual momentum in the azimuthal direction of the e - e + pair is compensated for by the slow moving recoil electron. This means that the recoil electron is moving perpendicular to the plane containing the produced pair and can attain large polar angles. M. Dugger, February

65 Energy deposited (MeV) Generated pairs and triplets with E γ = 9 GeV Required energy of e + e - pair to be within 1.75 GeV of each other Simulation Required energy deposition in detector to be greater than 200 kev Converter: 35 μm beryllium φ (degrees) Used full calculation (all diagrams included) 65