1. Update from the UCSC/SLAC ESTB T-506 Irradiation Study
LCWS 2016
Aiina Center & MALIOS
Morioka, Iwate, Japan
December 5-9, 2016
Bruce Schumm
UC Santa Cruz Institute for Particle Physics 1

2. Main Points and Updates
Summary: Exposures and progress in characterizing radiated samples
Reprise: Results from 270 Mrad exposure of p-type float-zone sensor, 300 Mrad exposure of n-type float-zone sensors
New Results: Industrial sapphire and LumiCal N-type Si Diode sensor (300 Mrad)

3. T-506 Motivation BeamCal maximum dose ~100 MRad/yr
BeamCal is sizable: ~2 m2 of sensors.
A number of ongoing studies with novel sensers: GaAs, Sapphire, SiC
 Are these radiation tolerant?
 Might mainstream Si sensors in fact be adequate?

4. Radiation Damage in Electromagnetic Showers
Folk wisdom: Radiation damage proportional to non-ionizing component of energy loss in material (“NIEL” model)
BeamCal sensors will be embedded in tungsten radiator
Energy loss dominated by electromagnetic component but non-ionizing contribution may be dominated by hadronic processes

5. Hadronic Processes in EM Showers
There seem to be three main processes for generating hadrons in EM showers (all induced by photons):
Nuclear (“giant dipole”) resonances
Resonance at MeV (~Ecritical)
Photoproduction
Threshold seems to be about 200 MeV
Nuclear Compton scattering
Threshold at about 10 MeV;  resonance at 340 MeV
 These are largely isotropic; must have most of hadronic component develop near sample 5 5

6. 2 X0 pre-radiator; introduces a little divergence in shower
Sensor sample
Not shown: 4 X0 “post radiator” and 8 X0 “backstop”

7. Irradiating the Sensors7 7

8. Mauro Pivi SLAC, ESTB 2011 Workshop, Page 8
LCLS and ESA
Use pulsed magnets in the beam switchyard to send beam in ESA.
Mauro Pivi SLAC, ESTB 2011 Workshop, Page 8 8

9. Daughter Board Assembly
Pitch adapter, bonds
Sensor
1 inch 9 9

10. 2 X0 pre-radiator; introduces a little divergence in shower
Sensor sample
Not shown: 4 X0 “post radiator” and 8 X0 “backstop”

11. Recent T506 Exposures 11 11

12. Both irradiated to 300 Mrad
Summer 2016: LumiCal Sensors and Industrial Sapphire
LumiCal sensor fragment via Sahsa Borisov, Tel Aviv
Industrial sapphire sensor courtesy of Sergej Schuwalow, DESY Zeuthen
Both irradiated to 300 Mrad 12 12

13. Other Recent Exposures and Summary
December 2015, Summer 2016 offered high-rate exposures: 10 24hr days of ~20 Mrad/hr
Sensor Type
Notable Exposures (Mrad)
GaAs
20, 100
SiC 80
Si PF
270, 570
Si NF
300
Si PC
600
Si NC
290
Red indicates results available; others await evaluation
Operated at GeV at close to 1 nA 13 13

14. Assessing the Radiation Damage14 14

15. Charge Collection Measurement
For pad sensors use single-channel readout
Daughter-board
Low-noise amplifier circuit (~300 electrons) 15 15

16. Charge Collection Apparatus
Readout: 300 ns
2.3 MeV e- through sensor into scintillator
Sensor +
FE ASIC
DAQ FPGA
with Ethernet 16 16

17. Pulse-height distribution for 150V bias Median pulse height vs. bias
Measurement time
Pulse-height distribution for 150V bias
Mean Pulse Shape
Single-channel readout example for, e.g., N-type float-zone sensor
Readout noise: ~300 electrons (plus system noise we are still addressing)
Median pulse height vs. bias 17 17

18. Reprised Results 18 18

19. Si Diode Results P-Type Float Zone (PF) to 270 Mrad
N-Type Float Zone (NF) to 300 Mrad
Just by way of reminder (reported at Santander in June) 19 19

20. PF Charge Collection after 270 Mrad
@600 V, ~20% charge collection loss (60C annealing) 20 20

21. PF I-V after 270 Mrad Exposure (-10 C)
At 600 V, about 80 A (0.05 W) per cm2 (sensor area ~ cm2)
Not much improvement with annealing
270 Mrad Exposure 21 21

22. NF Leakage Current after 300 Mrad
After normalizing for sensor area, results are similar to those for the PF sensor.
Sensor area = 0.1 cm2
Temperature  -15 C 22 22

23. NF Charge Collection after 300 Mrad
@600 V, ~55% charge collection loss (32C annealing) 23 23

24. New Results 24 24

25. Industrial Sapphire Sensor provided by Sergej Schuwalow
Short collection length for mobile carriers  intrinsically small signals
Current low (< 10 nA) after irradiation 25 25

26. Industrial Sapphire Charge Collection
Low pre-irradiation charge-collection and significant charge loss after irradiation
Sensors via Sergej Schuwalow, DESY Zeuthen
500 m thick Al2O3
300 Mrad Exposure 26 26

27. Industrial Sapphire High-Bias Annealing Trends
Annealing does not seem to significantly restore charge collection
500 m thick Al2O3
300 Mrad Exposure
Sensors via Sergej Schuwalow, DESY Zeuthen 27 27

28. LumiCal Sensor (N-Type)
Fragment cleaved from broken sensor provided by Tel Aviv
After treatment (heat, UV light) were able to bias center strip to ~150V
After 300 Mrad irradiation, could bias to > 300 V 28 28

29. N-Type LumiCal Prototype Fragment
Typical (~20 A/cm2) post-irradiation currents
300 Mrad Exposure 29 29

30. N-Type LumiCal Prototype Fragment Sensor via Sasha Borisov, Tel Aviv
Significant charge loss; annealing studies continue
300 Mrad Exposure
Sensor via Sasha Borisov, Tel Aviv 30 30

31. Summary and Outlook
For all tested technologies, so far only p-type Si seems to maintain good charge collection as dose  1 Grad (might have been expected…)
LumiCal sensors might work (charge collection and currents typicalfor n-type), but not optimal
Currents do develop, but preliminary estimates have suggested overall power draw remains quite tolerable; these estimates are being refined (FLUKA simulation)
A number of highly-irradiated Si Diode samples (300, 600 Mrad) await characterization, as does a 100 Mrad GaAs exposure (but poor performance was observed for 20 Mrad for GaAs)

32. BackUp
BackUp…
Bruce Schumm

33. GaAs
21 Mrad Exposure 33 33

34. GaAs Dark Current (-100 C) for 21 Mrad
45C anneal
Room temp anneal
21 Mrad Exposure
Before annealing
Dark current as a function of annealing temp 34 34

35. GaAs Charge Collection (21 Mrad Exposure)
Collected Charge (fC)
Vbias (V)
Charge Collection v. Bias and Annealing Temp 35 35

36. GaAs Charge Collection (21 Mrad Exposure)
 Try even higher annealing temperatures
 Higher exposure in next T506 run
21 Mrad Exposure
Vbias = 600 V
Slice at VB=600 vs. function annealing temp 36 36

37. Compare to Direct Electron Radiation Results (no EM Shower)
A bit better performance than direct result
kGy
Pre-anneal
Post-anneal at room temp
Georgy Shelkov, JINR
1000 kGy = 100 Mrad 37 37

38. SiC Results Bohumir Zatko, Slovak Institute of Science
4H-SiC crystal geometry
Irradiated to 80 Mrad 38 38

39. SiC Dark Current Before/After Annealing
80 Mrad Exposure 39 39

40. SiC Charge Collection after 80 Mrad
@600 V, ~25% charge collection loss (60C annealing)
80 Mrad Exposure 40 40

41. Luc d'Hauthuille Bruce Schumm University of California, Santa Cruz
Power Draw of the Beam Calorimeter as a function of Temperature & Radiation Dosage
Luc d'Hauthuille
Bruce Schumm
University of California, Santa Cruz

42. Assumptions Power modeled as a function of radiation and temperature
Power drawn scales linearly with radiation dosage
Temperature dependent IV data was taken at SCIPP for a Si sensor exposed to 270 MRads of radiation after a 60˚C annealing process, by Cesar Gonzalez & Wyatt Crockett.
A 3rd degree polynomial was fit to this I vs. T data, for a Bias Voltage = 600V

43. Overview
The LCSIM framework was used to compute the energy deposited from 10 simulated background events (bunch crossings at 500 GeV collision energy)
Energy deposited was then extrapolated for 3 years of runtime, and converted to radiation dosage
Temperature was input and combined with radiation dosage to compute the power draw for each mm^2 pixel, at each layer, for 600V bias (charge-collection about 90% after 270 Mrad)
Power draw of these pixels was plotted on a heatmap for a range of temperatures (-7, 0,7, 15 ˚C)

44. IV Curves at various Temperatures

45. Polynomial Fit for Temperature Dependent Current (600 V)

46. P(R,T) = (R/270MRads)*(600V)*I(T)
Model for Power Draw
Using these assumptions, power drawn by a
pixel is:
P(R,T) = (R/270MRads)*(600V)*I(T)
where R is radiation dosage, T is temperature, 600V is the Bias Voltage and I(T) is the current given by the fit.

47. Layers 2 & 10 of BeamCal at T = 0˚C
P_max = mW
(for a single mm2 pixel)

48. Power Drawn(Watts) of BeamCal collapsed
T = -7 ˚C
T = 0 ˚C
P_total = W
P_total = W
P_max = mW
P_max = mW
(for a single pixel)
(for a single pixel)

49. Total Power Draw (3 Years of Running with Si Diode Sensors
Operating Temperature (0C)
Total Power Draw (W)
Maximum for 1mm2 Pixel (mW) 15 56 23 7 25 10 11
4.6 -7
4.5
1.9

50. Summary
GaAs after 20 Mrad exposure retains low current. Charge loss severe but recovers with annealing. Need to try higher annealing temp and then larger exposure.
4H-SiC after 80 Mrad exposure suffers ~25% CC loss; possible annealing gain at higher temperatures. Currents remain low.  Try higher temp and larger exposure also.
PF and NF silicon diodes shows significant CC after 3-year equivalent dose. Significant currents but overall power draw still low. Additional diode sensors (up to ~600 Mrad) await evaluation.
Sapphire sensors now characterized and mounted. Low-noise amplifier being commissioned. 50 50

51. BACKUP 51 51

52. Looking Forward Cointue GaAs, SiC annealing studies
300 Mrad exposures of PC, NC, NF silicon diode sensors awaiting evaluation
PF sensor exposed to another 300 Mrad (total Mrad); awaiting study
Low-noise amlipfier (<300 electrons) under development for exporation of Sapphire sensors; initial probe evaluation underway.
Ongoing offer for more beam time at SLAC, but large backlog of sensors to study at SCIPP 52 52

53. SiC CC Before/After Annealing
80 Mrad Exposure 53 53

54. Confirmed with RADFET to within 10%
Dose Rates (Including 1 cm2 Rastering)
Mean fluence (cm-2) per incident e-
Confirmed with RADFET to within 10%
Maximum dose rate (e.g GeV; 10 Hz; 150 pC per pulse):
20 Mrad per hour 54 54

55. Summer 2013: Initial Si Doses
“P” = p-type “N” = n-type
“F” = float zone “C” = Czochralski 55 55

56. T-506 Idea Embed sample sensors in tungsten:
“Pre-radiator” (followed by ~50 cm air gap) spreads shower a bit before photonic component is generated
“Post-radiator” brings shower to maximum just before sensor
“Backstop” absorbs remaining power immediately downstream of sensor
Realistic EM and hadronic doses in sensor, calibrated to EM dose

57. Charge Collection Measurement
For strip sensors use multichannel readout
Median Collected Charge
Channel-over-threshold profile
Efficiency vs. threshold 57 57

58. GaAs I-V after 21 Mrad Exposure (-10 C)
At 600 V, about 0.7 A ( W) per cm2
GaAs IV
GaAs
Dose of 21 Mrad
Post-anneal
Pre-anneal 58 58

59. Results: NF Sensor to 90 Mrad, Plus Annealing Study
Dose of 90 Mrad
Limited beneficial annealing to 90oC (reverse annealing above 100oC?) 59 59

60. ~15% charge loss at 300 ns shaping
Results: NC sensors
Dose of 220 Mrad
Incidental annealing
~15% charge loss at 300 ns shaping 60 60

61. Results: PF sensors
Doses of 5 and 20 Mrad
No annealing 61 61

62. Results: PC sensors
Dose of 20 Mrad
No annealing 62 62

63. G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)
Departure from NIEL (non-ionizing energy-loss) scaling observed for electron irradiation
NIEL e- Energy
2x MeV
5x MeV
1x MeV
2x MeV
G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)
Also: for ~50 MRad illumination of 900 MeV electrons, little loss of charge collection seen for wide variety of sensors
[S. Dittongo et al., NIM A 530, 110 (2004)]
But what about the hadronic component of EM shower? 63 63

64. Results: NF sensor for low dose
Doses of 5 and 20 Mrad
No annealing 64 64