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Jim Brau David Strom 18 Jan 2001 University of Oregon

Oregon RPC status report

Test setup Status of chambers E ciency and charge measurements Results of heating with low voltage Results of heating with high voltage Conclusion and Plans

Undergraduate student: P. Csonka


Test Setup
S1 736 740 556 563 620 619 853 887 892 857

S2

Trigger is from scintillators. Top scintillator is 20 cm deep, bottom scintillator is 90 cm deep. Gas is 40 Freon 134A, 4.2 isobutane and the balance Ar. For most measurements reported here 736, 556, 563, 887 and 857 are recorded using a TDC attached to the minicrate fast-or outputs. ADC's can be attached to any of the chambers. For most of these measurements all 32 channels of chamber 892 are attached to ADCs. HV uses old CAEN system. HV distribution boxes have 21M of series resistance.n


Chamber Status 736 good 740 leaky not tried on voltage 556 good 563 some ine cient regions 620 sparks, may have popped buttons 619 may have popped buttons 853 no strips, used for mechanical tests 887 good presently being heated 892 good 857 e cient with high enough voltage 8500V, very uneven gain.


Typical Plateau Curves For scintillators placed in center of detectors. ADC hits required in top chamber 736.
Efficiency 1 Ch 3 (556) 0.8 Ch 4 (563) Ch 8 (887) 0.6 Ch 9 (892)

0.4

0.2

0

6000

6250

6500

6750

7000

7250

7500

7750

8000 Voltage

System is also stable over time:
Efficiency 1

0.95

0.9

0.85 Ch 3 (556) 0.8 Ch 4 (563) Ch 8 (887) 0.75 Ch 9 (892) 0.7

25

30

35

40

45 50 days (Oct 1 = 1)

These data were taken in October with smaller scintillators


Currently Heating Chamber 8 E ciency of chamber 8 887 as scintillators are moved to front", middle" and back" positions: Nominal Voltage is 7500V actual 7350V and position is that measured in chamber 9 892. Strip not shown are outside of the geometric acceptance of the scintillators. Front
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

Middle
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

Back
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

all hits 8



From good" part of production.


Streamer peak all channels chamber 8 887. Somewhat broader than for other chambers.
6000 4000 2000 0 0 100 200 300 400 500 600 700 800 900 Triplet charge (pC)
All Strips

150 100 50 0 200

Strip 10

600 400 200

Strip 15

400 600 800 Triplet charge (pC)

0

200

400 600 800 Triplet charge (pC)

800 600 400 200 0 200

Strip 20

1000 750 500 250

Strip 25

400 600 800 Triplet charge (pC)

0

200

400 600 800 Triplet charge (pC)


Streamer peak pulse height versus voltage for chamber 8 887. Chamber produces somewhat smaller charges than were in seen chamber 1 with the same gas mixture.
Streamer peak charge (pC) 600 51% 134A Chamber 736 500 40% 134A Chamber 736 40% 134A Chamber 887 (before heating) 400 40% 134A Chamber 887 (after heating) 300

200

100

0

6000

6250

6500

6750

7000

7250

7500

7750

8000 Voltage


Streamer peak versus strip position in chamber 8 before heating.
Charge (pC) 90 80 70 60 50 40 30 20 10 0 5 10 15 20 25 30 strip number

peak width versus strip, ch:8
Charge (pC) 350 300 250 200 150 100 50 0 5 10 15 20 25

peak versus strip, ch:8

30 strip number

7375 Volts


Test of heating cooling system using chamber 7 853. Voltage applied to chamber is -10V. Chamber is open to the air. No permanent change in current seen after heating.
Temperature (deg. C) 40 35 30 25 20 15 10 80 48 50 52 54 56 58 60 days (Oct. 1 = 1) 60 100 Current (nA) 45 140 120

t7 VS. day+sec/(24*3600)
current (nA) 140 120 100 80 60 40 20 0 48 50 52 54 56

40

20

i7 VS. day+sec/(24*3600)

58 60 days (Oct. 1 = 1)

0

Energy = 0.98 eV

0

5

10

15

20

25

30

35 40 45 50 Temperature (deg. C)

Current versus temperature follows an exponential: I = I0e,E=kT where T is the absolute temperature and E is of order 1 eV:


Similar results are observed with chamber 8 887:
Temperature (deg. C) 40 35 30 25 20 60 15 63 64 65 66 67 68 69 70 71 days (Oct. 1 = 1) 50 40 30 20 10
Energy = 0.99 eV

Current (nA)

45

100 90 80 70

tc VS. day+sec/(24*3600)
current (nA) 70 60 50 40 30 20 10 0 63 64 65 66 67 68 69

imon VS. day+sec/(24*3600)

70 71 days (Oct. 1 = 1)

0

0

5

10

15

20

25

30

35 40 45 50 Temperature (deg. C)

Possible small permanent increase in current seen, but more likely just an e ect with a very long time constant. Could be due to chemistry of impurities in gas e.g. O2.
10 9 8 7 6 5 4 3 2 1 0 Current (na)

0

10

20

30

40

50

60

70 hours

Note these results are for -10V applied. At low voltage this chamber acts like a diode, current for+10V is larger by a factorof 2 or more.


E ciency in central region before and after heating with only low voltage. Before 7350V
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

After 7350V
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

all hits 8

Slight decline in e ciency noted at high strip number. Measurements made at nominal voltage of 7500V actual 7350 V. Can be recovered by increasing V .


After heating at High Voltage, a permanent increase in current from 7.5A to 9.9A is seen:
Heater Temperature (deg. C) 32.5 30 25 20 15 10 27.5 22.5 17.5 12.5 82.5 85 87.5 90 92.5 95 97.5 100 102.5 105 Days (1 Oct = 1)

water temp
Current (µA) 35 30 25 20 15 10 5 0 82.5 85 87.5 90 92.5 95 97.5

current chamber 8

100 102.5 105 Days (1 Oct = 1)

Nominal voltage is 7500 V. Some data were taken at nominal voltages of 8000 and 7000 V. Note that rate of current increase is faster at higher voltages, e.g. 4 day, versus 0:2 day.


E ciency in bad" part of chamber rapidly declines as the current increased at the high temperature T =28:5 C, primarily due to drop across 21M resister Start of heating 7100 Volts
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

End of heating 7025 Volts
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

End of heating 7500 Volts
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

all hits 8


A high singles rate does not seem to be associated with the ine cient region of the chamber:
2000 1500 1000 500 0 0 10 20 30 strip number Average singles rate rate (Hz) 1000 900 800 700 600 500 400 0 10 20 30 strip number 300 200 100 0

rate (Hz) rate (Hz)

2000 1500 1000 500 0

2000 1500 1000 500 0 0 10 20 30 strip number

10

20 30 40 Temperature (deg C)

Plots on left show singles rates with 10mV threshold for the three temperatures, 28.5, 20 and 10.5 C


Even correcting for voltage drop in 21M resistor, average size of streamer peak appears to decline after heating both sets of data at 20 C.
Streamer peak charge (pC) 600 40% 134A Chamber 887 control (before heating) 500 40% 134A Chamber 887 control (after heating) 40% 134A Chamber 887 bad (before heating) 400 40% 134A Chamber 887 bad (after heating) 300

200

100

0

6000

6250

6500

6750

7000

7250

7500

7750

8000 Voltage

Bad region is strips 23-29 Control region is strips 10-20


Streamer peak position versus position, end of heating, 7750 Volts.

Charge (pC)

160 140 120 100 80 60 40 20 0 5 10 15 20 25 30 strip number

peak width versus strip, ch:8
Charge (pC) 500 400 300 200 100 0

5

10

15

20

25

peak versus strip, ch:8

30 strip number


Does the chamber become e cient at high enough voltage? 7340 Volts
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

7750 Volts
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

8170 Volts
Efficiency 1 0.8 0.6 0.4 0.2 0 10 15 20 25 30 strip number

all hits 8

all hits 8


Conclusion Chamber current and singles rate are a very sensitive function of temperature. Keep chamber temperature below 25 Cor even lower not exactly news. No measurable permanent change in current seen when heating at low voltage only. Permanent change in current with heating and high voltage is seen for a chamber in the good" part of the previous production at only 28.5 C. Rate of increase in chamber current at high temperatures is faster at higher voltage. Keep high voltage low.


Plans Continue to increase temperature of chamber 8 to 40 C. Perform autopsy if chamber fails. Repeat procedure on chamber 3 556 Should be likely to fail because it is from the bad part of the production. Repeat procedure on a new Babar RPC is it possible to get one? Explore gas mixtures with still lower fractions of 134A Does rate of current increase depend on steamer charge or on electric eld? Try to understand loss in e ciency in chamber 10 857 and chamber 4 563 Attempt to use a radioactive source to do radiography