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This study aims to evaluate the long-term stability of PMTs used in the Time-of-Flight (TOF) counter and endplug EM calorimeter of the CDF Run-II experiment. The PMTs were tested under various conditions, including different amounts of light, gain levels, and pulse frequencies. The results show the stability of the PMTs in the Run-II environment.
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Long term stability test of PMTs used for TOF & endplug EM calorimeter of CDF Run-II experiment DPF2006 & JPS2006 October 31, 2006 Sheraton Waikiki Hotel Honolulu, Hawaii, USA Yoshinori Yamada University of Tsukuba, Japan
CDF experiment • CDF Run II started in 2001 • proton-antiproton collision at • >2×1032cm-2s-1 peak luminosity • 1.5 fb-1 data recorded PEM TOF
TOF counter • Measure Time-of-Flight of charged particles. • Separate low-momentum charged pions and kaons • Kaon ID using TOF data enable to observe BsBs-bar oscillations. • dE/dx separation • 1.3 s for >2 GeV • ~0 around 1 GeV • TOF with 100 ps resolution provides >2s separation up to 1.6GeV.
TOF counter • consists of scintillator bars and photomultiplier tubes (PMTs) . • is installed between main tracking chamber and the solenoid (r=1.4 m) 216 scintillator bars & 432 PMTs are used. p p-bar collision cross-section s=50 mb TOF counter Peak luminosity L=2×1032 cm-2 s-1 10 charged particles produced within TOF coverage (|h|<1) Hit rate : s×L×10 / 216 ~ 0.5 MHz ~1000 photoelectrons per MIP
Fine-mesh Photomultiplier Tube • Gain ~105 in a 1.4 T magnetic field • Time resolution < 100 ps Requirements on PMTs HAMAMATSU Photonics R7761 • Cathode : Bialkali (Q.E.=20%) • # of dynodes : 19 • typical gain : ~105 (2200V, 1.4T) • dynode type : Fine mesh • Transit Time Spread : • ~350 ps (FWHM, B=0) • Max. anode current : 10 mA Anode charge per MIP = e x 1000 photoelectrons x 105 gain = 16 pC / MIP 0.5 MHz input rate ⇒ 8 mA anode current
PEM calorimeter PEM is divided to 24 wedges in f Plug EM calorimeter for measuring the energy of photons and electrons. 4.5 mm thick lead tile 4 mm thick scintillator tile 22 layers (6 photoelectrons/MIP/tile) Read out by PMT Signals from 22 layers input to 1 PMT HAMAMATSU R4125G PMT is used Cathode : Bialkali (Q.E. = 20%) Dynodes : Line focus, 10 stages Gain : ~5x104 Max. anode current : 100 mA 2 GeV p0: ~103 photoelectrons per shower Anode charge per shower = e x 1000 photoelectrons x 5x104 gain = 8 pC / shower 1 MHz input rate 0.1 MHz input rate ⇒ 8 mA anode current ⇒0.8 mA Signal frequency 1 MHz at h=3.00 to 3.49 0.1 MHz at h=1.10 to 1.20 (for 2x1032 ) anode current is different in h
Long-term stability Run-II will continue for another 3 years. Should check the long-term stability of R7761 PMTs under the Run-II conditions. Irradiated PMTs with pulsed-LED lights, measured output. Run II environment : ~103 photoelectrons : ~105 : 0.5 MHz (2×1032) • Amount of light • PMT Gain • Signal frequency Parameters that can affect PMT stability are : Test under the conditions bellow: Amount of light (photoelectrons) ~1x103 ~1x104 ~1x102 ~1x103 ~2x103 Gain ~1x105 ~1x104 ~1x106 ~2x105 ~2x105 Charge/pulse (pC) ~16 ~16 ~16 ~32 ~64 Pulse Frequency 10 Hz 0.2 MHz 0.5 MHz A. B. C. D. E. nominal CDF condition
Measurement setup Conditions Npe ~103 ~103 ~102 ~103 ~2x103 Gain ~105 ~104 ~106 ~105 ~2x105 A. B. C. D. E. • Blue LED (l=470ns) as light source • Pulse operated light signal • N.D. filter to adjust the amount of light • LED output monitored with H1161 reference tubes • System in a constant temperature bath (20oC temperature, 60% humidity) Frequency is common to all PMTs • Two R7761 PMTs for each of 5 conditions • Total 10 PMTs • Four H1161 PMTs for monitoring. • PMTs are set on an aluminum • plate with 16 holes
Amount of light at 16positions Measured using H1161 Q : measured for a given signal Gain: measured with single photoelectron peak at 2000 V, calculated for another voltage using Q-V relation. Number of photoelectrons determined. Npe transferred to R7761, in proportion to the area of the photocathodes. Inserted ND filters to obtain desired amounts of light at 16 positions. Npe after adjustment
Monitoring the stability of LED and the amount of light Prepare reference PMTs with a small amount of light, m=<Npe> ~0.4. Measure the probability of zero-photoelectrons, and calculate the average number of photoelectrons m. Probability to observe zero-photoelectrons is Count the # of events for n=0, and determine
Monitoring the LED with reference tubes Reference 1 Reference 2 Normalized Npe Normalized Npe 10 Hz 0.2 MHz 10 Hz 0.2 MHz Time [hours] Time [hours] Reference 3 Reference 4 Normalized Npe Normalized Npe 0.2 MHz 0.2 MHz 10 Hz 10 Hz Time [hours] Time [hours]
Result for TOF PMTs (nominal CDF condition) 10 Hz 0.2 MHz Npe~103, Gain~105 Q = 16 pC / pulse IA=3.2 mA at 0.2 MHz (Nominal CDF condition) Time [hours] 0.2 MHz 0.2 MHz Previous result using laser pulse as light source (result of 2 tubes, operated at 0.2 MHz 4 times)
Result for TOF PMTs (condition B.) 0.2 MHz 0.2 MHz 10 Hz 0.2 MHz Npe~104, Gain~104 Q=16pC/pulse IA=3.2 mA at 0.2 MHz 10 times photons 1/10 Gain Time [hours] Previous data
Result for TOF PMTs (condition C.) 0.2 MHz 0.2 MHz 10 Hz 0.2 MHz Npe~102, Gain~106 Q=16pC/pulse IA=3.2 mA at 0.2 MHz Normalized Output Charge 1/10 photons 10 times Gain Time [hours] Previous data
Result for TOF PMTs (condition D.) 10 Hz 0.2 MHz Npe~103, Gain~2×105 Q=32 pC/pulse IA=6.4 mA at 0.2 MHz Normalized Output Charge 2 times Gain Time [hours]
Result for TOF PMTs (condition E.) 10 Hz 0.2 MHz Npe~2×103, Gain~2×105 Q=64pC/pulse IA=12.8 mA at 0.2 MHz Normalized Output Charge 2 times photons 2 times Gain Time [hours]
Summary • CDF TOF PMTs (Hamamatsu R7761) are measured for their stability by irradiating blue LED light. • Output decreases by 10~20% in ~300 hours under a condition similar to Run II environment (signal frequency 0.2 MHz, anode current ~3.2 mA). • Output seems to be stabilizing after initial decreases. • Similar decreases seen for different conditions (different Npe and Gains, but same anode currents) To Do • Change signal frequency back to 10 Hz Recovery. • Repeat test at 0.5 MHz Permanent damage. • Understand the mechanisms for the output changes. • Test the stability of PEM PMTs.
APPENDIX BUCK UP
B. TOF counter Kaons tag with TOF information The time of flight difference Δt of two particle i & j is, , where r is flight length, p is momentum (common to i & j) and mi,j is the mass of particle.
C. TOF PMT The model figure of Fine mesh PMT (R7761) 19 meshed dynodes are set close to the other.
D. PEM endplug EM calorimeter. 24 wedges in f, and each wedge is divided to 24 towers. Each towers has 22 layers. The model figure of R4125G PMT. The light signal from the PEM scintillator tile is delivered by Y-11 wave length shifter fiber.The figure above is Emission Spectra and Absoption Spectra of Y-11.
E. Estimate amount of light Q=output charge, H.V.=applied voltage, a, b is constant parameters. S.P.=Single Photoelectron Peak, Z.P.=Zero-Photoelectron Peak, CADC=ADC resolution=0.25pC/count, e=electron charge. The applied voltage is 2000 V.
F. Pulse hight distribution of TOF PMTs A. B. D. C. E.
H. Previous data The previous setup using pulsed laser as a light source. Pulsed laser is divided with optical coupler.
H. Previous data h1161-1 The result of monitoring Laser output using 2 reference PMT. About after 12,000 hours operation, different result is seen.
H. Previous data The result of at nominal CDF condition. At a 0.5 MHz operation, output decrease by over 20 %. And at a 10 MHz operation ( after 0.5 MHz or 0.2 MHz operation), output recover. But after 0.5 MHz operation, output don’t recover completely at a 10 Hz operation.
