The photomultiplier tubes selection for KM2A electromagnetic particle detectors (EDs) hou chao IHEP The 2nd workshop of air shower detection at high altitudes

outline The requirements for PMT of KM2A Testing of candidate PMTs - Gain as a function of voltage - linearity - Single photoelectron (SPE) spectrum - PMT uniformity conclusion

The important requirements Signals produced by 1~4000 secondary charge particles passing through ED must keep linearity, 3.6 orders of magnitude The nonuniformity of PMT(the variation of signal’s amplitudes when light hits on different position of the photocathode) must be limited within 20% The operating gain is around

Candidate PMTs Type: end window, linear focus PMT: - Hamamatsu R in R1924A 1 in - Electron Tubes (ET) ET9903B 1.5 in

Gain as a function of voltage To determine the gain at our operating HV Gain and input voltage: G=kV β (G 1 /G 2 )=(V 1 /V 2 ) β =A 1 /A 2 R1924A: β=7.88±0.03 R11102: β=8.17±0.05 ET9903B: β=6.83±0.03

Linearity Space charge effect Light source: LED+light tube+2 layers teflon Change the distances between light and PMT, change the photon number PMT acceptted d>30cm (I 2 /I 1 )=(d 1 /d 2 ) 2 point light source d<30cm calibrate every position in linearity region The linearity region is 3.6 orders of magnitude. Dark box’s length is limited, so choose two different light intensity( 12.5:1 ),and use this ratio to combine them.

The test system Measuring distances: 6cm~280cm Light sources: LED V light (1W) Signal generator: pulse width 70ns, 1kHz Driving voltage of LED :10v and 6.975v OSC: pulses’ Amplitudes and width recorded

Data analysis Area integral: A*W=Q Anode current: I=Q/W The number of pe of cathode: Q/(e*gain)

Result PMT:ET9903B HV=1599.1v Gain=0.44*10 6

Result PMT:R11102 HV=982.3V gain=0.50*10 6

Result PMT:R1924A HV=787.45v gain= 0.73*10 6

Table: tests’ results Gain Max. Anode current (mA) (Nonlinea rity<5%) Cathode linearity scale (Npe) Orders of magnitud e R1924A0.73* ~6.4* R * ~ ET9903 B 0.44* ~

SPE spectrum To obtain the absolute gain at some certain voltage Adjust the light intensity very weak Npe distribution obeys Poisson function Signal generator: pulse width 70ns, 1kHz Driving voltage of LED :3~4v R1924A HV=1089.3v Gain=1.044*10 7 R11102 HV=1419.6v Gain= 1.046*10 7 ET9903B HV=2206v Gain= 3.92*10 6 SPE

PMT uniformity Scan PMT’s cathode LED controled by Stepping motor: 1mm/step 40*40steps covering area 4*4cm 2 Signal generator: pulse width 70ns, 1kHz Driving voltage of LED :4.5v Charges of pulses of each step are recorded

ET9903B_15292 Nonuniformity=17.06% within a radius of 7.0mm of PMT’s center

R11102_A49927 Nonuniformity=6.91%

R1924A_FG4412 Nonuniformity>20%

conclusion The characteristics of 3 candidate PMT have been studied in detail. Candidate R11102 and ET9903B PMTs both have good linearities to satisfy with our requirement Nonuniformity: R11102 and ET9903B are both less than 20%, while R11102 is better. R1924A is not suitable for our detectors