S. Nishida KEK 3rd Open Meeting for Belle II Collaboration 1
Contents Frontend Electronics Neutron Irradiation News from Hamamtsu 2
144ch HAPD HAPD (Hybrid Avalanche Photo Detector) photon bi alkali photocathode HV 8kV 300V bias e Pixel APD bombardment gain ~ O(1000) Total gain ~ 104 105 avalanche gain ~ O(10) Developed with Hamamatsu Photonics. 144 channels, 4 APD chips (36ch/chip) Effective area 64mm 64mm (65%). Quantum efficiency ~25%. 3
Status at March Meeting Number of Photons May not be enough; expecting higher QE by new photo cathode using new production facility at Hamamatsu. Tolerance to the Magnetic Field. Basically O.K. Radiation Tolerance. Neutron irradiation test just done. Noise increased!! Front end Electronics. ASIC are in development (SA01 in test, SA02 in design). Structure/Layout. Design started. Need to be careful on HV. Long Term Stability. HPK test shows good results. Will be tested with more samples. Delivery (and Budget). 2.5 years for production. 4
Frontend Electronics 4 trial productions of prototype ASICs (S01 S04) at VDEC. analog Preamp Shaper VGA digital Comparator Shift Register Used in the beam test. Successfully readout 1 p.e. signal from HAPDs. Now, we are developping new prototype ASIC (SA01,SA02). Production at MOSIS (TSMC 0.35 m process) Digital part for readout is provided with external FPGA for more flexibility to Super Belle DAQ More channels per chips (SA02: 36ch) Preamp Shaper Comparator 5
Frontend Electronics Status at the previous meeting SA01 itself worked fine. In the SA01 + HAPD configuration, noise is much larger than expected. Threshold scan after the previous meeting New board with 1 FPGA + 3 SA01 is developed. Now all the 36ch from 1 APD chip can be read. Very clean threshold scan: good S/N (the reason is not clear). 6
Frontend Electronics scan for 36ch (1 APD) SA01 status Noise problem is gone, though the reason is not clear yet. 2 dimensional scan successfully taken Another problem is the linearity at above 1 p.e. Will be fixed by changing the gain in SA02. No major problem now. We will produce more boards to read full channel of HAPD. Next version: SA02 36ch per chip. Simulation O.K. Production of chips is just finished. Package will be done. Test board is also designed. We can start the test next month. LTCC (Low temperature co fired ceramics) package will be tried for smaller package. 7
Frontend Electronics HAPD SA02 SA02 FPGA merger FPGA HAPD SA02 SA02 FPGA Need to develop compact front end board. Data merger is also necessary. Link between front end board and data merger. L1 buffer etc. DAQ group 8
Neutron Irradiation Test 1 1011 /cm2 neutrons per year are expected in Belle II. Need to be tolerant to 1 1012 /cm2 neutrons for 10 year's operation. Irradiation test is done at Yayoi (Fast neutron source reactor of the University of Tokyo; in Tokai). Only one HAPD sample (SHP99: one chip dead / low QE [9%]) 1 1010 /cm2 and 5 1011 /cm2. 9
Neutron Irradiation Test before irradiation pulse height 1 10^10 irradiation 5 10^11 irradiation [ A] 100 SHP99 Chip C 10 1 without LED gate 0.1 0.01 0 5 10^11 irradiation + 20days Leak current 100 200 300 400 With 5 1011 /cm2 neutrons, Leak current increased by factor of 3. S/N gets worse with LED gate 10
Neutron Irradiation Test Gain: ~ 20% down maybe due to the increase of leak current Channel dependence exists in S/N (2 5 after irradiation) S/N: become 1/5 Noise: 3.5 4 times worse Optimization of bias voltage slightly improves S/N, but does not change the situation so much. 11
Neutron Irradiation Test Scan with ASIC (S04) irradiated sample threshold = 4 above pedestal good sample threshold = 4 above pedestal threshold = 1.5 above pedestal If we set the threshold at 4 of noise above pedestal, efficiency is very low (even low QE of the sample is taken into account). Channels near center is relatively working. If threshold is lowered, noise increases. Consistent with the previous measurement. 12
Neutron Irradiation Test Another irradiation test was done at JAERI (Tokai) on Jul 1st 2nd. JRR 3 reactor. Beam line for PGA (Prompt Gamma ray Analysis). 2cm 2cm spot, 1 108 /cm2/s. Neutrons are irradiated to 9 APDs of 3 HAPDs (min 1 1010 /cm2 max 1 1012 /cm2) We could not bring back the HAPDs, need to wait a month or so. 13
Neutron Irradiation Test SHP94 A SHP94 B 0 1e10 SHP112 A 0 SHP112 B 5e11 SHP94 C 1e11 SHP94 D 5e10 SHP112 C SHP112 D 5e10 1e11 14
Neutron Irradiation Test SHP107 A 0 SHP107 B SHP107 C SHP107 D 5e11 5e11 1e12 S/N gets worse in some channels. Need further measurements, scan. General remarks The increase of leak current is somehow understandable. But, why so noisy? 15
News from Hamamatsu Newly produced HAPDs have reached Q.E. = 30%!! ~20% increase (i.e. 20% more photons). Serial Numbers 16
Revised Schedule 2.5 years for the full production machines for mass production 2010/06 order delivery 2012/03 2011/03 ~150 ~300 2012/12 ~200 Cost is the problem. HPK will re estimate the cost this year. 17
Summary Number of Photons Hamamatsu succeeded to produce HAPD with QE=30%. Tolerance to the Magnetic Field. Basically O.K. Radiation Tolerance. Result of 1st test at Yayoi: HAPD gots unexpectedly noisy. 2nd test at JAERI: 3 more samples, better than 1st result?, waiting. Front end Electronics. SA01 is now O.K. Producing more boards. SA02 will be delivered soon. Need to develop compact system (and merger). Structure/Layout. Design started. Need to be careful on HV. Long Term Stability. HPK test shows good results. Will be tested with more samples. Delivery (and Budget). 2.5 years for production. Cost? 18
Backup 19
Neutron Irradiation Test 20
Neutron Irradiation Test 21
Neutron Irradiation Test 22
Neutron Irradiation Test 23
HAPD Performance Single Photon Response Noise level 1 p.e. 2 p.e. Multi Photon Response Full depletion at ~50V 1 p.e. Leakage current at >300V Clear separation between pedestal and 1 p.e. peak!! Noise ~1500e @ 300V 2 p.e. 3 p.e. 4 p.e. 24
Beam Test @ Fuji Test Beam Line 8 GeV electro n KEKB Belle 3 km Bremsstrahlung photon e ~2 GeV electron beam converted from Bremsstrahlung photons from KEKB main ring (electron) at Fuji area (opposite site of Belle detector). Fuji e Linac We performed beam tests for prototype Aerogel RICH 2008 Mar. Jun. 25
Beam Test Setup Aerogel SC HAPD ASIC MWPC MWPC 200mm Black box Tracking using 2 MWPC 2 3 array of 144 ch HAPD HV at 7kV. Bias voltage of HAPD is chosen at avalanche gain = 40. (or maximum bias voltage). Readout using 48 ASICs. ASIC offset is adjusted so that the noise is below the threshold. threshold is typically ~ 0.5 p.e. level, but depends on each channel's gain and noise level. Standard aerogel (n = 1.045, thickness = 20mm, transmission length = 41mm @400nm), and many other aerogels. SC e- 26
Beam Test Result Focusing Scheme 20mm aerogel radiator of n=1.045 Thicker aerogel increases N(p.e.), but makes resolution worse. Np.e N(p.e.) = 4.6 c = 12.8 mrad n1 n2 (n1<n2) One solution is focusing RICH. Superimpose rings from two (or more) radiators with different indices. Angle [rad] Clear Cherenkov ring is observed! Single track resolution 6.0 mrad corresponding to ~4 K/ separtation. resolution 27
Backgound Background component is observed. Explanation: Reflection @ AD beam induced hits, but why two peaks? Cherenkov Ring additional structure Cherenkov @ glass (+ reflection) halo? Back scattered electron HAPD Effect is expected to be smaller in magnetic field. 28
Magnetic Field Test Reduction of the effect of back scattered electrons. Reduction of the distortion of the electric field in the edge channels. Confirm the operation under 1.5 T magnetic field. Photon Glass Photo cathode Channels in edge has inefficiency, cross talk. Metal Ceramic Metal photo electron back scattered electron APD 29
Magnetic Field Test One dimensional scan 1.5T Count Count 0T Light incidence position (mm) Light incidence position (mm) Performance improvement is seen in the magnetic field. Strange behaviour at 0T in edge channels is fixed at 1.5T. Tail parts get smaller in the magnetic field test. 30
Aerogel RICH Development cherenkov ring by image intensifier 6 6 multi anode PMT (R5900 M16) 4 4 flat panel PMT (H8500) (angle) = 14mrad N(p.e.) = 6 systematic study basic principle 2000 2006 2001 2005 2002 2004 (angle) = 13mrad N(p.e.) = 9 HAPD etc. 2003 Try to increase detected photons without making the resolution worse Focusing Type performance improvement 31
Higher QE? Photo cathode of present HAPDs is bi alkali, but there exist other photo cathode with better QE. QE Peak QE Bi alkali 25% Super Bi alkali 37% Ultra Bi alkali 42% @350nm 300 400 500 600 (nm) 700 32
Higher QE? Photons reaching the photo cathode Detected photons w/ Ultra bi alkali With three kinds of aerogel thickness: 20mm, 30mm, 40mm Number of detected photons (270nm 650nm): 20mm : 30mm : 40mm = 1 : 1.29 : 1.51 33
Higher QE? Number of detected photons assuming 30mm aerogel Bi alkali Super Bi alkali Ultra Bi alkali Number of detected photons (270nm 650nm): 20mm : 30mm : 40mm = 1 : 1.29 : 1.51 34
Layout 516 HAPDs 540 HAPDs One issue is the HV (How close can we arrange the HAPD?) 35