Development of HPDs with a 18-mm-diameter GaAsP - NDIP 11

Development of HPDs
18-mm
with a 18 mm-diameter diameter GaAsP
Photocathode for the MAGIC II
1. Introduction
2. Performances
1. Basic parameter
2. Quantum Efficiency [WLS study]
3. Lifetime [incl. simulation study]
3. Summary and outlook
Masaaki Hayashida,
R.Mirzoyan, M.Teshima

Major ajor Atmospheric
tmospheric Gamma amma-Ray Ray
Imaging maging Cherenkov
herenkov (MAGIC MAGIC)
GeV – TeV
cosmic γ-ray
observation
17m diameter
largest in the world
Aim: 30 GeV E th
Camera;
PMT ~600 pixel
Lower E th,
More sources!!
AGNs SNRs
GRBs
MAGIC–II:
MAGIC-I telescope
+ 2 nd 17 m φ telescope
•High QE photo sensor
•2GHz sampling FADC
23 Jun 05: Beaune M.Hayashida et al. 2

Imaging Atmospheric
Cherenkov Telescope (IACT)
Gamma
ray
Particle
shower
Cherenkov light
~ 120 m
~ 1 o
~ 10 km
Detects the
Cherenkov light
from air shower
23 Jun 05: Beaune M.Hayashida et al. 3

Requirements on the Photo
Sensor for 2 nd MAGIC
High QE; 50 % at peak – for 15 GeV E th
– A prime candidate – GaAsP
Time response; a few ns --- reduce background (NSB)
– Light flash during 1-3ns, 2 Gsampling/s FADC
Photocathode Size; 18 mm
– needed pixel size 30 mm: light concentrator is necessary
Gain; > 10 4
Lifetime; 10 year (for field operation)
– Night sky background, bright starlight, temperature….
HPD with a GaAsP photocathode
23 Jun 05: Beaune M.Hayashida et al. 4

Previous Work
Presentations at Beaune Conference
1 st Conf.; “Test of the new hybrid INTEVAC intensified photocell
for the use in air Cherenkov telescopes”
S.M. Bradbury, et al., NIM A 387 (1997) 45-50
2 nd Conf.; “An evaluation of the new compact hybrid
photodiodes R7110U-07/40 from Hamamatsu in high-speed light
detection mode”
R. Mirzoyan, et al., NIM, A442 (2000) 140-145
3 rd Conf.; “Progress in the development of a high QE, red
extended hybrid photomultiplier for the second phase of the
MAGIC telescope”
E. Lorenz, et al., NIM, A504 (2003) 280-285
23 Jun 05: Beaune M.Hayashida et al. 5

HPD Structure
HPD (Hybrid PhotoDetector).
Structure
– Photocathode
– an avalanche diode as anode.
– High vacuum tube (~10 -7 Pa)
Gain mechanism (2 stages)
– Electron bombardment
– Avalanche effect
Much better pulse height resolution than PMT.
23 Jun 05: Beaune M.Hayashida et al. 6

HPD with 18-mm 18 mm GaAsP
Photocathode (R9792U-40)
(R9792U 40)
Designed for MAGIC-II camera
(developed with Hamamatsu Photonics )
Photocathode
Cathode Size
Avalanche Diode
Sensor shape
GaAsP (for high QE)
18 mm [old < 8 mm]
3 mm Silicon
hexagonal 28 mm
39 mm height
23 Jun 05: Beaune M.Hayashida et al. 7

Measurement Set-up Set up
(MPI)
23 Jun 05: Beaune M.Hayashida et al. 8

Signal Gain
Overall Gain ~ 50000
(Photocathode: -8 kV [1600], AD bias: 320 V [30])
(AD bias – fixed)
0 1 2 3 4 5 6 7 8 9
Photocathode applied voltage [-kV]
(Photocathode HV --- fixed)
0 50 100 150 200 250 300 350 400
AD Reverse Bias Voltage [V]
23 Jun 05: Beaune M.Hayashida et al. 9

Output Signal
0 2 4 6 8 10 12 14 16
Times [ns]
FWHM ~ 2.7 ns
23 Jun 05: Beaune M.Hayashida et al. 10

Dynamic Range
~ 5000
(condition –8 kV, 333V)
– Measured by pulse area
Linear
scale
[50 ~15000 p.e.]
[log]
[50 ~ 10 5 p.e.]
5 % ↓
Line
slope = 1
23 Jun 05: Beaune M.Hayashida et al. 11

Quantum Efficiency (QE)
Spectrophotometer
based setup for
measuring QE
•Absolute value,
Calibrated Pin-Photodiode
(S6337-01, Hamamatsu)
•Photocathode; -800V
•AD; cathode-anode short
•Measured at AD anode
•Peak value
(ET 9116A)
over 50%(@~ 500 nm)
23 Jun 05: Beaune M.Hayashida et al. 12

First Tests with
WaveLength Shifter (WLS)
PE ( comparison to PMT ,PMT = 1)
ZA
PE ∫ ( ) × ( )
No WLS
With WLS
0°
Shifter (WLS)
WLS
– Butyl- PBD
(260-340 to 360-460 nm)
– POPOP
(300-400 to 400-500 nm)
– Paraloid B72
(n = 1.4)
in Toluene
On the Input window
= 1.90 QE1.92
λ Ch 2.00λ
d2.14
λ < effect of WLS>
1.99
25°
2.00
45°
2.07
60°
2.17
17 m→24 m
+3 ~ 10 %
23 Jun 05: Beaune M.Hayashida et al. 13

HPD
with 10ns integ.
Window
(2 Gsampling/s FADC)
PMT
with 20ns integ.
Window
(0.3 Gsampling/s FADC)
γ Shower Event
( by MC simulation)
E = γ energy
r = impact
parameter
23 Jun 05: Beaune M.Hayashida et al. 14

GaAsP Photocathode Lifetime
Definition of
Lifetime
(~ 10 times larger intensity than NSB)
Expectation!
Total charge; 3.5 mC in Photocathode
(ca. 100 C in APD output [at gain 30000])
23 Jun 05: Beaune M.Hayashida et al. 15

Lifetime Measurement
(acceleration test)
Photocathode current
200 pA
(~3 times of NSB)
Quartz Halogen Lamp
(Iwazaki Electric
JC12V20W20H/G1)
– whole area of photocathode
Gain 50000
(-8kV, 330V)
AD anode current
preliminary
Measured in Hamamatsu
systematically still on going…(MPI
and Hamamatsu)
84% at 3500 h (= 2.52 mC of total PC harge)
(expect. 80 % at 3.5 mC of PC charge)
→ Consistent with expectation
More tubes will be measured
23 Jun 05: Beaune M.Hayashida et al. 16

10
Star Light and NSB
# Objects
4 degree
# stars

Simulation Results of
the Stars and Night Sky
After After 10yearoperation
1yearoperation 2yearoperation 5yearoperation
23 Jun 05: Beaune M.Hayashida et al. 18

1.Summary
18mm GaAsP HPDs are almost ready to be used in
IACTs with low energy threshold like MAGIC-II.
The QE peak value of 50 % doubles the photon
collection efficiency.
(corresponding increase of mirror diameter: 17m → 24m)
additional improvement achieved with WLS : ~10%
GaAsP photocathode is expected to have sufficiently long
lifetime to survive starlight and NSB during 10 years
– Only several tubes will degrade by bright starlight.
23 Jun 05: Beaune M.Hayashida et al. 19

2.Outlook
2003 ; the first prototype of 18 mm GaAsP HPD
(E. Lorenz, et al., NIM, A504 (2003) 280-285)
2004-2005; almost fulfil the requirements
Next step… Further improvement and check of stability
go for higher QE
– Increase the absolute value, enhance blue sensitivity
New Avalanche Diode
– Reduce integration window -- Faster time response ( ~2ns),
– Lower HV, longer lifetime --- higher gain (>50)
Environment Test
– Lifetime for light, Temperature stabilization
Demonstration in MAGIC-II (>500 tubes )
– HPD camera will be built in 2006
23 Jun 05: Beaune M.Hayashida et al. 20