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April 22, 2017Active medium TPC Workshop
KEK
Hiroyasu Tajima for LArGO teamInstitute for Space–Earth Environmental Research
Nagoya University
Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
✤ Pair-conversion telescope❖ Good background rejection due to “clear” gamma-ray signature
✤ Tracker (TKR): pair conversion, tracking❖ Angular resolution is dominated by scattering below ~GeV
✤ Calorimeter: energy measurement❖ 8.4 radiation length❖ Use shower development
to compensate for the leakage✤ Anti-coincidence detector:
❖ Efficiency > 99.97%
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Fermi LAT (Large Area Telescope)
Si Tracker70 m2 , 228 µm pitch~0.9 million channels(Japanese contribution)
CsI Calorimeter8.4 radiation length
Anti-coincidence DetectorSegmented scintillator tiles99.97% efficiency
e+ e-
γ
2
Gamma-ray Burst
Monitor
Large Area Telescope (LAT)
Energy band: 20 MeV to >300 GeVEffective area: > 8000 cm2 (~6×EGRET)Field of view: > 2.4 sr (~5×EGRET)Angular resolution: 0.04 – 10°Energy resolution: 5 – 10%
✤ We have large sensitivity gap between 0.1 MeV and 100 MeV❖ > 10 MeV: Pair conversion is a dominant process
• Angular resolution limited by scattering in conversion material❖ < 10 MeV: Compton scattering is a dominant process
• Incident direction is not well constrained• Backgrounds are hard to reject (activation of detector materials)
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
MeV Gap
3
10 -14
10 -13
10 -12
10 -11
10 -10
10 -9
10 -8
10 -2 10 -1 1 10 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10
SPI
IBIS-ISGRI
IBIS-PICsIT
JEM-X
COMPTEL
EGRET
CTA North
CTA South
Fermi-LAT
LHAASO
HiSCORE
MAGIC VERITAS
Energy (MeV)
Sens
itivity
(erg
cm-2 s-1 )
/HESS
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Improvements from Fermi LAT✤ Trade off between pair-conversion efficiency (more material) vs.
angular resolution (less material)❖ Tungsten converter + Si tracking
• Angular resolution is determined by thickness of Tungsten converter (not active)- 3% X0 × 12 layers + 18% X0 × 3 layers- Total 76% X0
✤ General approach to improve the situation❖ Focus on 1 MeV – 1 GeV energy region❖ Remove tungsten converter to improve
angular resolution• Effective area may be reduced
❖ Employ double-sided silicon strip detector to minimize the detector thickness and obtain 2D position• Tracking of recoil electrons due to Compton
scattering• 0.5% X0 × 56 layers ≈ 25% X0
4
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
eASTROGAM✤ 56 layers of 0.5 mm thick DSSDs
❖ (9.5×9.5 cm2) × (5×5) × (2×2)❖ Spacing: 10 mm❖ ~700 W
✤ CsI calorimeter (8 cm thick, 4.3 X0)❖ (0.5×0.5 cm2) × (8×8) × (23×23)
5
10-14
10-13
10-12
10-11
10-10
10-9
10
10 -2 10 -1 1 10 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10
e-ASTROGAM
SPI
IBIS-ISGRI
IBIS-PICsIT
JEM-X
COMPTEL
EGRET
CTA North
CTA South
Fermi-LAT
LHAASO
HiSCORE
MAGIC VERITAS
Energy (MeV)
Sens
itivi
ty (e
rg cm
-2 s-1
)
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Alternative Approach✤ Liquid Argon Time-Propagation Chamber
❖ Fully active tracking detector (and converter)• 3% X0 (6.5 mm) × 32 LAr-TPCs
- X0 = 20.4 cm @ 83.8 K, 68.9 kPa• ~100% X0 diluted in 1 m
❖ Inter-layer distance ≈ 2.5 cm❖ Conversions close to the bottom of the TPC
layer gives better angular resolution due to less material and longer lever arm
❖ 5× better angular resolution than Fermi LAT
6
— average aperture angle of e+e- pair
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Compton Telescope Performance✤ It also functions as Compton telescope
❖ Full tracking of recoil electrons provide better background rejection• Si sensors can provide only 2–3 hits
✤ Compton telescope performance❖ Energy resolution ~ 3%❖ Angular resolution ~ 1° @ 1.8 MeV❖ Attenuation length ~ 18 cm @ 1 MeV
7
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
LAr TPC Layer✤ Multi-layer printed cross strips
❖ 100 µm pitch❖ 45° with respect to z axis
• Length of the longest strip is ~ 1cm to minimize capacitance❖ ~32,500 e−h/layer (5,000 e−h/mm @ ~70 kPa)
8
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Scintillation light from LAr TPC✤ Scintillation light
❖ 36,400 photons/layer (5,600 photons/mm)❖ λ ~ 128 nm❖ Primary function is to provide triggers
• Start time of TPC❖ Constrain fiducial volume of the track
• Reduce effect of cosmic-ray backgrounds• 0.4 particles expected during the drift time
❖ Time of flight to constrain the direction oftracks (~1 ns resolution required)
✤ SiPM readout❖ PMT is too bulky and too much material
between TPC modules❖ Photon detection efficiency is low (~10%)
at ~128 nm❖ Tetraphenyl-butadiene (TPB) coating as
wave length shifter to increase P.D.E.❖ R&D required to optimize photon yield
(energy resolution) and time resolution 9
Drifting e−
Scintillation light
Fiducial volume
SiPMs
SiPMs
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Single Module✤ Dewar is needed to keep the LAr temperature (~84 K) and
pressure (~70 kPa)✤ Passive radiators can dissipate ~1 W/m2@ 80 K
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Dewar containing a tracker module
Calorimeter
Top and bottom windows
/11Liquid Argon TPC for Next Generation of MeV Gamma-ray Satellite
Active medium TPC Workshop, APR 22, 2017 KEK
Satellite Design✤ A total geometrical area of 4 m2 and 1 m height
❖ ~6 ton✤ Full FoV > 60° × 60°
❖ FoV of each module 45° × 30°✤ The 8 modules are covered
by an Anti Coincidence Detector
✤ > ×5 effective area of Fermi LAT
11
10
5 c
m
55 cm
21
5 c
m
100 cm
50
cm
Cat
ho
de
Re
ad
ou
t
Dewar containing a tracker module
