Transcript riken_20091221_v1

Design and performance of
Active Target GEM-TPC
R. Akimoto, S. Ota, S, Michimasa, T. Gunji, H. Yamaguchi,
T. hashimoto, H. Tokieda, T. Tsuji, K. Kawase,
H. Hamagaki, T. Uesaka, S. Kubono
(Center for Nuclear Study, University of Tokyo)
T. Kawabata (Kyoto), T. Isobe (Riken),
A. Ozawa, H. Suzuki, D. Nagae, T. Morimoto, Y. Ito,
Y. Ishibashi, H. Oishi (Tsukuba)
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Contents
• Motivation
• Design of TPC
• Simulation for the performance of TPC
• Performance test
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Recoiled particle (a)
Motivation
Beam
(78Ni :200MeV/u)
 Study of the unstable nuclei
Helium gas
Incompressibility, Gamow-Teller strength, etc.
 Forward scattering
• Need for identifying the DL of the reaction.
← For each DL, shape of ds/dW is very different.
• Measurement of the recoiled light nuclei can lead to precise
measurement.
→ Energy of the recoiled nuclei is very small.
→ Active-Target TPC
 Requirement
Following spec are required to identify the DL of the reaction,
• Angular resolution : < 7.45mrad(RMS)
• Energy resolution : < 10%(RMS)
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Design of Active-Target GEM-TPC
Beam
 Active-Target TPC
Reaction occurs inside TPC. (Target is gas.)
→ Material budget can be smaller
 Gas
Recoil
25cm
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Depend on target → He, He, d2 etc.
 Mask the beam track area
TPC can be operate in high rate beam condition
(~ 106Hz).
Pad
(Rate of recoil nuclei has to be taken into account.)
GEM
 Use of GEM
GEM can multiply electron at higher rate than wire. (10cm×10cm)
 Pad shape : rectangular triangle
• Charge ratio of the neighboring pads
(perpendicular to drift direction)
Wire 16.45mm
• Arrival time(drift direction)
4cm
Beam
 Field cage
Double layered, 2.5mm pitch.
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Simulation study
 Following items were evaluated
• Distortion of electric field by ions created by beam
• Position resolution, angular resolution
 Gas
He(90%) + CO2(10%) was used for simulation.
• Electric field : 1.0 [kV/cm]
• Ion mobility : 2.5×103[cm2·Torr·V-1·s-1]
• Pressure : 760 [Torr]
• Temperature : 300 [K]
• Transverse diffusion coefficient : 250mm for 1cm
 Electron velocity : 3 [cm/ms]
 Ion velocity : 3.3×10-3 [cm/ms]
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Distortion of electric field by ions
 High beam rate condition
• When the beam rate is high, ions
(electrons) created by beam are piled up,
and distorts the electric field.
• Shielding wire is used to suppress the
effect from distortion.
 Effect of distortion of electric field
• Drift electrons and evaluate the position
difference.
• The electric field was simulated using
Garfield 9.
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Field cage Field cage
y=24cm
Shielding
wire
mesh
Field cage Field cage
Position difference
: Without beam
: Without shielding wire
: With shielding wire (2.5mm pitch)
x
Beam
• Beam rate : 107 cps
• Energy loss : 300 [keV/mm]
~ 104 ions/mm
← Ni with 50 [MeV/u]
• Beam spread :
5cm (RMS) for drift direction
1cm (RMS) for other direction
← Dispersion matching mode
beam in RIBF
Active area of GEM
• Without shield wire : Position difference is over 1mm
• Shielding wire pitch : 2.5mm : Maximum position difference is 0.3mm
→ Change of track angle is less than 3mrad.(for flight length : 10cm)
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Recoiled particle
Position resolution
 Position derivation
Position is derived by charge ratio of neighboring pads.
 Pad size : 16.45 ×16.45 mm2
: 10 [electrons/mm]
 Recoil particle : a
: 50 [electrons/mm]
 Energy loss
: 100 [electrons/mm]
• 10 [electrons/mm]
: 190 [electrons/mm]
: 300 [electrons/mm]
• 50 [electrons/mm]
•100 [electrons/mm]
• 190 [electrons/mm]
← a with 30MeV in He/CO2(5%)
• 300 [electrons/mm]
→ Position resolution : < 300mm (RMS)
for energy loss > 100 [electrons/mm] Edge of pad
Center
Edge of pad
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Recoil particle
Angular resolution
x
z
q = -30°
q = 0°
q = 30°
Angular resolution : ~ 5 mrad < 7.45 mrad
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Performance test @Tsukuba
4He
• Date : Dec. 1 - 3 / 2009
• Accelerator : 12UD Pelletron
Beam
• Particle : 4He2+
• Energy : 30MeV
• Beam rate : ~ 102 cps
Scatterer
• Au (thickness : 2mm)
• Scattering angle ： 7°
Q
Quadrupole
magnet
Dipole magnet
Au
D
Q
TPC
Collimator :
1mmf
Scintillator
TPC
Quadrupole
magnet
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10
16.45
Setup
beam
16.45
• Gas : He(95%) / CO2(5%) (1 atm)
• Edrift : 700 [V/cm]
 Drift velocity : 2 [cm/ms]
 Diffusion (transverse) : 250 [mm/1cm drift]
 Diffusion (longitudinal) : 180 [mm/1cm drift]
• Voltage applied to GEM : 450 V, 420 V, 390 V
→ Gas gain : 102 - 103
• Pad size : 16.45×16.45 mm2 (Only 36 pads are used)
• Readout : FADC (SIS3301; 100MHz)
• Trigger system : TPC (self-trigger; signal sum for 4 pads)
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Typical event
Beam
Beam
Inclined incidence
Position resolution 1
3D position derivation
• Charge ratio of the neighboring two pads.(2D)
• Arrival time.(drift direction)
Perpendicular to
drift direction
Drift direction
Position resolution is less than 700mm by charge division
and about 50mm by arrival time
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Position resolution 2
Dependence of the drift length
Perpendicular to
drift direction
Drift direction
• Charge ratio : no dependence of drift length.
• Arrival time : position resolution is improved as drift length
become shorter.
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Position resolution 3
Dependence of the gas gain
Perpendicular to
drift direction
Drift direction
Position resolution is improved as gas gain become larger.
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Energy resolution
Particle : a with ~ 5.8 MeV/u
→ Energy deposit at field cage : ~ 700 keV
s ~ 3.3%
Energy resolution ~ 3.3 % < 10 %
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Summary
• We are developing Active-Target TPC for study of nuclear
property using unstable nuclei.
 Detect track and energy of recoiled particle with very
low energy. (~ 1MeV/u)
• Position difference in high beam rate condition : < 0.3mm
→ Can be used in high beam rate condition
• Performance test has done.
 Position resolution : < 700mm
 Energy resolution: < 3.3 % (s)
for a with 5.8MeV/u
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End
Recoil particle
Position resolution
x
z
 Position derivation
Position is derived by charge ratio of neighboring pads.
: 8.3mm(x)×25mm(z)
: 16.6mm(x)×25mm(z)
: 20mm(x)×20mm(z)
: 16.6mm(x)×16.6mm(z)
 Recoil particle
a (energy : < 30 MeV/u)
 Four kinds of pad size were used
• 8.3mm(x)×25mm(z)
• 16.6mm(x)×25mm(z)
• 20mm(x)×20mm(z)
• 16.6mm(x)×16.6mm(z)
→ 16.6mm×16.6mm : ~ 300mm
Edge of pad
Center
Edge of pad
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Typical event 2
Beam scatters inside field cage
Use degrader to stop beam
inside field cage
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