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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Study of the unstable nucleiIncompressibility, Gamow-Teller strength, etc.

Forward scattering • Need for identifying the L of the reaction.

← For each L, shape of d/d 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

RequirementFollowing spec are required to identify the L of the reaction,• Angular resolution : < 7.45mrad(RMS)• Energy resolution : < 10%(RMS)

Recoiled particle ()

Beam(78Ni :200MeV/u)

Helium gas

Motivation

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Design of Active-Target GEM-TPCBeam

Pad

Recoil 25cm

GEM(10cm×10cm)

Beam

Wire

4cm

Active-Target TPCReaction occurs inside TPC. (Target is gas.)→ Material budget can be smaller

GasDepend on target → 4He, 3He, d2 etc.

Mask the beam track areaTPC can be operate in high rate beam condition(~ 106Hz).(Rate of recoil nuclei has to be taken into account.)

Use of GEMGEM can multiply electron at higher rate than wire.

Pad shape : rectangular triangle• Charge ratio of the neighboring pads (perpendicular to drift direction)• Arrival time(drift direction)

Field cageDouble layered, 2.5mm pitch.

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16.45mm

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Following items were evaluated• Distortion of electric field by ions created by beam• Position resolution, angular resolution

GasHe(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 : 250m for 1cm

Electron velocity : 3 [cm/s] Ion velocity : 3.3×10-3 [cm/s]

Simulation study

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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.

y=24cmField cage Field cage

Shielding wire mesh

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: Without beam : Without shielding wire : With shielding wire (2.5mm pitch)

• 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)

Active area of GEM Beam• Beam rate : 107 cps• Energy loss : 300 [keV/mm]~ 104 ions/mm← Ni with 50 [MeV/u]• Beam spread :

5cm (RMS) for drift direction1cm (RMS) for other direction← Dispersion matching mode beam in RIBF

Position differenceField cage Field cage

x

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Position resolution Position derivation

Position is derived by charge ratio of neighboring pads. Pad size : 16.45 ×16.45 mm2

Recoil particle : Energy loss• 10 [electrons/mm]• 50 [electrons/mm]•100 [electrons/mm]• 190 [electrons/mm]← with 30MeV in He/CO

2(5%)

• 300 [electrons/mm]

→ Position resolution : < 300m (RMS)for energy loss > 100 [electrons/mm] Center

: 10 [electrons/mm] : 50 [electrons/mm] : 100 [electrons/mm] : 190 [electrons/mm] : 300 [electrons/mm]

Edge of pad Edge of pad

Recoiled particle

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Angular resolution

Angular resolution : ~ 5 mrad < 7.45 mrad

= -30° = 0° = 30°

z

xRecoil particle

• Date : Dec. 1 - 3 / 2009• Accelerator : 12UD Pelletron

Scatterer• Au (thickness : 2m)• Scattering angle ： 7°

4He

TPC

Scintillator

Beam• Particle : 4He2+

•Energy : 30MeV• Beam rate : ~ 102 cps

Q

D

Q

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Collimator : 1mm

Performance test @Tsukuba

Dipole magnet

TPC

Quadrupole magnet

Quadrupole magnet

Au

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Setup

• Gas : He(95%) / CO2(5%) (1 atm)• Edrift : 700 [V/cm]

Drift velocity : 2 [cm/s] Diffusion (transverse) : 250 [m/1cm drift] Diffusion (longitudinal) : 180 [m/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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16.45

16.45

beam

Typical eventBeam

Beam

Inclined incidence

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Position resolution 1

Perpendicular to drift direction

Drift direction

Position resolution is less than 700m by charge division and about 50m by arrival time

3D position derivation• Charge ratio of the neighboring two pads.(2D)• Arrival time.(drift direction)

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Position resolution 2Dependence of the drift length

Drift directionPerpendicular to 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

Perpendicular todrift direction

Drift direction

Dependence of the gas gain

Position resolution is improved as gas gain become larger.

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Energy resolution

~ 3.3%

Energy resolution ~ 3.3 % < 10 %

Particle : with ~ 5.8 MeV/u→ Energy deposit at field cage : ~ 700 keV

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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 : < 700m Energy resolution: < 3.3 % ()for with 5.8MeV/u

End

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Position resolution

Position derivationPosition is derived by charge ratio of neighboring pads.

Recoil particle (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 : ~ 300m

z

x

Center

: 8.3mm(x)×25mm(z) : 16.6mm(x)×25mm(z) : 20mm(x)×20mm(z) : 16.6mm(x)×16.6mm(z)

Edge of pad Edge of pad

Recoil particle

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Typical event 2

Use degrader to stop beam inside field cage

Beam scatters inside field cage