Active Target Development in CNS

Shinsuke OTA Center for Nuclear Study (CNS), the University of Tokyo

Two Types of “Active” TargetBeam inactive and active type

(α,p) astrophysical

test experiment (19 Jan.)

Outline

History and collaboration

Physics

Design and prototype

Result of Test Experiment

History

Collaboration begins at 2009

Budget at the beginning of FY2009 in CNS (6M yen) + a part of Grant-in-aid for Scientific Research (~4M yen)

Design was fixed in September

Construction of prototype was done in November

Test experiment in December, 2009 for one type and January and February in 2010 for the other type.

CollaborationCNS RIKEN

High Energy(GEM, Electronics)

SHARAQ(Physics, Electronics, DAQ)

Astrophysics(Physics, Construction)

Kyoto Univ.Univ. of Tsukuba

(test experiment,potential users)

Collaborators

S. Ota, R. Akimoto (Master Thesis in preparation),S. Michimasa, T. Gunji, H. Yamaguchi, T. Hashimoto,H. Tokieda, S. Kawase, T. Tsuji, H. Hamagaki, T. Uesaka, S. Kubono (CNS),T. Kawabata (Kyoto), T. Isobe (Riken),A. Ozawa, H. Suzuki, D. Nagae, T. Morimoto, Y. Ito,Y. Ishibashi, H. Oishi (Tsukuba)

Missing Mass Spectroscopy w/ RI beam

Structure of unstable nuclei

Inelastic scattering, Gamow-Teller, Transfer...

Giant resonances : incompressibility

Isoscalar/Isovector Monopole

via Traditional reactions in inverse kinematics

(a,a’), (d,d’), (d,2He), (3He,t), (d,p), (p,d), (3He,a),...

(1,1)

(1,0)(0,1)

Spin(S)-Isospin(T) Selectivities

Gamow-Teller

ΔL=0, ΔT=1, ΔS=1

Fermi

ΔL=0, ΔT=1, ΔS=0

Isoscalar monopole

ΔL=0, ΔT=0, ΔS=0

Incident beam energy: 100-300 MeV/u => RIBF

Spin-Isospin Selectivities

ΔS=0 ΔS=1

ΔT=0 (p,p’), (d,d’),(α,α’)

(p,p’)(d,d’)

ΔT=1(p,p’)(p,n)(3He,t’)

(p,p’), (p,n), (3He,t’)(d,2He)

Gamow-Teller: (d,2He)Isoscalar monopole: (α,α’)

Momentum Transfer If the reaction occurs in the vicinity of nuclear surface,

dσ

dΩ∼ |jl(qR)|2

M. Itoh

Forward angle measurement is important

(deg)lab!"0 10 20 30 40 50 60 70 80 90

(MeV

)la

b! E

0

1

2

3

4

5

6 He 200 MeV/u4Ni)68Ni,68He(4

Ex = 0 MeV

Ex = 10 MeV

Ex = 20 MeV

Ex = 30 MeV

°=0.5cm"°=1.0cm"

°=1.5cm"

°=2.0cm"

°=2.5cm"

°=3.0cm"

°=3.5cm"

°=4.0cm"

°=4.5cm"

Inverse kinematics

4He(68Ni,68Ni)4He @200MeV/u

Recoil angle is large enough to measure

Recoil energy is very small, less than 1 MeV for forward angle (<2 deg in c.m.) scattering

Recoil energy at forward scattering is very small

Energy (MeV)0 1 2 3 4 5

Ran

ge (m

m a

tm)

0

20

40

60

80

100

120

140

160

180

200

Range in He gas

ρ(4He) = 0.2 mg/cm3

0.1 MeV : 6.9 mm atm

0.5 MeV : 17.8 mm atm

1.0 MeV : 28.3 mm atmθcm~1 deg θcm~4 deg

To measure forward angle scattering,an “active” target is needed

Effect on Electric Field by Intense Heavy Ion Beam

Required beam intensity for 300 events / day

Target : 3 x 1020 particle/cm2 (= 100 mm atm)

Cross section: 0.1 mb (assumed)

then, 100-kHz beam is needed

=> considerable space charge effect, delta ray, ...

Concept of CNS Active Target

Beam-view

Top-view

α

α

field shaping wires

GEMs

Beam particles are not measured but tracked by beam-line detectors.Space charge effect is small enough (by simulation).

Simulation of Space Charge Effect

7

• 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)

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

Field cage Field cage

x

Active area

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

4 CHAPTER 2. ACTIVE TARGET GEM-TPC

Figure 2.2: The layout of the field cages, the GEMs and the readout pad boards. The top figuresshows the overall view of the TPC and the bottom figure shows the GEMs and the bases of the fieldcage.

2.2 GasSince the gas inside TPC is used as a target, gas is decided by the target; for example, 4He, 3He,

d2, organic gas used as proton target. In addition to the targeted gas, some quenching gas is neededfor stable operation. But, the following negative effects are caused by adding quenching gas;

• Since the mass of quenching gas is much larger than that of the gas which is used as a target,the range of the recoil particle becomes short.

• Some background signal are produced by the reaction of the beam and the quenching gas parti-cle, especially when the quenching gas includes the nucleus whose mass is near to the mass ofthe targeted nucleus.

The properties of the gas used for the TPC were simulated. The simulated gases were as follows;He (90%) + CO2 (10%), He (95%) + CO2 (5 %), He (99%) + CO2 (1 %) and d2 (90%) + CO2 (10%).Furthermore, Ar (70 %) + CO2 (30 %), which is widely used for gas detectors was also simulated. Thesimulations were performed using Magboltz [1]. Magboltz solves the Boltzmann transport equationsfor electrons in gas mixtures under the influence of electric and magnetic fields.The simulated items were as follows; drift velocity, transverse and longitudinal diffusion and Townsendcoefficient. The results are shown in Fig.2.4 and Fig.2.5. The left figure and the right figure in Fig. 2.4

Geometrical DesignThe region along beam path is masked.

250mm

12 CHAPTER 2. ACTIVE TARGET GEM-TPC

Figure 2.11: The left figure shows the readout chamber and the right figure shows the layout of thereadout chamber.

Mixture gas !E! Wi Required gas gainHe (90 %) + CO2 (10 %) 128.0 keV 40.2 eV ! 2000He (95 %) + CO2 (5 %) 98.7 keV 40.6 eV ! 2500He (99 %) + CO2 (1 %) 75.2 keV 40.9 eV ! 3300

Table 2.2: The energy loss, the effective average energy to produce a ion-electron pair and the requiredgas gain for each mixture gases.

Since ! particle with 30 MeV was measured in the performance test and the dynamic range of thepreamplifier used for the performance test was 1 pC, following value was required for gas gain of theGEM.

GGEM =1 " 10!12

qe · !E!:30 MeV in16.45 mm/Wi

. (2.4)

The!E!, Wi and the required gas gains for each mixture gases are summarized at Tab.2.2. The!Esare calculated using LISE code [4] and Wis are calculated by the Wis of helium and carbon dioxide(41 eV and 33 eV, respectively [5]).

The setup for the gas gain measurement is shown in Fig.2.12. A compounded radioactive source

Figure 2.12: The setup for gas gain test.

of ! particle of 241Am and 244Cm was used. The energies of ! particle from 241Am and from 244Cmare 5.49 MeV and 5.80 MeV, respectively. The voltage difference between the mesh and the GEMwas 500 V/cm when the mixture proportion of CO2 is 5 % and 10 %. When the mixture proportion of

12 CHAPTER 2. ACTIVE TARGET GEM-TPC

Figure 2.11: The left figure shows the readout chamber and the right figure shows the layout of thereadout chamber.

Mixture gas !E! Wi Required gas gainHe (90 %) + CO2 (10 %) 128.0 keV 40.2 eV ! 2000He (95 %) + CO2 (5 %) 98.7 keV 40.6 eV ! 2500He (99 %) + CO2 (1 %) 75.2 keV 40.9 eV ! 3300

Table 2.2: The energy loss, the effective average energy to produce a ion-electron pair and the requiredgas gain for each mixture gases.

Since ! particle with 30 MeV was measured in the performance test and the dynamic range of thepreamplifier used for the performance test was 1 pC, following value was required for gas gain of theGEM.

GGEM =1 " 10!12

qe · !E!:30 MeV in16.45 mm/Wi

. (2.4)

The!E!, Wi and the required gas gains for each mixture gases are summarized at Tab.2.2. The!Esare calculated using LISE code [4] and Wis are calculated by the Wis of helium and carbon dioxide(41 eV and 33 eV, respectively [5]).

The setup for the gas gain measurement is shown in Fig.2.12. A compounded radioactive source

Figure 2.12: The setup for gas gain test.

of ! particle of 241Am and 244Cm was used. The energies of ! particle from 241Am and from 244Cmare 5.49 MeV and 5.80 MeV, respectively. The voltage difference between the mesh and the GEMwas 500 V/cm when the mixture proportion of CO2 is 5 % and 10 %. When the mixture proportion of

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2.4. READOUT CHAMBER 13

CO2 is 1 %, the voltage difference between the mesh and the GEM was 250 V/cm since a dischargeoccurred. A charge sensitive preamplifier was used and a signal was recorded using a charge sensitiveADC module (V792; CAEN). Two feedback capacitor with different capacity, 1 pF and 10 pF wereused since the dynamic range of the measurement was wide. The feedback resistors were adjusted tobe the same time constant, 50 ns.

The right figure in Fig.2.13 shows a ADC spectrum and the result of the gain measurements.Two peaks are shown in ADC spectrum The higher peak corresponds to the energy loss of the !particle with 5.49 MeV which was radiated from 241Am and the other peak corresponds to that with5.80 MeV which was radiated from 244Cm. The energy resolution for the ! from 241Am was 3.9 %(in ") and that from 244Cm was 4.2 % (in "). The left figure in Fig.2.13 shows the result of the gasgain for several mixture gases of helium and carbon dioxide. A discharge occurred when the voltagedifference between the electrodes of the GEM was 540 V for both He (90 %) + CO2 (10 %) andHe (95 %) + CO2 (5 %) and 410 V for He (99 %) + CO2 (1 %). The required gains were achieved forHe (90 %) + CO2 (10 %) and He (95 %) + CO2 (5 %). Although the required gain was not achievedfor He (99 %) + CO2 (1 %), the gas gain over 103 was achieved.

ADC count500 1000 1500 2000 2500

Yiel

d

0

20

40

60

80

100

120

140

160

180

200

[V]GEM V!350 400 450 500 550

Gai

n

210

310

(10%)2

He(90%)+CO(5%)

2He(95%)+CO

(1%)2

He(99%)+CO

Figure 2.13: The ADC spectrum for the signal of the radioactive source with He (90 %) + CO2 (10 %)and the result of gas gain test. The fitting function of the ADC spectrum is the function superposedtwo Gaussian. The left figure shows the ADC spectrum and the right figure shows the result.

Frame of GEM

Since the GEM is very thin, A frame for the GEM is needed to put the GEM flatly. The thickness ofthe frame is 500µm and the GEM is fixed by being sandwiched using two frames. In order to achieveuniform electric field in the area between the metallic mesh and the readout pad and to eliminatecharge up at the surface of the frame, the frame is plated by copper and the same voltage as the GEMsupplied to the frame. Figure 2.14 shows the electric field around the GEM in the case with andwithout the frames.

Property of He+CO2 Gas

6 CHAPTER 2. ACTIVE TARGET GEM-TPC

E [V/cm]10 210 310 410

s]µ

Drift

vel

ocity

[cm

/

0

1

2

3

4

5

6

7

8

9

10 (10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

E [V/cm]410

]-1

Tow

nsen

d [c

m

210

310

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

Figure 2.4: Simulation results about drift velocity (left) and Townsend coefficient (right)

E [V/cm]10 210 310 410

m fo

r 1cm

drif

t]µ

Tran

sver

se d

iffus

ion

[

0

100

200

300

400

500

600

700

800

900

1000 (10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

E [V/cm]10 210 310 410

m fo

r 1cm

drif

t]µ

Long

itudi

nal d

iffus

ion

[

0

100

200

300

400

500

600

700

800

900

1000 (10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

(10%)2He(90%)+CO(5%)2He(95%)+CO(1%)2He(99%)+CO

(10%)2(90%)+CO2d(30%)2Ar(70%)+CO

Figure 2.5: Simulation results about diffusion coefficients. The left figure shows the result abouttransverse diffusion coefficient and the right figure shows the result about longitudinal diffusion co-efficient.

• The electric field inside the field cage is kept to be uniform in high beam rate condition (! 106 cps).

In order to minimize the material budget, wires are used to make the electric field. They aremade of gold-plated copper beryllium and their diameter is 50 µm. They are connected to each otherthrough a 1 M!.A Metallic mesh is mounted at the bottom of each field cage. It is made of SUS304. The diameterand the pitch of the wires of the mesh are 30µm and 254µm, respectively.

2.3.2 Simulation for Electric FieldThe wire configuration was optimized by a simulation using Garfield [2] in order to achieve uni-

form electric field. The simulations for the electric field inside the field cage were performed for two

3.2. SETUP 21

Particle 4He2+Kinematic energy (before scatterer) 30 MeVKinematic energy (after scatterer) 29.8 MeV

B · ! (after scatterer) 0.788 T mBeam current (before scatterer) 1 ! 10 enA

Table 3.1: Summary of the beam condition.

3.2.2 BeamThe condition of the beam which was used at the performance test is summarized at Tab.3.1.An Aluminium foil was used to degrade the energy of the beam. It was put at the end of the beam

line.

3.2.3 TPCThe setup of the TPC are as follows;

• Gas: He (95 %) + CO2 (5 %) was used to keep flowing. The flow rate was 200 sccm.

• Electric field of the drift region: The electric field of the drift region was 700 V/cm.

• Readout pad: The 36 pads were used for the performance test. Figure 3.3 shows the numberingof the readout pad. When the beam passed at the center of the active area of the field cage, atthe third line, the pads from the second line to the fourth line were used. When the beam passedat the end of the active area of the field cage, the first line, the pads from the first line to thethird line were used.

The drift velocity of electrons, the transverse diffusion coefficient and the longitudinal diffusion co-efficient for the condition were about 2 cm/µs, 250 µm and 160 µm, respectively.

Figure 3.3: The numbering of the readout pad. The pads which colored yellow are in the second rowand in the forth line.

16.45 mm

Readout PadBackgammon shape is chosen to optimize the resolutions and the number of readout channels

Designed Resolutions0.3 mm(RMS)~5 mrad (RMS)

Optimized: res. and # of ch.

Position = Charge ratio

2.4. READOUT CHAMBER 15

Therefore the positions of the tracks are derived by the charge proportion of the neighboring twopads. The way to derive the position is different by the type of pad pair and by the incident condi-tion (Tab.2.3.

x = Q1!Q2Q1+Q2

·Lx

2+ P0;x x = !

Q1!Q2Q1+Q2

·Lx

2+ P0;x

z = Q1!Q2Q1+Q2

·Lz

2+ P0;z z = !

Q1!Q2Q1+Q2

·Lz

2+ P0;z

x = P0;x x = P0;x

z = !Q1!Q2Q1+Q2

·Lz

2+ P0;z z = Q1!Q2

Q1+Q2·

Lz

2+ P0;z

x = !Q1!Q2Q1+Q2

·Lx

2+ P0;x x = Q1!Q2

Q1+Q2·

Lx

2+ P0;x

z = P0;z z = P0;z

Table 2.3: The position derived by the charge proportion of the neighboring two pad for differenttypes of pad pair and for different incident conditions. Q1 and Q2 are the charges for each pad. Lx

and Ly are the lengths of each side of the pad. P0;x and P0;y are the center positions of the two pads.

In order to decide the pad size, simulations for position resolution were performed.

2.4.3 Simulation for Position ResolutionMonte-Carlo simulations for position resolution were performed with different energy resolutions

and with different pad sizes since the position resolution is affected by the energy resolution and thesize of the readout pad. The simulations were performed for the ideal case where there was no angularstraggling which limits the minimum angular resolution and where the energy loss was constant. Aprocedure of the simulation is as follows;

Step 1. Generate a uniform random number which corresponds to the position where a ionization oc-curs.

Step 2. Drift the electron with transverse diffusion from the generated point to the GEM and calculate

2.4. READOUT CHAMBER 15

Therefore the positions of the tracks are derived by the charge proportion of the neighboring twopads. The way to derive the position is different by the type of pad pair and by the incident condi-tion (Tab.2.3.

x = Q1!Q2Q1+Q2

·Lx

2+ P0;x x = !

Q1!Q2Q1+Q2

·Lx

2+ P0;x

z = Q1!Q2Q1+Q2

·Lz

2+ P0;z z = !

Q1!Q2Q1+Q2

·Lz

2+ P0;z

x = P0;x x = P0;x

z = !Q1!Q2Q1+Q2

·Lz

2+ P0;z z = Q1!Q2

Q1+Q2·

Lz

2+ P0;z

x = !Q1!Q2Q1+Q2

·Lx

2+ P0;x x = Q1!Q2

Q1+Q2·

Lx

2+ P0;x

z = P0;z z = P0;z

Table 2.3: The position derived by the charge proportion of the neighboring two pad for differenttypes of pad pair and for different incident conditions. Q1 and Q2 are the charges for each pad. Lx

and Ly are the lengths of each side of the pad. P0;x and P0;y are the center positions of the two pads.

In order to decide the pad size, simulations for position resolution were performed.

2.4.3 Simulation for Position ResolutionMonte-Carlo simulations for position resolution were performed with different energy resolutions

and with different pad sizes since the position resolution is affected by the energy resolution and thesize of the readout pad. The simulations were performed for the ideal case where there was no angularstraggling which limits the minimum angular resolution and where the energy loss was constant. Aprocedure of the simulation is as follows;

Step 1. Generate a uniform random number which corresponds to the position where a ionization oc-curs.

Step 2. Drift the electron with transverse diffusion from the generated point to the GEM and calculate

total 144 ch

Chapter 3

Performance test and discussion

The performance test of the TPC was carried out using 4He2+ beam accelerated by the 12UDPelletron tandem accelerator at the University of Tsukuba Tandem Accelerator Center (UTTAC) [6].In the performance test, the beam passed thought the two field cages (Fig.3.1) or stopped inside theTPC.

Figure 3.1: A typical event at the performance test.

A global coordinate was set (Fig.3.1). X-axis was defined as the axis along the axis of the beamwith incident angle of 0 !, y-axis was defined as the axis along the drift direction, z-axis was definedas the other axis.

3.1 Purpose of the Performance TestIn the performance test, position resolution, angular resolution and energy resolution were evalu-

ated for following conditions;

• Beam incident condition.The beam incident condition was changed as the condition of the recoil particles.

– Incident position in z-axis.– Incident position in y-axis.

19

Test Experiment in Tsukuba Position and angular

resolution

Incident position

Iincident angle

Gas gain

Alpha particle at 30 MeV

100-10kHz

4He 30MeV

20 CHAPTER 3. PERFORMANCE TEST AND DISCUSSION

– Incident angle in z-axis.

– Kinematic energy of the beam.Until the particles which stop inside the field cage.

• Gas gain.

• Long term stability for the performance.

3.2 Setup

3.2.1 Alignment

The performance test was carried out using the spectrograph course of the 12UD Pelletron tan-dem accelerator. Figure 3.2 shows the beam line. A scatterer can be set at the course. The beam

Figure 3.2: The beam line used for the performance test.

rate can be adjusted roughly using a scatterer. The beams scatter with the scatterer elastically awaywith an angle and the TPC was set at the position where the particles which scattered away with aproper angle were injected. In the performance test, a gold foil whose thickness was 2 µm was usedas the scatterer and the TPC was set at the position where the particles which scattered away witha proper angle were injected. The angle of 7 ! was decided using the differential cross section ofRutherford scattering so that the beam rate before the TPC would be around 100 cps. There weretwo quadrupole magnets and a dipole magnet after the scatterer. The energy of the beam can be fo-cused using the dipole magnet and the beam rate can be adjusted finely using the quadrupole magnets.

The beam line was terminated by an aluminized Mylar with the thickness of 50 µ. The TPC wasput at about 75 mm downstream the end of the beam line. The TPC had windows which were madeof an aluminized Mylar with the thickness of 25 µ. The beams passed the window to enter the TPC.

Setup

(Au)

Beam mask(φ 1mm)

He 30 MeV, ~102 Hz (~200 electrons/mm)

He+CO2(5%) 1 atm.Edrift 700 [V/cm]vdrift : 2 [cm/μs]

Diffusion : 250 [μm/cm]VGEM: 390-450 V (gain: 102-103)

DAQ System 3 x 6 x 2 pads readout preamp

RPA-210 (REPIC) 24ch -1.0pC - 1.0pC 0.8 V/pC τ=80 ns GEM-Preamp: 80cm flat cable

FADC SIS3301 (commercial, 100 MHz, 14

bit) Preamp-FADC: 200 cm

Trigger Discrimination of analog sum of 4

pads

!"

! #"

!!

"

!""

!"

!"#$%&&

!"#$%&&

Preamp. (RPA-210) REPIC

3.2. SETUP 21

Particle 4He2+Kinematic energy (before scatterer) 30 MeVKinematic energy (after scatterer) 29.8 MeV

B · ! (after scatterer) 0.788 T mBeam current (before scatterer) 1 ! 10 enA

Table 3.1: Summary of the beam condition.

3.2.2 BeamThe condition of the beam which was used at the performance test is summarized at Tab.3.1.An Aluminium foil was used to degrade the energy of the beam. It was put at the end of the beam

line.

3.2.3 TPCThe setup of the TPC are as follows;

• Gas: He (95 %) + CO2 (5 %) was used to keep flowing. The flow rate was 200 sccm.

• Electric field of the drift region: The electric field of the drift region was 700 V/cm.

• Readout pad: The 36 pads were used for the performance test. Figure 3.3 shows the numberingof the readout pad. When the beam passed at the center of the active area of the field cage, atthe third line, the pads from the second line to the fourth line were used. When the beam passedat the end of the active area of the field cage, the first line, the pads from the first line to thethird line were used.

The drift velocity of electrons, the transverse diffusion coefficient and the longitudinal diffusion co-efficient for the condition were about 2 cm/µs, 250 µm and 160 µm, respectively.

Figure 3.3: The numbering of the readout pad. The pads which colored yellow are in the second rowand in the forth line.

16.45 mm beam

trigger

Circuit Diagram

Linear FIFO

Discriminator

FADC

Sampling Clock

Scaler

GEM OUT Pre-Amp.

PMT OUT Discriminator

FADC

FADC

FADC

FADC

Logic FO

4 pads’ anode signal

add analog signal

Logic Unit

Latch OutputRegister

trigger making

LatchLogic OR

beam rate (if available)

analog signal (to all FADC)

veto

requested trigger

busy mask

scaler can count w/ and w/o maskedTimer Clock

measurement time

Typical signal!

!"#$

very low noise (~1mV)

Output of preamplifier

22 CHAPTER 3. PERFORMANCE TEST AND DISCUSSION

3.2.4 Front End ElectronicsA charge sensitive preamplifier modules (RPA-211; REPIC Co., Ltd) were used to convert the

charge signal from the readout pads to the voltage signal. CXA3653Q ADS chip (Sony, Inc.) wasused for the preamplifier module. The gain, the time constant and the dynamic range for the inputsignal of the preamplifier module were 0.8 V/pC, 80 ns and -1.0 pC ! +1.0 pC, respectively.

A VME-FADCmodules (SIS3301; SIS GmbH) were used to digitize the signal from the TPC. Thedynamic range and the resolution of the FADC module were -2.5 V! +2.5 V and 14 bit, respectively.Although the maximum sampling rate of the FADC module was 105 MHz, 100 MHz external clockwas used as the clock for sampling the signals. The FADC modules were operated in the wrap modeduring the measurement. When the FADC module is operated in the wrap mode, it will acquire dataand write data to a ring buffer until it is stopped by the stop condition. The stop condition was madeby the stop trigger signal. Figure ?? shows the trigger logic for the stop trigger. Since the width ofa pulse was several hundreds nano-seconds, the number of the sampling for one event was set to be128, which corresponds to 1.28 µs.

3.3 ResultFigure 3.4 shows a typical event. Each histogram shows the pulse from each readout pad in the

second, third and the fourth line. A beam passed at the third line of the pads.

Figure 3.4: A typical event. Each histogram shows the pulse from each readout pad in the second,third and the fourth line.

3.2.SETU

P21

Particle4He2+

Kinem

aticenergy

(beforescatterer)

30MeV

Kinem

aticenergy

(afterscatterer)29.8

MeV

B·!(afterscatterer)

0.788Tm

Beamcurrent(before

scatterer)1!10enA

Table3.1:Sum

mary

ofthebeam

condition.

3.2.2Beam

Thecondition

ofthebeam

which

wasused

attheperform

ancetestissum

marized

atTab.3.1.AnAlum

iniumfoilw

asusedtodegrade

theenergy

ofthebeam

.Itwasputattheend

ofthebeam

line.

3.2.3TPC

Thesetup

oftheTPC

areasfollow

s;

•Gas:H

e(95

%)+CO

2 (5%)wasused

tokeep

flowing.The

flowrate

was200

sccm.

•Electric

fieldofthe

driftregion:Theelectric

fieldofthe

driftregionwas700

V/cm

.

•Readoutpad:The36

padswere

usedforthe

performancetest.Figure

3.3show

sthenumbering

ofthereadoutpad.W

henthe

beampassed

atthecenterofthe

activearea

ofthefield

cage,atthethird

line,thepadsfromthesecond

linetothefourth

linewereused.W

henthebeam

passedatthe

endofthe

activearea

ofthefield

cage,thefirstline,the

padsfrom

thefirstline

tothe

thirdline

were

used.

Thedriftvelocity

ofelectrons,thetransverse

diffusioncoefficientand

thelongitudinaldiffusion

co-efficientforthe

conditionwere

about2cm/µs,250

µmand

160µm,respectively.

Figure3.3:The

numbering

ofthereadoutpad.The

padswhich

coloredyellow

areinthe

secondrow

andinthe

forthline.

16.45 mmbeam

Typical Events

Position resolutions

Perpendicular to drift direction

Drift direction

less than 700um from charge division

less than 50 um from time projection

Effect of diffusion

Drift directionPerpendicular to drift direction

dependency on the drift length

almost constant resolution=> diffusion does not largely affect

Dependence on Gas GainPerpendicular todrift direction Drift direction

gas gain was varied by changing high voltage supply to GEMAs expected, larger gain (up to 103), better resolution.

angular resolution

Less than 7 mrad resolution was achieved

Energy resolution3.3. RESULT 27

Row0 1 2 3 4 5 6 7

Ener

gy re

solu

tion

[%]

0

2

4

6

8

10

12

14

16

18

20

Figure 3.10: The energy resolution for the energy deposit in each row.

resolution of each row were the same. From the propagation of the errors, the position resolutions,!zi,j;1 and !zi,j;2 were calculated by the following equation;

!zi,j;1 =

!

2

3· ! (!zi,j;1) =

!

2

3· !

"

zi,j;1 !zi,j!1;1 + zi,j+1;1

2

#

(3.3)

!zi,j;2 =

!

2

3· ! (!zi,j;2) =

!

2

3· !

"

zi,j;2 !zi,j!1;2 + zi,j+1;2

2

#

, (3.4)

where !x represents the standard deviation of a Gaussian which fits the distribution of x.

Figure 3.12 shows the results of the position resolutions in z-axis.

Position Resolution in Y-Axis

The position in y-axis was calculated by the arrival time and the drift velocity of electrons. Theabsolute position in y-axis can not be calculated since the arrival time of the beam was not detected.But, the position resolution in y-axis can be evaluated by the relative positions to the position of theother pads which was calculated by the difference of the arrival times at each pad. The arrival timewas calculated for each lot. The signals from the pads at the same lot were summed up and the arrivaltime was calculated for the summed signal. The position in y-axis of the lot at i-th line and at the j-throw which was named yi,j was calculated by the following equation.

yi,j = vd · ti,j, (3.5)

where vd is the drift velocity of electrons and ti,j is the arrival time of the lot at the i-th line and atj-th row. The position resolution in the y-axis were derived with the same way in z-axis.

Figure ?? shows the result of the position resolution in y-axis.

energy resolution ~ 10% (σ) for one row3.3% (σ) for total (6) rows

Summary and Outlook Prototype works well and resolutions of 0.7 mm from charge division and

0.05 mm from drift time is achieved.

Optimization of pad size and electronics

Conventional FADC, COPPER or GET...?

D2 gas property study for (d,d’), (d,2He) ...

Upgrade mounting NaI/CsI calorimeter to measure high energy recoil (proton)

Reaction measurement : FY2010 (at HIMAC, RCNP?)

Physics run FY2011 (hopefully)

Giant monopole and Gamow-Teller strength,

(a,p) reaction

Thank you!

Target for high-resolution measurement

PROBLEM: Target thickness

Ex.) Charge Exchange: energy loss difference between projectile and target

Projectile Ejectile

dE/dx(proj.) != dE/dx(ejec.)

To achieve higher resolution

Ex.) Charge Exchange: energy loss difference between projectile and target

Combination with SHARAQ Spectrometer and Gamma detector

p/dp ~ 15000 (design)

~1 MeV energy resolution for A~50@100 MeV/u

Kinematics He vs 2H

(deg)labH2!0 10 20 30 40 50 60 70 80 90

(MeV

)la

bH2 E

0

0.5

1

1.5

2

2.5

3

3.5 H 200 MeV/u2Ni)68Ni,68H(2

Ex = 0 MeV

Ex = 10 MeV

Ex = 20 MeV

Ex = 30 MeV

°=0.5cm!°=1.0cm!

°=1.5cm!

°=2.0cm!

°=2.5cm!

°=3.0cm!

°=3.5cm!

°=4.0cm!

°=4.5cm!

(deg)lab!"0 10 20 30 40 50 60 70 80 90

(MeV

)la

b! E

0

1

2

3

4

5

6 He 200 MeV/u4Ni)68Ni,68He(4

Ex = 0 MeV

Ex = 10 MeV

Ex = 20 MeV

Ex = 30 MeV

°=0.5cm"°=1.0cm"

°=1.5cm"

°=2.0cm"

°=2.5cm"

°=3.0cm"

°=3.5cm"

°=4.0cm"

°=4.5cm"

Range He vs 2H

Energy (MeV)0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Ran

ge (m

m a

tm)

0

20

40

60

80

100

120

140

160

180

200

Energy (MeV)0 1 2 3 4 5

Ran

ge (m

m a

tm)

0

20

40

60

80

100

120

140

160

180

200