Transcript MSU_presen

Design of active-target TPC
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Contents
I.
Physics requirements
II. Basic structure
III. Gas property
IV. Electric field
• Distortion by ground
• Distortion of electric filed by ions created by beam
V. Pad shape
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Physics requirements
 Study for nuclear property of unstable nuclei
→ Use of inverse kinematics is needed.
 Measurement of forward scattering
→ Measuring the recoil light nuclei can lead to precise measurement.
→ But the energy of the recoil nuclei for forward scattering is very
small.
→ Gaseous target (or thin foil) is needed.
 Gas
Target : a → He gas
Target : d → d gas (or Cd4)
 To separate the objective reaction from other reaction,
• Angler resolution : 7.45mrad(RMS)
• Position resolution of vertex point : 1mm(RMS)
• Energy resolution : 10%(RMS)
is needed for .
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Basic structure
 Mask the beam track area
•TPC can be operate in high rate beam condition.
(Only the rate of recoil nuclei has to be taken into account.)
 Use of GEM
Electron multiplication can be done at high rate.
 Pad shape(rectangular triangle)
•To lessen the number of pads, rectangular triangle is used for the
pad shape.
•Position is derived by the charge ratio of the neighboring two pads.
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Schematic view
Beam
25cm
Recoil nuclei
Field cage
GEM
Total volume :
565mm ☓ 668mm ☓ 520mm
Pad
10cm ☓10cm
Thickness : 100mm
Schematic view 2
Wire
(pitch: 2.5mm)
GEM
Field cage
Field cage
Recoil nuclei
Beam
25cm
4cm
Beam
GEM
Mesh
GEM
Recoil nuclei
Pad
NaI (CsI)
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Gas property (simulated by Garfield)
• He(90%) + CO2(10%) (760 Torr, 300 K)
Drift velocity
Longitudinal diffusion
Townsend coefficient
Transverse diffusion
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• D2(100%) (760 Torr, 300 K)
Drift velocity
Longitudinal diffusion
Townsend coefficient
Transverse diffusion
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Distortion by ground
y
Field cage
Field cage
 The effect of ground is checked for 3
configurations.
•pitch : 2.5mm; double wire
• pitch : 5mm; double wire
y=24cm • pitch : 2.5mm; single wire
 Put electrons at
• x : every 5mm from x=0.5cm to
x=13.0cm(active area of GEM : 2.5<x<12.5)
• y : 24.0cm
x
0
13cm
 Drift electrons to the end of field cage, and
subtract the point where electron is put from
end point.
→ Position difference < 0.745mm.
 The effect of diffusion is not considered.
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Result
Active area of GEM
2.5mm pitch; single
Active area of GEM is
2.5cm < x < 12.5cm
Active area of GEM
5mm pitch; double
Active area of GEM
2.5mm pitch; double
Wire of field cage has to be double.
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Distortion of electric field by ions
 If the beam rate is very high, beam comes before the ions
created by previous beam go away.
→ Ions (electrons) created by beam are piled up, and distorts the
electric field.
 After a few seconds, charge distribution will be stationary.
← This Charge distribution is simulated by Monte-Carlo
simulation.
Distortion of the electric field is simulated by Garfield,
← Put stationary charge distribution into Garfield’s
configuration, substitute wire for electric charge.
and simulation of the position gap during electron drift has done.
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Condition for simulation
 Gas property
• Gas: He(90%) + CO2(10%)
• Electric field : 1kV/cm
• Pressure : 760 Torr
• Temperature : 300 K
 Drift velocity : 3 [cm/ms]
 Ion mobility : 2.5☓103[cm2·Torr·V-1·s-1]
Beam
•Beam rate : 107 Hz
• Energy loss : 4 MeV/cm = 105 ions(electrons)/cm
← corresponds to Sn with 100MeV/u
• Beam spread :
5cm (RMS) for drift direction
1cm (RMS) for the other direction
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y
Field cage
Charge distribution
Field cage
Recoil nuclei
25cm
Beam
• Generate random number
(Gaussian; mean: 12.5cm, RMS: 5cm).
← corresponds to beam hit position,
where ions(electrons) are created.
• Add to the histogram.
count
GEM
Pad
• Move each bin data to the next bin.
← corresponds to time change, the
move of ions(electrons).
count
y
repeat
y
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Distribution of ion
Ion distribution for each 1[ms]
stationary
Take the average of these histogram
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Position difference
y
Field cage
Field cage
 Put electrons at
• x : every 5mm from x=2.5cm to
x=13.0cm
y=24cm
• y : 24.0cm
 Drift electrons to the end of field cage,
and subtract the point where electron is put
from end point.
→ Position difference < 0.745mm.
 The effect of diffusion is not considered
x
0 2cm
Shield wire
13cm
 Simulate position difference in 3 different
shield wire configuration.
• Without shield wire
• 5mm pitch
• 2.5mm pitch
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Result
Active area of GEM
Without shield wire
Active area of GEM is
2.5cm < x < 12.5cm
Active area of GEM
Shield wire : 5mm pitch
Active area of GEM
Shield wire : 2.5mm pitch
• Without shield wire : Maximum position difference is over 1mm
• Shield wire : 5mm pitch : Maximum position difference : ~ 0.745mm
• Shield wire pitch : 2.5mm : Maximum position difference is 0.3mm < 0.745mm
→ Change of track angle is less within 3mrad.(flight length: 10cm)
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Pad shape
16mm
16mm
• Pad shape : rectangular triangle
(16mm☓16mm)
• Position is derived by the charge
ratio of the neighboring two pads.
• Angler resolution < 7.45mrad(RMS)
• Hit position is fitted by line using the
least squares method.
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Derivation of position 1
Recoil nuclei
Q1
z = Q2 / (Q1 + Q2) ☓ 16mm
x = Q2 / (Q1 + Q2) ☓ 16mm
x
z
Q1
Q2
Recoil nuclei
Q2
x
z = Q1 / (Q1 + Q2) ☓ 16mm
x = Q1 / (Q1 + Q2) ☓ 16mm
z
Q2
Q1
x
z
Derive wrong position!
→ Thinking about the algorism to
derive correct position in such case
Recoil nuclei
Derivation of position 2
Recoil nuclei
x
Q1
Q2
For these cases, position is derived
by the same way.
z
Recoil nuclei
Q1
x
z
Q2
Condition
 Energy loss of recoil nuclei : 500 electrons/cm
proton 30MeV @Ar(70%)+CO2(30%) : 700 electrons/cm
a with 15MeV/u @He(90%)+CO2(10%) : 500 electrons/cm
 Transverse diffusion （RMS）
Transverse diffusion coefficient of He(90%)+CO2(10%) :
200mm for 1cm(RMS)
• 200mm
• 400mm
• 600mm
• 1000mm
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
Simulation
x
16mm
16mm
z
 Arrival position of electron
x : Ru  sin   Rdx  Rdz
z : Ru  cos   Rdx  Rdz  z0
Ru : uniform random number between -1 and flight length+1
Rdx : Gaussian random number, which corresponds to diffusion
length for x direction
Rdz : Gaussian random number, which corresponds to diffusion
length for y direction
 : incident angle
z0 : incident position
 Number of generated random number : n±√n
n=500[electrons/cm]×(flight length+2)
 Number of events : 10000
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Diffusion
z
0
Diffusion
: 200mm
: 400mm
: 600mm
: 1000mm
z : injection position for z
• Other than the border of 2 pads → Almost same
• Border of 2 pads → Tracking algorism is not good.
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Pad size
Pad size
: 8mm×50mm
: 16mm×50mm
: 16mm×25mm
: 16mm×16mm
: 20mm×20mm
Diffusion : 1000mm
z : injection position for z
16mm×16mm : best angular resolution
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
Inclined incidence
16mm
x
16mm
z
 In the case of inclined incidence, angular resolution and
position resolution of vertex point are simulated.
  : -30°, -15°, 0°, 15°, 30°
 Pad size : 16mm × 16mm
 Number of generated random number : n±√n
n=500[electrons/cm]×(flight length+2)
 Number of events : 10000
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Result (angular resolution)
 = 30°
 = 15°
 = 0°
Diffusion : 1000mm
Better angular
resolution can be
achieved in the case
of <0 than in the
case of >0.
 = -15°
 = -30°
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Result (vertex resolution)
 = 30°
 = 15°
 = 0°
Diffusion : 1000mm
Vertex resolution is less
than 1mm.
 = -15°
 = -30°
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Summary & Outlook
 Final design is
• Wire pitch : 2.5mm (double)
• Pad size : 16mm × 16mm
→ Performance
• Angular resolution : < 4.5mrad
• Position resolution of vertex point : 0.5mm
• Position difference : < 0.3mm
 Outlook
• Tracking algorism
• Include the effect of straggling
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Backup
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Substitution wire
 To consider the beam spread for x-axis,
wires are put at x=1.
y
Field cage
Field cage
 The voltage which supplied to
substitution wire(V) is
V  V0 
0
Substitution wire for
electric charge (x=1)
x
q
20
 ln(
l ground
lwire
)
V0 : electrical potential made by field
wires
q : electric charge at unit length
lground : distance from wire to ground
lwire : diameter of wire
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• Ar(70%) + CO2(30%) (760 Torr, 300 K)
Drift velocity
Townsend coefficient
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• Ar(70%) + CO2(30%) (760 Torr, 300 K)
Longitudinal diffusion
Transverse diffusion
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Electric field(distorted)
Without shield wire
Shield wire : 5mm pitch
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Electric field(distorted)
Shield wire : 2.5mm pitch
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Position difference between mesh to pad
GEM
Pad
Frame of GEM
0.6
-1.3
-15.4 -12.7
-2.3
x
1.3
2.3
0.25
0.19 ~ 0.20
0.14
0
12.7 15.4
 Put electrons at
• x : every 1mm (-13.5cm<x<-11.5cm & -3.5cm<x<-1.5cm)
•y:
Between mesh and GEM
→ 0.59cm(0.01cm below Mesh)
Between GEM(or frame) and pad
→ 0.18cm(-12.6cm<x<-11.5cm or -3.5cm<x<-2.4cm; 0.01cm below GEM)
or 0.13cm(other area; 0.01cm below frame)
 Drift electrons from mesh to GEM & from GEM(frame) to pad, and derive the
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position difference.
Result (Mesh-GEM)
Active area of
GEM
Frame width : 10mm
-13.5 < x < -11.5
-3.5 < x < -1.5
Overlap with GEM &
frame : 1mm
Overlap with GEM &
frame : 0.5mm
Overlap with GEM &
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frame : 0mm
Result (GEM-Pad)
Active area of
GEM
Frame width : 10mm
-13.5 < x < -11.5
-3.5 < x < -1.5
Overlap with GEM &
frame : 1mm
Overlap with GEM &
Frame : 0.5mm
Overlap with GEM &
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Frame : 0mm
Result (Mesh-GEM)
Active area of
GEM
Overlap with GEM & frame : 0mm
-13.5 < x < -11.5
-3.5 < x < -1.5
Frame width : 5mm
Frame width : 10mm
Frame width : 15mm
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Result (GEM-Pad)
Active area of
GEM
Overlap with GEM & frame : 0mm
-13.5 < x < -11.5
-3.5 < x < -1.5
Frame width : 5mm
Frame width : 10mm
Frame width : 15mm
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