property of lcp-gem in pure dimethyl ether under low pressure
DESCRIPTION
Property of LCP-GEM in Pure Dimethyl Ether under Low Pressure. RIKEN / Tokyo Univ. of Sci. Yoko Takeuchi [email protected]. T. Tamagawa A , T. Kitaguchi A , W. Iwakiri A , F. Asami A , B , A. Yoshikawa A.B , K. Kaneko A,B ,T . Enoto A,C , A. Hayato A , Y . Kohmura D , - PowerPoint PPT PresentationTRANSCRIPT
Property of LCP-GEM in Pure Dimethyl Ether under Low Pressure
RIKEN / Tokyo Univ. of Sci.Yoko Takeuchi
T. TamagawaA, T. KitaguchiA, W. IwakiriA, F. AsamiA,B, A. YoshikawaA.B, K. KanekoA,B,T. EnotoA,C, A. HayatoA, Y. KohmuraD,
and The GEMS/XACT team
RIKENA , Tokyo Univ. of Sci.B , NASA/GSFCC , Kogakuin Univ.D
MPGD 2013 @Zaragoza 1
1-1.Cosmic X-ray Polarimetry
image Polarization
?time variation Energy
History of X-ray polarimetry
Observation of cosmic X-ray objects
MPGD 2013 @Zaragoza
Cosmic X-ray Polarimeter Developed• Using GEM-TPC technique• Sensitivity with > 100 times higher than ever before.
year mission type1972’ Sounding Rocket (Norvick+1972) Bragg1976’ OSO-8 satellite(Weisskopf+1976, 78) Bragg
== No mission since 1970’s ==
Few significant detection of X-ray polarization.
2
Plan to mount polarimeter on sounding rocket
1-2. XACT rocket Experiment
MPGD 2013 @Zaragoza
XACT rocket • X-ray Advanced Concepts Testbed • NASA’s sounding rocket program• Scheduled to be launched in 2015
• Energy range : 1-10 keV• Observation time :〜 6 min• Target : Crab Nebula
[K. Gendreau + 2012]
3
- One of the brightest X-ray objects- Only X-ray polarized source detected
by Bragg polarimeter so far- Strong X-ray emission around 2 keV
2.8 m
Mirror
GEM-TPC polarimeter
Focal length 2.8 m
Using photoelectric effect
• Direction of X-ray polarization : E of the incident X-ray
• distribution of photoE emission :
• Polarization can be measured by photoE distribution.
• Sensitive to only linear polarization
1-3. Photoelectric Effect
X-ray
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PhotoE Track
Photoelectric Effect
E
4
cos2Φ
θΦ
optaxis
x : time
y : strip[ Black +2007 ]GEM
Drift Electrode
Trigger
Readout strip
Photoelectron
1-3. GEM-TPC X-ray Polarimeter
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- Single GEM- Strip pitch : 121 μm - Readout ASIC: APV25 (20 MHz sampling)
5
Gas Electron Multiplier (LCP-GEM)
developed at RIKEN
140 um70 um
LCP
Thickness :100 um
About LCP-GEM, See Tamagawa’s Talk (7/3 12:30).
[Tamagawa + 2009]
2D photoE track image
optaxis
x : time
y : strip[ Black +2007 ]GEM
Drift Electrode
Trigger
Readout strip
Photoelectron
1-3. GEM-TPC X-ray Polarimeter
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- Single GEM- Strip pitch : 121 μm - Readout ASIC: APV25 (20 MHz sampling)
2D photoE track image
target gas: Pure Dimethyl Ether (DME)
requirement for property of target gasslow drift velocity …… coarse sampling with APV25small diffusion .…… avoid blurring track image
5
1-4. Requirement of Polarimeter
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DME pressure is optimized by calculating track length and count rate.
6
Trac
k le
ngth
(2 k
eV)
[mm
]
DME Pressure[Torr]
Coun
t Ra
te [
/sec
]
Optimum pressure range: 50-150 Torr
LCP-GEM has NOT been operated under low pressure in DME.
As pressure goes down, -track length increases
-count rate decreases
We estimate optimum pressure range by simulation.
1-4. Requirement of Polarimeter
MPGD 2013 @Zaragoza
DME pressure is optimized by calculating track length and count rate.
6
Trac
k le
ngth
(2 k
eV)
[mm
]
DME Pressure[Torr]
Coun
t Ra
te [
/sec
]
Optimum pressure range: 50-150 Torr
LCP-GEM has NOT been operated under low pressure in DME.
As pressure goes down, -track length increases
-count rate decreases
We estimate optimum pressure range by simulation.
Measure property of LCP-GEM in Pure DME under low pressure - Gain curve
sufficient gain without discharge
- Energy scale check linearity
- Lower pressure limit of normal GEM operation
Our study
2-1. Experimental Setup
Drift electrode
readout pad
preamplifierAMPTEK A225
20.5 mm
1 mm
R3
Ed
Ei
pure DME 10 ~ 190 TorrVd
ADC
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Vc
preamplifierORTEC 109PC
ΔVGEM
LCP-GEM
・ Single LCP-GEM ( 30 mm x 78 mm x 0.1 mm )
・ Constant drift velocity, 0.24 um/nsex.) Ed = 196 V/cm at 190 Torr
・ To avoid electron amplification in the induction region, Ei is set suitable value.・ Signals are read from pad &
GEM anode
・ DME pressure: 10-190 Torr
・ X-ray beam from X-ray generator- Collimated with Φ200 μm - Parallel to LCP-GEM- Energy :
* 6.4 keV (gain curve) * 4.5, 6.4, 8.0 keV
(Energy scale)
X-ray
7
10 M
Ω10
MΩ
3-1. Gain Curve
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- One data : 30000 event
At 190 Torr
- Exponential function
- Maximum gain :~ 20000 (ΔVGEM=560 V)
w/o discharge rate of 0.1%
- ΔE/E(FWHM) ~20 % 19
0 Torr
ΔVGEM
Effec
tive
Gain
readout pad
Next slide, gain curves <190 Torr Please check the point !! - function shape
- maximum gain
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
- One data : 30000 event
At 110 Torr
- Non exponential function
- Maximum gain :~ 20000 (ΔVGEM=520 V)
110 Torr
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
- One data : 30000 event
At 70 Torr
- Non exponential function
- Maximum gain :~ 10000 (ΔVGEM=500 V)
110 Torr
70 Torr
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
- One data : 30000 event
At 50 Torr
- exponential function
- Maximum gain :~ 5000 (ΔVGEM=510 V)
110 Torr 70 To
rr
50 Torr
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
- One data : 30000 event
At 40 Torr
- Non exponential function
- Maximum gain :~ 2000 (ΔVGEM=500 V)
110 Torr 70 To
rr
50 Torr
40 Torr
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
- One data : 30000 event
At 30 Torr
- Non exponential function
- Maximum gain :~ 1000 (ΔVGEM=490 V)
110 Torr 70 To
rr
50 Torr
40 Torr
30 Torr
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
- One data : 30000 event
At 20 Torr
- Non exponential function
- Maximum gain :~ 300 (ΔVGEM=470 V)
110 Torr 70 To
rr
50 Torr
40 Torr
30 Torr
20 Torr
3-1. Gain Curve
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190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
110 Torr 70 To
rr
50 Torr
40 Torr
30 Torr
20 Torr
The pressure dependence of gain curve seems complex.
To understand this behavior of gain curve, we derived the first Townsend coefficient α
Difference of each gain curve 1) Slope and offset of curve 2) Non exponential <110 Torr
3-2. The First Townsend coef. α/p vs. E/p
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190 Torr110 Torr
70 Torr50 Torr
20 Torr
α / p
[
/cm
/Tor
r]
40 Torr30 Torr
E / p [V/cm/Torr]
definition :
α = ln (Gain)/xGEM
xGEM : 100 μm fix (GEM thickness)
)(
The data is well fitted by the empirical formula.
fitting by α/p = A × exp( -B p/E )
● α [/cm] ・・・
※ Gain=Gainpad+GainGEM ano. This is why we wanted to collect all of the amplified electrons in the GEM channels
● E [V/cm] ・・・ΔVGEM /GEM thickness
(100 μm)
3-3. Measured α vs. MAGBOLTZ
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α/p
[ /c
m/T
orr]
E/p [V/cm/Torr]
MAGBOLTZExperimental Data
11
[Sharma + 1993]
- Experimentally-measured α grossly agree with MAGBOLTZ’s result.- Although the GEM and parallel plate are different each other,
both results are well fit to the MAGBOLTZ estimation.
MAGBOLTZ parametersp=10 - 190 TorrE=10 - 60 kV/cm
3-4. Linearity of Energy Scale
gain ~200
gain ~300gain ~400gain ~500gain ~700●
●
●
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• Charge Q[fC] incident Energy ∝• Operated in proportional region• Linear energy scale above 30 Torr.
incident Energy 4.5 keV (Ti)6.4 keV (Fe)8.0 keV (Cu)
At 30 Torr
12
Incident Energy [keV]
Mea
sure
d Ch
arge
Q [f
C]
ΔVGEM = 440 V
5 sec
200 mV
3-5. Odd Pulse Profile at 10 Torr
4 ms
200 mV
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the signal profile dramatically changed above ΔVGEM= 437 V.
ΔVGEM = 430 V
* duration : ~10 μs* pulse height : 4 mV ( gain ~40)
* duration: 1~10 ms* pulse height : ~200 mV
※ No Signal when X-rays were stopped. ==> Those signals were triggered by X-rays.
10 us
4 mV
ΔVGEM = 437 V
Preamp-out signal captured by an oscilloscope from readout pad
13
* duration: 2~5 sec* pulse height: ~200 mV
Normal signal
We challenged to operate LCP-GEM at much lower pressure.
E/ P[V/cm/Torr] Ch
arge
col
lect
ed
Geiger region
Proportional region
Ion chamberregion
High voltage and/or
low pressure
The operation mode of gas chamber transits from the proportional region to the Geiger region.
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1) Change of pulse profile at 10 Torr- longer duration time- higher pulse height
2) As ΔVGEM gets higher,-longer duration-almost same pulse
height
14
3-6. GEM operated in Geiger region?
Observation results suggest that GEM are probably operated in the Geiger region.
We understand from those signal of oscilloscope,
4. Summary
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We have developed Cosmic X-ray polarimeter using GEM-TPC. Polarimeter requirement of DME pressure : 50 – 150 Torr
We measured the properties of LCP-GEM in pure DME at low pressure. - gain curve (10-190 Torr) .. The data is well fitted by empirical formula.
- Energy scale (4.5-8.0 keV) … Linear from 30 to 190 Torr.
- Odd pulse phase at 10 Torr … GEM are probably operated in the Geiger region.
LCP-GEM can be operated in proportional region at pressure of 50-150 Torr.
15
Thank you for your attention !!
Backup side!
LCP-G
EM(d/p/t: 70/140/50 um)
double
LCP-G
EM(d/p/t:
70/140/1
00 um) sin
gle
ΔVGEM/100 um (V)
Effec
tive
Gain
ArCO2(70%:30%) gas flow, 55Fe
LCP-GEM Performance
500 600 700 800
ArCO2(70%:30%) gas flow, 55Fe
CERN GEM (d/p/t: 70/140/50 um)
elapsed time after HV ON (min)
rela
tive
gain
Gain curveLCP-GEM (t100 um) is achieved higher gain than one of t50 um as same ΔVGEM.
Time variation Gain of LCP-GEM does not change.
200 400 600 800 1000
LCP-GEM (d/p/t: 70/140/50 um)
Drift Velocity of Electron
DMECO2
Ar-CO2(70%:30%)
0.24
(MAGBOLTZ Calculation)
DME gas is very slow gas !!
Drift velocity of electron and ion(Magboltz Calculation)
DMEDME
Ar-CO2
electronAr-CO2
Ion
* discharge point : the highest ΔVGEM without discharge rate 0.1 %
* Paschen curve of DME is non data.
* Discharge point is similar with Paschen curve.
※calculation as d=100 μm(GEM thickness)
Discharge Point Br
eakd
own
Vol
tage
[V
]
P ・ d [Torr cm]
Energy Resolution
Energy Resolution
Table of Ed & Ei
readout pad
preamplifierAMPTEK A225
20.5 mm
1 mm
10 M
Ω10
MΩ
R3
Ed
Ei
ADC
Vc
preamplifierORTEC 109PC
LCP-GEM
Ed [V/cm] Ei [V/cm]190 Torr 196 4000-5500110 Torr 113 3500-530070 Torr 72.2 300-55050 Torr 51.6 300-55040 Torr 41.3 300-55030 Torr 30.9 300-55020 Torr 20.6 400-52010 Torr 10.3 ~150
Drift electrode
Vd
Detection Efficiency in the DME gas & Effective Area of X-ray Mirror
X-ray
Directi
on of
X-ray P
olarization
Strip
(12
1 um
pitc
h)2D Electron Track Image
- APV25 (20 MHz sampling) - Drift velocity : 0.24 um/cm
photoE dist
ribution
Electron Track Length
(Tabata + 1972 )
Polarimeter Design for XACT
Effective area : 31.6 cm
Close chamber
With MXS (Modulated X-ray Source)
Gain Curve at 10 Torr- One data : 30000 event
At 10 Torr
- Only one data point
- Maximum gain :~ 40 (ΔVGEM=430 V)
Strange signal appear at ΔVGEM > 437 V
190 T
orr
ΔVGEM
Effec
tive
Gain
readout pad
110 Torr 70 To
rr
50 Torr
40 Torr
30 Torr
20 Torr
10 Torr
Energy scale at 190 Torr
• charge Q[fC] incident Energy ∝• At 190 Torr, Operated in proportional region
gain 600
gain 2500gain 4300
gain 7500 ●
●
●
incident Energy 4.5 keV (Ti)6.4 keV (Fe)8.0 keV (Cu)
gain 350
Townsend coef. vs Ei at 190 Torr[Y. Takeuchi 2011]
Ei [V/cm]
α [/
mm
]
CROSS SECTION of DME
Ionization
ADC Spectrum
Incident energy: 6.4 keV At 70 TorrdVGEM= 460 V
Future Works
Future plan is measurement of the energy scale.In MPGD
- below 30 Torr …. check linearityIn XACT mission, X-ray emission of Crab Nebula is strong around 2 keV
- with less than 4.5 keV X-rays at 10-190 Torr.
Linearity of Energy Scale at 30 Torr