gem r&d activity in ustc
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Department of Modern Physics
GEM R&D Activity in USTC
Yi Zhou
University of Science & Technology of China
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Department of Modern Physics
Outline
GEM Chamber Design and Test
Delay-Line Readout Method
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Department of Modern Physics
Structures of GEM
Cu 5µm
60µm
80µm
Kapton 50µm 140 μm
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Department of Modern Physics
GEM Chamber Design and Test Double-Layer Chamber1. 55Fe Test Energy Resolution-HV Gain-HV
2. Position Resolution(8keV X-ray Imaging)
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Department of Modern Physics
Double-GEM Detector Design
Two orthogonal sets of parallel strips at 0.8 mm pitch, 0.35 mm wide on upper side, 0.65 mm wide on lower side. The thickness of the PCB is 0.2mm
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Gain Measurement (Source: 55Fe)
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Effective Gas Gain 1
( 70%Ar+30%CO2 )
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Energy Resolution(FWHM/Peak) 1
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( 60%Ar+40%CO2 )
Effective Gas Gain 2
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Energy Resolution(FWHM/Peak) 2
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GEM1=420VGEM2=370V
P1
P1
GEM1=370VGEM2=420V
P2
P2
HV Optimization
While the effective gas gain is large enough,higher 1st GEM HV and lower 2nd GEM HV will give a better energy resolution.
( 70%Ar+30%CO2 )
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Count ability and stability
Facula area of X-ray: 2mm2;Counted by a scaler
Test time ： ~2 weeks；Effective gain varied: <1%。
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X-ray Imaging Experiment
X: 6 readout channelsY: 6 readout channels8-channel charge sensitive pre-amplifier × 2 Sensitivity: 0.8V/pc, designed by HEPG
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The Images
m
m
y
x
86~
78~
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Department of Modern Physics
The Images
m
m
y
x
86~
78~
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Department of Modern Physics
Delay-Line Readout Method
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Department of Modern Physics
Why Delay-Line?
Channel by Channel readout electronics cost too much; The readout electronics based on integrated chip will be available soon (in China), but not now;
Delay-Line readout method can be used for low-rate application and the cost is much lower, the position resolution is not bad.
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The Delay-Line circuit is a chain of Inductor-Capacitor (LC) cells, an ideal LC cell could delay the input signal for a certain period with very small distortion.
Delay-line Readout Method
0
1
LCZ
1
1
0
2 L
C L
C =
0
( )
1
0
1
3
0
3
LC =
0
• Parameters of Delay-Line:
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Department of Modern Physics Department of Modern Physics
The Delay-Line PCB
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Simulation of the Delay-Line System
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Simulation and Calibration Signals
Simulation: 1.38ns/cell
Experiment: 1.41ns/cell
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Department of Modern Physics
The Triple GEM Detector
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2D Images
σx~148.4μm
σy~157.0μm
COG imaging
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Department of Modern Physics
2D Images
σx~148.4μm
σy~157.0μm
COG imaging
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Department of Modern Physics
Summary & Outlook
A detailed test of gain & energy resolution for the double GEM detector has been performed; The energy resolution can be optimized by change the HV distribution while the gas gain is fixed. Two readout methods have been studied; The channel by channel (COG) readout method has a good position resolution but costs too much. The delay-line readout costs low, when its position resolution can be accepted, it is a good choice for low-rate application.
Construct a prototype of a large area GEM;Structure and HV optimization;Readout PCB design.
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