1. Development of GEM at CNS
Hideki Hamagaki
Center for Nuclear Study
University of Tokyo

2. Contents of This Presentation
What is GEM
How to make GEM
Plasma etching and its improvement
Test of gain variation
GEM application
GEM-TPC
HBD
X-ray detector with Xe gas
Summary and outlook
Improve GEM performance and stability
Applications
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

3. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
What is GEM
Gas Electron Multiplier
Developed at CERN by Sauli et al.
Foil of Kapton with Copper coated at both sides
typical: Kapton 50mm, Copper 5mm
with holes:
typical: pitch 140mm, and 70mmf
Electron multiplication in the strong field inside the holes
typical voltage between the two Copper foils = 300 ~ 550V
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

4. Characteristics of GEM
simple structure with lost cost material
low mass
multiple stacking  high gain
less risk of severe sparks/breakdown
S.Bachmann et al, NIM A438 (1999) 376
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

5. How GEM is or will be used
COMPASS
tracking chambers near beam-pipe
high rate ~150 kHz
low mass & high resolution
Possible applications
Time Projection Chamber
PHENIX, STAR, TESLA, JLC, …
UV photon detector with CsI photocathode
Gas Cherenkov counter: e.g. PHENIX HBD
X-ray detection
Cosmology  T. Tamagawa’s talk
Biology/Medical applications
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

6. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
How to make GEM
step1
put proper masks to the copper foils
step2
wet etching of masked copper foils
step3
make holes to the Kapton foil
wet etching --- CERN GEM
laser etching --- persued by T. Tamagawa
plasma etching --- persued by us (CNS)
hybrid of the above --- persued by us (CNS)
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

7. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
Plasma Etching Method
A method different from CERN
Fuchigami Micro has expertise on this
inherent gain variation in CERN GEM
our suspicion is on the hole shape
CERN-GEM CNS-GEM
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

8. Characterstics of CNS-GEM
Low resistance or sparks at low HV in the beginning  aging
surface roughness
small residues
Similar gain to CERN-GEM
Lower breakdown point than CERN-GEM
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

9. Improvement of CNS-GEM
CERN-GEM
Earlier breakdown
cleaning process
surface roughness
due to over-hung of Copper edges
Succeed to reduce over-hung
Still breakdown at lower HV
This is only crucial for high HV operation, needed for CF4 gas
CNS-GEM
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

10. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
Test of Gain Variation
gain measurement with Fe55 source
gain of CNS-GEM seems to stabilize in shorter time
After the first try, gain seems to stabilize much sooner, as long as GEM is kept inside the chamber
Need further work
condition; temperature, oxygen, moisture, …
simultaneous comparison
Blue : CERN-GEM（Gas : flow）
Black: CNS-GEM（Gas : noflow）
Red: CNS-GEM(Gas: flow)
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

11. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
GEM-TPC; motivation
Need of 3D-tracking device durable under high particle density and high rate at RHIC
position resolution, two-track separation, energy measurement
Expected advantage of GEM
small ion feedback; no need of gating grid
simple structure
flexible readout configuration
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

12. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
GEM-TPC prototype
Tested at KEK-PS
two types of readout pads
rectangular & chevron type
1.09 mm x 12 mm
charge-sensitive pre-amp
1 ms time-constant
readout with 100 MHz FADC
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

13. Performance of GEM-TPC (I)
Position resolution
z direction
x direction
resolution gets worse with increase of drift length
diffusion effect
magnitude depends on gas species
P10
Ar+C2H6(30%)
CF4
Electric field
(V/cm)
Drift velocity
(cm/ms)
Diffusion
(mm)
Ar(90%)+CH4(10%)
130
5.5
570
360
Ar(70%)+C2H6(30%)
390
5.0
320
190
CF4
8.9
110 80
R : P10 chevron
B : P10 rect.
Y : Ar+C2H6 rect.
G : CF4 chevron
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

14. Performance of GEM-TPC (II)
36 mm of P10 gas
drift length = 85mm
Energy loss measurement
P10: s(55Fe;5.9 keV) = 11 %
Ne(primary) ~ 222 for 5.9keV X-ray in P10  ~1.7 times larger than statistical estimate
obtained energy loss is as expected for various particles with different momentum
Beam rate effect
no change up to 5000 cps/cm2
good enough for HI applications
further studies may be needed
Z direction
R : P10 chevron
B : P10 rectangular
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

15. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
Hadron Blind Detector
UV photon detector
with CsI cathode
CF4 gas radiator
Ne(Cherenkov) > Ne(ionization)
development at Weizmann Institute
Use to measure low mass electron pairs at RHIC
Rejection of Dalitz pairs and external conversion pairs
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

16. MICRO PATTERN GAS DETECTOR 研究会 ＠京大
Summary and Outlook
How to improve GEM performance and stability
improve etching procedure
cleaning procedure after etching
use wet etching (cleaning) to smoothen the surface
washing out small residues
choice of material
base: insulator  resistive plastics
prevent gain variation due to charge up
Copper  Aluminum
low mass, long radiation length
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大

17. Summary and Outlook (cont.)
X-ray detector with Xe gas
for medical/biological use; two versions
2D radiation dose monitor
taking advantage of simple structure, and flexible configuration
precise 2D tomography
started development of a custom ADC chip with Tanaka’s group at NIAS
12/27/2018
MICRO PATTERN GAS DETECTOR 研究会　＠京大