- Email: [email protected]
A new spiral MGSC
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78 www.elsevier.com/locate/nima
A new spiral MGSC Hiroyuki Takahashia,, Kosuke Nishia, Sebastien Paesa, Hisako Nikoa, Kaoru Fujitab, Prasit Siritiprussameea, Masashi Ohnoa, Boxuan Shib, Masaharu Nakazawab, Hidenori Toyokawac, Shunji Kishimotod, Takashi Inod, Michihiro Furusakae a Department of Nuclear Engineering and Management, Faculty of Engineering, The University of Tokyo, Japan Department of Quantum Engineering and Systems Science, Faculty of Engineering, The University of Tokyo, Japan c Japan Synchrotron Radiation Research Institute, Japan d Institute of Materials Structure Science, High Energy Accelerator Research Organization, Japan e Department of Mechanical Intelligence Engineering, Graduate School of Engineering, Hokkaido University, Japan
b
Available online 7 April 2007
Abstract Conventional MicroStrip Gas Counters (MSGCs) are composed of parallel strips. However, the geometry of MSGC is not limited to the traditional parallel electrodes. Here, we introduce a new geometry of spiral electrodes for our new MSGC. With the new geometry, we can implement a complete two-dimensional array of these spiral pixels. We have fabricated a test detector. First test results showed a gas gain greater than 500. Spiral geometry with a single grid is also tried and the first test result was successfully ensured a principle of this new micropattern gas counter. r 2007 Published by Elsevier B.V. Keywords: X-rays; Proportional counters; MSGC; Pixels
1. Introduction Conventional MicroStrip Gas Counters (MSGCs) are equipped with parallel arrangement of many linear strips. The MSGC is invented on a concept similar to the multiwire proportional counters [1]. However, the advantage of MSGC lies in its very flexible patterning capability through a microfabrication technique. We think the MSGC technology is still promising because the twodimensional patterning can realize flexible structures, which can be completely different from conventional wire detectors. Here we introduce a new fully two-dimensional version of MSGC–Spiral MSGC. Conventional MSGCs are composed of narrow anode strips and wide cathode strips. Anode strips are kept at a positive high voltage. Created electrons by incident radiation are attracted to the anode strips and trigger the avalanche process. In this principle, the thin anode collects electrons and the avalanche occurs near the strip. However, recently, people Corresponding author. Fax: +81 3 3208 0850.
E-mail address: [email protected] (H. Takahashi). 0168-9002/$ - see front matter r 2007 Published by Elsevier B.V. doi:10.1016/j.nima.2007.04.016
are interested in fully pixel devices such as GEMs [2], glass capillary plate gas counters [3], and micropixel chambers [4]. One advantage of pixel array of micropattern gas counters is its fully parallel operation of individual pixels. Such a detector can sustain the operation even if some pixels are irradiated more than the saturation count rate. Another advantage of the geometry is robustness of the detector for the defect or local discharge in case that some portion of bad pixels is allowed. 2. Spiral MSGC In order to define a pixel, we have used trunks and branches for both anodes and cathodes. Anode branch strips and cathode branch strips meet in the spiral region where the avalanche occurs and created electrons and ions are immediately absorbed. Based on this idea, we have designed and fabricated a pixel array of spiral strips. Fig. 1 shows an example of this new MSGC pattern. We have arranged the anode bias line and the cathode bias line alternatively. In order to provide the avalanche region, we added fine spiral branch strips from the anode and the
ARTICLE IN PRESS 76
H. Takahashi et al. / Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78
cathode. This amplification region can occupy large area on the detector surface, expect for a high counting rate capability and minimum ‘‘dead’’ region. Thus, if the primary electrons are approaching from the cathode, they are successfully trapped in the amplification region. The electric field around the pixel is calculated by ELFIN [5] which is based on a three-dimensional integral element method. Fig. 2 shows a result for nine pixels. As seen in the result, narrow curved strips are quite difficult for accurate calculation; however, higher electric field is observed in the region between the fine anode and the fine cathode strips. In particular, the center part shows a considerable intensity of the electric field.
3. First test results on a fabricated spiral MSGC We have fabricated test detectors using an electron beam lithography machine at the University of Tokyo. Fig. 3 shows a photograph of a test detector where the width of spiral curve is 10 mm and the anode strip width and the cathode strip width are 35 and 150 mm, respectively. In the center part of the spiral pixel, we locate thick round terminators to suppress the electric field in the center region. Characteristics of the test plate were first evaluated using X-rays. The spiral MSGC (1 mm anode-bias-line pitch, 400 mm 400 mm spiral pattern size, the active area of 20 mm 20 mm: The total number of pixels is 2500) showed the gas gain of 500 at the bias voltage of 380 V. Note that the pixel size is the half of the anode pitch due to the electrode geometry. Fig. 4 shows measured waveforms obtained from the anode and the cathode signals at the
Fig. 2. Calculated electric field for the spiral geometry is shown in Fig. 1 where the anode pitch was 1 mm, the pattern width was 10 mm, applied voltage was 500 V. Calculation, which is based on the integral element method, was performed by the ELFIN code.
Fig. 3. Photograph of a fabricated spiral MSGC plate. Spiral pattern size is 400 mm 400 mm. Width of spiral curve is 10 mm. Anode strip width and cathode strip width are 35 and 150 mm, respectively.
Fig. 1. Spiral geometry of MSGC.
charge-sensitive preamplifier output. Fast rise times of less than 100 ns are observed for both of the output signals. Pulse height spectra were obtained by irradiation of 14 keV X-rays (see Fig. 5). Although the pulse height spectrum could not show a nice photoelectric peak for the test detector, the preliminary result successfully ensured the amplification principle of the new pixellated MSGC.
ARTICLE IN PRESS H. Takahashi et al. / Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78
2e-007
77
ANODE CATHODE
AMPLITUDE (a.u.)
1.5e-007 1e-007 5e-008 0 -5e-008 -1e-007
06
06
5e
-0
06
-0 4e
06
3e
-0
06
-0 2e
0
-0 1e
6
6 -1
e-
00
6 -2
e-
00
6 -3
e-
00
6
00
-4
e-
00 e-
-5
-6
e-
00
6
-1.5e-007
TIME (sec) Fig. 4. Waveform signals obtained for the anode and cathode strips.
Fig. 6. Photograph of a spiral plate with a single grid between the anode and the cathode. The grid electrode can be unicursal through pixels in the vertical direction.
4000
6.00E-03 IRRADIATED BG
5.00E-03 4.00E-03
3000
Amplitude (V)
COUNTS/CHANNEL
3500
2500 2000
3.00E-03 2.00E-03 1.00E-03
1500 0.00E+00 1000
-1.00E-03
500
0
1
2
3
4
5
-2.00E-03 Time (us)
0 0
50
100
150
200
CHANNEL NUMBER Fig. 5. Pulse height spectra obtained with the spiral plate. Red curve shows a pulse height spectrum for 14 keV X-rays and the green curve shows a pulse height spectrum without X-rays.
The gas gain of the spiral plate with constant gap between the cathode and the anode is not uniformly distributed since the electric field is more concentrated in the inner spiral than the outer spiral. To compensate the electric field and flatten it, we could use a slightly modified pattern with a gradually increasing gap between the anode and the cathode. Another improvement for the gas amplification is to utilize the intermediate grid electrode as used in the multi-grid-type MSGC (M-MSGC) [6]. The grid electrodes can be inserted through the spiral curves to separate the anode curve and the cathode curve. They are unicursal through pixels. We have also fabricated the single-grid version of the spiral plate and tested it. The plate is shown in Fig. 6 and the higher applied voltages across the anode and the cathode are possible with this structure. A measured preamplifier output pulse waveform
Fig. 7. Pulse waveform obtained with a spiral plate with single-grid version. Applied voltage was 456 V for the anode and 130 V for the grid.
from the anode line is shown in Fig. 7. Although detailed characteristics of the plate are still under investigation, we think this new geometry opens a new possibility of the MSGC. In future, we plan to optimize the spiral geometry and develop a more suitable spiral pattern for the amplification region by enhancing a wider amplification region, as well as a new position readout method for the pixellated device.
4. Conclusions A new spiral MSGC is proposed. In this new geometry of the MSGC, spiral patterns are branched from the anode and the cathode strips and they occupy a large gas amplification area over detector-sensitive area. First test results showed a successful operation of this new geometry. Observed gas gain was up to 500 but a considerable variation in the gas gain was also observed, which is attributed to the nonuniformity of the electric field in the spiral pattern. Multi-grid version of the spiral MSGC is
ARTICLE IN PRESS 78
H. Takahashi et al. / Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78
also possible and the test plate with a single grid was also fabricated and tested. Higher applied voltage and higher gas gain are possible with this plate. Acknowledgment This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (B), 16360469.
References [1] [2] [3] [4]
A. Oed, Nucl. Instr. and Meth. A 263 (1988) 381. F. Sauli, Nucl. Instr. and Meth. A 386 (1997) 531. H. Sakurai, et al., Nucl. Instr. and Meth. A 374 (1996) 341. A. Ochi, T. Nagayoshi, et al., Nucl. Instr. and Meth. A 478 (1–2) (2002) 196. [5] Elf Corp., Osaka, Elfin home page, [Online], Available: /http:// www.elf.co.jp/index.htmlS (in Japanese). [6] H. Takahashi, et al., Nucl. Instr. and Meth A 477 (1-3) (2002) 13.
Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78 www.elsevier.com/locate/nima
A new spiral MGSC Hiroyuki Takahashia,, Kosuke Nishia, Sebastien Paesa, Hisako Nikoa, Kaoru Fujitab, Prasit Siritiprussameea, Masashi Ohnoa, Boxuan Shib, Masaharu Nakazawab, Hidenori Toyokawac, Shunji Kishimotod, Takashi Inod, Michihiro Furusakae a Department of Nuclear Engineering and Management, Faculty of Engineering, The University of Tokyo, Japan Department of Quantum Engineering and Systems Science, Faculty of Engineering, The University of Tokyo, Japan c Japan Synchrotron Radiation Research Institute, Japan d Institute of Materials Structure Science, High Energy Accelerator Research Organization, Japan e Department of Mechanical Intelligence Engineering, Graduate School of Engineering, Hokkaido University, Japan
b
Available online 7 April 2007
Abstract Conventional MicroStrip Gas Counters (MSGCs) are composed of parallel strips. However, the geometry of MSGC is not limited to the traditional parallel electrodes. Here, we introduce a new geometry of spiral electrodes for our new MSGC. With the new geometry, we can implement a complete two-dimensional array of these spiral pixels. We have fabricated a test detector. First test results showed a gas gain greater than 500. Spiral geometry with a single grid is also tried and the first test result was successfully ensured a principle of this new micropattern gas counter. r 2007 Published by Elsevier B.V. Keywords: X-rays; Proportional counters; MSGC; Pixels
1. Introduction Conventional MicroStrip Gas Counters (MSGCs) are equipped with parallel arrangement of many linear strips. The MSGC is invented on a concept similar to the multiwire proportional counters [1]. However, the advantage of MSGC lies in its very flexible patterning capability through a microfabrication technique. We think the MSGC technology is still promising because the twodimensional patterning can realize flexible structures, which can be completely different from conventional wire detectors. Here we introduce a new fully two-dimensional version of MSGC–Spiral MSGC. Conventional MSGCs are composed of narrow anode strips and wide cathode strips. Anode strips are kept at a positive high voltage. Created electrons by incident radiation are attracted to the anode strips and trigger the avalanche process. In this principle, the thin anode collects electrons and the avalanche occurs near the strip. However, recently, people Corresponding author. Fax: +81 3 3208 0850.
E-mail address: [email protected] (H. Takahashi). 0168-9002/$ - see front matter r 2007 Published by Elsevier B.V. doi:10.1016/j.nima.2007.04.016
are interested in fully pixel devices such as GEMs [2], glass capillary plate gas counters [3], and micropixel chambers [4]. One advantage of pixel array of micropattern gas counters is its fully parallel operation of individual pixels. Such a detector can sustain the operation even if some pixels are irradiated more than the saturation count rate. Another advantage of the geometry is robustness of the detector for the defect or local discharge in case that some portion of bad pixels is allowed. 2. Spiral MSGC In order to define a pixel, we have used trunks and branches for both anodes and cathodes. Anode branch strips and cathode branch strips meet in the spiral region where the avalanche occurs and created electrons and ions are immediately absorbed. Based on this idea, we have designed and fabricated a pixel array of spiral strips. Fig. 1 shows an example of this new MSGC pattern. We have arranged the anode bias line and the cathode bias line alternatively. In order to provide the avalanche region, we added fine spiral branch strips from the anode and the
ARTICLE IN PRESS 76
H. Takahashi et al. / Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78
cathode. This amplification region can occupy large area on the detector surface, expect for a high counting rate capability and minimum ‘‘dead’’ region. Thus, if the primary electrons are approaching from the cathode, they are successfully trapped in the amplification region. The electric field around the pixel is calculated by ELFIN [5] which is based on a three-dimensional integral element method. Fig. 2 shows a result for nine pixels. As seen in the result, narrow curved strips are quite difficult for accurate calculation; however, higher electric field is observed in the region between the fine anode and the fine cathode strips. In particular, the center part shows a considerable intensity of the electric field.
3. First test results on a fabricated spiral MSGC We have fabricated test detectors using an electron beam lithography machine at the University of Tokyo. Fig. 3 shows a photograph of a test detector where the width of spiral curve is 10 mm and the anode strip width and the cathode strip width are 35 and 150 mm, respectively. In the center part of the spiral pixel, we locate thick round terminators to suppress the electric field in the center region. Characteristics of the test plate were first evaluated using X-rays. The spiral MSGC (1 mm anode-bias-line pitch, 400 mm 400 mm spiral pattern size, the active area of 20 mm 20 mm: The total number of pixels is 2500) showed the gas gain of 500 at the bias voltage of 380 V. Note that the pixel size is the half of the anode pitch due to the electrode geometry. Fig. 4 shows measured waveforms obtained from the anode and the cathode signals at the
Fig. 2. Calculated electric field for the spiral geometry is shown in Fig. 1 where the anode pitch was 1 mm, the pattern width was 10 mm, applied voltage was 500 V. Calculation, which is based on the integral element method, was performed by the ELFIN code.
Fig. 3. Photograph of a fabricated spiral MSGC plate. Spiral pattern size is 400 mm 400 mm. Width of spiral curve is 10 mm. Anode strip width and cathode strip width are 35 and 150 mm, respectively.
Fig. 1. Spiral geometry of MSGC.
charge-sensitive preamplifier output. Fast rise times of less than 100 ns are observed for both of the output signals. Pulse height spectra were obtained by irradiation of 14 keV X-rays (see Fig. 5). Although the pulse height spectrum could not show a nice photoelectric peak for the test detector, the preliminary result successfully ensured the amplification principle of the new pixellated MSGC.
ARTICLE IN PRESS H. Takahashi et al. / Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78
2e-007
77
ANODE CATHODE
AMPLITUDE (a.u.)
1.5e-007 1e-007 5e-008 0 -5e-008 -1e-007
06
06
5e
-0
06
-0 4e
06
3e
-0
06
-0 2e
0
-0 1e
6
6 -1
e-
00
6 -2
e-
00
6 -3
e-
00
6
00
-4
e-
00 e-
-5
-6
e-
00
6
-1.5e-007
TIME (sec) Fig. 4. Waveform signals obtained for the anode and cathode strips.
Fig. 6. Photograph of a spiral plate with a single grid between the anode and the cathode. The grid electrode can be unicursal through pixels in the vertical direction.
4000
6.00E-03 IRRADIATED BG
5.00E-03 4.00E-03
3000
Amplitude (V)
COUNTS/CHANNEL
3500
2500 2000
3.00E-03 2.00E-03 1.00E-03
1500 0.00E+00 1000
-1.00E-03
500
0
1
2
3
4
5
-2.00E-03 Time (us)
0 0
50
100
150
200
CHANNEL NUMBER Fig. 5. Pulse height spectra obtained with the spiral plate. Red curve shows a pulse height spectrum for 14 keV X-rays and the green curve shows a pulse height spectrum without X-rays.
The gas gain of the spiral plate with constant gap between the cathode and the anode is not uniformly distributed since the electric field is more concentrated in the inner spiral than the outer spiral. To compensate the electric field and flatten it, we could use a slightly modified pattern with a gradually increasing gap between the anode and the cathode. Another improvement for the gas amplification is to utilize the intermediate grid electrode as used in the multi-grid-type MSGC (M-MSGC) [6]. The grid electrodes can be inserted through the spiral curves to separate the anode curve and the cathode curve. They are unicursal through pixels. We have also fabricated the single-grid version of the spiral plate and tested it. The plate is shown in Fig. 6 and the higher applied voltages across the anode and the cathode are possible with this structure. A measured preamplifier output pulse waveform
Fig. 7. Pulse waveform obtained with a spiral plate with single-grid version. Applied voltage was 456 V for the anode and 130 V for the grid.
from the anode line is shown in Fig. 7. Although detailed characteristics of the plate are still under investigation, we think this new geometry opens a new possibility of the MSGC. In future, we plan to optimize the spiral geometry and develop a more suitable spiral pattern for the amplification region by enhancing a wider amplification region, as well as a new position readout method for the pixellated device.
4. Conclusions A new spiral MSGC is proposed. In this new geometry of the MSGC, spiral patterns are branched from the anode and the cathode strips and they occupy a large gas amplification area over detector-sensitive area. First test results showed a successful operation of this new geometry. Observed gas gain was up to 500 but a considerable variation in the gas gain was also observed, which is attributed to the nonuniformity of the electric field in the spiral pattern. Multi-grid version of the spiral MSGC is
ARTICLE IN PRESS 78
H. Takahashi et al. / Nuclear Instruments and Methods in Physics Research A 579 (2007) 75–78
also possible and the test plate with a single grid was also fabricated and tested. Higher applied voltage and higher gas gain are possible with this plate. Acknowledgment This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (B), 16360469.
References [1] [2] [3] [4]
A. Oed, Nucl. Instr. and Meth. A 263 (1988) 381. F. Sauli, Nucl. Instr. and Meth. A 386 (1997) 531. H. Sakurai, et al., Nucl. Instr. and Meth. A 374 (1996) 341. A. Ochi, T. Nagayoshi, et al., Nucl. Instr. and Meth. A 478 (1–2) (2002) 196. [5] Elf Corp., Osaka, Elfin home page, [Online], Available: /http:// www.elf.co.jp/index.htmlS (in Japanese). [6] H. Takahashi, et al., Nucl. Instr. and Meth A 477 (1-3) (2002) 13.