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Okada K, Nishiura M, Kubo S, Shimozuma T, Yoshimura Y, Igami H, Takahashi H, Tanaka K, Kobayashi S, Ito S, Mizuno Y, Ogasawara S. Development of fast steering mirror control system for plasma heating and diagnostics. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11E811. [PMID: 25430376 DOI: 10.1063/1.4891044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A control system for a fast steering mirror has been newly developed for the electron cyclotron heating (ECH) launchers in the large helical device. This system enables two-dimensional scan during a plasma discharge and provides a simple feedback control function. A board mounted with a field programmable gate array chip has been designed to realize feedback control of the ECH beam position to maintain higher electron temperature by ECH. The heating position is determined by a plasma diagnostic signal related to the electron temperature such as electron cyclotron emission and Thomson scattering.
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Affiliation(s)
- K Okada
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - M Nishiura
- Department of Advanced Energy, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - S Kubo
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - T Shimozuma
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - Y Yoshimura
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - H Igami
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - H Takahashi
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - K Tanaka
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - S Kobayashi
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - S Ito
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - Y Mizuno
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
| | - S Ogasawara
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
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Jawla SK, Shapiro MA, Idei H, Temkin RJ. Corrugated Waveguide Mode Content Analysis Using Irradiance Moments. IEEE TRANSACTIONS ON PLASMA SCIENCE. IEEE NUCLEAR AND PLASMA SCIENCES SOCIETY 2014; 42:3358-3364. [PMID: 25821260 PMCID: PMC4376011 DOI: 10.1109/tps.2014.2349797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present a novel, relatively simple method for determining the mode content of the linearly polarized modes of a corrugated waveguide using the moments of the intensity pattern of the field radiated from the end of the waveguide. This irradiance moment method is based on calculating the low-order irradiance moments, using measured intensity profiles only, of the radiated field from the waveguide aperture. Unlike the phase retrieval method, this method does not use or determine the phase distribution at the waveguide aperture. The new method was benchmarked numerically by comparison with sample mode mixtures. The results predict less than ±0.7% error bar in the retrieval of the mode content. The method was also tested using high-resolution experimental data from beams radiated from 63.5 mm and 19 mm corrugated waveguides at 170 and 250 GHz, respectively. The results showed a very good agreement of the mode content retrieved using the irradiance moment method versus the phase retrieval technique. The irradiance moment method is most suitable for cases where the modal power is primarily in the fundamental HE11 mode, with <8% of the power in high-order modes.
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Affiliation(s)
- Sudheer K. Jawla
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Michael A. Shapiro
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Hiroshi Idei
- Advanced Fusion Research Center, Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
| | - Richard J. Temkin
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
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Kowalski EJ, Shapiro MA, Temkin RJ. Simple Correctors for Elimination of High-Order Modes in Corrugated Waveguide Transmission Lines. IEEE TRANSACTIONS ON PLASMA SCIENCE. IEEE NUCLEAR AND PLASMA SCIENCES SOCIETY 2014; 42:29-37. [PMID: 25067859 PMCID: PMC4109364 DOI: 10.1109/tps.2013.2288493] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
When using overmoded corrugated waveguide transmission lines for high power applications, it is necessary to control the mode content of the system. Ideally, overmoded corrugated transmission lines operate in the fundamental HE11 mode and provide low losses for long distances. Unwanted higher order modes (HOMs), particularly LP11 and HE12, are often excited in the experimental systems due to practical misalignments in the transmission line system. This paper discusses how the unwanted modes propagate along with the fundamental mode in the transmission line system by formulating an equation that relates the center of power offset and angle of propagation of a beam (for the HE11 and LP11 modes) or the waist size and phase front radius of curvature of a beam (for the HE11 and HE12 modes). By introducing two miter bend correctors into the transmission system-miter bends that have slightly angled or ellipsoidal mirrors-the HOMs can be precisely manipulated in the system. This technique can be used to eliminate small quantities of unwanted modes, thereby creating a nearly pure fundamental mode beam with minimal losses. Examples of these applications are calculated and show the theoretical conversion of up to 10% HOM content into the fundamental HE11 mode with minimal losses.
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