Power and polarization monitor development for high power millimeter-wavea) R. Makino, S. Kubo, K. Kobayashi, S. Kobayashi, T. Shimozuma, Y. Yoshimura, H. Igami, H. Takahashi, and T. Mutoh Citation: Review of Scientific Instruments 85, 11D831 (2014); doi: 10.1063/1.4891162 View online: http://dx.doi.org/10.1063/1.4891162 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/85/11?ver=pdfcov Published by the AIP Publishing Articles you may be interested in High power millimeter wave experiment of ITER relevant electron cyclotron heating and current drive system Rev. Sci. Instrum. 82, 063506 (2011); 10.1063/1.3599418 Collective Thomson scattering of a high power electron cyclotron resonance heating beam in LHD (invited)a) Rev. Sci. Instrum. 81, 10D535 (2010); 10.1063/1.3481165 Millimeter-wave reflectometry for electron density profile and fluctuation measurements on NSTX Rev. Sci. Instrum. 72, 348 (2001); 10.1063/1.1329657 A two color millimeter-wave interferometer for the measurement of line integral electron density on large helical device Rev. Sci. Instrum. 70, 695 (1999); 10.1063/1.1149274 Multichannel millimeter wave interferometer for W7-AS Rev. Sci. Instrum. 68, 1162 (1997); 10.1063/1.1147878
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REVIEW OF SCIENTIFIC INSTRUMENTS 85, 11D831 (2014)
Power and polarization monitor development for high power millimeter-wavea) R. Makino,1,b) S. Kubo,1,2 K. Kobayashi,1 S. Kobayashi,2 T. Shimozuma,2 Y. Yoshimura,2 H. Igami,2 H. Takahashi,2 and T. Mutoh2 1 2
Department of Energy Engineering and Science, Nagoya University, Nagoya 464-8603, Japan National Institute for Fusion Science, Toki 509-5292, Japan
(Presented 2 June 2014; received 1 June 2014; accepted 13 July 2014; published online 29 July 2014) A new type monitor of power and polarization states of millimeter-waves has been developed to be installed at a miter-bend, which is a part of transmission lines of millimeter-waves, for electron cyclotron resonance heating on the Large Helical Device. The monitor measures amplitudes and phase difference of the electric field of the two orthogonal polarizations which are needed for calculation of the power and polarization states of waves. The power and phase differences of two orthogonal polarizations were successfully detected simultaneously. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4891162] I. INTRODUCTION
Millimeter-waves are used for electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) on magnetic confinement fusion devices. High power millimeter-waves are generated by gyrotron and transmitted to the main body of the magnetic confinement fusion devices through the ECRH transmission lines. The ECRH systems of Large Helical Device (LHD) have gyrotron systems with the output power of more than 1 MW. Polarization states of millimeter-waves significantly affect the mode excitation purity, and therefore the trajectory of millimeter-waves and the power absorption in plasmas.1 The coupling rate to ordinary mode (O-mode) and extraordinary mode (X-mode) depends on the polarization states of waves in relation to the directions of the magnetic field and the wave propagation vector near the last closed flux surface.2 Measurements of the power and polarization states of high power millimeter-waves are important to optimize ECRH and ECCD. Two grating mirror polarizers (the depth of λ/4 and λ/8) set at miter-bends can generate arbitrary polarization states of millimeter-waves3 in the ECRH transmission system on LHD. Polarization states of waves are estimated only from calculation with ideal model of grating mirror polarizers, miterbends, and corrugated waveguides because ECRH transmission system has no direct polarization measuring system so far. Each transmission line is over 100 m and has more than 10 miter-bends, which bend the wave direction by 90◦ . Since the calculation of polarization states is complicated in such transmission line, the power and polarization monitor is required for optimization and reliable operation of ECRH. A new type of monitor of power and polarization states in the transmission line has been developed to be installed on a miter-bend on LHD. a) Contributed paper, published as part of the Proceedings of the 20th
Topical Conference on High-Temperature Plasma Diagnostics, Atlanta, Georgia, USA, June 2014. b) Email: [email protected] 0034-6748/2014/85(11)/11D831/3/$30.00
Power and polarization monitors of several types have been designed.4–6 This paper reports a new type of monitor on LHD. II. POWER/POLARIZATION MONITOR
The electric field of the electromagnetic waves can be written by the two orthogonal electric fields as follows: Ex = Ex0 cos(ωt),
(1)
Ey = Ey0 cos(ωt + φ),
(2)
where Ex0 and Ey0 are amplitudes of two orthogonal polarizations and ϕ is a phase difference between Ex and Ey . The polarization states can be expressed by the polarization angle α and the ellipticity β, as shown in Fig. 1. The sign of β indicates the direction of rotation of the electric field. The polarization angle α, the ellipticity β, and the power Pin of injected millimeter-waves can be written as follows:7 E tan−1 tan 2 tan−1 Ey0 cos ϕ x0 , (3) α= 2 E sin−1 sin 2 tan−1 Ey0 sin ϕ x0 , (4) β= 2 Pin = C Ex2 + Ey2 . (5) Power and polarization states can be evaluated from amplitudes and a phase difference of the electric field of two orthogonal polarizations simultaneously. Figure 2 shows a diagram of the power and polarization monitor. The power and polarization monitor is composed of bi-linear polarization directional coupler and heterodyne interferometer. The bi-linear polarization directional coupler is composed of square waveguide in a miter-bend with a row of coupling holes to pick-up both orthogonal polarizations simultaneously injected to the miter-bend. Only TE01 and
85, 11D831-1
© 2014 AIP Publishing LLC
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11D831-2
Makino et al.
Rev. Sci. Instrum. 85, 11D831 (2014)
Monitor
Heating Equipment Room 3 - 77GHz 1 - 154GHz 1 MW, 5 s 1 MW, 5 s
LHD Hall
1 - 84GHz 200kW,CW
3-88.9mm non-evacuated waveguides
FIG. 1. Definitions of the polarization angle α, the ellipticity β. 2- 31.75mm evacuated waveguides
FIG. 4. Temporal evolution of (a) the power of millimeter-waves as setting of a gyrotron, (b) amplitudes, and (c) phase difference of phase difference of the electric field of two orthogonal polarizations. (d) Frequency response of amplitudes of electric field of two orthogonal polarizations.
Frequency [MHz]
300
RF
Miterbend
Orthomode transducer
280
0.8
260
0.6
240
0.4
220
0.2
VCO
300
3 (b)
5 4 Time [sec]
6
2 1
260
0 240
-1
220 LO
IF ~400MHz Harmonic mixer
Amp
Fast ADC with FPGA (800MSPS)
FIG. 2. Diagram of a power and polarization monitor for millimeter-waves.
0 3
280 Frequency [MHz]
Amp
1.0
200
-2
3
5 4 Time [sec]
6
Phase Difference [rad.]
Harmonic IF mixer LO Bi-linear polarization directional coupler RF
Millimeterwaves 77GHz
(a)
200
~400MHz
1 - 82.7 GHz 450kW,2s
FIG. 3. Schematic view of ECRH systems on LHD. Power and polarization 1 , 2 for performance tests. Installation points monitor was set on positions 1 and 2 . of the monitor are indicated by
III. EXPERIMENTS
Performance tests of the power and polarization monitor were carried out by installing the monitor at a miter-bend
Monitor
3-88.9mm evacuated waveguides
Amplitude [a.u.]
TE10 mode waves can pass through the sub-waveguide.8 The millimeter-waves are separated to two orthogonal polarizations by an orthomode transducer. Both polarization components are down converted to a few hundreds MHz intermediate frequency (IF) by utilizing harmonic mixers and voltage controlled oscillator (VCO) as a local oscillator. The IF signals of the two orthogonal polarizations are acquired directly by a fast ADC using FPGA (Field Programmable Gate Array), with sampling rate of 800 MHz. Amplitudes and phase difference of the electric field of two orthogonal polarizations can be obtained by fast Fourier transforming (FFT) the data acquired by the fast ADC. Time resolution of measurements of amplitudes and phase difference is limited by the data transfer speed from ADC to PC. So far, 4096 data points were transferred and applied FFT every 15 ms. Power spectrum is calculated by FFT with hanning window. The typical amplitude is estimated by taking square root of integration of power spectrum in frequency near the peak. The phase difference is obtained at the frequency of peak of power spectrum. The number of IF devices can be eliminated and simplified by using fast ADC with FPGA. It reduces adjustments of the devices and increases reliability, and therefore suitable for practical use. Setting ADC and data transfer is controlled by FPGA, and the analysis by FPGA is also possible. The time resolution of measurements of the power and polarization monitor is 15 ms and can be improved by optimization of FPGA programming. Furthermore, using FPGA allows the feedback control of the polarization states of millimeterwaves for ECRH in the future. The sensitivity can be adjusted by changing the gain of amplifier of the monitor and the size of coupling holes at the miter-bend mirror. The applicable condition of the monitor can be adjusted by changing the coupling coefficient of the pick-up holes in the coupler and the sensitivity of the detection system. The sensitivity for this particular test set was adjusted to be able to measure the level of more than 100 kW millimeter-waves in the LHD transmission line.
-3
FIG. 5. Temporal evolution of spectra of (a) amplitude and (b) phase difference of the electric field of two orthogonal polarizations measured by the power and polarization monitor.
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11D831-3
Makino et al.
Rev. Sci. Instrum. 85, 11D831 (2014)
FIG. 6. β dependences of (a) amplitudes and (d) phase difference of the electric field of two orthogonal polarizations at α ∼ 0◦ . β dependences of (b) amplitudes and (e) phase difference at α ∼ 15◦ . α dependences of (c) amplitudes at β ∼ 0◦ . Markers and lines show experimental values and theoretical values, respectively.
in 77 GHz ECRH transmission line. Figure 3 shows ECRH systems on LHD, and installation points of the monitor are 1 and 2 . Millimeter-waves from a gyrotron are indicated by transformed to HE11 mode by matching optics unit (MOU), and propagate in the oversized corrugated waveguides with the diameter of 88.9 mm. 1 of Fig. 3. First, the monitor installed at a position 759 kW 77 GHz millimeter-waves were injected in the ECRH transmission line. Figure 4(a) shows the temporal evolution of the power of millimeter-waves expected from applied gyrotron high voltage. Figure 4(d) shows frequency responses to normalized amplitudes of the electric field of two orthogonal polarizations. IF signals of two orthogonal polarizations, which have a specific frequency less than 400 MHz, were detected by fast ADC with FPGA. Figure 5 shows the temporal evolution of frequency responses of the amplitude and phase difference measured by the power and polarization monitor. The gyrotron frequency shifts 50 MHz during initial 700 ms due to the thermal expansion of the gyrotron cavity. Even with this frequency shift, the phase difference between bi-linear polarization is kept constant. The typical amplitudes of IF signals were calculated by the square root of integration of power spectrum in the frequency space near the peak of the power spectrum. The phase difference can be obtained at the frequency of the peak of the power spectrum. Figures 4(b) and 4(c) show the temporal evolution of the typical amplitudes and phase difference of the electric field of two orthogonal polarizations. The amplitudes and phase difference were approximately constant during millimeter-wave injection. Polarization scan experiments were also performed. The power and polarization monitor was set at a miter-bend near 2 . the injection antenna of LHD, as shown in Fig. 3 point 210 kW 77 GHz millimeter-wave is transmitted through rotatable grating polarizers to change polarization states. The polarization angle α and ellipticity β were changed. The amplitudes and phase difference were measured by the power and polarization monitor. Figure 6 shows polarization dependences of the amplitudes and phase difference. The measured values are approximately consistent with theoretical values.
The power and phase differences of two orthogonal polarizations, which are needed for the calculation of polarization states, were successfully detected simultaneously. In order to measure the absolute value of power and polarization of waves, calibration of amplitudes and offset of phase caused by the pick-up and detection components are needed to get the information of the polarization states. IV. SUMMARY
The power/polarization monitor has been developed for ECRH on LHD. The monitor is composed of bi-linear directional coupler with an array of coupling holes, heterodyne interferometer, and fast ADC with FPGA. The performances test was carried out on a LHD-ECRH transmission line. The time resolution of measurements of the power and polarization monitor is 15 ms, which is now limited by a data transfer rate from FPGA to PC. IF signals, which have specific frequency less than 400 MHz, were directly acquired by the fast ADC. The power and phase differences of two orthogonal polarizations, which are needed for calculation of polarization states, were successfully detected simultaneously. ACKNOWLEDGMENTS
The authors would like to thank staffs of ECRH group of the LHD team for discussions and performing experiments. This work was supported by NIFS under ULRR701, ULRR804, KEKO00, and JSPS KAKENHI Grant No. 21360455. 1 T.
Stix, Waves in Plasmas (Springer, New York, 1992). Prater, Phys. Plasmas 11, 2349 (2004). 3 J. L. Doane, Int. J. Infrared Millimeter Waves 13(11), 1727 (1992). 4 T. Shimozuma et al., J. Microwave Power Electromagn. Energy 43, 1 (2009). 5 T. Notake et al., Rev. Sci. Instrum. 76, 023504 (2005). 6 F. Felici et al., Rev. Sci. Instrum. 80, 013504 (2009). 7 M. Born and E. Eolf, Principles of Optics (Pergamon, New York, 1974), p. 25. 8 R. Makino et al., Plasma Fusion Res. 9, 3405024 (2014). 2 R.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.220.8.15 On: Thu, 08 Jan 2015 11:00:51
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.220.8.15 On: Thu, 08 Jan 2015 11:00:51
REVIEW OF SCIENTIFIC INSTRUMENTS 85, 11D831 (2014)
Power and polarization monitor development for high power millimeter-wavea) R. Makino,1,b) S. Kubo,1,2 K. Kobayashi,1 S. Kobayashi,2 T. Shimozuma,2 Y. Yoshimura,2 H. Igami,2 H. Takahashi,2 and T. Mutoh2 1 2
Department of Energy Engineering and Science, Nagoya University, Nagoya 464-8603, Japan National Institute for Fusion Science, Toki 509-5292, Japan
(Presented 2 June 2014; received 1 June 2014; accepted 13 July 2014; published online 29 July 2014) A new type monitor of power and polarization states of millimeter-waves has been developed to be installed at a miter-bend, which is a part of transmission lines of millimeter-waves, for electron cyclotron resonance heating on the Large Helical Device. The monitor measures amplitudes and phase difference of the electric field of the two orthogonal polarizations which are needed for calculation of the power and polarization states of waves. The power and phase differences of two orthogonal polarizations were successfully detected simultaneously. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4891162] I. INTRODUCTION
Millimeter-waves are used for electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) on magnetic confinement fusion devices. High power millimeter-waves are generated by gyrotron and transmitted to the main body of the magnetic confinement fusion devices through the ECRH transmission lines. The ECRH systems of Large Helical Device (LHD) have gyrotron systems with the output power of more than 1 MW. Polarization states of millimeter-waves significantly affect the mode excitation purity, and therefore the trajectory of millimeter-waves and the power absorption in plasmas.1 The coupling rate to ordinary mode (O-mode) and extraordinary mode (X-mode) depends on the polarization states of waves in relation to the directions of the magnetic field and the wave propagation vector near the last closed flux surface.2 Measurements of the power and polarization states of high power millimeter-waves are important to optimize ECRH and ECCD. Two grating mirror polarizers (the depth of λ/4 and λ/8) set at miter-bends can generate arbitrary polarization states of millimeter-waves3 in the ECRH transmission system on LHD. Polarization states of waves are estimated only from calculation with ideal model of grating mirror polarizers, miterbends, and corrugated waveguides because ECRH transmission system has no direct polarization measuring system so far. Each transmission line is over 100 m and has more than 10 miter-bends, which bend the wave direction by 90◦ . Since the calculation of polarization states is complicated in such transmission line, the power and polarization monitor is required for optimization and reliable operation of ECRH. A new type of monitor of power and polarization states in the transmission line has been developed to be installed on a miter-bend on LHD. a) Contributed paper, published as part of the Proceedings of the 20th
Topical Conference on High-Temperature Plasma Diagnostics, Atlanta, Georgia, USA, June 2014. b) Email: [email protected] 0034-6748/2014/85(11)/11D831/3/$30.00
Power and polarization monitors of several types have been designed.4–6 This paper reports a new type of monitor on LHD. II. POWER/POLARIZATION MONITOR
The electric field of the electromagnetic waves can be written by the two orthogonal electric fields as follows: Ex = Ex0 cos(ωt),
(1)
Ey = Ey0 cos(ωt + φ),
(2)
where Ex0 and Ey0 are amplitudes of two orthogonal polarizations and ϕ is a phase difference between Ex and Ey . The polarization states can be expressed by the polarization angle α and the ellipticity β, as shown in Fig. 1. The sign of β indicates the direction of rotation of the electric field. The polarization angle α, the ellipticity β, and the power Pin of injected millimeter-waves can be written as follows:7 E tan−1 tan 2 tan−1 Ey0 cos ϕ x0 , (3) α= 2 E sin−1 sin 2 tan−1 Ey0 sin ϕ x0 , (4) β= 2 Pin = C Ex2 + Ey2 . (5) Power and polarization states can be evaluated from amplitudes and a phase difference of the electric field of two orthogonal polarizations simultaneously. Figure 2 shows a diagram of the power and polarization monitor. The power and polarization monitor is composed of bi-linear polarization directional coupler and heterodyne interferometer. The bi-linear polarization directional coupler is composed of square waveguide in a miter-bend with a row of coupling holes to pick-up both orthogonal polarizations simultaneously injected to the miter-bend. Only TE01 and
85, 11D831-1
© 2014 AIP Publishing LLC
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.220.8.15 On: Thu, 08 Jan 2015 11:00:51
11D831-2
Makino et al.
Rev. Sci. Instrum. 85, 11D831 (2014)
Monitor
Heating Equipment Room 3 - 77GHz 1 - 154GHz 1 MW, 5 s 1 MW, 5 s
LHD Hall
1 - 84GHz 200kW,CW
3-88.9mm non-evacuated waveguides
FIG. 1. Definitions of the polarization angle α, the ellipticity β. 2- 31.75mm evacuated waveguides
FIG. 4. Temporal evolution of (a) the power of millimeter-waves as setting of a gyrotron, (b) amplitudes, and (c) phase difference of phase difference of the electric field of two orthogonal polarizations. (d) Frequency response of amplitudes of electric field of two orthogonal polarizations.
Frequency [MHz]
300
RF
Miterbend
Orthomode transducer
280
0.8
260
0.6
240
0.4
220
0.2
VCO
300
3 (b)
5 4 Time [sec]
6
2 1
260
0 240
-1
220 LO
IF ~400MHz Harmonic mixer
Amp
Fast ADC with FPGA (800MSPS)
FIG. 2. Diagram of a power and polarization monitor for millimeter-waves.
0 3
280 Frequency [MHz]
Amp
1.0
200
-2
3
5 4 Time [sec]
6
Phase Difference [rad.]
Harmonic IF mixer LO Bi-linear polarization directional coupler RF
Millimeterwaves 77GHz
(a)
200
~400MHz
1 - 82.7 GHz 450kW,2s
FIG. 3. Schematic view of ECRH systems on LHD. Power and polarization 1 , 2 for performance tests. Installation points monitor was set on positions 1 and 2 . of the monitor are indicated by
III. EXPERIMENTS
Performance tests of the power and polarization monitor were carried out by installing the monitor at a miter-bend
Monitor
3-88.9mm evacuated waveguides
Amplitude [a.u.]
TE10 mode waves can pass through the sub-waveguide.8 The millimeter-waves are separated to two orthogonal polarizations by an orthomode transducer. Both polarization components are down converted to a few hundreds MHz intermediate frequency (IF) by utilizing harmonic mixers and voltage controlled oscillator (VCO) as a local oscillator. The IF signals of the two orthogonal polarizations are acquired directly by a fast ADC using FPGA (Field Programmable Gate Array), with sampling rate of 800 MHz. Amplitudes and phase difference of the electric field of two orthogonal polarizations can be obtained by fast Fourier transforming (FFT) the data acquired by the fast ADC. Time resolution of measurements of amplitudes and phase difference is limited by the data transfer speed from ADC to PC. So far, 4096 data points were transferred and applied FFT every 15 ms. Power spectrum is calculated by FFT with hanning window. The typical amplitude is estimated by taking square root of integration of power spectrum in frequency near the peak. The phase difference is obtained at the frequency of peak of power spectrum. The number of IF devices can be eliminated and simplified by using fast ADC with FPGA. It reduces adjustments of the devices and increases reliability, and therefore suitable for practical use. Setting ADC and data transfer is controlled by FPGA, and the analysis by FPGA is also possible. The time resolution of measurements of the power and polarization monitor is 15 ms and can be improved by optimization of FPGA programming. Furthermore, using FPGA allows the feedback control of the polarization states of millimeterwaves for ECRH in the future. The sensitivity can be adjusted by changing the gain of amplifier of the monitor and the size of coupling holes at the miter-bend mirror. The applicable condition of the monitor can be adjusted by changing the coupling coefficient of the pick-up holes in the coupler and the sensitivity of the detection system. The sensitivity for this particular test set was adjusted to be able to measure the level of more than 100 kW millimeter-waves in the LHD transmission line.
-3
FIG. 5. Temporal evolution of spectra of (a) amplitude and (b) phase difference of the electric field of two orthogonal polarizations measured by the power and polarization monitor.
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11D831-3
Makino et al.
Rev. Sci. Instrum. 85, 11D831 (2014)
FIG. 6. β dependences of (a) amplitudes and (d) phase difference of the electric field of two orthogonal polarizations at α ∼ 0◦ . β dependences of (b) amplitudes and (e) phase difference at α ∼ 15◦ . α dependences of (c) amplitudes at β ∼ 0◦ . Markers and lines show experimental values and theoretical values, respectively.
in 77 GHz ECRH transmission line. Figure 3 shows ECRH systems on LHD, and installation points of the monitor are 1 and 2 . Millimeter-waves from a gyrotron are indicated by transformed to HE11 mode by matching optics unit (MOU), and propagate in the oversized corrugated waveguides with the diameter of 88.9 mm. 1 of Fig. 3. First, the monitor installed at a position 759 kW 77 GHz millimeter-waves were injected in the ECRH transmission line. Figure 4(a) shows the temporal evolution of the power of millimeter-waves expected from applied gyrotron high voltage. Figure 4(d) shows frequency responses to normalized amplitudes of the electric field of two orthogonal polarizations. IF signals of two orthogonal polarizations, which have a specific frequency less than 400 MHz, were detected by fast ADC with FPGA. Figure 5 shows the temporal evolution of frequency responses of the amplitude and phase difference measured by the power and polarization monitor. The gyrotron frequency shifts 50 MHz during initial 700 ms due to the thermal expansion of the gyrotron cavity. Even with this frequency shift, the phase difference between bi-linear polarization is kept constant. The typical amplitudes of IF signals were calculated by the square root of integration of power spectrum in the frequency space near the peak of the power spectrum. The phase difference can be obtained at the frequency of the peak of the power spectrum. Figures 4(b) and 4(c) show the temporal evolution of the typical amplitudes and phase difference of the electric field of two orthogonal polarizations. The amplitudes and phase difference were approximately constant during millimeter-wave injection. Polarization scan experiments were also performed. The power and polarization monitor was set at a miter-bend near 2 . the injection antenna of LHD, as shown in Fig. 3 point 210 kW 77 GHz millimeter-wave is transmitted through rotatable grating polarizers to change polarization states. The polarization angle α and ellipticity β were changed. The amplitudes and phase difference were measured by the power and polarization monitor. Figure 6 shows polarization dependences of the amplitudes and phase difference. The measured values are approximately consistent with theoretical values.
The power and phase differences of two orthogonal polarizations, which are needed for the calculation of polarization states, were successfully detected simultaneously. In order to measure the absolute value of power and polarization of waves, calibration of amplitudes and offset of phase caused by the pick-up and detection components are needed to get the information of the polarization states. IV. SUMMARY
The power/polarization monitor has been developed for ECRH on LHD. The monitor is composed of bi-linear directional coupler with an array of coupling holes, heterodyne interferometer, and fast ADC with FPGA. The performances test was carried out on a LHD-ECRH transmission line. The time resolution of measurements of the power and polarization monitor is 15 ms, which is now limited by a data transfer rate from FPGA to PC. IF signals, which have specific frequency less than 400 MHz, were directly acquired by the fast ADC. The power and phase differences of two orthogonal polarizations, which are needed for calculation of polarization states, were successfully detected simultaneously. ACKNOWLEDGMENTS
The authors would like to thank staffs of ECRH group of the LHD team for discussions and performing experiments. This work was supported by NIFS under ULRR701, ULRR804, KEKO00, and JSPS KAKENHI Grant No. 21360455. 1 T.
Stix, Waves in Plasmas (Springer, New York, 1992). Prater, Phys. Plasmas 11, 2349 (2004). 3 J. L. Doane, Int. J. Infrared Millimeter Waves 13(11), 1727 (1992). 4 T. Shimozuma et al., J. Microwave Power Electromagn. Energy 43, 1 (2009). 5 T. Notake et al., Rev. Sci. Instrum. 76, 023504 (2005). 6 F. Felici et al., Rev. Sci. Instrum. 80, 013504 (2009). 7 M. Born and E. Eolf, Principles of Optics (Pergamon, New York, 1974), p. 25. 8 R. Makino et al., Plasma Fusion Res. 9, 3405024 (2014). 2 R.
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