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• The new analysis method is proposed in the point of view that the response of a polarizer is represented by rotational operators in the Stokes space. • The response parameters could be determined for individual polarizer by the polarization measurement. • Based on determined response parameters of two polarizers, the output polarizations after the two polarizers were simulated and confirmed to be sufficiently close to the measurement. • Simulation also tells the direction of polarization circularity which could not be directly known from the simplified measurement. For successful tokamak operation with adequate mode selection of the electron cyclotron wave, launching wave polarization should be accurately controlled. In this study, a new method is proposed to efficiently identify the response of polarizers using a geometric approach in the Stokes space, focusing on the fact that polarization can be represented as a vector in Stokes space and the response of a polarizer can be described as a rotation. The proposed methods are intended (i) to determine the response parameters of a polarizer or (ii) to determine the response parameters of two polarizers simultaneously. A simple measurement system was prepared to observe the polarizers' output polarization in the 110/138 GHz transmission line. The determined response parameters of two polarizers can reproduce measured polarizations with sufficient accuracy above 99%. The direction of an output polarization circularity, the only feature of a polarization that could not be directly known from the prepared measurement, could also be determined with sufficient accuracy. [ABSTRACT FROM AUTHOR]

• A transmission efficiency of ECH/CD transmission line for JT-60SA was evaluated. • Transmission efficiencies of ∼70 % and 80–85 % were achieved for ∼100 m transmission. • Measured efficiency of large diameter WG was in good agreement with theory. • Tokamak injection power is expected to be >1.5 MW and >0.8 MW for 110 and 82/138 GHz. An electron cyclotron heating and current drive (ECH/CD) system with two transmission lines (TLs), TL#1 (waveguide inner diameter ⌀=31.75 mm) and TL#2 (⌀=60.3 mm), has been installed and operated on JT-60SA for the integrated commissioning phase. In order to evaluate the transmission efficiency of the TLs, the theoretical loss of each TL component is calculated assuming pure HE 11 mode. In addition, the millimeter wave power at the beginning and end of two TLs was measured experimentally by calorimetric dummy loads (DLs) at high-power of ∼ 400 kW for ∼ 0.3 s. The output power of the gyrotron is estimated by using the measured power at the beginning of each TL with the theoretical loss between the DL and the gyrotron. The injection power to the tokamak from a launcher is also estimated by using the measured power at the end of each TL with the theoretical loss between the DL and the launcher. Using these values, the transmission efficiencies, defined as the ratio of the gyrotron output power to the tokamak injection power, are evaluated for both TLs, which are ∼70% for TL#1 at 110 GHz, and 80 % (82 GHz), 82 % (110 GHz), and 84 % (138 GHz) for TL#2. The total power injected into the tokamak by the combination of TL#1 and TL#2 is expected to be 1.5 MW. It is found that the measured transmission efficiency of TL#2 shows a good agreement with the theory, while the measured transmission efficiency of TL#1 was slightly lower than the theoretical value. To investigate this result, power measurements are also performed at additional locations on the TL#1 with additional DLs. [ABSTRACT FROM AUTHOR]

• High-power test of the waveguide transmission line for the ECH/CD system in JT-60SA. • A transmission line with a pre-load enabled simulation of tokamak experiment without reflection from the dummy load. • The waveguide temperature rise of 120 K for 1 MW/100 s operation at 110 GHz in the worst case. • The head load evaluated as 23 kW/m^2 for 1 MW long-pulse operation in the worst case. Temperature rise of the waveguide transmission line for high-power long-pulse ECH/CD system has been evaluated experimentally using the dummy load transmission line in JT-60SA. It has been demonstrated that the waveguide components with the inner diameter of 60.3 mm are applicable for 1 MW/100 s transmission at 110/138 GHz required in JT-60SA. A newly developed pre-load installed in front of the dummy load reduced the temperature rise of the waveguide due to the reflection from the dummy load. With this pre-load, the temperature rise distribution in the 37 m-long test transmission line was measured to simulate the real transmission line condition for tokamak experiment. As a result of the high-power experiments, it has been clarified that the temperature of the waveguides close to miter-bends could be increased by approximately 120 K for 1 MW/100 s operation at 110 GHz, in the worst case, and it is marginal for the stable operation with the waveguides made of aluminum alloy. The heat loads on the waveguides have been evaluated as 23 kW/m2 for the worst case between miter bends, 12–23 kW/m2 within 4 m from miter bend and 4–12 kW/m2 for waveguide far from miter bends. The evaluated heat loads will be taken into account for the final design of the TL components and cooling for the JT-60SA ECH/CD system. [ABSTRACT FROM AUTHOR]

Abstract: Design study of an ECRF antenna for JT-60SA is being carried out. In JT-60SA, pulse duration of 100s and wide range of poloidal injection angle are required. Reliabilities of a cooling structure and a steering mechanism of mirrors in the JT-60SA vacuum vessel are essential in an environment of high neutron flux. Conceptual design has been performed based on an idea in which poloidal beam injection angle can be altered widely only by a linear motion of a mirror in front of a waveguide. This concept has advantages of decreasing the risk of cooling-water leakage and eliminating a link mechanism in the primary vacuum of JT-60SA. Beam width at various positions in plasma was evaluated by a numerical code. Then dependence of beam width on mirror curvature was investigated, and ranges of the poloidal injection angle and beam width were shown. Moreover, an effect of a modification of the linearly driven mirror from flat mirror to curved mirror was clarified quantitatively. [Copyright &y& Elsevier]

Abstract: Initial testing on the Japan Atomic Energy Agency Gyrotron Test Stand of ITER-relevant TL components, has shown reasonable efficiencies, but identified that trapped modes between closely located miter bends, as well as mode conversion at miter bends can lead to excessive heating of the connecting waveguides. General Atomics has designed, built, and will test components to address this issue as well as ITER relevant components that have not been tested at the levels of 1MW, 170GHz, for extended pulse lengths. Some of the components that will be tested are ultra low loss miter bends, dc breaks, polarizers, power monitors, bellows, waveguide switches, waveguide cooling clamps, etc. Details of the components and test results will be presented. [Copyright &y& Elsevier]

Abstract: Advanced Tokamak research in DIII-D seeks to develop a scientific basis for steady-state high-performance tokamak operation. Fully noninductive (f NI ≈100%) in-principle steady-state discharges have been maintained for several confinement times. These plasmas have weak negative central shear with q min ≈1.5–2, β N ≈3.5, and large, well-aligned bootstrap current. The loop voltage is near zero across the entire profile. The remaining current is provided by neutral beam current drive (NBCD) and electron cyclotron current drive (ECCD). Similar plasmas are stationary with f NI ≈90–95% and duration up to 2s, limited only by hardware. In other experiments, β N ≈4 is maintained for 2s with internal transport barriers, exceeding previously achieved performance under similar conditions. This is allowed by broadened profiles and active magnetohydrodynamic instability control. Modifications now underway on DIII-D are expected to allow extension of these results to higher performance and longer duration. A new pumped divertor will allow density control in high triangularity double-null divertor configurations, facilitating access to similar in-principle steady-state regimes with β N >4. Additional current drive capabilities, both off-axis ECCD and on-axis fast wave current drive (FWCD), will increase the magnitude, duration, and flexibility of externally driven current. [Copyright &y& Elsevier]