Variation of Heating Efficiency of Magnetically Sheared CHS Plasmas by Polarization Control of 106GHz EC-Wave

To clarify the effect of polarization on electron cyclotron heating (ECH) in magnetized plasmas, experiment controlling the polarization of injected EC-waves is carried out in Compact Helical System (CHS). In the experiment, plasmas are generated and sustained only with 106.4 GHz ECH power. Magnetic field at the magnetic axis is 1.9 T so that the wave frequency is second harmonic. The optimum direction of linear polarization for the shortest time-delay of density start-up from the start of power injection and the optimum direction for the highest electron temperature and plasma stored energy during plasma duration show clear difference. The difference is attributed to the CHS magnetic configuration with strong shear and the plasma volume expansion from magnetic axis to the last closed flux surface

The Effect of Non-Axisymmetry of Magnetic Configurations on Radial Electric Field Transition Properties in the LHD

Transition property of the radial electric field (Er) in LHD have been theoretically investigated and also applied to explain experimental results. Especially, effects of the helicity of the magnetic configuration on the condition to realize the electron root are examined. Larger helicity makes the threshold collisionality higher. This is attributed to the nonlinear dependence of Γe(Er) in a low collisional regime. This interesting feature predicts that the threshold temperature becomes higher for a case of smaller helicity. The variation of the threshold density anticipated from the analysis for cases with different magnetic axis position is qualitatively verified in the density scan experiment

Efficient Heating at the Third-Harmonic Electron Cyclotron Resonance in the Large Helical Device

Efficient heating at the third-harmonic electron cyclotron resonance was attained by injection of millimeterwave power with 84 GHz frequency range at the magnetic field strength of 1 T in LHD. The electron temperature at the plasma center clearly increased, and the increment in the temperature reached 0.2-0.3 keV. The dependence of the power absorption rate on the antenna focal position was investigated experimentally, showing that the optimum position was located in the slightly high-field side of the resonance layer. Ray-tracing calculation was performed in the realistic three-dimensional magnetic configuration, and its results are compared with the experimental results

First Observation of ECH by Electron Bernstein Waves Excited via X-B Mode Conversion Process in LHD

In a magnetic field configuration of the Large Helical Device (LHD), when the extraordinary mode (X-mode) waves are obliquely injected from a bottom antenna, it can directly access the upper hybrid resonance (UHR) layer from the high field side and excite electron Bernstein waves (EBWs) without the need for any additional reflecting mirror antenna. A localized power absorption is observed in the low field side of the electron cyclotron resonance (ECR) layer. This result suggests electron cyclotron heating (ECH) by mode converted EBWs excited via X-B mode conversion process

Collective Thomson Scattering Study using Gyrotron in LHD

The collective Thomson scattering (CTS) is one of the most promising methods for evaluating the ion velocity distribution function. The study of CTS diagnostic has been started utilizing the gyrotron and antenna/transmission systems installed in LHD for high power local electron heating. One of the high power gyrotrons at 77 GHz is selected as a probing power source and a set of highly focused antenna system is used for the probing and receiving antenna. The specific feature of the system, receiver design are described and preliminary data obtained in for ECRH plasma in LHD are discussed

Collective Thomson Scattering Study Using Gyrotron in LHD

The collective Thomson scattering (CTS) is one of the most promising methods for evaluating the ion velocity distribution function. The study of CTS diagnostic has been started utilizing the gyrotron and antenna/transmission systems installed in LHD for high power local electron heating. One of the high power gyrotrons at 77 GHz is selected as a probing power source and a set of highly focused antenna system is used for the probing and receiving antenna. The specific feature of the system, receiver design are described and preliminary data obtained in for ECRH plasma in LHD are discussed

Quadratic nonlinear optical properties of the organic N-benzyl-2-methyl-4-nitroaniline (BNA) biaxial crystal

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