Development of a compact thermal lithium atom beam source for measurements of electron velocity distribution function anisotropy in electron cyclotron resonance plasmas.

The anisotropy of the electron velocity distribution function (EVDF) in plasmas can be deduced from the polarization of emissions induced by anisotropic electron-impact excitation. In this paper, we develop a compact thermal lithium atom beam source for spatially resolved measurements of the EVDF anisotropy in electron cyclotron resonance (ECR) plasmas. The beam system is designed such that the ejected beam has a slab shape, and the beam direction is variable. The divergence and flux of the beam are evaluated by experiments and calculations. The developed beam system is installed in an ECR plasma device with a cusp magnetic field, and the LiI 2s-2p emission (670.8 nm) is observed in low-pressure helium plasma. The two-dimensional distributions of the degree and direction of the polarization in the LiI emission are measured by a polarization imaging system. The evaluated polarization distribution suggests the spatial variation of the EVDF anisotropy.

In situ spectral calibration method for the impurity influx monitor (divertor) for ITER using angled physical contact fibers.

The in situ calibration method for the impurity influx monitor (divertor) is experimentally examined. The total reflectance of the optical path from the focal point of the Cassegrain telescope to the first mirror is derived using a micro retroreflector array. An optical fiber with angled physical contact (APC) connectors reduces the return edge reflection. APC fibers and a multimode coupler increase the signal-to-noise ratio by about one order compared to that of triple-branched fibers and enable measurement of the wavelength dependence of the total reflectance of the optical system even after potential deterioration of mirror surfaces reduces reflectance.

Development of multiwavelength-range fine-resolution spectrometer for hydrogen emissions and its application to large helical device periphery plasmas.

We developed a spectrometer specialized for simultaneous observation of the hydrogen Balmer-alpha, -beta, -gamma lines and the Fulcher-alpha v(')=v(")=2 rovibronic transition band. The spectrometer was optimized for the light input coupled by nine optical fibers having 400 microm core diameters. The spectral resolutions were 0.02-0.03 nm for these wavelength ranges at the entrance slit width of 20 microm. The polarization resolved spectra of these emissions from the peripheral region of large helical device (LHD) plasmas were measured simultaneously and showed the polarization dependence coming from the magnetic field in the LHD plasma.