Hidetoshi Suemitsu

Spectroscopic determination of hydrogen and electron densities in plasma in the ionizing phase: Application to WT-III

The Balmer line intensities of atomic hydrogen from the WT-III tokamak plasma have been observed and interpreted in terms of the collisional-radiative model. The atomic and molecular hydrogen densities are deduced together with the electron density. Going from the plasma centre to the edge region along the minor radius, the atomic hydrogen density increases slightly and molecular hydrogen is found only in the periphery. In the edge region, the atomic hydrogen density reaches 1 × 1016 m−3 and the molecular hydrogen density 4 × 10l7 m−3. The electron density distribution is consistent with that determined by infrared laser interferometry.

In situ sensitivity calibration of an XUV spectrometer for plasma spectroscopy: Branching ratio method and collisional‐radiative model

We have observed spectra of lithium‐like oxygen and carbon ions from the WT‐3 tokamak plasma with an XUV spectrometer. On the basis of the branching ratios to visible UV spectral lines and the collisional‐radiative model calculation for excited level populations, we have determined the absolute sensitivity of the spectrometer from 11.5 through 31.2 nm. From the line intensities emitted from the scrape‐off layer plasma, we have estimated the charge exchange recombination rate coefficients of helium‐like oxygen ions colliding with neutral hydrogen atoms or molecules.

Processes of multiphoton ionization of Cs2 in the wavelength range 620-670 nm

The relative production rates of Cs 2 + ions produced through two-photon ionization of cesium dimers Cs 2 were measured in the wavelength range 620–670 nm. The calculated production rates of Cs 2 + ions produced via the intermediate state C 1 Π u from X 1 Σ g + agreed fairly well with the experimental results. The production rates via the intermediate state 1 Σ u + , which is close to C 1 Π u , were calculated. The calculated results, however, showed the completely different function of wavelength from that of the experimental results. Thus we concluded that C s 2 + ions are mainly produced by the processes via the intermediate state C 1 Π u . It was made clear that most of the cesium dimers Cs 2 excited in the super excited states Cs 2 ** by absorption of two photons are autoionized to produce Cs 2 + ions.

Two-Photon Ionization of Cs2 in the Wavelength Range 5300-6200 Å

The relative cross sections of the production of Cs + and Cs 2 + ions through the two-photon ionization of Cs 2 were measured in the 5300-6200 A wavelength range. A linear polarized dye laser was operated in the CW mode as a light source. The results showed that (1) the cross sections for Cs + ions have a broad peak at around 5570 A and the threshold at around 6010 A, and (2) those for Cs 2 + ions have the largest peak at around 5940 A and many structures in the wavelength range longer than it. Through consideration of the above results, we suggested that Cs + ions are produced not only by two-photon ionization of Cs 2 , but also by a participation of a third photon. The threshold for Cs + ions at around 6010 A is concerned with the intermediate excited-state Cs 2 (C 1 ∏ u + (ν ′ )), which can be excited from the ground state X 1 Σ g + (ν ′′ =0).

Vacuum Ultraviolet Emissions from Linear Pinch Rare Gas Plasmas and Their Applications as a Light Source

The vacuum ultraviolet emissions from rare gas plasmas in a Z-pinch tube have been measured with a Seya-Namioka Spectrograph between 1000 and 500 A and with a grazing incidence spectrograph between 500 and 100 A. In the former region, besides the photographic observations of O2 and N2 absorptions, the photoelectric measurements have been made on the absorpption of Ar window-type resonance series as well as on the emission spectra of Ar, Kr and Xe plasmas by a repetitive operation of the Z-pinch tube. In the latter region only the photographic observations have been made and it has been found that He pinch plasma gives rise to strong HeII continuum, which enables us to observe HeI absorption due to double excitation, and that Ne pinch plasma emits NeII continuum between 320 and 150 A or NeIII continuum between 200 and 100 A depending on the filling gas pressure in the tube.

Nonlinear ion Bernstein wave heating experiment in the WT-3 tokamak

Ion Bernstein wave (IBW) heating at ion cyclotron half-harmonic frequencies was performed in hydrogen (H) discharges in the WT-3 tokamak. The bulk ion temperature increase was measured by a charge exchange analyser and a spatially scanning polychrometer. The latter diagnostics can provide radial ion-temperature profiles. The incremental ion temperature has shown a peak at the exact location where the IBW frequency omega equals 3/2 of the ion cyclotron frequency, indicating the nonlinear direct acceleration of H ions. The wave electric field was measured by a Langmuir probe in the scrape-off layer. The electric field at the second harmonic of the excited IBW frequency was observed to vary depending on the power level and the toroidal magnetic field. These experimental results are compared with the theoretical prediction of nonlinear IBW damping. The measured dependences of the ion heating and the wave amplitude at 2 omega on the toroidal magnetic field are in reasonable agreement with the prediction.

Multiphoton ionization of RbCs in the wavelength range 540-620 nm

The relative cross sections for the production of Cs + , RbCs + and Rb + ions through the multiphoton ionization of RbCs are measured in the wavelength range 540-620 nm. It is made clear that (1) Cs + and RbCs + ions are produced by the two-photon ionization of RbCs. It is suggested that (2) the peak of the cross section for Cs + ions at 565 nm corresponds well to the dissociation limit of the ground state 2 Σ + of RbCs + , (3) the thresholds of the cross sections for Cs + and Rb + ions at around 597 nm is quite different from the value obtained so far, as the electronic energy T e of an intermediate state 1 ∏ of RbCs, and (4) the super excited states of the RbCs molecules play an important role for the production of Rb + ions in the wavelength range 579-596 nm and RbCs + ions in the wavelength region longer than 565 nm.

Radial distribution of ion temperature in a WT-III tokamak plasma, as determined from Abel inversion of impurity line profiles

Abstract By using a spectrometer fitted with a multichannel detector, we have observed a chord dependence of emission-line profiles of OV and CV impurities in a WT-III tokamak plasma in a Joule-heating mode. After Abel-inversion of the observed intensity for each channel of the detector, we obtained a Doppler-line profile as a function of radius. Ion temperatures derived from the two lines agree with each other and are consistent with the energy distribution of neutral particles emanating from the plasma.

Non-Thermal Radiation at Runaway Electron Instability

Non-thermal microwave radiation from a tokamak NOVA \(\varPi\) operated in a runaway mode exhibited two distinct time behaviors at X-band synchronized with the positive spikes in loop voltage, depending on the vertical magnetic field. One can be explained by synchrotron radiation through the pitch angle scattering of the runaways. The other is closely related with the ratio ω c e /ω p e .

Multiphoton Ionization of K2 in the Wavelength Range 600–670 nm

The relative production rates of K + and K 2 + ions through the multiphoton ionization of K 2 are measured in the wavelength range 600–670 nm. These rates for K 2 + ions have a threshold at about 600 nm and a broad peak at about 620 nm. These for K + ions have the threshold at about 612 nm and the position of the peak is roughly equal to that of K 2 + ion. The effective order of nonlinearity k , which is the minimum number of photons necessary to ionize the K 2 molecule, is measured as a function of the wavelength. k for K + ions is about 3 in 613–650 nm, except for that at 634 nm, at which k is about 2.3. On the other hand, k for K 2 + is about 2 in the wavelength range shorter than 611 nm and two values of k in 632–637 nm are about 1.6. Beyond 637 nm, k increases with an increase of wavelength and reaches about 2.6 at 650 nm. From these results, the production processes of K + and K 2 + ions are discussed.