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The chemical sputtering yields of CH₄/CD₄ and C₂H_x/C₂D_x have been measured at the divertor plates of JT-60U. Spectroscopic measurements for CH/CD and C₂ spectral bands are applied to estimate the CH₄/CD₄ and the C₂H_x/C₂D_x flux. At the surface temperatures of 380, 440 and 560 K, the CH₄ yield is, respectively, ~0.8%, 1-2% and 2-3%, the C₂H_x yield 1-2%, 3-4% and 4-5%, and the total sputtering yield by hydrogen ions 3-4%, ~8% and ~10%. With increasing ion flux to the divertor plates (Γ_ion), the sputtering yields (Y) decrease, i.e. Y∝Γ_ion^{(-0.05 to -0.40)}. With increasing electron temperature (T_e), the sputtering yields increase, i.e. Y∝T_e^0.5. It is concluded from the result of regression analysis of Y∝T_e^0.5 that the negative dependence of the yields on the ion flux is attributed to the incident ion energies to the carbon plates. The ratio of the sputtering yields by deuterium ions and hydrogen ions is estimated to be ≥1.5 based on the ion flux measurement by H_α/D_α intensity. The C₂H_x/C₂D_x sputtering yield accounts for ~80% of the total number of sputtered carbon atoms.

The many closely crowded lines (pseudo-continuum) of high-Z gold impurities are studied in detail with a calibrated grazing-incidence monochromator in hydrogen plasma, in the upgraded DIVA tokamak device with a divertor; the toroidal field is 20 kG and the peak plasma current is 40 kA. The emission spectrum of the many lines is observed in the wavelength region of 42 to 200 Å. The time-resolved spatial distribution of the emission of the many lines was measured in each element in the wavelength region. It was found that the radiation due to the many lines in the wavelength region of 120 to 200 Å concentrated in an intermediate region of the plasma column, and that the emission of the many lines in the wavelength region of 42-110 Å peaked at the plasma centre. The radiation power loss due to the many lines in the 120-200 Å region was dominant during the whole discharge. The radiation power due to the many lines corresponded to 40-70% of the total radiation power loss from the plasma volume.

ICRF heating experiments were carried out in the JFT-2 tokamak with pure high-field-side excitation. Almost pure electron and ion heating regimes were made possible in the experiment so that the metal impurities were reduced. Power balance of the plasma heated by ICRF is revealed by a transport analysis of the experimental results. RF power deposition profiles of each heating regime are obtained. The results of this analysis may serve as an experimental basis for refining the present theoretical treatment of ICRF heating.

Deuterium and hydrogen energy spectra during ICRF heating as well as nH/nDwere measured with the E||B type mass-separated neutral particle energy analyser. High-energy tails of deuterium and hydrogen were observed in the dilute-minority case. From Fokker-Planck calculations of the charge-exchange spectrum and power-balance analysis it is shown that second-harmonic cyclotron damping by the majority deuterium is the dominant mechanism of ion heating in the dilute-minority case.

ICRF heating of impurity-free tokamak plasmas is studied in DIVA. The frequency is fixed at 25 MHz, which is a second-harmonic cyclotron frequency of deuteron with a toroidal magnetic field of 16.4 kG. The toroidal field BTand the ratio of proton-to-deuteron density pare varied over ranges of 12 ? BT? 19 kG and 2 p40%, respectively. The most favourable ion heating is obtained at BT= 18 kG and p= 5 ~ 10%. Ion temperature increases from 200 to 300 eV were measured by charge-exchange neutral analysis and also by spectroscopy, where 100 kW RF net power were applied. The results are consistent with mode-conversion theory.

Impurities in JT-60 were studied by visible and VUV spectroscopy over two periods of operation. The two periods were distinguished by the use of different first wall materials: from April 1985 to March 1987, TiC coated molybdenum was used as limiter material; from June to October 1987, graphite was used. Quantitative spectroscopic measurements of Zeff, impurity concentrations and radiated power losses were made for ohmically heated and neutral beam heated discharges with limiter and divertor configurations. In the first phase with metallic first wall material, oxygen, carbon and titanium were identified as the main plasma impurities. In neutral beam heated, diverted discharges, Zeffwas 1.6 at e= 4 × 1019m?3. The concentrations of oxygen, carbon and titanium were 1%, 0.1% and 0.006% of ne, respectively. In the second phase with graphite material, the metallic impurities were reduced, and the contribution of metallic impurities to the radiated power loss was less than 1%. However, Zeffincreased up to 3 in neutral beam heated discharges. In limited plasmas, the concentrations of oxygen and carbon were 1% and 5%, respectively, at e= 4 × 1019m?3; in diverted plasmas, these concentrations were 2% and 0.4% at the same e. The radiated power loss from the main plasma was 20-40% of the input power in neutral beam heated, limited discharges, and 7-25% in diverted discharges. The contributions of oxygen and carbon to the radiated power in limited discharges were comparable, and in diverted discharges the contribution of oxygen was dominant.

The active beam scattering method was applied to ion temperature measurements in JT-60 plasmas. The ion temperature found was in reasonable agreement with that obtained from Doppler broadening of the Ti XXI and Ti XXII resonance lines in the temperature range of 1.5 to 10 keV. With the help of the scattering system, the central ion temperature of JT-60 plasmas during 40 keV and 70-75 keV NBI heating was measured. Higher ion temperature was obtained during 70 to 75 keV than during 40 keV NBI heating. These data and a possible explanation are presented. A numerical simulation of this diagnostic indicates that the ion temperature as deduced from the diagnostic is almost equal to the bulk temperature when the ratio of high energy ion component to the total ion stored energy is less than 0.3.

The impurity transport characteristics of ohmically and neutral beam heated diverted plasmas in JT-60 have been studied. In sawtoothfree, ohmically heated plasmas with Ip= 1.5 MA, e= (2?3) × 1019m?3, q(a) = 3.2, no radiation buildup is observed. The temporal evolution of injected titanium has been measured by VUV and X-ray crystal spectrometers and PIN diodes. The spectral lines of Ti XX (259.3 Å) and Ti XXI (2.6097 Å) are compared with one-dimensional diffusive/convective impurity transport calculations. The transport calculations for Ohmic discharges with Ip= 1.5?2 MA, e= (1-3) × 1019m-3, q(a) = 3?3.7, show that DA=(1?2) m2s?1and that the inward convective velocity is small. In neutral beam heated plasmas with Ip= 1.5 MA, e= 4 × 1019m-3, q(a)= 3.6, Pb= 8 MW, no difference is observed in the global time evolution of the Ti XXI line emissions between co- and counter-injected discharges. The experimental observations are well represented by choosing DA= (1-2) m2s?1and a small inward velocity.

Characteristics are presented of the energy confinement time resulting from neutral hydrogen beam heating of JT-60 tokamak plasmas with a plasma current, Ip, of 1-2 MA, a line averaged electron density, e, of 1.5-7 × 1019m?3and an absorbed beam power, Pabs, up to 20 MW. The plasma energy content follows an offset linear relation to the absorbed power. The incremental energy confinement time for thermal components, , is almost independent of Ipand eat 60 ms, while the incremental energy confinement time for the total plasma energy, , decreases with plasma density. The value of in JT-60 coincides with the prediction of the Shimomura-Odajima scaling of L-mode discharges.

Impurity contamination and radiation power have been studied with a vacuum UV monochromator (10-1300 Å) on JFT-2 for typical 160-kA and 18-kG hydrogen discharges. Oxygen has been found to be a dominant impurity element (5-7% of the electron density) and to be radially distributed according to the ionization sequence. The ground level population densities of the O6+and O7+ions in the central hot region have been determined, and that of fully ionized oxygen has been also estimated, combined with enhanced bremsstrahlung radiation measurement. The radial profile of the effective ionic charge Zeffhas been determined from that of the impurity ions. The Zeffvalue has been found to be consistent with the value derived from the electrical conductivity. The total power of line radiation from the first resonance transitions of the oxygen ions amounts to 100-50 kW (34-17% of Joule heating power).

A pulse of methane gas and a short burst of aluminium have been injected into DIVA plasma at the point farthest from the divertor. For the same amount of injected impurity, the accumulation of injected impurity in the main plasma is reduced by a factor of 2 to 4 by the action of the divertor. The impurity shielded by the scrape-off plasma is rapidly guided into the burial chamber. The time needed for the poloidal excursion of the injected impurity ions in the scrape-off layer is roughly equal to that of the scrape-off plasma. Sweeping-out of the impurity ions diffusing from the main plasma into the burial chamber is also observed.

The radiation loss in DIVA is measured quantitatively by a pyroelectric detector calibrated by heavily contaminated resistive discharges. The results are: (1) radiation loss power due to low-Z impurities does not play an important role; (2) radiation loss power due to the pseudo-continuum from high-Z impurities affects the power balance of the confined plasma; (3) the time dependence of energy loss channels is clarified in the gross power balance, a fact which attests to the reliability of the radiation measurements carried out by the pyroelectric detector.

A pulse of methane gas is injected into the DIVA tokamak. The major portion of the injected impurity is shielded by the outer edge plasma, i.e. only 20% of the injected carbon are introduced into the discharge. After radial penetration of the injected carbon has been accomplished, accumulation doubles and a new steady state is sustained over the period of proton confinement. The transient radial diffusion process of the carbon is compared with calculations using an impurity transport code. The behaviour of the carbon impurity in the whole minor radius is well described by assuming perfect re-cycling at the gold-plated shell surface and using neoclassical diffusion superposed by anomalous diffusion of protons. It is shown that spreading caused by anomalous diffusion is important. The calculated result indicates that the carbon ions are lost dominantly in a He-like state.

It is shown that the presence of a clean gold shell surface and titanium gettering of the burial chamber reduce light impurities in the DIVA plasma significantly.Formation and discharge characteristics of the light-impurity free plasma are presented.