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Measurements of spectra in the wavelength range from vacuum ultraviolet (VUV) to soft X-ray are important means to diagnose impurities in magnetically confined plasmas used in fusion plasmas such a...

After the last Novosibirsk Conference (1998), GAMMA 10 experiments have advanced in long sustainment of confining potential and higher density experiments. An experiment which attained doubling of ...

In the GAMMA10 tandem mirror, the first pellet injection experiments in open systems have started.1 The tandem mirror machine is suitable for measuring propagation of pellet-fueled particles along ...

This paper describes characteristics of end loss electrons (ELE's) from a tandem mirror. Without electron cyclotron resonance heating (plug ECRH), ELE's issue from an ICRF heated hot ion plasma Their temperature increases with the hot ion diamagnetism. Drag heating of electrons on hot ions balances with axial loss due to Coulomb scattering. Landau damping of an Alfven ion cyclotron wave is also observed in this phase. On application of the plug ECRH, an intense loss flux of warm electrons is generated. The axial heat flow carried by the warm electrons significantly increases. Control of the axial flux of the warm electrons is tried A highly transparentmesh is put up over an end plate and a bias voltage negative to the end plate is applied to the mesh. Then secondary electrons emitted from the end plate are suppressed and the loss flux of the warm electrons decreases to about one third of that without the mesh bias. This reduction factor is much smaller than the value expected from the rate of ion plugging. A possible cause of this is an ion current through a plasma behind the end plate.

Potential confinement of an ICRF-heated high-ion temperature plasma in GAMMA 10 is experimentally studied. The potential confinement was shown from data of one-end plugging and both-end plugging. The waveform of end loss current and an analysis of end loss ion energies have also indicated potential formation and confinement. The central cell line density increases 50% by the potential confinement. Some radial losses were observed in the anchor andlor plug/barrier regions and a rate of the radial loss was measured by using the data from one-end plugging. Under an experimental condition, the radial loss rate was estimated to be about 3%. In order to reduce the radial loss, conducting plates were installed adjacent to the plasma in the anchor transition region. The density increase of 60 % was attained after installation of the conducting plates and a higher density increase can be expected in the near future. The density increase was 50% before installation of the conducting plates. Controllability and reproducibility of the potential confinement are also improved after installation of the conducting plates.

Gentle hump structure on energy spectra of end-loss ions was observed in the RF driven tandem mirror plasma by use of an end-loss energy component analyzer (ELECA), which has been developed in order to directly measure velocity distribution functions of the end-loss ions. 1 Ions are heated anisotropically in the central cell of the tandem mirror by the ICRF wave injection, and Alfven ion-cyclotron (AIC) fluctuations are excited due to the anisotropic ion temperature. 2 The correlation between the hump structure and the excitation of the AIC fluctuations was observed experimentally. From the viewpoints of the heating characteristics and the resonance condition, the hump energy was estimated and successfully compared with the experimetal results. Influence of the ICRF waves on the hump structure was investigated using a bounce averaged Fokker Planck code. 3 The AIC fluctuations enhance the end-loss ions scattered from the trapped region to the loss region, and have direct effects upon the ion confinement. The energy flux of the enhanced end-loss ions due to the AIC fluctuations was estimated and the enhancement factor was obtained. The strong anisotropic ion heating is dangerous for the ion confinement in the open systems which contain necessarily the loss regions.

The microwave reflectometry using FM and ultrashortpulse radar techniques have been applied to GAMMA 10 in order to diagnose plasma density profile and fluctuations. The reliability of profile measurement using the FM reflectometer is investigated for various sweep times and local path length. It is demonstrated that the reconstructed density profiles seem to be improved when the sweep time is faster than 50-100 μs. The several reconstruction algorithms are introduced to analyze the fast time-varying data, such as, the maximum-entropy method and wavelet analysis as well as zero-cross fringe counting and digital complex demodulation method. The reflectometers are applied to the measurement of density/magnetic fluctuations. The space- and time-resolving spectra of rf waves as well as low-frequency waves are obtained The density and magnetic-field fluctuations are evaluated from both the reflectometer and cross-polarization scattering diagnostic method.

We have constructed a 2-dimensional Hα line-emission measurement system in order to study neutral hydrogen behavior. We can obtain 2-dimensional radial profiles of hydrogen density by considering a collisional-radiativ model. We have also constructed space- and time-resolving spectrograph system in the range of vacuum ultraviolet (VUV). 15 - 105 nm. studying ion density profiles which directly relates to impurity transport. We measure both Hα line-emissions and VUV spectra from the hot ion mode plasmas in the GAMMA 10 for studying plasma particle confinement and impurity behavior. We found that both particle and energy confinement of the GAMMA 10 plasma was slightly improved during electron cyclotron resonant heating (ECRH) over that without ECRH. From the VUV measurement it is concluded that the impurity ions mainly came into the plasma during its formation phase.

Loss-cone boundaries have been directly measured using a newly developed diagnostic device in the tandem mirror GAMMA 10. Double loss boundaries clearly appeared in the velocity space of the end-lo...

Magnetohydrodynamic (MHD) stability of the GAMMA 10 tandem mirror is extensively studied in ICRF-heated, hot ion plasmas. Stability boundary for a flute interchange mode is predicted to depend on a pressure-weighted curvature integrated along the magnetic field line. It is found that the upper limit of the central-cell beta {beta}{sub C} increases linearly with the anchor-cell beta {beta}{sub A}. The critical beta ratio {beta}{sub C}/{beta}{sub A} above which the plasma cannot be sustained strongly depends on the pressure anisotropy P{sub PRP}/P{sub PLL} of hot ions. Stronger anisotropy greatly expands the stable region up to a higher critical beta ratio, owing to the reduction of the pressure weighting in the bad curvature region of the central cell. On both sides of the quadrupole anchor cells, there are flux-tube-recircularizing transition regions where the normal curvature is highly bad. Then the density and ion temperature of the cold plasma in the transition region are measured. Theoretical prediction on the flute stability boundary calculated by using the measured axial pressure profile of the hot-ion and the cold-plasma pressure can explain well the experimental results. 16 refs., 7 figs.