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In order to evaluate deposition of cesium (Cs) in the plasma grid (PG) and investigate the origin of the gradual degradation of the negative ion current in a 100 s long pulsed operation in the JT-60SA negative ion source, Cs behavior in the source is model. To do this, Cs adsorption/desorption coefficient with a wide range of temperature is experimentally measured by a surface ionization detector and a quartz crystal microbalance. As a result, both of the adsorption and desorption are drastically varied at temperature range from room temperature to 100 °C. Based on these data, the model calculates the amounts of the Cs mass in the chamber wall and PG. The calculation result shows that, in the operation, an increase of temperature in the chamber wall (Twall) causes the evaporation of the huge amount of Cs in it. This leads to over pilling-up of Cs in the PG and the slight degradation of the negative ion production. Therefore, it is found that the constant temperature operation is needed to sustain the thickness of the Cs monolayer in the PG, and the Twall is desired to be less than 60 °C to suppress the evaporation of Cs in the chamber wall. According to this model, it is showed that there are many combinations of the temperatures to achieve it with low Cs consumption. [ABSTRACT FROM AUTHOR]

Pure volume production of D- negative ions is studied in rectangular negative ion source equipped with an external magnetic filter (MF). Plasma parameters (ne and Te) in D2 plasmas are varied mainly in the downstream region by changing the magnetic field intensity of the MF (i.e., BMF). Production and control of D2 plasma is nearly the same as that of H2 plasmas, although the values of ne and Te in D2 plasma are slightly higher than that of H2 plasmas in both the source and the extraction regions. On D-/H- production, however, it appears some different points. By varying the BMF, H- production in the extraction region is remarkably changed corresponding to the variation of ne and Te in the extraction region. On the other hand, D- production is not so varied under the same discharge conditions in H2 plasmas. This difference in D- production is not well explained only variation of ne and Te in D2 plasmas. Optimum BMF and gas pressure for D- production is slightly higher than that for H- production. [ABSTRACT FROM AUTHOR]

Ar plasmas are produced by using spatially- and temporally-rotating radio-frequency (f[SUBRF]) electromagnetic fields in very weak uniform magnetic fields. The plasma density is observed to increase greatly compared with ICP mode when the RF fields rotate in the electron-diamagnetic direction and (f[SUBce]/f[SUBRF] ∼ 4 is satisfied (f[SUBce]: electron cyclotron frequency). Then the Trivelpiece-Gould wave with large amplitude propagates and damps toward the downstream. The existence of the damped wave appears to contribute to the efficient plasma production. [ABSTRACT FROM AUTHOR]

When electrons are emitted in the form of current channel along magnetic-field lines into a fully-ionized collisionless plasma column, the ion-density and low-frequency fluctuations are experimentally observed to increase greatly and grow in the channel, respectively, both of which appear to have a causal relation to the inward cross-field transport of ions. A transition from widely-flattened to sharply-peaked density and potential profiles is caused with an increase in the electron-emission quantity. The ion-density increase in the channel saturates as the radial density profile steepens. [ABSTRACT FROM AUTHOR]