Investigation on Total Bremsstrahlung Radiation in High-Density Operation of Large Helical Device Based on Visible Bremsstrahlung Profile Measurement

概要

論文の詳細を見る
Visible bremsstrahlung emission profiles have been studied over a wide range of electron densities in H2 gas puff and solid-H2-pellet-fueled discharges of large helical device (LHD). Peaked profiles are observed in high-density discharges ($n_{\text{e}}\geq 10^{14}$ cm-3) with pellet injection, whereas hollow profiles appeared in the normal discharges ($n_{\text{e}}\leq 10^{14}$ cm-3) with gas puffing. The total bremsstrahlung radiation is analyzed from the visible bremsstrahlung profile by integrating the energy and plasma volume. It is found that the total bremsstrahlung radiation rapidly increases with the density in the pellet discharges, of which the increment is scaled by the square of density, while it is roughly constant against the density in the gas puff discharges. The total bremsstrahlung radiation becomes equal to the total radiation loss in the pellet discharges. The ratio of the total bremsstrahlung radiation to the total input power has only a range of 3–10% in the gas puff discharges. In contrast, the ratio increases with the density and reaches 30–40% in the pellet discharges. Flat $Z_{\text{eff}}$ profiles are observed not only in the gas puff discharges but also in the pellet discharges. This indicates that no impurity accumulation occurs in the high-density operation with H2 pellet injection.
2010-10-25