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Improved stability period in high-current-density operation of reversed-field pinch on ETL-TPE-1R(M)

The improved stability period of a reversed-field-pinch (RFP) configuration with high current density (500 A·cm−2, on average) is well understood on TPE-1R(M) with a metal liner whose size is the smallest among the RFP experimental devices being operated at present (r/R = 9/50 cm unit). Plasma parameters of Ip = 130 kA (duration time about 1 ms), ne0 = 6 × 1013 cm−3, Te0 ≈ 600 eV, and βp ≈ 10% are obtained. The improved stability period is characterized by a remarkably reduced fluctuation level (δBp/Bp ≈ 1%) and a steady improvement of plasma confinement. Possible explanations for the interesting phenomena in the setting-up phase and the improved stability period of TPE-1R(M) are given, i.e. relaxation phenomena, toroidal-flux enhancement within the plasma, and current disruption. The scaling of electron temperature and density, depending on the plasma current in the improved stability period, are described with a discussion of the energy confinement time. The entire performance of TPE-1R(M) is discussed in relation to that of other RFP machines.