This paper describes the recent progress in divertor simulation research using the GAMMA 10/PDX tandem mirror towards the development of divertors in fusion reactors. During a plasma flow generation experiment in the end cell of the GAMMA 10/PDX, ICRF heating in the anchor cell successfully extended the particle flux up to 3.3  ×  1023 m2 s−1. Superimposing the short pulse of the ECH also attained a maximum heat flux of ~30 MW m−2. We have succeeded in achieving and characterizing the detachment of the high-temperature plasma, which is equivalent to the SOL plasma of tokamaks, by using the divertor simulation experimental module (D-module) in the GAMMA 10/PDX end cell, in spite of using a linear device with a short magnetic field line connection length. Various gases (Ar, Xe, Ne and N2) are examined to evaluate the effect of radiation cooling against the plasma flow at the MW m−2 level in the divertor simulation region and the following results are obtained: (i) Xe gas was most effective in the reduction of heat and particle fluxes (1%, 3%, respectively) and has a stronger effect on electron cooling (down to ~1.6 eV) in the used gas species. (ii) Ne gas was less effective. On the other hand, (iii) N2 gas showed more favorable effects than Ar in the lower pressure range. These results will contribute to the progress in detached plasma operation and in clarifying the radiation cooling mechanism towards the development of future divertors.

This research investigated the radiation cooling mechanism and formation of detached plasma in the case of gas injection in the D-module of GAMMA 10/PDX. In GAMMA 10/PDX, divertor simulation experiments have been started by using a divertor simulation experimental module (D-module). A V-shaped target made of tungsten has been installed in this module. In order to understand the effect of impurity injection into divertor simulation experimental module, we injected H 2 and Ar gases to the D-module and measured the heat flux and ion flux. According to the increase of gas injection, reduction of ion and heat fluxes have been observed. In the Ar injection experiments, H 2 gas has been injected simultaneously to examine the effect of molecular process on detached plasma formation. In this case, both the heat flux and ion flux are drastically reduced. These results indicate radiation cooling and formation of detached plasma due to gas injection. Simultaneous injection of noble gas and hydrogen gas showed the most effective results on detached plasma generation.

The linear divertor analysis with fluid model (LINDA) code has been developed in order to simulate plasma behavior in the end-cell of linear fusion device GAMMA 10/PDX. This paper presents the basic structure and simulated results of the LINDA code. The atomic processes of hydrogen and impurities have been included in the present model in order to investigate energy loss processes and mechanism of plasma detachment. A comparison among Ar, Kr and Xe shows that Xe is the most effective gas on the reduction of electron and ion temperature. Xe injection leads to strong reduction in the temperature of electron and ion. The energy loss terms for both the electron and the ion are enhanced significantly during Xe injection. It is shown that the major energy loss channels for ion and electron are charge-exchange loss and radiative power loss of the radiator gas, respectively. These outcomes indicate that Xe injection in the plasma edge region is effective for reducing plasma energy and generating detached plasma in linear device GAMMA 10/PDX.

We have investigated the synergistic effect of a combination of various impurity gases and hydrogen gas on plasma detachment of high temperature plasma, equivalent to scrape-off layer plasma of tokamaks in the GAMMA 10/PDX end region, utilizing an open magnetic field configuration. A small puff of an impurity gas (N 2 , Ne, Ar, Kr, Xe) in combination with a puff of H 2 gas is examined to evaluate their synergistic effect on the formation of detached plasma; the following results are obtained. (i) A combination of N 2 and H 2 puffs showed a clear decrease of electron density and ion flux; (ii) N 2 and H 2 puffs form a strong density gradient along the axial direction; and (iii) other noble impurity gases showed an insufficient synergistic effect. The new results indicate the possibility of achieving a reliable divertor operation scheme and the importance of a deeper understanding of the H 2 and N 2 assisted recombination process.

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This paper describes the behavior of plasma parameters in the E-divertor region of GAMMA 10/PDX numerically by using the multi-fluid code (LINDA) during injection of hydrogen (H) and Argon (Ar). A remarkable reduction in the electron temperature (T e) has been recognized due to Ar injection. For only Ar 6.0 × 10 17 m −3 injection, T e on the target plate decreases to nearly 10 eV. T e also reduces according to the increment of H injection. The ion temperature (T i) on the target plate also decreases according to the increment of injected H neutral density. A tendency of saturation in the particle flux and the electron density is observed at the higher H injection in the case of simultaneous injection of H and Ar. The charge exchange loss enhances significantly during H injection. The radiation power loss also enhances for Ar injection.

In order to understand the effect of impurity injection into divertor plasma, a multi‐fluid code was developed and applied to the region from west plug/barrier‐cell to end cell in GAMMA 10/PDX. In this research, Ar is applied as impurity neutrals. To investigate the effect of impurity injection on plasma parameters, interactions between Ar impurity and hydrogen bulk plasma were included in this model. Under the condition of injecting neutral hydrogen and impurity Ar, the charge exchange loss between hydrogen ion and neutrals reaches to about 95% and the radiation loss for electron is enhanced to about 45%. Therefore, hydrogen ion and electron temperatures decrease from about 55 eV to 4 eV and 15 eV to 4 eV, respectively. The heat load on the target plate is also reduced by nearly 80% compared with the condition of low injection rate of neutral hydrogen and impurity. It is also observed that the particle flux increases with neutral density and then shows a tendency to saturate in the higher neutral density (> 2.1 × 1018 m–3). (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)