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For plasma spectroscopy, Stokes spectropolarimetry is used as a method to spatially invert the viewing-chord-integrated spectrum on the basis of the correspondence between the given magnetic field profile along the viewing chord and the Zeeman effect appearing on the spectrum. Its application to fusion-related toroidal plasmas is, however, limited owing to the low spatial resolution as a result of the difficulty in distinguishing between the Zeeman and Doppler effects. To resolve this issue, we increased the relative magnitude of the Zeeman effect by observing a near-infrared emission line on the basis of the greater wavelength dependence of the Zeeman effect than of the Doppler effect. By utilizing the increased Zeeman effect, we are able to invert the measured spectrum with a high spatial resolution by Monte Carlo particle transport simulation and by reproducing the measured spectra with the semiempirical adjustment of the recycling condition at the first walls. The inversion result revealed that when the momentum exchange collisions of atoms are negligible, the velocity distribution of core-fueling atoms is mainly determined by the initial distribution at the time of recycling. The inversion result was compared with that obtained using a two-point emission model used in previous studies. The latter approximately reflects the parameters of atoms near the emissivity peak.

When the hydrogen isotope atom is injected into the amorphous carbon with the incident energies Ein of 20, 50, and 80 eV, we obtain the following physical quantities of hydrogen isotope atoms/molecules emitted from the amorphous carbon using molecular dynamics and heat conduction hybrid simulation. The physical quantities are the time evolution of the emission rate, the depth distribution of the original location of the hydrogen emitted from the target, the polar angular dependence, and the translational, rotational, and vibrational energy distributions. In addition, the approximate analysis yields the emission distributions at the vibrational (v) and rotational (J) levels. Using these distributions, we evaluate the rotational temperature Trot for v = 0 and small J states. From the above, it is found that molecules with higher rotational levels J tend to be emitted as Ein increases or as the mass of hydrogen isotope increases. Moreover, the isotope effect appears in the mass dependence of Trot., source:Hiroaki Nakamura et al 2022 Jpn. J. Appl. Phys. 61 SA1005, source:https://doi.org/10.35848/1347-4065/ac2435, identifier:0000-0002-0593-8810

When an ion or atom is injected into a target material, the incident energy increases the temperature around the injection point. Owing to the energy transfer to the surrounding atoms, the temperature of the material recovers to the initial temperature in the real system because heat is transferred to the bulk of material which consists of an almost infinite number of atoms. However, if we simulate the system by the molecular dynamics (MD) method, it is difficult to prepare a sufficiently large system to calculate the process of heat transfer to the bulk. Therefore, in this study, we develop an MD simulation model which includes the effect of heat transfer to the bulk by solving heat conduction equation. The simulation result shows that the process of heat removal proceeds on a time scale of approximately 1000 times slower than the time scale of the incident energy transfer from the incident atom to the target material., source:https://doi.org/10.1585/pfr.15.2403073

This paper presents carbon impurity flow velocity and temperature measurements in the divertor region for a wide density range ne = (1 - 14) × 1019 m−3, central electron temperature Te = 1.5 - 3.5 keV, and with total neutral beam injection power of 9 - 12 MW. The isotope effect on the transport is studied in hydrogen (H) and deuterium (D) discharges. Flow velocities for D plasma are systematically slower, by the factor of 1.4 - 2, compared to H plasma. For all selected discharges, the carbon ions flow toward the divertor in both H and D plasmas. Different velocities are obtained depending on the charge states. For C+ and C2+ they are in the range of 10 - 30 km/s, and 5 - 20 km/s for C3+ ions. It is also found that there is no change of flow direction even in the lowest density, where the impurity transport model predicts flow toward upstream in the thermal force dominant regime. In H discharges velocities increase proportionally to the plasma density, while in D discharges this dependency is weaker. Possible mechanism to interpret these observations is discussed based on the parallel momentum balance of impurity transport., source:https://doi.org/10.1585/pfr.13.3402058, identifier:0000-0002-8429-3298

The progress in the understanding of the physics and the concurrent parameter extension in the large helical device since the last IAEA-FEC, in 2012 (Kaneko O et al 2013 Nucl. Fusion 53 095024), is reviewed. Plasma with high ion and electron temperatures (Ti(0) ~ Te(0) ~ 6 keV) with simultaneous ion and electron internal transport barriers is obtained by controlling recycling and heating deposition. A sign flip of the nondiffusive term of impurity/momentum transport (residual stress and convection flow) is observed, which is associated with the formation of a transport barrier. The impact of the topology of three-dimensional magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum, particle/impurity transport and magnetohydrodynamic stability is also discussed. In the steady state operation, a 48 min discharge with a line-averaged electron density of 1 × 1019 m−3 and with high electron and ion temperatures (Ti(0) ~ Te(0) ~ 2 keV), resulting in 3.36 GJ of input energy, is achieved., source:K. Ida et al 2015 Nucl. Fusion 55 104018, source:https://doi.org/10.1088/0029-5515/55/10/104018, identifier:0000-0002-0585-4561

Impurity flow velocity measurements have been conducted for different magnetic field configurations in a wide plasma parameter range in the divertor leg region of LHD for understanding of the edge impurity transport. In all cases (densities, magnetic configurations, hydrogen (H) & deuterium (D) discharges), flows of several tens of km/s are observed. It is found that the flow in thick stochastic layer is faster than in thin stochastic layer configuration by a factor of 3. Different velocities of different charge states of carbon impurity are observed. The simulation with EMC3-EIRENE code shows similar trend as the experiments, but only qualitatively: faster flow in H compared to D discharges due to the mass effect, faster flow in the case of thick stochastic layer. However, synthetic spectra show discrepancy with experiments in the absolute Doppler shift, where the impurity velocity in the experiments is one order faster compared to the simulations., source:https://doi.org/10.1016/j.nme.2018.11.009, identifier:0000-0002-8429-3298

The intensity ratios between specific pairs of helium atom (HeI) emission lines are functions of the electron temperature (Te) and density (ne), and these functions have been used for the analysis of Te and ne in various types of discharge plasma. We applied this method to a low-density (ne < 10¹⁸ m⁻³) plasma, where the procedure of the analysis is markedly different from that of higher-density plasmas. The 2¹S and 2³S metastable atom densities are affected by transport, making it practically necessary to set Te, ne, the metastable atom densities, and the optical escape factors, which represent the effect of photoexcitation, as unknown variables and determine them simultaneously. Conversely, the transport of metastable atoms can be evaluated from the analysis.