Abstract
We have investigated plasma detachment phenomena of high-density helium plasmas in the linear plasma device Pilot-PSI, which can realize a relevant ITER SOL/Divertor plasma condition. The experiment clearly indicated plasma detachment features such as drops in the plasma pressure and particle flux along the magnetic field lines that were observed under the condition of high neutral pressure; a feature of flux drop was parameterized using the degree of detachment (DOD) index. Fundamental plasma parameters such as electron temperature (Te) and electron density in the detached recombining plasmas were measured by different methods: reciprocating electrostatic probes, Thomson scattering (TS), and optical emission spectroscopy (OES). The Te measured using single and double probes corresponded to the TS measurement. No anomalies in the single probe I–V characteristics, observed in other linear plasma devices [, , ], appeared under the present condition in the Pilot-PSI device. A possible reason for this difference is discussed by comparing the different linear devices. The OES results are also compared with the simulation results of a collisional radiative (CR) model. Further, we demonstrated more than 90% of parallel particle and heat fluxes were dissipated in a short length of 0.5 m under the high neutral pressure condition in Pilot-PSI.
Highlights
Handling enormous plasma heat and particle loads to divertor plates is essential to the achievement of high fusion gain in magnetically confined fusion
In order to understand the fundamental properties of high-density and high-flux detached recombining helium plasma under the more ITER relevant conditions, Te and ne have been measured by using reciprocating electrostatic probes, Thomson scattering (TS) measurement and optical emission spectroscopy (OES) in Pilot-PSI
It was shown that the Te obtained by using OES was the lowest among all values obtained by using the measurement techniques considered in the present study, and exhibited only a small dependence on P
Summary
Handling enormous plasma heat and particle loads to divertor plates is essential to the achievement of high fusion gain in magnetically confined fusion. In ITER with fusion power (Pfus) of 500 MW, most of the exhausted power crossing the separatrix from the core (PSOL) of ~ 100 MW must flow along open field lines in the scrape-off layer (SOL) connecting directly to the divertor target plates [1, 2]. Assuming Pfus ~ 3 GW class DEMO fusion reactor with the ITER-size plasma, PSOL is expected to be. The technologically feasible capability for heat handling of the divertor is typically 10 MW m–2 for an actively cooled structure in ITER [4], while in DEMO it could be below 10 MW m–2 due to neutron irradiation effects [5,6,7]. A radiative divertor scenario should be developed to reduce PSOL below 50 MW handled by total heat sink in divertors, where a radiation loss fraction (Prad/PSOL, Prad is radiation power) of larger than 50% in ITER and 90%
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