Transport Characteristics in the Stochastic Magnetic Boundary of LHD: Magnetic Field Topology and Its Impact on Divertor Physics and Impurity Transport

A Tracer-encapsulated Solid Pellet (TESPEL) injection method has been shown to be useful for many fields of plasma diagnostics. In order to provide more flexibility for such plasma diagnostics, we are developing various types of TESPELs. Here we report a new type TESPEL with a thin shell made of poly-dichlorostyrene useful for the impurity transport study. The new multilayer TESPEL configuration is also discussed. This type of TESPEL is not only useful for impurity transport study but also for the neutron observation due to the transient increase of the deuterium in the local position in the plasma for the upcoming LHD D-D experiment. A Tracer-encapsulated Solid Pellet (TESPEL) injection method has contributed so far to the various fields of plasma diagnostics as reported [1]. However, we noticed that more detailed control of the tracer deposition location is necessary in particular for promoting the impurity transport study. Thus, we are developing new TESPEL configurations for aiming at more flexible tracer deposition with a multilayer concept. From the technical viewpoint, regarding the production of the conventional TESPEL, we need to first drill a polystyrene ball, then insert relevant tracers, and, finally, cover the hole with a tiny polystyrene ball as a lid. Making TESPELs thus requires much time. Moreover, the tracer material is often in an irregular form, so it is difficult to estimate the precise amount of the tracer, although it is possible to estimate the amount roughly from the visually observed volume. In order to solve these problems, a new type TESPEL with mixing tracers as a compound or as a colloidal dispersion in the base polystyrene becomes a candidate.Recently we reported two types of TESPEL configurations [1], namely, (i) thick-shell-type and (ii) thin-shelltype [2] for the accurate impurity transport diagnostics. In particular, it was shown that the impurity transport feature depends on the source location of the impurity and also on the collisionality (between impurities and bulk ions).Regarding (i), the polystyrene ball (polymer in the form of (C 8 H 8 ) n ) with a diameter of up to 0.9 mm is drilled with a typical diameter of 0.2 mm, and the tracers are put inside the polystyrene ball, and then the hole is covered with a tiny polystyrene ball (a typical diameter of 0.2 mm) as a lid. In case (ii), the polystyrene shell with a typical shell thickness of ∼75 µm is produced for the shallower

Section: Development Of Tespel Configurations For Plasma Diagnosticsmentioning

confidence: 99%

Development of TESPEL Configurations for Plasma Diagnostics

Sudo

Tamura

Suzuki

et al. 2014

“…The suppression of the Ar Kα line intensity in case of the PS regime indicates the shielding effect of the Ar particles. The suppression mechanism of the LHD plasma was studied by Kobayashi et al [20,21], and it will be briefly discussed later. In contrast to the Ar Kα line emission, we observed the Be-like and Li-like line emissions from the Ar particles with enough S/N ratio even in case of the PS regime.…”

Section: Present Impurity Transport Studiesmentioning

confidence: 99%

“…Considering the fact that the property of the tracers deposited within ρ = 0.85 is the same as in the case for the inner deposition of the tracers, it is concluded that the location of the discriminating the impurity property is around ρ = 0.9 (0.85 -0.93) in case of the PS regime. So, the shielding mechanism is working in the plasma periphery [20,21]. In the edge surface layers where the connection length is short, the friction force is working stronger in the higher density case.…”

Section: Present Impurity Transport Studiesmentioning

confidence: 99%

Plasma Diagnostics with Tracer-Encapsulated Solid Pellet

Sudo

Tamura

Muto

et al. 2014

The diagnostics method of a tracer-encapsulated solid pellet (TESPEL) has been developed. TESPEL consists of polystyrene as an outer shell and of specific material as a tracer in the core. Owing to the advantages of the TESPEL, the following results have been successfully obtained: (1) distinctive different feature of impurity transport between the plateau and Pfirsch-Schlüter regimes depending on the impurity source location which is analyzed with the STRAHL code, (2) specific feature of a non-local thermal transport such as abrupt increase of electron temperature in the plasma core in case of plasma cooling in the plasma periphery due to a small TESPEL injection, (3) spatially resolved energy distribution of the high energy particles obtained by a pellet charge exchange method, (4) longer impurity containment inside the magnetic island which is observed by depositing the tracers in the magnetic island by means of the TESPEL, and (5) identification of new spectral lines using interested atoms contained in the core of the TESPEL.

“…Profiles of background plasma parameters (ion/electron density and temperature, plasma flow velocities, etc.) are supplied from a three-dimensional edge plasma fluid code (EMC3) coupled with the EIRENE in a standard magnetic configuration (the radial position of the magnetic axis: R ax = 3.60 m) [10]. In the calculation by the EMC3-EIRENE code, the heating power and the plasma density at the Last Closed Flux Surface (LCFS) have to be fixed as initial conditions.…”

Section: Setup For Dust Transport Simulationmentioning

confidence: 99%

Simulation Analysis of Dust-Particle Transport in the Peripheral Plasma in the Large Helical Device

Shoji

Tanaka

Pigarov

et al. 2014

The function of the peripheral plasma in the Large Helical Device (LHD) on transport of dusts is investigated using a dust transport simulation code (DUSTT) in a non-axisymmetric geometry. The simulation shows that the transport of the dusts is dominated by the plasma flow (mainly by ion drag force) formed in the peripheral plasma. The trajectories of dusts are investigated in two probable situations: release of spherical iron dusts from the inboard side of the torus, and drop of spherical carbon dusts from a divertor plate installed near an edge of an upper port. The trajectories in these two situations are calculated in various sized dust cases. From a viewpoint of protection of the main plasma from dust penetration, it proves that there are two functions in the LHD peripheral plasma. One is sweeping of dusts by the effect of the plasma flow in the divertor legs, and another one is evaporation/sublimation of dusts by heat load onto the dusts in the ergodic layer.