Development of a tracer-containing compact-toroid injection system

Abstract

The accumulation and behavior of impurities is one of the most important subjects in the development of magnetically confined fusion reactors because impurities can potentially cause cooling and worsen the confinement of the hot core plasma. Tracer-encapsulated solid pellets (TESPELs) have demonstrated some results for impurity injection for fusion-reactor plasma studies [N. Tamura et al., J. Phys. Conf. Ser. 823, 012003 (2017)]. However, the TESPEL technique has several shortcomings, for example, the penetration depth and the amounts of tracer impurities. In the present study, we have developed a tracer-containing, compact-toroid (TCCT) injection system that utilizes a magnetized coaxial plasma gun (MCPG). The discharge current through the MCPG sputters and ionizes the electrode material, and the Lorenz self-force accelerates it as a plasmoid. The MCPG easily accelerates a magnetized plasmoid to speeds greater than the ion thermal velocity of several tens of kilometers per second. The accelerated and ejected plasmoid that contains the tracer ions is itself a warm, ionized plasma. Therefore, a TCCT can potentially be injected into the core region of a target plasma with less adverse effect.

Behavior of a Tracer-Containing Compact Toroid in a Transverse Magnetic Field

“…Gas puffing [1], laser blow-off [2], and pellet injection [3] have been used to inject tracer particles so far. As a new tracer injection method, we have proposed a tracer-containing compact toroid (TCCT) injection [4] to expand the experimental range of impurity transport studies. It consists of a compact toroid (CT) doped with tracer ions.…”

“…In a previous experiment, we generated CTs doped with tracer ions using a magnetized coaxial plasma gun (MCPG) that has an inner electrode made of conductive tracer elements, e.g., aluminum, tungsten, manganese, and zirconium [4]. The inner electrode is sputtered during discharge and tracer ions are integrated into the CTs.…”