Creation of Impurity Source inside Plasmas with Various Types of Tracer-Encapsulated Solid Pellet

Abstract

A Tracer-Encapsulated Solid Pellet (TESPEL) was developed for promoting an impurity transport study in a magnetically-confined plasma. One of the advantages of the TESPEL is that it can make a three-dimensionally localized impurity source in the plasma. This enables us to inject the tracer impurity inside or in the vicinity of the region of interest. Recently, a new-type TESPEL with a thinner outer shell has been developed in order to achieve a shallower deposition of the tracer impurity. With the TESPEL having the thinner shell, we have achieved about 4 cm shallower deposition of the tracer impurity, compared with the case of the conventional thick-shell type TESPEL with the same outer diameter of about 700 µm. Moreover, for the achievement of the further shallower deposition of the tracer impurity, we also developed the TESPEL with a tracer-impurity-doped thin shell. After the injection of the TESPEL with the tracer-impurity-doped thin shell, the line emissions from the highly-ionized doped impurity are clearly observed with a vacuum ultraviolet spectrometer, which clearly demonstrates its ability to carry the impurity as a new tool.

A new multi-tracer pellet injection for a simultaneous study of low- and mid/high-Z impurities in high-temperature plasmas

“…From past experience with such polystyrene shells, and to be on the safe side, the polystyrene shell with an outer diameter of 900 μm and an inner core diameter of 660 μm (the shell thickness being 120 μm) is currently under development. Compared with the thick-shell-type TESPEL 24 having the outer diameter of 900 μm and the inner core diameter of 300 μm, i.e., a shell thickness of 300 μm (used in the proof-ofprinciple experiment), the TESPEL payload capacity will increase approximately tenfold. Therefore, based on the results of the second test of the proof-of-principle experiment, a single TESPEL containing a sufficient amount of the inorganic compound impurity tracer will be applicable in the very near future.…”

Hollow pellet injection for magnetic fusion

“…Core-shell spheres have also been developed and adopted in MF applications-see two examples shown in figure 10. Small hollow pellets are excellent tools for the calibration of spectroscopic diagnostics in tokamaks and stellarators like LHD [9,39], as a well-known quantity of the desired mat erial can be delivered to the plasma core. The shell protects the core material from ablation and loss in the launch tube and plasma edge region and ensures that the desired quantity of mat erial to be studied reaches the core.…”

The 7th Asia-Pacific Transport Working Group (APTWG) meeting

“…Preliminary results showed that the edge flow structure is oscillated in the condition near the density threshold of transition and turbulence intensity is related with the flow, but it is changed during the oscillatory phase. Solitary and mono-cycle shaped flow structure appears by the small pellet (TESPEL [51]) injection in which the local potential change travels towards the core with two different time scales and the sign of flow velocity in the edge region changes abruptly.…”