The beryllium limiter experiment in ISX-B

Abstract

An experiment to test beryllium as a limiter material has been performed in the ISX-B tokamak. The effect of the plasma on the limiter and the effect of the limiter on the plasma were studied in detail. Heat and particle fluxes to the limiter were measured, and limiter damage by melting was documented as a function of power flux. Strong melting and evaporation of the limiter caused beryllium gettering of the vacuum vessel. Postmortem analysis of the limiter was performed to document the amount of retained hydrogen and the erosion and impurity deposition on the limiter. The effect of the limiter on the plasma performance was studied in terms of parameter space, impurity content, and confinement for the ungettered and gettered cases. Operational experience with beryllium in a fusion experiment is discussed.

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

“…However, beryllium has several negative features, including, a low melting temperature (1560 K), potential toxicity in manufacturing and relatively high physical sputtering rates. Nevertheless, two small tokamaks successfully tested beryllium (ISX-B [101], UNITOR [102]), and this led to extensive JET operation with beryllium limiters, divertor plates and evaporative gettering [100]. In fact, melting and evaporation of the beryllium limiters was extensive in all three cited tokamak experiments [100][101][102].…”

“…Nevertheless, two small tokamaks successfully tested beryllium (ISX-B [101], UNITOR [102]), and this led to extensive JET operation with beryllium limiters, divertor plates and evaporative gettering [100]. In fact, melting and evaporation of the beryllium limiters was extensive in all three cited tokamak experiments [100][101][102]. One immediate and clearly beneficial effect of beryllium operation was the observation of strong oxygen gettering by the evaporated beryllium.…”

Model for movement of molten limiter material during the ISX-B beryllium limiter experiment

“…The droplets may or may not break up during their trajectory through the plasma although it appears that many droplets do break up [6]. (2) The mean diameter of the elongated droplets is 1 mm, and their corresponding mass, m, is 2 mg. (3) The effective length, L, for the current path is 10 mm. (4) The horizontal protrusion movement before detachment is 5 mm.…”

“…This experiment was a collaborative effort involving both ORNL and JET personnel. The beryllium limiter has been described and discussed elsewhere [1,2], as have the plasma physics results [2,3], the movement of beryllium on the limiter [4,5], and the migration of beryllium to the tokamak walls [4,6].…”

“…The possibility of designing a tokamak fusion reactor which does not require to breed (or obtain from an external source) tritium has been the subject of several studies [ 1,2]. Such a reactor requires a high plasma performance in order to reach conditions under which the deuterium-deuterium (D-D) reaction is…”