Molecular hydrogen density measurements of short-pulse, high-density fuelling from a molecular cluster injector

Abstract

A molecular cluster injector (MCI) has been developed to provide short-pulse, high-density fuelling for the lithium tokamak experiment (LTX). Using an electron-beam fluorescence method, the molecular density profiles produced by the injector are measured with sub-cm spatial resolution. The system, which is cryogenically cooled to promote the formation of molecular clusters, demonstrates a significant increase in molecular density relative to room-temperature supersonic gas injectors. The transient characteristics of short pulses (3–5 ms) are measured with 250 µs temporal resolution, and the jet shock structure is found to evolve significantly on that time scale. Supplemental measurements with a pressure transducer validate the electron-beam measurements. The measured density profiles are consistent with supersonic flows suitable for producing substantial populations of molecular clusters. The measured densities and flow rates are appropriate for high-density fuelling of LTX plasmas. The MCI will be used to investigate the physics of molecular cluster fuelling of LTX plasmas.