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

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 νs 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.