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.

Particle control and plasma performance in the Lithium Tokamak eXperiment

“…We have now studied the fueling efficiency of gas injection techniques, including a simple pulsed gas valve mounted on the chamber wall, a pulsed valve with a gas duct, a supersonic gas injection (SGI), and molecular cluster injection (MCI). 18,19 With the exception of the wall-mounted pulsed valve, which is mounted at the top of the vacuum chamber, and injects gas through a 3 in. diameter aperture in one of the shell quadrants, all the fueling systems are on the outboard midplane of the device.…”

Results and future plans of the Lithium Tokamak eXperiment (LTX)

“…injection. We have studied the fueling efficiency of a number of different gas injection techniques, including traditional gas puffing, supersonic gas injection (SGI), and molecular cluster injection (MCI) [5]. The use of either highly directed gas jet system (SGI or MCI) results in high fueling efficiencies, up to about 35%, which is about 2-3 times more efficient than the wall-mounted gas puffing systems.…”

Particle Control and Plasma Performance in the Lithium Tokamak Experiment (LTX)

“…We have now studied the fueling efficiency of gas injection techniques, including a simple pulsed gas valve mounted on the chamber wall, a pulsed valve with a gas duct a supersonic gas injection (SGI), and molecular cluster injection (MCI). 18,19 With the exception of the wall-mounted pulsed valve, which is mounted at the top of the vacuum chamber, and injects gas through a 3" diameter aperture in one of the shell quadrants, all the fueling systems are on the outboard midplane of the device. In LTX, a simple wall mounted valve is found to fuel the plasma with approximately 15% efficiency; the plasma density rise seen during gas injection indicates that 15% of the injected gas accounts for the rise in the total plasma particle count.…”