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Molecular Cluster Injection for Short-Pulse, High-Density Fueling on the Lithium Tokamak eXperiment

Author: Daniel P. Lundberg
Requested Type: Poster Only
Submitted: 2009-12-04 10:28:12

Co-authors: R. Kaita, R. Majeski, D.P. Stotler

Contact Info:
Princeton Plasma Physics Laboratory
PO Box 451
Princeton, NJ   08543
USA

Abstract Text:
LTX is designed to reduce global recycling with a liquid lithium wall. Gas-based fueling systems, such as wall-mounted gas puffers or supersonic gas injectors, are limited in their ability to fuel past the plasma edge, particularly under low recycling conditions. Wall-mounted puffers also have a slow response, making temporal localization of the fueling difficult. While small pellet injection could be used for core fueling, a simpler and less expensive system is preferable. Following experiments on the HL-2A tokomak by Yao, et al. (Nucl. Fusion 47(2007) 1399), a molecular cluster injector was designed to supply an increased fraction of core fueling on LTX. A fast solenoid valve is cooled with liquid nitrogen, lowering the temperature of the gas in the valve body below 80K. As the gas expands through a supersonic nozzle into vacuum, additional cooling yields the formation of molecular clusters. These clusters have a reduced velocity transverse to the jet axis, improving the focusing of the jet. With cluster sizes anticipated to be on the order of 1000 molecules, it is expected that penetration into LTX plasmas will be improved over other gas-based fueling systems. The molecular cluster injector is capable of sourcing 700 torr-liters per second with a 250psia backing pressure. For a 1ms pulse, this provides a total particle source comparable to a 1mm pellet. The valve can provide pulses as short as 500 microseconds, with fine temporal control and a variable backing pressure. For these reasons, the molecular cluster injector will provide a flexible system for fueling and perturbation studies with wide applicability for magnetic confinement devices. Details of the design, construction, and characterization of the system are presented, and its application to LTX discussed.

*Supported by US DOE contract DE-AC02-09CH11466

Characterization: A4

Comments:
please group (1)R. Majeski, (2)L. Berzak, (3)D. Lundberg together