A new disruption mitigation valve (DMV) and gas flow in guiding tubes of different diameter

Abstract

A new disruption mitigation valve, the DMV-30, has been developed and tested. The orifice output area of the valve is a factor of 2.4 and 12.25 times larger than that of its predecessors, DMV 20 and DMV 10, and the gas reservoir amounts to 1.3 l while the older version used at JET had only 0.65 l. The coil which provides the magnetic field pulse for the activation of the piston by an eddy current is outside of the working gas volume such that now all gas volumes are now made of stainless steel. The valve has the advantages of the previous developments: it is robust and reproducible, opens fully within three milliseconds and releases 50% of the gas within about 5 ms (He) to 10 ms (Ar). The valve is attached subsequently to two different guiding tubes, one with an inner diameter of 38 mm as used presently at JET and one with 102 mm inner diameter; an aim of this article is the analysis of the gas flows for the different diameters. The front of the gas pulse propagates with a Mach number of about 2.5 through the tubes, independent of the two diameters. This high speed agrees with theoretical expectations of a flow expansion of a half infinite tube in vacuum. In the quasi-stationary phase of the expansion, the gas flows with about sound speed in the 102 mm tube and with about half of the sound speed in the 38 mm tube.

Fuelling efficiency of massive gas injection in TEXTOR: mass scaling and importance of gas flow dynamics

“…The flow model was validated with available measurements of a TEXTOR-like injection system [13,14]. At the same time the calibration set from [13] was improved due to a more suitable processing The model correction factor was found to depend on the ratio of the orifice area to the delivery tube area.…”

“…The 10 and 18 mm valves were calibrated with the 38 mm tube, while the 28 mm valve was used with both For the tests of the 28 mm valve a commercially available interferometer was employed, whereas for the 10 and 18 mm valves a self built interferometer was used. In the latter case the processing procedure has recently been significantly improved with respect to [13,14]. Since the improvements result in a noticeable change of the pulse form, first a short reanalysis of the data for the 10 and 18 mm valves is presented below.…”

“…To explain the efficiency variation with the gas mass and pressure a simple model of the gas flow from the valve to the plasma edge is proposed. The flow model is validated by using available laboratory flow measurements of a TEXTOR-similar injection system [13,14]. The unsteady gas flow and a premature plasma disrupting are shown to explain the mass dependence: the gas pulse is smeared out and a small fraction of atoms at its front causes the disruption before the bulk can reach the plasma.…”

Disruption mitigation by massive gas injection in JET

“…Figure 5b gives the number of particles injected before start of the current quench , as calculated from adiabatic expansion into vacuum. This approach has been validated with lab measurements using the JET set-up [18,19,20]. The fraction of gas injected before the current quench , decreases with increasing pressure because of the shorter cooling phase.…”

Fast acting eddy current driven valve for massive gas injection on ITER

“…The design of the MGI valve presented here is largely based on previous designs deployed on TEXTOR, ASDEX upgrade, and JET [1][2][3], with considerations made for operation in the ITER environment.…”