skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Main characteristics of the fast disruption mitigation valve

Abstract

The article presents a detailed investigation of the fast disruption mitigation valve developed at FZJ Juelich. The essence of this study is the novel direct observation of the piston motion by means of a fast framing camera. The piston stroke and the injection duration are shown to strongly depend on the operational pressure and the used gas. The same is true for the valve throughput. The analysis revealing the leading contribution of the injection duration in this modification is given. The knowledge of the injection duration is also used to reconstruct the characteristic pressure decay rates and the gas outflow rates. The means to increase the gas outflow are discussed. The main found valve characteristics are: (1) valve reaction time, i.e., the delay between the application of the trigger signal and the achievement of reliably observable opening 0.5 mm, is about 0.3 ms; (2) the maximum achieved throughput is 7.5 bar l for argon and 9.5 bar l for helium; (3) the maximum delivery rates are 500 bar l s{sup -1} for Ar and 1500 bar l s{sup -1} for He.

Authors:
; ; ;  [1]
  1. Institute of Plasma Physics, Forschungzentrum Juelich GmbH, EUROATOM-Association, Trilateral Euregio Cluster, D-52425 Juelich (Germany)
Publication Date:
OSTI Identifier:
20960236
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 78; Journal Issue: 3; Other Information: DOI: 10.1063/1.2712798; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ARGON; CAMERAS; HELIUM; MITIGATION; OPENINGS; PISTONS; PLASMA INSTABILITY; SIGNALS; VALVES

Citation Formats

Bozhenkov, S. A., Finken, K.-H., Lehnen, M., and Wolf, R. C. Main characteristics of the fast disruption mitigation valve. United States: N. p., 2007. Web. doi:10.1063/1.2712798.
Bozhenkov, S. A., Finken, K.-H., Lehnen, M., & Wolf, R. C. Main characteristics of the fast disruption mitigation valve. United States. doi:10.1063/1.2712798.
Bozhenkov, S. A., Finken, K.-H., Lehnen, M., and Wolf, R. C. Thu . "Main characteristics of the fast disruption mitigation valve". United States. doi:10.1063/1.2712798.
@article{osti_20960236,
title = {Main characteristics of the fast disruption mitigation valve},
author = {Bozhenkov, S. A. and Finken, K.-H. and Lehnen, M. and Wolf, R. C.},
abstractNote = {The article presents a detailed investigation of the fast disruption mitigation valve developed at FZJ Juelich. The essence of this study is the novel direct observation of the piston motion by means of a fast framing camera. The piston stroke and the injection duration are shown to strongly depend on the operational pressure and the used gas. The same is true for the valve throughput. The analysis revealing the leading contribution of the injection duration in this modification is given. The knowledge of the injection duration is also used to reconstruct the characteristic pressure decay rates and the gas outflow rates. The means to increase the gas outflow are discussed. The main found valve characteristics are: (1) valve reaction time, i.e., the delay between the application of the trigger signal and the achievement of reliably observable opening 0.5 mm, is about 0.3 ms; (2) the maximum achieved throughput is 7.5 bar l for argon and 9.5 bar l for helium; (3) the maximum delivery rates are 500 bar l s{sup -1} for Ar and 1500 bar l s{sup -1} for He.},
doi = {10.1063/1.2712798},
journal = {Review of Scientific Instruments},
number = 3,
volume = 78,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • Injection of massive quantities of gas is a promising technique for fast shutdown of ITER for the purpose of avoiding divertor and first wall damage from disruptions. Previous experiments using massive gas injection (MGI) to terminate discharges in the DIII-D tokamak have demonstrated rapid shutdown with reduced wall heating and halo currents (relative to natural disruptions) and with very small runaway electron (RE) generation [1]. Figure 1 shows time traces which give an overview of shutdown time scales. Typically, of order 5 x 10{sup 22} Ar neutrals are fired over a pulse of 25 ms duration into stationary (non-disrupting) discharges.more » The observed results are consistent with the following scenario: within several ms of the jet trigger, sufficient Ar neutrals are delivered to the plasma to cause the edge temperature to collapse, initiating the inward propagation of a cold front. The exit flow of the jet [Fig. 1(a)] has a {approx} 9 ms rise time; so the quantity of neutrals which initiates the edge collapse is small (<10{sup 20}). When the cold front reaches q {approx} 2 surface, global magnetohydrodynamic (MHD) modes are destabilized [2], mixing hot core plasma with edge impurities. Here, q is the safety factor. Most (>90%) of the plasma thermal energy is lost via impurity radiation during this thermal quench (TQ) phase. Conducted heat loads to the wall are low because of the cold edge temperature. After the TQ, the plasma is very cold (of order several eV), so conducted wall (halo) currents are low, even if the current channel contacts the wall. The plasma current profile broadens and begins decaying resistively. The decaying current generates a toroidal electric field which can accelerate REs; however, RE beam formation appears to be limited in MGI shutdowns. Presently, it is thought that the conducted heat flux and halo current mitigation qualities of the MGI shutdown technique will scale well to a reactor-sized tokamak. However, because of the larger RE gain from avalanching and the presence of a RE seed population due to Compton-scattered fast electrons, it is possible that a RE beam can be formed well into the CQ, after the flux surfaces initially destroyed by the TQ MHD have had time to heal. Crucial MGI issues to be studied in present devices are therefore the formation, amplification, and transport of RE and the transport of impurities into the core plasma (important because the presence of impurities can, via collisional drag, help suppress RE amplification). In the study of impurity transport, both neutral delivery (directly driven into the core by the jet pressure) and ion delivery (mixed into the core by MHD) are of interest, as both contribute to RE drag.« less
  • An important and urgent issue for ITER is predicting and controlling disruptions. Tokamaks and spherical tokamaks have the potential to disrupt. Methods to rapidly quench the discharge after an impending disruption is detected are essential to protect the vessel and internal components. The warning time for the onset of some disruptions in tokamaks could be <10 ms, which poses stringent requirements on the disruption mitigation system for reactor systems. In this proposed method, a cylindrical boron nitride projectile containing a radiative payload composed of boron, boron nitride, or beryllium particulate matter and weighing similar to 15 g is accelerated tomore » velocities on the order of 1 to 2 km/s in <2 ms in a linear rail gun accelerator. A partially fragmented capsule is then injected into the tokamak discharge in the 3- to 6-ms timescale, where the radiative payload is dispersed. The device referred to as an electromagnetic particle injector has the potential to meet the short warning timescales for which a reactor disruption mitigation system must be built. The system is fully electromagnetic, with no mechanical moving parts, which ensures high reliability after a period of long standby.« less
  • The emission of hydrogen isotopes with kinetic energy greater than 25 MeV/nucleon from the breakup of nuclear emulsion nuclei bombarded by 200-Gev/c protons is studied. The E/sub 0/-dependences of the production cross sections for particles of various masses are found to be identical. It is found that the energy of the emitted particles does not depend on the size of the star. The energy and momentum spectra and the angular distributions of p, d, t, and He nuclei with E/sub kin/> or =25 MeV/nucleon respectively coincide. It is suggested that the main contribution to the production of fast singly chargedmore » particles comes from quasielastic knockout of complex substructures by high-energy intranuclear particles.« less
  • Data on the discharge behavior, thermal loads, halo currents, and runaway electrons have been obtained in disruptions on the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. {bold 8}, 2A 441 (1985)]. These experiments have also evaluated techniques to mitigate the disruptions while minimizing runaway electron production. Experiments injecting cryogenic impurity {open_quotes}killer{close_quotes} pellets of neon and argon and massive amounts of helium gas have successfully reduced these disruption effects. The halo current generation, scaling, and mitigation are understood and are in good agreement with predictions of a semianalytic model. Results from {open_quotes}killer{close_quotes} pellet injection have been usedmore » to benchmark theoretical models of the pellet ablation and energy loss. Runaway electrons are often generated by the pellets and new runaway generation mechanisms, modifications of the standard Dreicer process, have been found to explain the runaways. Experiments with the massive helium gas puff have also effectively mitigated disruptions without the formation of runaway electrons that can occur with {open_quotes}killer{close_quotes} pellets. {copyright} {ital 1999 American Institute of Physics.}« less
  • Plasma fueling with pellet injection, pacing of edge localized modes (ELMs) by small frequent pellets, and disruption mitigation with gas jets or injected pellets are some of the most important technological capabilities needed for successful operation of ITER. Tools are being developed at Oak Ridge National Laboratory that can be employed on ITER to provide the necessary core pellet fueling and the mitigation of ELMs and disruptions. Here we present progress on the development of the technology to provide reliable high throughput inner wall pellet fueling, pellet ELM pacing with high frequency small pellets, and disruption mitigation with gas jetsmore » and pellets. Examples of how these tools can be employed on ITER are discussed.« less