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Effects of CT injector acceleration electrode configuration on tokamak penetration

Yee, J. and Bellan, P. M. (1998) Effects of CT injector acceleration electrode configuration on tokamak penetration. Nuclear Fusion, 38 (5). pp. 711-721. ISSN 0029-5515. http://resolver.caltech.edu/CaltechAUTHORS:YEEnf98

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Abstract

Through compact toroid (CT) injection experiments on the TEXT-U tokamak (with BT simeq 10 kG and IP simeq 100 kA), it has been shown that the acceleration electrode configuration, particularly in the vicinity of the toroidal field (TF) coils of the tokamak, has a strong effect on penetration performance. In initial experiments, premature stopping of CTs within the injector was seen at anomalously low TF strengths. Two modifications were found to greatly improve performance: (a) removal of a section of the inner electrode and (b) increased diameter of the 'drift tube' (which guides the CT into the tokamak after acceleration). It is proposed that the primary drag mechanism slowing CTs is toroidal flux trapping, which occurs when a CT displaces transverse TF trapped within the flux conserving walls of the acceleration electrodes (or drift tube). For a simple two dimensional (2-D) geometry, a magnetostatic analysis produces a CT kinetic energy requirement of 1/2ρv2 ≥ α(B02/2μ0), with α = 2/(1-a2/R2) a dimensionless number that is dependent on the CT radius a normalized by the drift tube radius R. For a typical CT, this can greatly increase the required energies. A numerical analysis in 3-D confirms the analytical result for long CTs (with length L such that L/a gtrsim 10). In addition to flux trapping, the CT shape is also shown to affect the energy criterion. These findings indicate that a realistic assessment of the kinetic energy required for a CT to penetrate a particular tokamak TF must take into account the interaction of the magnetic field with the electrode walls of the injector.


Item Type:Article
Additional Information:© 1998 IOP Publishing Ltd. Received 11 August 1997, accepted for publication 30 January 1998, Print publication: Issue 5 (May 1998). It is our pleasure to acknowledge the technical assistance of F. Cosso and L. Begay, and the considerable previous work of P. Loewenhardt and M. Brown in the development of the injector. We are indebted to R. Raman for sharing his knowledge and expertise with us. We would also like to thank W. Rowan and the entire TEXT-U team, whose co-operation and support made this work possible. We are also grateful to S. Sanders for helpful discussions. This work was performed under USDOE Grant No. DE-FG03-86ER53232.
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Deposited On:09 Jun 2005
Last Modified:26 Dec 2012 08:40

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