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On improved confinement in mirror plasmas by a radial electric field
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Kharkov Inst Phys & Technol, Natl Sci Ctr, Inst Plasma Phys, Akad St 1, UA-61108 Kharkov, Ukraine..
2017 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 11, article id 115001Article in journal (Refereed) Published
Abstract [en]

A weak radial electric field can suppress radial excursions of a guiding center from its mean magnetic surface. The physical origin of this effect is the smearing action by a poloidal E x B rotation, which tend to cancel out the inward and outward radial drifts. A use of this phenomenon may provide larger margins for magnetic field shaping with radial confinement of particles maintained in the collision free idealization. Mirror fields, stabilized by a quadrupolar field component, are of particular interest for their MHD stability and the possibility to control the quasi neutral radial electric field by biased potential plates outside the confinement region. Flux surface footprints on the end tank wall have to be traced to avoid short-circuiting between biased plates. Assuming a robust biasing procedure, moderate voltage demands for the biased plates seems adequate to cure even the radial excursions of Yushmanov ions which could be locally trapped near the mirrors. Analytical expressions are obtained for a magnetic quadrupolar mirror configuration which possesses minimal radial magnetic drifts in the central confinement region. By adding a weak controlled radial quasi-neutral electric field, the majority of gyro centers are predicted to be forced to move even closer to their respective mean magnetic surface. The gyro center radial coordinate is in such a case an accurate approximation for a constant of motion. By using this constant of motion, the analysis is in a Vlasov description extended to finite beta. A correspondence between that Vlasov system and a fluid description with a scalar pressure and an electric potential is verified. The minimum B criterion is considered and implications for flute mode stability in the considered magnetic field is analyzed. By carrying out a long-thin expansion to a higher order, the validity of the calculations are extended to shorter and more compact device designs.

Place, publisher, year, edition, pages
2017. Vol. 59, no 11, article id 115001
Keywords [en]
radial invariant, radial electric field, biased potential plates, magnetic mirror, mirror machine, hybrid reactor, minimum B
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-336287DOI: 10.1088/1361-6587/aa8544ISI: 000411155900001OAI: oai:DiVA.org:uu-336287DiVA, id: diva2:1177316
Available from: 2018-01-25 Created: 2018-01-25 Last updated: 2018-01-25Bibliographically approved

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Ågren, Olov

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