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icc2011_proceedings_gota.pdf2011-09-09 20:14:22Hiroshi Gota
icc2011_gota_talk_8_16_11.pdf2011-08-17 05:02:37Hiroshi Gota
icc2011_abstract_gota.pdf2011-07-07 17:48:50Hiroshi Gota

A Well-Confined Field-Reversed Configuration Plasma Formed by Dynamic Merging of Two Colliding Compact Toroids in C-2

Author: Hiroshi Gota
Requested Type: Consider for Invited
Submitted: 2011-06-10 19:14:22

Co-authors: M.W. Binderbauer, H.Y. Guo, M. Tuszewski, D. Barnes, L. Sevier, and the TAE Team

Contact Info:
Tri Alpha Energy, Inc.
PO BOX 7010
Rancho Santa Margarita, CA   92688
USA

Abstract Text:
A high temperature, stable, long-lived field-reversed configuration (FRC) plasma state has been produced in the C-2 device by dynamically colliding and merging two oppositely directed, highly supersonic compact toroids (CTs) [1, 2]. The two individual CTs are formed by a dynamic version of field-reversed theta-pinch technique, they are translated into a central confinement chamber at a speed of ~250 km/s, and they collide near the midplane of the machine. During the collision of two plasmoids, rapid axial compression and radial expansion occur, followed by an axial expansion, before finally merging to form an FRC. The merging process lasts 10’s of microseconds. The process of forming, translating, colliding and merging CTs has also been demonstrated by a 2-D resistive magnetohydrodynamic (MHD) code, LamyRidge. The final merged state exhibits a hollow density profile derived from a 6-chord CO2/He-Ne laser interferometry, and a reversed-field structure has been verified directly by internal magnetic field measurements at the midplane. About half of the axial kinetic energy is converted into thermal energy with total temperature (Tt = Ti + Te) exceeding 0.5 keV upon merging, predominantly into the ion channel as evidenced by ion Doppler broadening spectroscopy. Multi-point Thomson scattering data indicates Ti ~ 4Te in the quiescent phase of the merged FRC. The merged FRC also exhibits the following properties: FRC lifetime ≥ 1 ms, separatrix radius (rs) ~ 0.4 m, length (ls) ~ 3 m, poloidal flux (p) ~ 10 mWb, electron density (ne) ~ 5x1019 m-3, external magnetic field (Be) ~ 0.1 T, average external beta (<β>) ~ 0.9, and average diffusivity (D) derived from flux decay time ~ 15 m2/s.
Recently, wall conditioning by Titanium and Lithium coatings has been applied to the C-2 vacuum chamber, significantly reducing neutral recycling based on Dα emission measurement by a factor of 4–5 compared to data without wall coating. This, coupled with reduction in background pressure and impurities, further improves the global FRC performance (lifetime and confinement) with higher plasma temperature. Detailed edge (outside of FRC separatrix) measurements, e.g., by movable triple Langmuir probes and Dα detection fan-arrays, have also been made to further understand scrape-off layer plasma/neutral characteristics. These new advances will also be presented at the meeting.

[1] M.W. Binderbauer, H.Y. Guo et al., Phys. Rev. Lett. 105, 045003 (2010).
[2] H.Y. Guo, M.W. Binderbauer et al., Phys. Plasmas 18, 056110 (2011).

Characterization: A2

Comments:
In the abstract, there are several mising fonts (symbols) "Tau_p" and "D_perpendicular" so that please correct them before making abstract booklet. Thanks.

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011