Abstract:An increase in the global energy confinement time (TE) was obtained in the CTX spheromak by replacing the high-field-error mesh-wall flux conserver with a low-field-error solid-wall flux conserver. The maximum TE is now 0.18 ms, an order of magnitude greater than previously reported values of ;S0.017 ms. Both TE and the magnetic energy decay time ixw) now increase with central electron temperature, which was not previously observed. These new results are consistent with a previously proposed energyloss mechani… Show more
“…The T i measurement is chord averaged, but we assume T i T e and decreases with minor radius even though the majority of anomalous ion heating is expected in the edge. This results in t E ഠ 150 6 70 ms, the same as the highest value previously reported (CTX [19]) for a decaying spheromak and is the highest value reported for a driven spheromak.…”
Magnetic fluctuations have been reduced to approximately 1% during discharges on the Sustained Spheromak Physics Experiment by shaping the spatial distribution of the bias magnetic flux in the device. In the resulting quiescent regime, the safety factor profile is nearly flat in the plasma and the dominant ideal and resistive MHD modes are greatly reduced. During this period, the temperature profile is peaked at the magnetic axis and maps onto magnetic flux contours. Energy confinement time is improved over previous reports in a driven spheromak.
“…The T i measurement is chord averaged, but we assume T i T e and decreases with minor radius even though the majority of anomalous ion heating is expected in the edge. This results in t E ഠ 150 6 70 ms, the same as the highest value previously reported (CTX [19]) for a decaying spheromak and is the highest value reported for a driven spheromak.…”
Magnetic fluctuations have been reduced to approximately 1% during discharges on the Sustained Spheromak Physics Experiment by shaping the spatial distribution of the bias magnetic flux in the device. In the resulting quiescent regime, the safety factor profile is nearly flat in the plasma and the dominant ideal and resistive MHD modes are greatly reduced. During this period, the temperature profile is peaked at the magnetic axis and maps onto magnetic flux contours. Energy confinement time is improved over previous reports in a driven spheromak.
“…Previous work at the CTX spheromak at Los Alamos [6] resulted in temperatures of >150 eV for driven spheromaks and toroidal currents of >250 kA in discharges up to 2 ms in duration. Decaying spheromaks on CTX heated to 400eV [7].…”
The Sustained Spheromak Physics Experiment (SSPX) [E.B. Hooper, et. al., Nuclear Fusion, Vol. 39,No. 7] explores the physics of efficient magnetic field buildup and energy confinement,
“…This success was due in part to the use of close-fitting, solid flux conservers and proper wall conditioning. [6][7][8][9] The key to proper conditioning was the incorporation of titanium gettering of the flux conserver walls. 10,11 In addition, the CTX group had perfected the slow-formation technique 12 so that spheromaks could be sustained for times that were long compared with their resistive decay times.…”
Section: Previous Workmentioning
confidence: 99%
“…where 8 is the interelectrode gap and Vfi ow is the flow velocity of toroidal flux and plasma out of the gun. To compute the flow velocity, we note that in steady state, Vfl OW is fixed, and the J X B force acting on the plasma is (9) gun are straightforward. A direct measurement of the mass flow rate m = dm/dt would help corroborate this model.…”
An experiment is described that incorporates the use of separate magnetized plasma guns for formation and sustainment of a spheromak. It is shown that energy coupling efficiency approaches unity if the gun and spheromak are of comparable size. A large gun should be able to operate at lower current and therefore lower voltage. In addition, it is expected that a gun matched to the size of the spheromak will cause less perturbation to the equilibrium. It is proposed to use a smaller gun for spheromak formation and a large, efficient gun for sustainment. The theoretical basis for the experiment is developed, and the details of the experiment are described. A prediction of the equilibrium magnetic flux surfaces using the EFIT code is presented.
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