Observation of Macroscopic Stability Limits in a Tandem Mirror

Molvik, A.W.; Breun, R.; Golovato, S.; Hershkowitz, N.; McVey, B.D.; Smatlak, D.L.; Yujiri, L.

doi:10.1103/physrevlett.48.742

Cited by 35 publications

(18 citation statements)

References 8 publications

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“…Here the quantity Γ ks is related to the particle flux per unit magnetic flux Γ ks from a single end of the tandem mirror as indicated in (4). The spread in magnetic moments of the kinetic stabilizer beam is determined by ∆µ; we use µ T = E 0 /B T where the subscript T refers to the target position; the values of ∆µ and µ T effects the maximum density at the target.…”

Section: Kstm Model a Distribution Of Ions In The Kinetic Stabilmentioning

confidence: 99%

Trapped particle stability for the kinetic stabilizer

Berk

Pratt²

2011

Nucl. Fusion

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A kinetically stabilized axially symmetric tandem mirror (KSTM) uses the momentum flux of low-energy, unconfined particles that sample only the outer end-regions of the mirror plugs, where large favorable field-line curvature exists. The window of operation is determined for achieving MHD stability with tolerable energy drain from the kinetic stabilizer. Then MHD stable systems are analyzed for stability of the trapped particle mode. This mode is characterized by the detachment of the central-cell plasma from the kinetic stabilizer region without inducing field-line bending. Stability of the trapped particle mode is sensitive to the electron connection between the stabilizer and the end plug. It is found that the stability condition for the trapped particle mode is more constraining than the stability condition for the MHD mode, and it is challenging to satisfy the required power constraint. Furthermore a severe power drain may arise from the necessary connection of low-energy electrons in the kinetic stabilizer to the central region.

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Section: Kstm Model a Distribution Of Ions In The Kinetic Stabilmentioning

confidence: 99%

Trapped particle stability for the kinetic stabilizer

Berk

Pratt²

2011

Nucl. Fusion

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“…More detailed results on MHD stability experiments in Phaedrus are described elsewhere. 13 We have shown that a tandem-mirror plasma with isolated end plugs can be sustained by rf and gas fueling for 8 ms beyond gun turnoff. This time appears to be limited only by the rf pulse length and is much longer than the characteristic decay times of the plugs and central cell.…”

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Experiments in a Tandem Mirror Sustained and Heated Solely by rf

et al. 1981

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A tandem-mirror plasma has been sustained and heated by rf alone without the need for neutral beams. End plug density and energy are maintained by ion cyclotron-resonance heating which traps and heats a fraction of the central-cell loss stream. The central-cell plasma is maintained by gas fueling and rf heating. Magnetohydrodynamic stability limits the ratio of the central-cell to plug plasma pressure, and the central-cell electron temperature must be kept high enough for ionization. A quasi steady state is achieved that lasts much longer than the decay times of the plugs and central cell.PACS numbers: 52.55. Mg, 52.50.Gj, 52.55.Ke The tandem-mirror approach to the development of a fusion reactor promises to have many advantages over simple mirrors as well as other magnetic confinement devices. 1 In a tandem mirror, a central-cell plasma in a solenoid is bounded by "plug" plasmas in mirror cells. The TMX experiment 2 demonstrated that electrostatic confinement of central-cell ions by the plug plasmas significantly reduced end losses. Calculations indicate that the overall Q (power gain) of a tandem-mirror fusion reactor can be quite high (~5-10) if the volume of the central cell greatly exceeds that of the plugs. 3 In previous experiments, plug plasmas were fueled and heated by energetic neutral beams. However, technological constraints on neutral-beam heating when scaled to a reactor could be eased or eliminated by supplementing or replacing neutral-beam power with rf power. We show in the Phaedrus experiment that a tandem-mirror plasma can be sustained by rf alone, without the application of neutral beams.The operation of a tandem mirror can be thought of as taking place in two stages, a transient stage followed by a quasi-state stage. In the transient stage, plasma is injected into the machine by stream guns. In fact, earlier experiments with Phaedrus 4 and Gamma 6 5 were restricted to the transient stage. Such plasmas side-stepped many of the issues of tandem-mirror physics because plasma characteristics were dominated by the external plasma between the plugs and the stream guns. The high-density external plasma line-tied the plasma to the stream guns, significantly reducing both magnetohydrodynamic (MHD) instabilities and microinstabilities and fixing the electron temperature. When the stream guns were turned off in Phaedrus, the plasma decayed away in approximately 150 jus in the plugs and 400 JUS in the central cell. Quasi-steady-state operation after stream guns are turned off requires sources of particles and energy for both the plug and central-cell plasmas and also adds constraints that must be satisfied in order to maintain microstability and MHD stability. In TMX, fueling and heating were provided by neutral beams in the plugs and gas puffing in the central cell. In the Phaedrus experiment, fueling is provided only by gas puffing in the central cell while rf provides heating. In both experiments, stability was provided by high plug energy density and the presence of the central-cell loss flow.The ...

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“…1 " 3 Weighting of the good field-line curvature in anchor ceils with sufficient plasma pressure provides interchange stability. 4 Disadvantages of this design are the enhanced radial ion loss due to the nonaxisymmetric field regions associated with the minimum-\B\ ceils 5 and the difficulty and expense in construction of the necessary coil sets. At present there is a significant effort directed toward the design of inter change-stable axisymmetric tandem mirrors.…”

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rf Stabilization of an Axisymmetric Tandem Mirror

et al. 1983

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Plasma with significant central-cell beta can be sustained in a tandem mirror composed of three axisymmetric simple mirror cells by the use of ion-cyclotron resonant heating. Radial ponderomotive force due to the rf electric field opposes the centrifugal force due to the field-line curvature to ensure interchange stability. This is indicated by the sensitive dependence of the plasma stability on the sign of the difference between the rf frequency and the ion-cyclotron frequency.

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Observation of Macroscopic Stability Limits in a Tandem Mirror

Cited by 35 publications

References 8 publications

Trapped particle stability for the kinetic stabilizer

Trapped particle stability for the kinetic stabilizer

Experiments in a Tandem Mirror Sustained and Heated Solely by rf

rf Stabilization of an Axisymmetric Tandem Mirror

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