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[en] A variety of passive stabilization techniques compatible with S-1 inductive spheromak formation was evaluated for effectiveness against the MHD tilting instability. A line tying stabilization effect was previously identified theoretically. In this work, the effects were experimentally identified and investigated. The perturbed current patterns within passive stabilizing structures were measured, and line typing current were identified. The simple ring model of tilting was expanded to include line tying, and gives estimates for growth rates that agree well with the measured values
[en] The Precision Laser Inclinometer was tested at thermo-stabilized conditions, and the ground angular stability of 1 μrad (observation during 24 h) and 7 nrad (observation during 60 min) was measured.
[ru]Прецизионный лазерный инклинометр протестирован в термостабильных условиях. Измерена угловая стабильность земной поверхности - 1 мкрад (время измерения 24 ч) и 7 нрад (время измерения 60 мин).
[en] The properties of the n = 1 tilting instability in both Proto S-1/A and Proto S-1/C are examined. The plasma behavior is determined experimentally by mapping the evolution of the magnetic field configuration in the toroidal plane perpendicular to the tilt axis with small magnetic probes. The mode is found to be not quite rigid, with the outer portions of the plasma having a roughly constant growth rate which is faster than that of the region near the magnetic axis for most cases. Growth rates measured for the tilting instability are compared to the predictions of a simple current ring model, and to the results of numerical simulations. The growth rates scale approximately as predicted by a simple model. Two different configurations of passive coils are shown to be effective in stabilizing the tilting mode in both Proto S-1/A and Proto S-1/C. These are the figure eight coils and the saddle coils. The figure eight coils are effective against both tilting and shifting modes, but restrict access to the plasma. The saddle coils permit free access, but are effective only against the tilting. A peak value of approximately 4% of the toroidal plasma current induced in the coils appears sufficient to suppress the tilting instability for the lifetime of the plasma in these experiments. This level of current in the coils corresponds to an applied horizontal field in the plane of the tilt which is less than or equal to 4% of the toroidal field at the magnetic axis
[en] In recent years, part of the experimental effort on the FRX-C/LSM device has been devoted to understanding why good FRC confinement is observed only in a narrow window of the operating parameter space (fill pressures less than 5 mtorr and bias fields less than 0.8--0.9 kG). The transition from good to bad confinement has been shown for some time to correlate with strong axial shocks, suggesting a formation or stability problem. More recently, FRC magnetic asymmetries have been observed whenever the confinement was poor. To gain further understanding, a 64-coil probe array was built, and data from over 700 discharges were collected during the summer of 1989. We summarize in this paper the results of a preliminary analysis of these data. 5 refs., 4 figs
[en] A stability criterion for the tilt mode of a spheromak-ion ring hybrid configuration has been developed for the case where the ring current is small compared to the spheromak azimuthal current. It is shown that the stability is related to the distortion of the spheromak separatrix
[en] The experimental investigation of the effectiveness of figure-8 coils in stabilizing the n=1 tilting mode of spheromak plasmas in Proto S-1 A/B is extended. In addition, another coil configuration, the saddle coil, is examined
[en] The stability of spheromak equilibria with a flux core, or reversal coil, is studied by means of an ideal MHD code. Results depend critically upon whether the flux hole region (the current free area just inside the separatrix) is treated as perfectly conducting plasma or as vacuum. This indicates that the tilt and shift modes persist as resistive instabilities if they are stable in ideal MHD. Specifically, for nonoptimally shaped equilibria, the flux core must nearly touch the current channel if the flux hole is vacuum, whereas the core may be slightly outside the separatrix if the flux hole has conducting plasma. A larger margin exists for optimally shaped equilibria
[en] In the earleir stages of acceleration in a heavy-ion-induction linac, acceleration and bunching rates are constrained by the allowable value of head-to-tail velocity tilt at a given location. If focusing parameters at a given location are fixed, the velocity tilt should be less than a certain upper bound to avoid too much envelope variation and consequent beam losses. For space charge dominated beams, we found some favorable particle distributions in longitudinal phase space for which the maximum-matched-beam envelope at a given location is almost constant with respect to time, in spite of the presence of a large velocity tilt. Mismatch oscillations can be reduced by slow variation of the velocity tilt and slow current amplification. Under these circumstances, the velocity tilt can be as large as allowed by the usable range of σ/sub o/. Behavior of Cs ion beams with very large velocity tilts (up to 40%) are studied experimentally in MBE-4 and the results are presented
[en] This paper discusses the tilting instability phenomena of spheromak plasma by three-dimensional simulation. Special attention is paid to the stabilizing effect of the center conductor. The helical instability is also discussed. 6 references, 15 figures
[en] Field reversed configurations with equilibrium separatrix radii up to 0.18 m have been formed and studied in FRX-C/LSM. For best formation conditions at low fill pressure, the particle confinement exceeds the predictions of LHD transport calculations by up to a factor of two; however, the inferred flux confinement is more anomalous than in smaller FRCs. Higher bias field produces axial shocks and degradation in confinement, while higher fill pressure results in gross fluting during formation. Field reversed configurations have been formed in TRX with s from 2 to 6. These relatively collisional FRCs exhibit the flux lifetimes of 10-20 kinetic growth times for the internal tilt mode. The coaxial slow source has produced annular FRCs in a coaxial coil geometry on slow time scales using low voltages. (author). 16 refs, 4 figs, 1 tab