Spheromak Impedance and Current Amplification

Fowler, T K ; Hua, D D ; Stallard, B W

Lawrence Livermore National Laboratory

关键词: Amplification;    Decay;    70 Plasma Physics And Fusion Technology;    Feeding;    Helicity;   

DOI  :  10.2172/15004646
RP-ID  :  UCRL-ID-147087
RP-ID  :  W-7405-ENG-48
RP-ID  :  15004646

美国|英语

来源: UNT Digital Library

【 摘 要 】

It is shown that high current amplification can be achieved only by injecting helicity on the timescale for reconnection, {tau}{sub REC}, which determines the effective impedance of the spheromak. An approximate equation for current amplification is: dI{sub TOR}{sup 2}/dt {approx} I{sup 2}/{tau}{sub REC} - I{sub TOR}{sup 2}/{tau}{sub closed} where I is the gun current, I{sub TOR} is the spheromak toroidal current and {tau}{sub CLOSED} is the ohmic decay time of the spheromak. Achieving high current amplification, I{sub TOR} >> I, requires {tau}{sub REC} <<{tau}{sub CLOSED}. For resistive reconnection, this requires reconnection in a cold zone feeding helicity into a hot zone. Here we propose an impedance model based on these ideas in a form that can be implemented in the Corsica-based helicity transport code. The most important feature of the model is the possibility that {tau}{sub REC} actually increases as the spheromak temperature increases, perhaps accounting for the ''voltage sag'' observed in some experiments, and a tendency toward a constant ratio of field to current, B {proportional_to} I, or I{sub TOR} {approx} I. Program implications are discussed.