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2 Nukleonika

2 2001

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The role of anomalous resistivities in Plasma Focus discharges

Bruzzone H.

Nukleonika

2001

Vol. 46, suppl. 1

3--7

The existence of plasma microturbulence in Plasma Focus (PF) devices is a widely accepted fact within the PF community. This microturbulence must be generated as a final stage of microscopic instabilities, which could develop during certain phases of the plasma evolution. Among the candidate instabilities to occur in these devices, the lower hybrid drift instability is the one with better possibilities, because its triggering condition (electron drift velocity approaching ion thermal velocity) has reasonable chances to be fulfilled. The main effect of the development of this instability is the modification of the collision frequencies in the plasma, which adds an anomalous term to the plasma resistivity. The theory for evaluating this extra term exists, and has been already used in PF 1D numerical simulations and in Z-pinch calculations. The role of this anomalous resistivity in PF behaviour has been the subject of considerable speculations. In this work, a 1D MHD (magnetohydrodynamics) calculation of the pinch stage in a PF device will be presented, including anomalous resistivity effects and their influence on electric fields and the discharge current are discussed.

The need of using anomalous resistivity due to Lower Hybrid Instabilities in plasma-magnetic field interfaces

Bruzzone H., Bernal L.

Nukleonika

2001

Vol. 46, nr 2

59-61

Anomalous plasma can arise in dense plasmas as a consequence of the development resistivity of the Lower Hybrid drift Instability (LHI), which is triggered whenever the electron drift velocity becomes comparable to or larger than the thermal ion velocity. This effect was carefully evaluated for theta-pinch plasmas and later on used in the modelling of denser pinches, like Plasma Focus columns or Z-pinches, because of the diverging electron drift velocity expected in the classical equilibrium (uniform current, parabolic plasma density) pinch. Conceptually, the possibility of diverging drift velocities is far more a general situation than Z-pinches, and in this work we study it, in general, for plasma-magnetic field interfaces existing in other configurations, like that found in devices producing travelling current sheets (Plasma Focus devices, imploding pinches, etc.). We show that it is essential to account for this effect in steady state situations, and that it could be also important