The High Density Z-Pinch as a Fusion Reactor

Abstract

Recent experimental results on a compressional Z-pinch and on a laser-initiated gas-embedded Z-pinch show considerable enhancement of MHD stability over conventional theory. It is thought that this could be due to finite ion Larmor radius effects. Several theoretical models of energy and pressure balance of a linear Z-pinch with end-losses have been made; electron thermal conduction with ωτ = 0, with ωτ = ∞ and singular thermal ion transit time loss. All yield the same essential scaling laws showing that Z-pinch will satisfy Lawson conditions with a current of 10⁶ A, a line density of 10¹⁹m^-1, and a ratio of ion Larmor radius to pinch radius of about 0.3 which should give marked stabilising. A choice of operating length or time is possible but 0.1 to 1 M with τ 10^-7 to 10^-6 s seems most practical. The smaller case is most applicable to a laser or beam initiated discharge. Here we can consider a bubble of D-T gas at 4 x 10²¹ cm^-3 density being injected through a hollow ring electrode fixed to the insulating wall of a liquid lithium bath. Following beam preionisation on the axis of the electrode the pulsed Ohmic heating and confining discharge of several MV and current rising to 1 MA will occur between the ring electrode and the liquid lithium. The liquid lithium acts as moderator, first wall, breeder and return conductor. With an instantaneous thermal power of 10¹² W, and burn time 10^-7 s discharge frequencies of 10⁴ s^-1 will be required for a 1000 MW plant. The merits of the system are simplicity, scalability to small power stations since the discharges can be arranged in modular form, and no impurity or first wall problems. Further experimental work on compression and laser- initiated gas embedded Z-pinches extending studies to higher currents of 10⁶ A is required, with particular emphasis on large ion Larmor radius stabilisation.