Shape manipulation of a rotating liquid liner imploded by arrays of pneumatic pistons: Experimental and numerical study

Abstract

Shaping the inner surface of a rotating, imploding liquid metal liner as it compresses a magnetised plasma target is an important aspect of the Magnetised Target Fusion (MTF) scheme pursued by General Fusion. Reduced-order modelling has shown that the liner's inner surface shape can be manipulated during the implosion by spatially varying the amplitude and timing of pressure applied at the liner's outer surface. A sub-scale apparatus was constructed to investigate this concept, using water as the liner material. A simplified axisymmetric model of this apparatus was also developed using OpenFOAM software. Experimental pressure and rotational speed were used as inputs to numerical simulations. Very good agreement between numerical and experimental liner trajectories was obtained for a wide range of implosion parameters. Data analysis confirmed an initially cylindrical inner liner surface can be shaped and the shaped surface remains symmetrical to radial compression ratios of at least 7:1, despite driving the implosion using pneumatic piston arrays. Furthermore, experiments demonstrated suppression of Rayleigh-Taylor instability for shaped implosions by using liner rotation. This is significant, as literature only confirms this suppression for cylindrical implosions. These results increase confidence in simplified numerical modelling as a predictive tool for designing MTF machines.