Interaction of a spheromak-like compact toroid with a high beta spherical tokamak plasma

Recent experiments using accelerated spheromak-like compact toroids (SCTs) to fuel tokamak plasmas have quantified the penetration mechanism in the lo w beta regime; i.e. external magnetic field pressure dominates plasma therm al pressure. However, fusion reactor designs require high beta plasma and, more importantly, the proper plasma pressure profile. Here, the effect of t he plasma pressure profile on SCT penetration, specifically, the effect of diamagnetism, is addressed. It is estimated that magnetic field pressure do minates penetration even up to 50% local beta. The combination of the diama gnetic effect on the toroidal magnetic field and the strong poloidal field at the outer major radius of a spherical tokamak will result in a diamagnet ic well in the total magnetic field. Therefore, the spherical tokamak is a good candidate to test the potential trapping of an SCT in a high beta diam agnetic well. The diamagnetic effects of a high beta spherical tokamak disc harge (low aspect ratio) are computed. To test the penetration of an SCT in to such a diamagnetic well, experiments have been conducted of SCT injectio n into a vacuum field structure a which simulates the diamagnetic field eff ect of a high beta tokamak. The diamagnetic field gradient length is substa ntially shorter than that of the toroidal field of the tokamak, and the res ults show that it can still improve the penetration of the SCT. Finally, an alytic results have been used to estimate the effect of plasma pressure on penetration and the effect of plasma pressure was found to be small in comp arison with the magnetic field pressure. The penetration condition for a va cuum field only is reported. To study the diamagnetic effect in a high beta plasma, additional experiments need to be carried out on a high beta spher ical tokamak.