Toroidal electron plasma: design, operation and diagnostics in smartex

Summary form only given. Pioneering work in 1990's had shown that electron plasmas can be confined in toroidal geometries but the confinement times were poor. Recent experiments have however improved the confinement by orders of magnitude in large aspect-ratio traps by applying an external electric field. Renewed interest in these plasmas have led us to refocus our attention on the small aspect-ratio toroidal electron plasmas. A SMall Aspect Ratio Toroidal EXperiment (SMARTEX) has been therefore designed and developed. Several challenges have been met in developing the trap and in particular the diagnostics. Charge measurements are marred by severe complexities due to fast transit times. The complex plasma dynamics in an inhomogenous magnetic field and strong self-consistent electric fields requires appropriate models to interpret the capacitive probe diagnostics. Asymmetries need to be carefully removed as they shorten the lifetime of the plasma. Our efforts and achievements on several fronts have led to successful operation of the trap. Such plasmas are now seen to remain confined without any external force field. Besides, a low frequency electrostatic flute mode results due to a coherent rotating structure. The novel, nonlinear state is marked by the presence of coupled modes, a non-monotonic frequency shear and a nonlinear evolution to a universal saturated state, unseen in other traps. SMARTEX therefore marks a paradigm shift in the investigations of toroidal electron plasmas. The SMARTEX trap including its design, diagnostics and operation will be presented in this paper. The intrinsic confinement properties and unique mode structure of the plasma will be presented to showcase the novelty and immense potential of the trap. Ongoing experiments and ideas to further develop SMARTEX will also be discussed