Gas dynamic trap: experimental results and future prospects

The gas dynamic trap (GDT) is a version of a magnetic mirror with a long mirror-to-mirror distance far exceeding the effective mean free path of ion scattering into the loss cone, with a large mirror ratio ($R \sim 100$, $R=B_{\text{max}}/B_{\text{min}}$ is the ratio of magnetic field inductions at the mirror and at the trap center) and with axial symmetry. Under these conditions, in contrast to a conventional magnetic mirror, the plasma confined in a GDT is isotropic and Maxwellian. The plasma loss rate through the ends is governed by a set of simple gas dynamic equations; hence, the name of the device. The plasma lifetime in a GDT is on the order of $L R/V_{\text{Ti}}$, where $L$ is the mirror-to-mirror distance, and $V_{\text{Ti}}$ is the ion thermal velocity. Thus, increasing both the length of the device and the mirror ratio can, in principle, make the plasma lifetime sufficient for fusion applications. This paper discusses plasma confinement and heating results from the Novosibirsk GDT facility and examines prospects for using GDTs to develop a high-flux volumetric neutron source for fusion material testing and for driving subcritical fission reactors.