Magnetic Confinement of an Ultracold Neutral Plasma

TL;DR

This paper demonstrates magnetic confinement of ultracold neutral plasmas using a quadrupole magnetic field, showing prolonged confinement times and different trapping mechanisms for electrons and ions.

Contribution

It introduces a method to magnetically confine ultracold neutral plasmas and analyzes the distinct behaviors of electrons and ions within this setup.

Findings

Electrons are strongly magnetized across most of the plasma.

Confinement times reach approximately 0.5 milliseconds.

Unmagnetized plasmas dissipate in tens of microseconds.

Abstract

We demonstrate magnetic confinement of an ultracold neutral plasma (UCNP) created at the null of a biconic cusp, or quadrupole magnetic field. Initially, the UCNP expands due to electron thermal pressure. As the plasma encounters stronger fields, expansion slows and the density distribution molds to the field. UCNP electrons are strongly magnetized over most of the plasma, while ion magnetization is only significant at the boundaries. Observations suggest that electrons and ions are predominantly trapped by magnetic mirroring and ambipolar electric fields respectively. Confinement times approach 0.5 ms, while unmagnetized plasmas dissipate on a timescale of a few tens of microseconds.