Laser-Driven and Magnetized Ultracold Neutral Plasmas

This project will explore the fundamental behavior of a plasma, a soup of electrons and ions, in a virtual ‘magnetic bottle’ trap. In order to understand how the magnetic field of the Earth protects life from electrically charged particles streaming from the sun, or to generate clean energy from nuclear fusion, one has to understand how a plasma behaves in a magnetic field.

This is one of the key problems in the field of plasma physics. This project will provide a detailed understanding of the behavior of plasmas trapped by a magnetic field. The plasma will be created in a highly controlled manner that results in an ultracold plasma, which is colder than outer space.

Such low temperatures make it easier to isolate different processes in the system for study, such as the rate at which particles escape from the trap. Surprisingly, an ultracold plasma shows behavior that is similar to hot and dense astrophysical plasmas, so these experiments can answer fundamental questions on the properties of objects such as white dwarf stars, which can possess strong magnetic fields.

The project will also train students in a broad set of technical skills so they can contribute to the STEM workforce. Outreach and recruiting efforts will be pursued in order to increase participation by students from diverse backgrounds.

This project will combine recently developed tools for laser cooling ions in an ultracold neutral plasma (UCNP) with magnetic-confinement techniques. This offers exciting opportunities for discovery plasma science, such as characterizing equilibration and transport phenomena in crossover regimes of magnetization and Coulomb-interaction (or ‘coupling’) strength.

Combining laser and magnetic forces may provide a solution for long-standing challenges to plasma confinement in a quadrupole magnetic-field geometry, namely the escape of plasma through loss gaps along field lines. The combination of strong coupling and magnetization modifies transport phenomena and collective modes, and has attracted increasing interest from the dusty and high-energy-density plasma communities.

These experiments will create a new system for probing this physics, and will test recent theories describing collisional processes in this regime. The specific goals are to (1) characterize the loss processes and scaling of magnetic confinement times with magnetic field for UCNPs formed in a quadrupole magnetic field, (2) measure the self-diffusion constant for magnetized ions and observe effects of strong coupling, and (3) use laser forces to plug loss gaps that typically allow plasma to escape along guiding-center magnetic field lines in a quadrupole magnetic field, creating long-term confinement.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.