Magnetic field advection in high energy density plasmas

National Science Foundation award

Principal Investigator: Prof. Gourdain

Co-Principal Investigators: Profs. Kusse, Lovelace, Seyler

High energy density (HED) plasmas have reached far beyond their powerful x-ray source origins. They are now a key component in the study of degenerate state of matter and astrophysical plasmas. Yet, our understanding of the basic mechanisms ruling HED plasmas is still incomplete. In particular, the time evolution or geometrical distribution of the magnetic field in HED plasmas remains an open question, which the proposed research will start to address. The main experimental setup to conduct this reasearch will be a radial foil load, a thin metallic foil radially driven by a pulsed power generator. A pin cathode contacts the foil at its geometrical center while the foil periphery is connected to a circular anode. The experimental setup benefits from quasi axisymmetric plasma dynamics and excellent 360° diagnostic access. This symmetry permits accurate unfolding of local plasma properties from line average measurements using Abel inversion techniques. In this case, interferometry, Faraday rotation, x-ray backlighting and absorption spectroscopy can deliver three dimensional reconstructions of the plasma electron density, magnetic field, mass density and temperature. By combining multiple measurements spaced in time, the proposed research will analyze the time evolution of plasma properties and deduce the most fundamental mechanisms ruling field advection in HED plasmas generated by radial foil configurations. We will extend our research to understand the meachnics of astrophysical objects, such as strongly collimated plasma jets and accretion disks. The experimental results will be compared to numerical computations to check the validity of plasma models, in particular the impact of the Hall term. The research program aims at answering the folliwing questions:

• Determining the interaction between the magnetic field, the ablated plasma and the unmagnetized plasma jet
• Understanding the time evolution of the magnetic field during the formation and expansion of the magnetized plasma jet
• Investigation of the magnetic field interaction with supersonic and super-Alfvénic flows

The dynamics of high energy density plasmas in radial foil configurations

Cooperative Agreement DoE/NNSA award

Principal Investigator: Prof. Gourdain

Co-Principal Investigators: Profs. Hammer, Kusse, Seyler

In the past decade, high energy density (HED) physics has become a major contributor in unlocking the mechanisms occurring in matter under extreme conditions. Radial foil configuration has emerged recently as a potential contender to wire array Z-pinches in producing HED plasmas. In this novel experimental layout, very high electrical currents flow inside a thin metal foil in the shape of a disk, thereby creating a plasma. The foil is stretched on the anode of a pulsed-power generator. The foil is connected to the cathode via a small vertical pin placed at its geometrical center. Using this configuration in conjunction with theory and computer simulations, the proposed program will complement the large national and international research on high energy density plasmas by conducting a targeted experimental investigation of:

1. the evolution of magnetic fields in HED plasmas;
2. the impact of the Hall effect on HED plasma dynamics.
3. the applications of plasmas produced by radial foil geometries to laboratory astrophysics and inertial fusion.

By changing the foil material and the electrode geometry, it will be possible to vary the physical parameters (i.e. temperature, density, magnetic field, flow velocities) that govern plasma dynamics to better understand astrophysical- or fusion-like phenomena in the laboratory. This research program will answer the following questions:

• What are the most striking features of HED plasmas generated by radial foil configurations and what are their properties?
• Which foil geometries highlight best the fundamental mechanisms ruling HED physics?
• What are the major instabilities in radial foil configurations and can they be mitigated?
• What is the impact of intrinsic and external magnetic fields on plasma dynamics and stability?

This research will also deepen our understanding of magnetically threaded plasma jets, encountered near compact celestial objects, and the role of magnetic fields on plasma confinement in inertial fusion applications. Finally it will compare experimental data to computational results obtained with the newly developed PERSEUS code.

Center for Pulsed-Power-Driven High-Energy-Density Plasmas

NNSA Award

Principal Investigator: Prof. Hammer

Co-Principal Investigators: Profs. Gourdain, Kusse, Seyler

The mission of the Center is to carry out world class experimental, theoretical and computational high energy density laboratory plasma (HEDLP) physics research on fundamental studies and applications of magnetized high energy density (HED) plasmas produced by pulsed power machines and to train the next generation of HEDLP research scientists. This Center of Excellence renewal proposal addresses. We propose to carry out experiments in a variety of configurations that will be discussed shortly, all of which are current driven, hot, dense plasmas that fit within the general name "dense Z-pinches." The experiments will be supported by computer simulations and theoretical modeling in order to help achieve an understanding of the experimental results and to help validate the computer simulations and theoretical models.
The principal objective of our research center is now and will continue to be to improve our understanding of the physics of HED plasma through high quality experimental research, computer simulations and theory. In the process, our goals include advancing the capability of HED science in the United States and contributing substantially to the training of the next generation of HED research scientists for stockpile stewardship and other programs of importance to national security. Other goals include contributing to the application of magnetized HED plasmas to inertial fusion energy, intense radiation generation, to understanding observed high energy astrophysical phenomena.
In order to achieve these objectives in the large, we operate two pulsed power machines with state-of-the-art suites of diagnostics, and our graduate students at Cornell design and carry out world class magnetized HED plasma experimental research and also develop advanced computer simulation and analytic theory tools to help understand the experiments. Where necessary, we also develop our own diagnostic tools, including visible and X-ray spectroscopic and imaging devices. Although the bulk of this effort is now and will continue to be carried out at Cornell, where appropriate, we collaborate with HED researchers from elsewhere in the United States to enhance in-house capability and from outside the United States to enhance US scientific infrastructure by exposing ourselves and our students to world-class research capability that has been developed in foreign research laboratories.