Title: Local measurements of the spatial magnetic field distribution in a z-pinch plasma during and near stagnation using polarization spectroscopy

Abstract

We present here the detailed measurements of radial distribution of the magnetic field in a gas-puff z-pinch plasma at the final stages of the implosion phase and at stagnation. While the measurements are chordal, the radial distribution of different charge states was utilized to measure the magnetic field locally for certain radii, so that unlike chordal measurements in general, the magnetic field radial distribution was obtained with no need for the Abel inversion of the data. The distribution was measured using the Zeeman effect via a novel spectroscopic technique, at several axial locations, and demonstrates striking features such as the peak field remaining at a radius much larger than the stagnation radius at all times. Furthermore, while the distribution observed is sometimes monotonic with respect to the radius, it is often not, a behavior that can be linked to 2D features in the plasma column resulting from the Rayleigh–Taylor instability. The current flowing through the stagnating plasma was found to be a small fraction of the total current, resulting in clearly insufficient magnetic pressure to balance the plasma pressure at stagnation. The magnetic field data, taken over several axial positions, are used to obtain the true inductance in the implodingmore » plasma for the first time; it is found that the data cannot explain the current turnover at stagnation. A simulation with the MACH2-Tabular Collisional-Radiative Equilibrium magnetohydrodynamics code in the r–z plane shows that the peak of the magnetic field pinches to a much smaller radius than is observed in the spectroscopic data. Furthermore, the depth of the computed current turnover at stagnation is smaller than the measured one. The two observed features of a radially extended magnetic field at stagnation together with a deep current turnover are a challenge to match in simulations. Various calculations and estimates of the inductive and resistive load voltages are examined to ascertain if they are responsible for the observed current notch. Lastly, the results demonstrate that the knowledge of the true inductance in the driven load requires such magnetic-field-distribution measurements and that imaging data or electrical measurements are insufficient.« less

Authors:

Rosenzweig, G.  ^[1];

• Search DOE PAGES for author "Rosenzweig, G."
• Search DOE PAGES for ORCID "0000-0002-6365-666X"

Kroupp, E.  ^[1];

• Search DOE PAGES for author "Kroupp, E."
• Search DOE PAGES for ORCID "0000-0002-3384-9778"

Queller, T.  ^[1];

• Search DOE PAGES for author "Queller, T."
• Search DOE PAGES for ORCID "0000-0003-3841-0091"

Starobinets, A.  ^[1];

• Search DOE PAGES for author "Starobinets, A."
• Search DOE PAGES for ORCID "0000-0001-5517-1737"

Maron, Y. ^[1]; Tangri, V.  ^[2];

• Search DOE PAGES for author "Tangri, V."
• Search DOE PAGES for ORCID "0000-0003-1977-7779"

Giuliani, J. L.  ^[3];

• Search DOE PAGES for author "Giuliani, J. L."
• Search DOE PAGES for ORCID "0000-0001-6793-3786"

Fruchtman, A.  ^[4]

• Search DOE PAGES for author "Fruchtman, A."
• Search DOE PAGES for ORCID "0000-0001-9297-9233"

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+ Show Author Affiliations

1. Weizmann Inst. of Science, Rehovot (Israel)
2. Research Support Instruments, Lanham, MD (United States)
3. Naval Research Lab., Washington, D.C. (United States)
4. Holon Inst. of Technology (Israel)

Publication Date:

Wed Feb 12 00:00:00 EST 2020

Research Org.:

Naval Research Lab. (NRL), Washington, DC (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1637267

Alternate Identifier(s):

OSTI ID: 1599251

Grant/Contract Number:  

NA0003764; NA0001564

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 27; Journal Issue: 2; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY