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Evolution of the electrothermal instability from thick rod z pinches subject to dynamically and statically applied axial magnetic field

Technical Report ·
DOI:https://doi.org/10.2172/2999121· OSTI ID:2999121
 [1];  [1];  [2];  [1];  [3];  [1];  [1];  [1];  [1];  [1];  [4];  [5];  [1]
  1. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
  2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
  3. General Atomics, La Jolla, CA (United States)
  4. Oak Hill Engineering, Sumner, WA (United States)
  5. Milhous Company, Amherst, VA (United States)
+ Show Author Affiliations

LDRD Project 229427 aimed to determine how electrothermal instability (ETI) driven heating on a z-pinch rod pulsed with intense current evolves under mixed magnetic field (azimuthal + axial) conditions, which is pertinent to pulsed-power-driven magnetically-insulated transmission lines and physics targets. Experiments focused on diagnosing ETI-driven heating from deliberately-machined and well-characterized micron-scale surface defects (referred to as engineered defects or ED). Prior to the start of this project, understanding of how unmagnetized (Bz=0) ED evolve had been obtained—simulations largely reproduce the experimentally observed high temperature spots which develop at the poles of bare/uncoated ED. Project 229427 extended the Mykonos Facility ED experimental platform to include axial field. In the first class of experiments, axial field was provided “dynamically” via a helical return can (HRC). In this case, Bz and Bθ rise at the same rate. Generally, the HRC generated magnetic field at a fixed polarization angle ΦB=arctan(Bz/Bθ)=15° on the rod's surface. In the second class of experiments, axial field was provided “statically” via a slow-rising (millisecond) external Helmholtz coil pair. In this case, Bz was effectively constant/static throughout the 100 ns rise of the Mykonos current. For either case, a primary goal was to determine whether ETI provides a helical seed perturbation for the subsequent growth of the helical magneto Rayleigh-Taylor modes observed in MagLIF (static Bz) and dynamic screw pinch (DSP, dynamic Bz) experiments. When dynamic field was applied using an HRC, emissions from individual ED aligned toward ΦB, while emissions from ED within pairs elongated and preferentially merged along ΦB. These data strongly support that for a randomized defect distribution, heating from nearby current-density perturbations will favorably merge about ΦB to generate an extended seed perturbation that aligns toward the surface-field polarization, and this may impact the orientation of subsequent MRT growth on imploding liners. The results from the static field experiments were largely inconclusive, as any ETI heating rotation, if present, was obscured/overwhelmed by local/random heating from ED rim imperfections.

Research Organization:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
DOE Contract Number:
NA0003525
OSTI ID:
2999121
Report Number(s):
SAND--2025-13115R; 1789987
Country of Publication:
United States
Language:
English

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