Stanford Advisors


All Publications


  • Dynamic formation of stable current-driven plasma jets. Scientific reports Underwood, T. C., Loebner, K. T., Miller, V. A., Cappelli, M. A. 2019; 9 (1): 2588

    Abstract

    Instabilities play a prominent role in determining the inherent structure and properties of magnetized plasma jets spanning both laboratory and astrophysical settings. The manner in which prominent unstable modes dynamically evolve remains key to understanding plasma behavior and control. In astrophysical phenomena, self-similar jets are observed to propagate over vast distances while avoiding breakup caused by unstable mode growth. However, the production of stable dense plasma jets in the laboratory has been limited by the onset of unstable modes that restrict jet lifetime, collimation, and scalability. In this work, we visualize the formation of stable laboratory-generated, dense, super-magnetosonic plasma jets in real time, and we identify an underlying mechanism that contributes to this behavior. The current-driven plasma jets generated in our experiments form a flowing Z-pinch, which is generally unstable to the m=1 kink instability. Our results indicate that a stable dense plasma jet can be maintained for timescales over which a steady pinch current can be sustained, even at levels which would otherwise lead to rapid unstable mode growth and resultant pinch disassembly.

    View details for PubMedID 30796311

  • Laser-produced gaseous plasmonic resonators PHYSICS OF PLASMAS Quinones, R., Underwood, T. C., Cappelli, M. A. 2018; 25 (11)

    View details for DOI 10.1063/1.5054022

    View details for Web of Science ID 000451734600046

  • Predictive modeling of plasmas for gaseous plasmonics PLASMA SOURCES SCIENCE & TECHNOLOGY Biggs, D. R., Underwood, T. C., Cappelli, M. A. 2018; 27 (7)
  • Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators PLASMA SOURCES SCIENCE & TECHNOLOGY Subramaniam, V., Underwood, T. C., Raja, L. L., Cappelli, M. A. 2018; 27 (2)
  • Damage Morphologies in Targets Exposed to a New Plasma Deflagration Accelerator for ELM Simulation IEEE TRANSACTIONS ON PLASMA SCIENCE Loebner, K. T., Underwood, T. C., Wang, B. C., Cappelli, M. A. 2016; 44 (9): 1534-1540
  • Radial magnetic compression in the expelled jet of a plasma deflagration accelerator APPLIED PHYSICS LETTERS Loebner, K. T., Underwood, T. C., Mouratidis, T., Cappelli, M. A. 2016; 108 (9)

    View details for DOI 10.1063/1.4943370

    View details for Web of Science ID 000375329200065

  • Evidence of Branching Phenomena in Current-Driven Ionization Waves PHYSICAL REVIEW LETTERS Loebner, K. T., Underwood, T. C., Cappelli, M. A. 2015; 115 (17)

    Abstract

    This Letter reports the first fully consistent experimental observations of current-driven ionization waves conforming to the magnetohydrodynamic Rankine-Hugoniot model for hydromagnetic shocks. Detailed measurements of the thermodynamic and electrodynamic plasma state variables across the ionization region confirm the existence of two types of waves, corresponding to the upper and lower solution branches of the Hugoniot curve. These waves are generated by pulsed currents in a coaxial gas-fed plasma accelerator. The coupling between the state variables of this complex, transient, three-dimensional system shows a remarkable quantitative agreement of less than 8% deviation from the quasisteady, one-dimensional theoretical model.

    View details for DOI 10.1103/PhysRevLett.115.175001

    View details for Web of Science ID 000363016600002

  • A fast rise-rate, adjustable-mass-bit gas puff valve for energetic pulsed plasma experiments. Review of scientific instruments Loebner, K. T., Underwood, T. C., Cappelli, M. A. 2015; 86 (6): 063503-?

    Abstract

    A fast rise-rate, variable mass-bit gas puff valve based on the diamagnetic repulsion principle was designed, built, and experimentally characterized. The ability to hold the pressure rise-rate nearly constant while varying the total overall mass bit was achieved via a movable mechanical restrictor that is accessible while the valve is assembled and pressurized. The rise-rates and mass-bits were measured via piezoelectric pressure transducers for plenum pressures between 10 and 40 psig and restrictor positions of 0.02-1.33 cm from the bottom of the linear restrictor travel. The mass-bits were found to vary linearly with the restrictor position at a given plenum pressure, while rise-rates varied linearly with plenum pressure but exhibited low variation over the range of possible restrictor positions. The ability to change the operating regime of a pulsed coaxial plasma deflagration accelerator by means of altering the valve parameters is demonstrated.

    View details for DOI 10.1063/1.4922522

    View details for PubMedID 26133835

  • A fast rise-rate, adjustable-mass-bit gas puff valve for energetic pulsed plasma experiments. Review of scientific instruments Loebner, K. T., Underwood, T. C., Cappelli, M. A. 2015; 86 (6): 063503-?

    Abstract

    A fast rise-rate, variable mass-bit gas puff valve based on the diamagnetic repulsion principle was designed, built, and experimentally characterized. The ability to hold the pressure rise-rate nearly constant while varying the total overall mass bit was achieved via a movable mechanical restrictor that is accessible while the valve is assembled and pressurized. The rise-rates and mass-bits were measured via piezoelectric pressure transducers for plenum pressures between 10 and 40 psig and restrictor positions of 0.02-1.33 cm from the bottom of the linear restrictor travel. The mass-bits were found to vary linearly with the restrictor position at a given plenum pressure, while rise-rates varied linearly with plenum pressure but exhibited low variation over the range of possible restrictor positions. The ability to change the operating regime of a pulsed coaxial plasma deflagration accelerator by means of altering the valve parameters is demonstrated.

    View details for DOI 10.1063/1.4922522

    View details for PubMedID 26133835

  • Evidence of Branching Phenomena in Current-Driven Ionization Waves. Physical review letters Loebner, K. T., Underwood, T. C., Cappelli, M. A. 2015; 115 (17): 175001

    Abstract

    This Letter reports the first fully consistent experimental observations of current-driven ionization waves conforming to the magnetohydrodynamic Rankine-Hugoniot model for hydromagnetic shocks. Detailed measurements of the thermodynamic and electrodynamic plasma state variables across the ionization region confirm the existence of two types of waves, corresponding to the upper and lower solution branches of the Hugoniot curve. These waves are generated by pulsed currents in a coaxial gas-fed plasma accelerator. The coupling between the state variables of this complex, transient, three-dimensional system shows a remarkable quantitative agreement of less than 8% deviation from the quasisteady, one-dimensional theoretical model.

    View details for PubMedID 26551118