|Investigators and institutions||Science project details|
|The interaction of Alfvén waves with flowing plasmas: Mark Koepke (West Virginia U.), C. Chaston, (UC Berkeley), D. Knudsen (U. Calgary, Canada), R. Marchand (U. Alberta, Canada), R. Rankin (U. Alberta, Canada), S. Finnegan (West Virginia U.)||Magnetized plasmas are predicted to support electromagnetic perturbations that are static in a fixed frame if there is uniform background plasma convection. These stationary waves should not be confused with standing waves that oscillate in time with a fixed, spatially varying envelope. Stationary waves have no time variation in the fixed frame. In the drifting frame, there is an apparent time dependence as plasma convects past fixed electromagnetic structures. In this project, an off-axis, fixed channel of electron c urrent (and depleted density) is created in the Large Plasma Device, using a small, heated, oxide-coated electrode at one plasma-column end while the larger plasma column rotates about its cylindrical axis from a radial electric field imposed by a special termination electrode on the same end. A variety of methods will be explored to generate EXB plasma flows in the center of the bulk plasma. These include segmented electrodes, spiral electrodes, emitting electrodes and a biased center conductor. The interaction will be studied with a variety of probes as well as LIF. This campaign is on hold while Prof. Koepke is at DOE.|
|Investigators and institutions||Research topic details|
|Experimental and Numerical Studies of an Ionospheric Alfvén Resonator: A. Strelsov, Dept of Physics, Dartmouth College, W. gekelman, S. Vincena, P. Pribyl (UCLA)||This program is a study of the propagation of a linearly polarized shear Alfvén wave in a strongly inhomogeneous magnetic field. The experiment consists of launching shear Alfvén waves from one end of LAPD and measuring the wave amplitude at different distances from the antenna. The goal is to find the dependence of the wave reflection on the magnetic field ratio, B01/B00, the scale-size of the inhomogeneity, L, the wave frequency, and the perpendicular scale-size. The experimental studies will be compared to comprehensive numerical simulations at Dartmouth College. One experimental run has been completed and data is being analyzed.|
|Conversion of electrostatic Langmuir waves to electromagnetic waves in space plasmas: Cynthia Cattell, P. Kellogg, (Dept. of Physics, University of Minnesota.) W. Gekelman, P. Pribyl, B. Van Compernolle (UCLA)||The details of conversion of electrostatic Langmuir waves to electromagnetic waves in space plasmas are not well understood. The converted waves have been observed by satellites in the solar wind. The goal of this experiment is to study the relative efficiency of conversion in linear versus non-linear processes; the dependence of the efficiency on local density gradients and density fluctuations; the generation of harmonics. The waves are studied using miniature dipole probes that can measure polarization.|
|Search for electron solitary structures: Li-Jen Chen, B. Lefebvre, (U. of New Hampshire), Paul Kintner, (Cornell University), Jolene Pickett (U. Iowa), W. Gekelman, P. Pribyl, S. Vincena (UCLA-Physics), Jack Judy (UCLA-Engineering)||Electron solitary structures (ESS) have been observed by satellites in many very different regions of space. They are negatively charged structures which are several Debye lengths in diameter and travel at a substantial fraction of the electron thermal speed. To see them in a laboratory plasma, arrays of probes of order 10 microns in diameter willl be grown at the UCLA MEMs center in collaboration with Prof. Jack Judy and Franklin Chaing. Probes with 2 GHz amplifiers to enable identification of the fast moving structures have already been built and others with 12 Ghz bandwidth are under construction. Miniature velocity analyzers are also being fabricated.|
|Laboratory Investigation of the Dynamics of Magnetic Flux Ropes: James Chen, Naval Research Laboratory, Washington DC.||A 10 cm diameter oxide coated cathode and anode has been placed below a plasma column. Eventually their separation will be variable as well as their orientation to the background magnetic field. The small cathode and anode will be located inside of small, high current solenoids, which will be pulsed while the cathode is emitting, to create a magnetic arch and a flux rope. The field lines inside the arch is helical. Fast photography shows the development of rising arches, which pinch. Magnetic probes will be used to determine the proper conditions for the flux rope to rise as a Coronal Mass Ejection does. The event is pulsed at 1 Hz. and the The data will be compared with simulations done at NRL. Collaborators will be W. Gekelman and Pat Pribyl and S. Tripathi.|
|Experimental Study of Dynamic Alignment in Alfvenic Turbulence: Jean Perez, Stanislav Boldyrev, University of Wisconsin, Madison||This study addresses the structure of turbulence by attempting to measure the angle between velocity and magnetic field fluctuations. The turbulence will be generated using high power Alfvén waves. The structure scale size and alignment angle will be measured for various probe separations. The experiment results will be compared to theories of turbulent cascade in the solar wind and interstellar medium. The UCLA support group will consist of T. Carter, S. Vincena and W. Gekelman.|
The BaPSF welcomes international collaborations. The travel and housing expenses of the international users must be funded by grants for these purposes, but the use of the facility is free of charge.
|Investigators and institutions||Research topic details|
|Laser Based Plasma Flows and Jets at the UCLA BaPSF: Julio Herrera Velazquez :ICN-UNAM, Mayo Villagran Muniz: (CCADET-UNAM)||A laser target experiment is used to generate a high-density localized plasma with the LAPD plasma column. One magnet set on the LAPD was reversed so that the dense expanding plasma will propagate into, or originate inside of a cusp magnetic field. The experimental results will be compared with numerical simulations of astrophysical jets. Collaborators at UCLA are W. Gekelman, G. Morales, J. Maggs, and S. Vincena.|
The "local group" is the team that constructed the LAPD device and runs it as a user facility. The group consists of: Walter Gekelman, James Maggs, George Morales, Steve Vincena, David Leneman, Shreekrishna Tripathi and Patrick Pribyl.
|Title of topic||Research topic|
|Axial Plasma jets and Alfvén waves: S. Vincena, W. Gekelman, Frank Tsung||The present research program is divided into three main topics: 1) the creation of wakes and structure with supersonic flows, 2) the coupling of plasma jets to compressional Alfvén waves, and 3) the interaction of antenna-launched Alfvén waves with fast-flowing plasmas. In the LAPD fast flows are generated using a pulsed (1.5J,10ns) laser focused on a solid target placed in the 18-m plasma column. The experimental effort is being complemented by computer modeling of the properly scaled physical problems using the OSIRIS code -- a fully explicit, multi-dimensional, fully relativistic, parallelized PIC code. Preliminary data on the generation of Alfvén waves has recently been acquired. The wave spectra are sharply peaked at the ion cyclotron frequency of the carbon atoms of the laser-produced plasma and are observed as propagating shear Alfven waves in the background plasmat. The laser-produced carbon plasma cannot propagate to the measurement location in this time and must couple its ion cyclotron motions to waves in the background plasma. Simulations of the radiated magnetic field patterns are currently underway to compare with the data.|
|Fine Scale Structure on laser-produced plasma bubbles: W. Gekelman, Andrew Collette||When a dense laser produced plasma (LPP) expands in a uniform, magnetized background plasma in the LAPD the expansion perpendicular to B causes a wide range of effects, including a localized reduction of the background field and periodic structures on the expanding plasma surface. The LPP is diagnosed via small-scale (1mm) magnetic and floating probes. An in-vacuum dual axis ceramic motor drive was built and used to move the probes. Correlation techniques in the magnetic field and floating potentiual on the edge of the bubble indicate that the flute-like structures on the bubble edge are still standing and move past the probes at the bubble velocity. The structures are observed to grow faster than what is predicted by linear theory. The diamagnetic current within the bubble is also observed to be fully three dimensional.|