Current projects: Science campaigns

Investigators and institutions Science project details
The generation of Alfvén waves by an ion beam:
Bill Heidbrink (UCI ), M. Van Zeeland (GAT), B. Breizman (U.Texas, Austin), T. Carter (UCLA), H. Boehmer (UCI),R. McWilliams (UCI), R. Vann (Univ. York, England), and LAPD staff
An ion beam ( 25 kV , 0.5-3 A) will be injected at a variety of pitch angles into the LAPD plasma. The beam which will spiral along the magnetic field will match the phase velocity of Alfvén waves in the background LAPD plasma. The waves are expected to be generated by Cherenkov emission from the fast ions. The goal is to create an analogue of TAE modes and study them in great detail. The helium ion beam been constructed and suvccesfully tested The project also has related side studies such as the study of the propagation of shear waves in multiple mirrors. Measurement of transport in velocity and configuration space caused by harmonic heating with compressional Alfvén waves, resonances with shear Alfvén waves, and drift wave turbulence.
Investigation of Sheaths near RF antennas for fusion: Dan D'Ippolito (Lodestar), J. Myra (MIT), J. Wright (MIT), B.V. Compernolle, W. Gekelman, G. Morales, P. Pribyl, T. Carter, S. Vincena, G. Morales, (UCLA), M. Kushner (U. Michigan) Study of the RF sheaths on antennas immmersed in a magnetoplasma. The antennas radiate in the ICRF, Fast Wave, regime. Antennas will be constructed at UCLA and waves launched at low and high powers into the LAPD edge plasma. A variety of probes and optical techniques will be used to study the sheath plasma waves and their coupling to fast waves and under appropriate conditions to shear Alfven waves. The experiments will be complemented with a modelling effort at Lodestar and MIT.
Scattering of Fast Electron by Alfven and Whistler Waves: D. Papadopoulos, (U. Maryland) R. Sagdeev, R. Sharma, X. Shao, A. Karavaev (U. Maryland) , A. Strelsov (Dartmouth), W. Gekelman, G. Morales, J. Maggs, S. Vincena, P. Pribyl (UCLA) The campaign led by Prof. D. Papadopoulos (Univ. of Maryland) is focused on the interaction of energetic electrons with launched Alfvén and whistler waves. It is motivated by the desire to limit damage to satellites by using these waves to scatter mirror-trapped energetic electrons into the loss cone. Launching shear Alfvén waves of arbitrary polarization was accomplished by constructing an antenna consisting of two perpendicular coils with independent phase-controlled currents. The antenna was found to launch highly collimated, relatively large amplitude shear waves with wave decay resulting mainly from collisional dissipation. The measured radiation patterns of the right-hand mode compared favorably to the predictions of an MHD simulation by the Maryland group. The second antenna studied was a classic short electric dipole. The antenna current and voltage were measured within the dipole, avoiding transmission line effects The real and imaginary parts of the antenna impedance were measured as a function of frequency and time in a decaying, afterglow plasma. A pulsed microwave source constructed for the campaign was used to inject waves at 2.45 GHz into a local magnetic mirror established in the LAPD. The fast electrons vanish when a shear wave, launched by an antenna 5 meters away is switched on. When the wave is shut off the fast electrons reappear and persist until the microwave source is pulsed off.
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.

Current projects: External users

Investigators and institutions Research topic details
Study of Ion Transport in Turbulent Plasmas: William Heidbrink, Roger McWilliams, Hans Boehmer, Z. Yang Department of Physics, University of California, Irvine. A moderate energy ( 1 keV.) Lithium ion beam is mounted in the LAPD. The beam spirals along the background magnetic field in an argon or helium plasma. The beam profile will be measured with probes as it moves through localized turbulent layers. The layers are generated with antennas. The beam divergence and energy spread is being studied.
Laboratory Investigation of Auroral Alfvén Electron Acceleration: Craig Kletzing, Fred Skiff, Scott Bounds, Jan Drake, Department of Physics, University of Iowa This is a study of shear Alfvén waves with short perpendicular wavelengths as well as investigations of field-aligned acceleration of electrons due to the electric field of the waves. A series of antennas, which are phased arrays, has been developed at the University of Iowa and put on the LAPD. The propagation of waves launched by these antennas is studied and their dispersion mapped. Velocity analyzers will be used to measure the parallel electron distribution function. Electron distribution functions are inferred from whistler wave dispersion relations. The results will be compared with spacecraft measurements made in the Earth's auroral region.
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.
Study of Plasma Turbulence produced by counter-propagating Alfvén waves: C. Kletzing, F. Skiff, G. Howes (U. Iowa),Troy Carter, Dept of Physics UCLA In theories of weak turbulence based on the incompressible MHD model, interactions between counter-propagating shear Alfvén wavepackets are responsible for the cascade of energy in wavenumber space. This research will be an experimental investigation of these interactions, studying collisions between antenna launched Alfvén wave in the LAPD. The frequency and wavenumber spectrum of the resulting nonlinear perturbations will be studied, paying particular attention to the rate of energy transfer in wavenumber space and to the importance of non-ideal effects such as compressibility, perpendicular dispersion and wave particle interactions.
Whistler Wave Pitch Angle Scattering of Electrons: Jacob Bortnick, (UCLA Earth and Space Science), W. Gekelman, P. Pribyl, B Van Compernolle (UCLA-Physics) This is a study of whistler wave scattering of a beam of energetic electrons. A low-density electron beam, with adjustable pitch angle relative to the background magnetic field, will form the energetic electrons. The velocity distribution function will be measured with small velocity analyzers. This will be done with and without background whistler waves. The waves will be launched with a small loop antenna. Results will be compared to theoretical predictions.
Launching lower hybrid and whistler waves in the LAPD afterglow plasma: Pat Colestock, Max Light, Los Alamos National Laboratory, Walter Gekelman, Pat Pribyl, Bart Van Compernolle (UCLA) A Slow wave structure (16 element array) and 16 arbitarry waveform generators (2.5 GHz) are used to launch lower hybrid and whistler waves in the LAPD afterglow plasma. A probe that can simultaneously measure the electric and magnetic fields of these waves (10 MHz,f<200 MHz) is used to map the fields with and without a density striation placed in the center of the plasma column. The reflection and transmission of the wavesfrom the straition as well as modes within the striation are measured in three dimensions.
Experimental Measurements of VLF Wave Propagation in a High Aspect Ratio Plasma Cylinder, J. Matthews, L. Buksphun, R. Pradham (Physical Opitics Corp, Torrance, CA), T. Carter (UCLA) A VLF wave is launched, initially, with a multiturn coil antenna in a low density ( n< 10^11 cm-3) test cahamber (1.5 m long , 50 cm dia , B= 50-200 Gauss) The measurements using magnetic probes will study waves on the surface or in the plasma which is produced with a cathode source. The experimental goal is to study the coupling efficiency of the wave using different coil designs. Waveguiding properties of the plasma will be studied
Formation and Interaction of Magnetic Flux Ropes in Ion Scale Current Sheets. W. Daughton, J. Finn (LANL), H. Karimabadi (UCSD), W. Gekelman, T. DeHaas, B. Van Compernolle (UCLA) A fully 3D kinetic code developed at Los Alamos and using the largest multiprocessor computer in the world will be used to model the tearing of a current sheet into multiple magnetic flux ropes. In full 3D computations it has been observed taht the magnetic islands, which are the result of the tearing of the current sheet are helical flux ropes which interact with one another. A new high emssivity cathode, (to be installed in the summer of 2013) will be masked to make a thin (dy/dx=20) current sheet. The full three-dimensional eveolution of the current will be measured in teh LAPD and detailed comaprisons with theory and the petascale simulations will be done.

Quantifying Reconnection in Magnetic Flux Ropes. Anthony Yeates, Dept. of Mathematical Science, Durham University, United Kingdom, W. Gekelman, B. Van Compernolle (UCLA)

A new theorectical approach using a topological flux function developed by Yeates and Horning to study fully three dimesnional magnetic field line reconnection will be applied to existing and future volumetric data sets of magnetic flux ropes. The analysis can yield time series data of the reconnection rate and information about the topology of the magnetic fields. New invarients will be searched for (A classical well known invarient is the magnetic helicity). The identiccation of regions of reconnection in the complex geometry of interacting flux rope will be a great tool in the analysis of the experimental data.  
Production of Collisionless Shocks using a High Power Laser and target in the LAPD: Chris Niemann, Carmen Constantin, (UCLA). A high power (up to 50J) Nd-Yag laser (repetition rate 10 minutes) is focused on a target in the LAPD plasma. Calculations show the laser energy sufficient to drive collisionless shocks with Alfvén Mach numbers in excess of two down the machine axis of the LAPD. The interaction is studies with the use of multiple magnetic and Mach probes, fast (3 ns) photography and schleirn and shadowgraphy techniques. Work done in collaboration with W. Gekelman, P. Pribyl, S. Vincena.

Experimental Study of Alfvén wave damping processes relevant to the solar corona. Daniel Wolf Savin, Micheal Hahn, Department of Astrophysics, Columbia University, New York

Shear Alfvén wave damping and heating will be studied in the context of explaining heating in Coronal Holes. The waves will be launched in magnetic field and density gradients and their propagation will be studied and wave damping evaluated in a number of scenarios. Of special interest is the propagation of waves in cross field density gradients,. The gradients will be created using grids with variable transparany across B0z . Another area of study will be the reflection of shear Alfvén waves in large magnetic field gradients. The work will be done in collaboration with Walter Gekelman and Stephen Vincena.
Tests of Electron Emission and Plasma Production via LaB6 Cathodes at High Confining Magnetic Field: Y. Song , D. Bui (Tri Alpha Energy Inc), L. Schmitz, (UCLA). A Lanthanum Hexaboride (Lab6) cathode similar to the ones used in the ETPD and LAPD device will be tested in a1 Tesla magnetic field. These cathodes are of interest in industrial applications but not much is known about their behavior in high magnetic field. Teh experiments will search for the largest densities obtainable, new plasma instabilities and edge turbulance scaling with ion Larmor radius. The JXB forces on the cathode structure will be studied as well. The experiment will be done with a high field magnet, chamber and power suppy to be provided by TAE systems. The UCLA group (W. Gekelmam, P. Pribyl) will use their expertise with these cathodes and diagnostics and work with TAE scientists.

Current projects: International collaborations

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
Collabotation on RF Campaign from Laboratory of Plasma Physics, Brussels. K. Crombe, V. Kyrytsya, D. Van Ester (Lab. Plasma Physics, Brussels, Belgium), B. vanCompernolle, W. Gekelman, M. Martin, P. Pribyl, G. Morales, T. Carter (UCLA) Computer codes which model the behavior of RF antennas will be sued to (a) design an fast wave antenna for use in the LAPD and ETPD plasmas (b) provide quantitative information on wave-induced modifications of the plasma near RF antenna along with their impact on densities and flows. The codes will be compared to density, plasma potential and magnetic field fluctuations close to RF antennas. The antennas are presently driven by a 1 kW pulsed RF source. A source now under construction will operate at f>fci (2nd or 3rd harmonic heating)i at the 100 kW level.

Topology of MagneticReconnection.M. Berger J. Campbell (U. Exeter, Devon, U.K.), W. Gekelman, B. Van Compernolle (UCLA)

Topological quantities such as field line connectivity, twist, shear, kinking and briading will be calculated from data acquired on magnetic flux ropes in the LAPD device. Topological invarients such as the magnetic helicity which measures linking, twisting and coiling of field lines will be derived from the data. A method which is gauge invareint and involves calculation of mutual helicites of flux tubes will be employed.

Current projects: UCLA local group

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
Quasi-Seperatrix layers and Magnetic Flux Ropes: Walter Gekelman, t. DeHaas ,Bart Van Compernolle, Pat Pribyl, S. Vincena A study of the interaction of two parallel current channels was conducted. The channels are created by injection of electrons using two 9 cm diameter, LaB6 cathodes. Magnetic field data was acquired at 20,000 spatial locations and as a function of time. The volumetric data set allows the reconstruction of field lines as well as the three dimensional current systems that evolve in time. These detailed data sets allow the evaluation, for the first time, from laboratory measurements of the 'so-called' Quasi Separatrix Layer (QSL) or, in this case, the squashing factor (which includes the effect of the background magnetic field). Magnetic field lines, which are closely spaced on the side of the QSL near the current sources, diverge hyperbolically at the other end. Previously, the concept and calculation of a QSL had only been used in computer simulations of solar flares. The work has been extended to study the interaction of several magnetic flux ropes and current sheets.
Transport Studies of a Plasma with a hot dense core: Bart Van Compernolle, W. Gekelman, P. Pribyl, George Morales A Lanthanum HexaBoride cathode is used to create an 8 cm diameter plasma, with densities upwards of 1 x 1013 per cubic cm and electron temperatures of more than 10 eV. The LaB6 cathode is positioned in the center of the LAPD plasma column, creating a hot dense core plasma embedded in a background plasma. The peak density and temperature scale linearly with discharge power, as shown in the study. A high density, high temperature, high beta plasma can be produced at discharge powers larger than 200 kW (i.e. discharge powers of the same order as the main LAPD discharge power). Under certain conditions, density profiles are observed to be hollow, while temperature profiles are peaked at center. Figure 24A shows the sharp hollow ring profile from ion saturation measurements in a plane perpendicular to the machine axis. The transport code developed by M. Shi for narrow temperature filaments will be adapted for this experiment and will be extended in order to include density effects. Extensive comparisons between the code and the experiment are planned.
Study of heat transport associated with electron temperature gradients: J. Maggs, G. Morales, T. Carter This project is a comprehensive study of the transport phenomena resulting from electron temperature gradients created by heating the plasma with a small (about 3 mm diameter) electron beam. The project blends experiments, analytical methods, and computer simulations. Collective instabilities driven by electron temperature gradients can give rise to strongly nonlinear processes that significantly alter the properties of the ambient plasma environment. As a consequence, plasma flows develop that result in density changes and complex spatio-temporal structures. These secondary phenomena generate transport rates whose magnitude and parameter scaling deviate substantially from the classical predictions based on Coulomb interactions between individual charges.
Laboratory Simulation of Magnetic Flux Rope Eruptions in the Solar Atmosphere: Shreekrishna Tripathi, W. Gekelman, James Chen (NRL) Solar flare experiments are conducted in the SMPD, the 4m, low-field plasma device. The ingredients of the flare experiment geometry are a current aligned with an arc-shaped magnetic field, together with fast ions produced by striking, simultaneously, two carbon targets with laser pulses. This arrangement is embedded in background magnetic field and plasma. The laser strike represents the eruption of a magnetic flux loop that is meant to simulate a solar coronal loop. The laser strike generates plasma flows from the foot-points of the loop that significantly modify the magnetic field topology and link the magnetic field lines of the loop with the ambient plasma. Following this event, the loop erupts by releasing its plasma into the background. The resulting impulse excites intense magnetosonic waves, that transfer energy to the ambient plasma and subsequently decay.
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.
Electron Heat Transport: James Maggs, George Morales (UCLA) Two distinct experiments, involving pressure gradients across the confinement magnetic field in the LAPD-U, are found to exhibit a broadband turbulence characterized by an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfvén waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfvén waves. One experiment involves a controlled, pure electron temperature gradient associated with a microscopic 6 mm gradient-length hot electron temperature filament created by the injection a small electron beam. The other experiment is a macroscopic 3.5 cm gradient-length limiter-edge experiment in which a density gradient is established by inserting a metallic plate at the edge of the nominal plasma column of the LAPD. The temperature filament experiment permits a detailed study of the transition from coherent to turbulent behavior and the concomitant change from classical to anomalous transport. Turbulence in the limiter experiment is always fully developed. The similarity of the results in the two experiments strongly suggests a universal feature of pressure-gradient driven turbulence in magnetized plasmas that results in non-diffusive, cross-field transport. These results are similar to previous observations in helical confinement devices, research tokamaks, and arc plasmas.
Effect of Two-Ion species on the propagation of shear Alfvén waves: S.Vincena, James Maggs, George Morales A theoretical modeling study and experimental investigation of the propagation properties of shear Alfvén waves of small transverse scale in a plasma with two ion-species was conducted. In the two-ion plasma, depending on the mass of the heavier species, ion kinetic effects can become prominent, and significant parallel electric fields result in electron acceleration. Theory predicts the appearance of frequency propagation gaps at the ion-ion hybrid frequency and between harmonics of the lower cyclotron frequency. Within these frequency bands spatial structures arise that mix the cone-propagation characteristics of Alfvén waves with radially expanding ion Bernstein modes. Experimentally a clear signature of a shear wave propagation gap, as well as propagation between multiple harmonics, is found for the Helium-Neon gas combination. The evanescence of shear waves beyond the reflection point at the ion-ion hybrid frequency in the presence of an axial magnetic field-gradient was also documented.
Ion distribution functions above a RF biased wafer in a plasma processing tool: W. Gekelman, P. Pribyl, N. Moore.,Mark Kushner (U. Michigan) Measurement of the ion distribution function in the RF sheath of a plasma processing tool have been obtained. Laser-induced Fluorescence (LIF) in an Ar, O2 plasma was used to time resolve (for the first time) the ion distribution function as a function of the height above a silicon wafer. RF is commonly used in the plasma processing industry to provide the ion acceleration needed to etch the silicon wafer. Emissive probes are used to study standing waves above a wafer using correlation techniques. Waves with m=0, m=1 have been observed in detail for the first time.