DOCSLIB.ORG

3D Two-Fluid Braginskii Simulations of the Large Plasma Device

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
3D Two-Fluid Braginskii Simulations of the Large Plasma Device Large Plasma Device (LAPD) Model Equations and Numerical Setup Evolution of Turbulence and Transport LAPD Comparisons Conclusions 3D Two-Fluid Braginskii Simulations of the Large Plasma Device Dustin Fishery, Barrett Rogersy, Giovanni Rossi∗, Danny Guice∗ yDepartment of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA ∗Department of Physics and Astronomy , University of California, Los Angeles, California 90095, USA Conclusions: ? 3D global 2-fluid simulations show good agree- ment with data from LAPD in the low-bias pa- rameter regime explored so far. ? KH turbulence at relatively large scales is the dom- inant driver of cross-field transport in the low-bias simulations. ? Biased simulations are currently under study. The work presented here builds upon an initial numerical study [Rogers and Ricci, Phys. Rev. Lett., 104, 2010] of LAPD [Gekelman et al., Rev. Sci. Instrum., 62, 1991] using the Global Braginskii Solver code (GBS) [Ricci et. al., Plasma Phys. Control. Fusion, 54, 2012]. Dustin M. Fisher Sherwood 2015 Modeling the LAPD 1 / 21 Large Plasma Device (LAPD) Model Equations and Numerical Setup Evolution of Turbulence and Transport LAPD Comparisons Conclusions LAPD Primer for a Nominal He Plasma • Plasma 17 m in length, 30 cm in radius • Machine diameter 1m ' • n 2 1012 cm−3 ∼ × • Pulsed at 1 Hz for 10 ms ∼ • Axial magnetic field 1kG ∼ • Te 6 eV and T 0:5 eV ∼ i ∼ • Ion sound gyroradius, ρs 1:4 cm ∼ • Plasma β 10−4 ∼ 012304-2 T. A. Carter and J. E. Maggs Phys. Plasmas 16,012304͑2009͒ Discharge Circuit generation of primary electrons with energy comparable to − + the anode-cathode bias voltage. The mesh anode is 50% Electrical Breaks transparent, allowing half of these primaries to travel down the magnetic field into the main chamber leading to ioniza- tion and heating of the bulk plasma. The cathode is situated B at the mouth of the solenoid and therefore sits in a region of flaring magnetic field. The flared magnetic field maps the 50Ω 73 cm diameter cathode to a ϳ56 cm diameter region in the Cathode Anode main chamber. Primary electrons from the source are isolated 0.2Ω to this region in the chamber and lead to a fast electron Wall Bias Circuit − + tail for rՇ28 cm. Typical plasma parameters in LAPD 12 −3 discharges are ne Շ5ϫ10 cm , Te ϳ7 eV, Ti ϳ1 eV, and BϽ2 kG. In the experiments reported here, the primary T.A. Carter and J.E. Maggs, Physics of Plasmas, 16 (2009) FIG. 1. Schematic of LAPD including wall biasing circuit. plasma species was singly ionized helium and the magnetic http://plasma.physics.ucla.edu/pages/gallery.html (BaPSF) field strength used was 400 G. Modeling18 and spectroscopic measurements show that the ionization fraction of the LAPD Dustin M. Fisher Sherwood 2015 perform a detailedModeling study the of LAPD modifications of turbulence and2 / 21 plasma is տ50% and therefore Coulomb collisions are the turbulent transport in a system free from complications asso- most important collisional process. However, neutral colli- ciated with toroidal systems ͑e.g., field line curvature, poloi- sions ͑charge exchange in particular͒ are important for estab- dal asymmetry, trapped particles͒. Good diagnostic access to lishing the radial current during biasing. LAPD provides for detailed measurements of the spatial and Measurements of density, temperature, floating potential, temporal characteristics of the turbulence. and their fluctuations are made using Langmuir probes. A Here we summarize the primary results reported in this four-tip probe with 0.76 mm diameter tantalum tips arranged paper. Measured turbulent transport flux is reduced and then in a diamond pattern is used as a triple Langmuir probe and suppressed, leading to a confinement transition, as the ap- particle flux probe. Two tips are separated 3 mm along the plied bias is increased. The threshold in the applied bias is field and are used as a double probe to measure ion satura- linked to radial penetration of the driven azimuthal flow. tion current I ϰn ͱT . The remaining two tips are sepa- Two-dimensional measurements of the turbulent correlation ͑ sat e e͒ rated 3 mm perpendicular to the field and measure floating function show that the azimuthal correlation increases dra- potential for deriving azimuthal electric field fluctuations and matically during biasing, with the high-m-number modes in- temperature using the triple Langmuir probe method.24 Ra- volved in turbulent transport becoming spatially coherent. dial particle transport can be evaluated directly using mea- However, no significant change in the radial correlation sured density and electric field fluctuations through Eq. 1 . length is observed associated with the confinement transi- ͑ ͒ Flows are measured using a Gundestrup Mach probe with tion. As the bias is increased above threshold, there is an ͑ ͒ six faces.25 The flow measurements are corrected for the fi- apparent reversal in the particle flux ͑indicating inward trans- nite acceptance angle of the probe faces, which are smaller port͒. The peak amplitude of density and electric field fluc- than the ion gyroradius.26 tuations do decrease, but the reduction is only slight and does Using the difference in floating potential to determine not fully explain the transport flux reduction. The cross- the azimuthal electric field is problematic in the presence of phase between density and electric field fluctuations changes fast electron tails, such as exist on field lines connected to significantly as the threshold for confinement transition is the cathode source. In the presence of fast electrons, differ- reached, and explains the reduction and reversal of the mea- ences in floating potential may no longer be proportional to sured transport flux. The dynamics of the transition have also differences in plasma potential and thus may not accurately been studied and show a correlation between transport sup- measure the electric field. In addition, the fast electron tail, pression and the overlap of the flow ͑shear͒ profile and the which sets floating potential, is much less collisional than the density ͑gradient͒ profile. bulk plasma so that the floating potential is no longer a lo- calized quantity. This delocalization skews the correlation II. EXPERIMENTAL SETUP with locally measured density fluctuations and thereby af- The experiments were performed in the upgraded Large fects the flux measurement. Measurements of Isat are made Plasma Device ͑LAPD͒,21 which is part of the Basic Plasma with a double-Langmuir probe biased to 70 V to reject pri- Science Facility ͑BaPSF͒ at UCLA. The vacuum chamber of mary electrons, and therefore should not be affected by the LAPD is 18 m long and 1 m in diameter and is surrounded fast electron tail. Thus, in this study, we report on the prop- by solenoidal magnetic field coils. The plasma is generated erties of ion saturation fluctuations everywhere in the plasma by a cathode discharge.22 The cathode is 73 cm in diameter column. Properties of electric field fluctuations and cross- and is located at one end of the vacuum chamber, as shown correlation flux measurements are presented everywhere in schematically in Fig. 1. A molybdenum mesh anode is situ- the plasma column, but a caution is issued in regard to mea- ated 50 cm away from the cathode. A bias of 40–60 V is surements made on field lines where primary electrons are applied between the cathode and anode using a solid-state present ͑rՇ28 cm͒. switch,23 resulting in 3–6 kA of discharge current. An im- The edge plasma in LAPD is rotated through biasing the portant aspect of the operation of the plasma source is the vacuum vessel wall positively with respect to the source Downloaded 14 Jun 2010 to 129.170.241.133. Redistribution subject to AIP license or copyright; see http://pop.aip.org/pop/copyright.jsp Large Plasma Device (LAPD) Model Equations and Numerical Setup Evolution of Turbulence and Transport LAPD Comparisons Conclusions Standard Bohm Sheath B.C.'s at the End Walls Vki = ±cs (1) 0 ¨¨* Vke = ±cs exp([Λ − efφplasma − ¨φwallg=Te ]) (2) with p p cs = Te0=mi ; Λ = ln mi = (2πme ) ∼ 3 (3) The B.C.'s on the outflows of ions and electrons to the end walls lead to an approximate global balance Vki ∼ Vke , or φplasma ∼ Λ Te (4) Relaxation due to turbulence Dustin M. Fisher Sherwood 2015 Modeling the LAPD 3 / 21 Large Plasma Device (LAPD) Model Equations and Numerical Setup Evolution of Turbulence and Transport LAPD Comparisons Conclusions The code evolves a set of electrostatic two-fluid drift-reduced Braginskii equations assuming Ti Te : dn @ nV e = − k + Dn (n) + Sn (5) dt @z dTe @Te 2 Te @j = −V e + 0:71 k dt k @z 3 en @z 2 @V e − Te k + Dk (Te ) + DT (Te ) + ST (6) 3 @z Te e 2 dV e @V e 4 η0e @ V e ej me k = −me V e k + k + k dt k @z 3 n @z2 σ k @φ T @n @T + e − e − 1:71 e (7) @z n @z @z 2 dV i @V i 4 η0i @ V i 1 @pe mi k = −mi V i k + k − (8) dt k @z 3 n @z2 n @z 2 d! @! mi Ωci @j = −V i + k − νin! + S! (9) dt k @z e2n @z Dustin M. Fisher Sherwood 2015 Modeling the LAPD 4 / 21 Large Plasma Device (LAPD) Model Equations and Numerical Setup Evolution of Turbulence and Transport LAPD Comparisons Conclusions Evolution of Turbulence and Transport t = 0.25 ms t = 0.40 ms • Starting top-hat 0.5 0.54 shaped density 0.48 source. 0.0 0.42 y (m) • Onset of drift waves 0.36 a) b) 0.5 with kθρs ∼ 0:5, − 0.30 t = 1.13 ms t = 3.33 ms kkLeq ∼ 1.
Load more

Recommended publications
  • Fluctuation Induced Cross-Field Transport in Hall Thrusters and Tokamaks Michael Lane Garrett
    Fluctuation Induced Cross-Field Transport in Hall Thrusters and Tokamaks by Michael Lane Garrett B.A., Physics, Wesleyan University (1997) S.M., Applied Plasma Physics, M.I.T. (2012) Submitted to the Department of Aeronautics and Astronautics in partial fulfillment of the requirements for the degree of Master of Science in Aeronautics and Astronautics OF TECHNOLOGY at the NOVi22013 MASSACHUSETTS INSTITUTE OF TECHNOLOGY September 2013 LIBRARIES @ Massachusetts Institute of Technology 2013. All rights reserved. Author ......... ......... ...... .................. .. .. ......... Department of Aeronautics and Astronautics A August 22, 2013 Certified by... Manuel Martinez- Sanchez Professor Thesis Supervisor Certified by........ ......... Stephen J. Wukitch Research Scientist Thesis Reader Certified by.... ... .... .... .... ... Felix I. Parra Assistant Professor / a Thesis Reader A ccepted by ........................................... Eytan H. Modiano Professor of Aeronautics and Astronautics Chair, Graduate Program Committee 2 Fluctuation Induced Cross-Field Transport in Hall Thrusters and Tokamaks by Michael Lane Garrett Submitted to the Department of Aeronautics and Astronautics on August 22, 2013, in partial fulfillment of the requirements for the degree of Master of Science in Aeronautics and Astronautics Abstract One area of fundamental plasma physics which remains poorly understood is the transport of particles across magnetic field lines at rates significantly higher than predicted by theory exclusively based on collisions. This "anomalous" transport is observed in many different classes of plasma experiment. Notably, both magnetic confinement fusion devices and Hall thrusters exhibit anomalous cross-field particle diffusion. This higher than predicted "loss" of particles has significant practical im- plications for both classes of experiment. In the case of magnetic confinement fusion experiments, such as tokamaks, the Lawson criterion nTTE > 1021 [keV.
    [Show full text]
  • Nd AAS Meeting Abstracts
    nd AAS Meeting Abstracts 101 – Kavli Foundation Lectureship: The Outreach Kepler Mission: Exoplanets and Astrophysics Search for Habitable Worlds 200 – SPD Harvey Prize Lecture: Modeling 301 – Bridging Laboratory and Astrophysics: 102 – Bridging Laboratory and Astrophysics: Solar Eruptions: Where Do We Stand? Planetary Atoms 201 – Astronomy Education & Public 302 – Extrasolar Planets & Tools 103 – Cosmology and Associated Topics Outreach 303 – Outer Limits of the Milky Way III: 104 – University of Arizona Astronomy Club 202 – Bridging Laboratory and Astrophysics: Mapping Galactic Structure in Stars and Dust 105 – WIYN Observatory - Building on the Dust and Ices 304 – Stars, Cool Dwarfs, and Brown Dwarfs Past, Looking to the Future: Groundbreaking 203 – Outer Limits of the Milky Way I: 305 – Recent Advances in Our Understanding Science and Education Overview and Theories of Galactic Structure of Star Formation 106 – SPD Hale Prize Lecture: Twisting and 204 – WIYN Observatory - Building on the 308 – Bridging Laboratory and Astrophysics: Writhing with George Ellery Hale Past, Looking to the Future: Partnerships Nuclear 108 – Astronomy Education: Where Are We 205 – The Atacama Large 309 – Galaxies and AGN II Now and Where Are We Going? Millimeter/submillimeter Array: A New 310 – Young Stellar Objects, Star Formation 109 – Bridging Laboratory and Astrophysics: Window on the Universe and Star Clusters Molecules 208 – Galaxies and AGN I 311 – Curiosity on Mars: The Latest Results 110 – Interstellar Medium, Dust, Etc. 209 – Supernovae and Neutron
    [Show full text]
  • Yang Zhang UC Irvine Phd Thesis V5
    UNIVERSITY OF CALIFORNIA, IRVINE Fast Ions and Shear Alfvén Waves DISSERTATION submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in Physics By Yang Zhang Dissertation Committee: Professor William W. Heidbrink, Co-chair Professor Roger McWilliams, Co-chair Professor Zhihong Lin 2008 ©2008 Yang Zhang The dissertation of Yang Zhang is approved and is acceptable in quality and form for publication on microfilm ________________________ ________________________ ________________________ Committee Chair University of California, Irvine 2008 ii DEDICATION To my wife Lily, and my parents, for their love and support. The LORD is my rock, and my fortress, and my deliverer; my God, my strength, in whom I will trust; my buckler, and the horn of my salvation, and my high tower. Psalm 18:2 iii TABLE OF CONTENTS CONTENTS ………………………………………………………………………………….Page TABLE OF CONTENTS .........................................................................................................iv LIST OF FIGURES .................................................................................................................vi LIST OF TABLES....................................................................................................................ix LIST OF SYMBOLS.................................................................................................................x ACKNOWLEDGMENTS......................................................................................................xiii CURRICULUM VITAE ........................................................................................................
    [Show full text]
  • Study of Fast Ion Transport in Turbulent Waves in the Large Plasma Device (LAPD)
    Study of Fast Ion Transport in Turbulent Waves in the Large Plasma Device (LAPD) Shu Zhou, W. Heidbrink, H. Boehmer, R. McWilliams, University of California, Irvine T. Carter, S. K. P. Tripathi, S. Vincena, University of California, Los Angeles Due to gyroradius averaging and drift-orbit averaging, the transport of fast ions by microturbulence in tokamaks often is smaller than experienced by thermal ions [1]. In this experiment, strong drift wave turbulence (δn/n ~1, f ~5-20 kHz) is observed in LAPD in gradient regions produced by obstacles. Energetic lithium ions ( Efast /E thermal 300 , fast/~ s 10 ) orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating fields. The fast-ion transport decreases rapidly with increasing fast-ion gyroradius, which is explained well by gyro-averaging theory [2]. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon, and by modifying the bias on the obstacle. A transition from non-diffusive to diffusive transport is observed when the fast ion time-of-flight in the waves exceeds its correlation time ( corr ~0 . 1 ms ) with the waves. Different spatial correlation lengths of the wave potential fields also alter the fast ion transport. A Monte Carlo trajectory-following code simulates the interaction of the fast ions with stationary two-dimensional electrostatic wave potential fields and with three-dimensional, time-dependent fields. Comparison between observation and modeling is presented. [1] W. W. Heidbrink, M. Murakami, J. M. Park, et al., Plasma Phys.
    [Show full text]
  • Summary of Basic Plasma Session
    AAPPS‐DPP 2018, 2nd Asia‐Pacific Conference on Plasma physics November 12‐17, 2018 Summary of Basic Plasma Session Y. Kishimoto Kyoto University, Japan Basic Plasma Session : Large number of submission papers • Basic plasma session includes wider areas, which is highly interdisciplinary. BP in 1st Meeting courtesy of A. Sen Plenary : 4 Invited : 56 Oral : 15 Poster : 49 Total : 124 • Strongly coupled complex plasmas, dusty plasmas, quantum plasmas : 9 • Atomic and molecular process in plasmas : 15 • Non‐neutral plasmas and beam plasmas : 5 • Plasma propulsion and discharge for industrial and medical applications : 10 • Plasma sources, electromagnetic waves and radiations, plasma heating : 5 • Simulation and computation of plasmas : 11 • Plasma diagnostics : 2 • Apologies for selective summary without covering all papers. Basic Plasma Session : plenary and invited/oral • Basic plasma session includes wider areas, which is highly interdisciplinary. Basic Plasma Session : Poster • Basic plasma session includes wider areas, which is highly interdisciplinary. Various plasmas in wide parameter region • Basic plasma session includes wider areas, which is highly interdisciplinary. • Plasma, highly nonlinear medium with the freedom interacting with electromagnetic field, exhibits extremely rich dynamics and structure in wider parameter regions, which are very complex while behave with a synchronized an/or coherent manner. • Key : Linear and nonlinear “structure” and “dynamics”, and methodology identifying them courtesy of H. Totsuji Various plasmas in wide parameter region : classical : quantum TT F TTF Infinitesimally small dissipation r d low density high temperature plasmas Events dominant (Long range force dominant ) outside Debye sphere Vlasov‐Maxwellian system High temperature magnetically confined fusion plasmas 1 Dynamics and Structure Various plasmas in wide parameter region 2 2 kT 3 23 Ze n13 Ze 0 B 4 nd 41 1 λd 2 N D 23 rs nZe() 3 33４0kTBD N 0.272 akTB F 1 Dynamics and Structure Atomic and molecular.
    [Show full text]
  • Plasma Science
    Report of the Panel on Frontiers of Plasma Science Plasma: at the frontier of scientific discovery US Department of Energy Office of Science Office of Fusion Energy Science Report of the Panel on Frontiers of Plasma Science Plasma: at the frontier of scientific discovery The production of this report was sponsored by the U.S. Department of Energy, Office of Science, Fusion Energy Sciences in the year 2016. US Department of Energy Office of Science Office of Fusion Energy Science Contents Plasma: at the frontier of scientific discovery v Panel Membership vii Preface ix Executive Summary Chapter 1 1 Extreme States of Matter and Plasmas Chapter 2 23 Understanding the Physics of Coherent Plasma Structures Chapter 3 43 Understanding the Energies of the Plasma Universe Chapter 4 65 The Physics of Disruptive Plasma Technologies Chapter 5 83 Plasmas at the Interface of Chemistry and Biology 100 Appendix A: The Charge 102 Appendix B: Procedural Background 104 Appendix C: List of figures Panel Membership Plasma: at the frontier of scientific discovery Igor Adamovich Donald Lamb The Ohio State University University of Chicago Andre Anders Martin Laming Lawrence Berkeley National Laboratory Naval Research Laboratory Scott Baalrud Michael Mauel (Group Leader) University of Iowa Columbia University Stuart Bale Julia Mikhailova University of California, Berkeley Princeton University Michael Bonitz Philip Morrison (Group Leader) Christian-Albrechts-Universität zu Kiel University of Texas at Austin Alain Brizard Bruce Remington (Group Leader) St. Michael’s
    [Show full text]
  • UNIVERSITY of CALIFORNIA Los Angeles Simulations of Super Alfvénic Laser Ablation Experiments in the Large Plasma Device a Diss
    UNIVERSITY OF CALIFORNIA Los Angeles Simulations of Super Alfv´enic Laser Ablation Experiments in the Large Plasma Device A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Physics by Stephen Eric Clark 2016 c Copyright by Stephen Eric Clark 2016 ABSTRACT OF THE DISSERTATION Simulations of Super Alfv´enic Laser Ablation Experiments in the Large Plasma Device by Stephen Eric Clark Doctor of Philosophy in Physics University of California, Los Angeles, 2016 Professor Christoph Niemann, Chair Hybrid plasma simulations, consisting of kinetic ions treated using standard Particle- In-Cell (PIC) techniques and an inertialess charge-neutralizing electron fluid, have been used to investigate the properties of collisionless shocks for a number of years. They agree well with sparse data obtained by flying through Earth’s bow shock and have been used to model high energy explosions in the ionosphere. In this doctoral dissertation hybrid plasma simulation is used on much smaller scales to model collisionless shocks in a controlled laboratory setting. Initially a two-dimensional hybrid code from Los Alamos National Laboratory was used to find the best experimental parameters for shock forma- tion, and interpret experimental data. It was demonstrated using the hybrid code that the experimental parameters needed to generate a shock in the laboratory are relaxed compared to previous work that was done[1]. It was also shown that stronger shocks can be generated when running into a density gradient. Laboratory experiments at the University of California at Los Angeles using the high energy kJ-class Nd:Glass 1053 nm Raptor laser, and later the low energy yet high repetition rate 25 J Nd:Glass 1053 nm ii Peening laser have been performed in the Large Plasma Device (LAPD), which have pro- vided some much needed data to benchmark the hybrid simulation method.
    [Show full text]
  • Lithium Ion Sources for Investigations of Fast Ion Transport in Magnetized Plasmas ͒ Y
    REVIEW OF SCIENTIFIC INSTRUMENTS 78, 013302 ͑2007͒ Lithium ion sources for investigations of fast ion transport in magnetized plasmas ͒ Y. Zhang,a H. Boehmer, W. W. Heidbrink, and R. McWilliams Department of Physics and Astronomy, University of California, Irvine, California 92697 D. Leneman and S. Vincena Department of Physics and Astronomy, University of California, Los Angeles, California 90095 ͑Received 3 August 2006; accepted 9 December 2006; published online 10 January 2007͒ In order to study the interaction of ions of intermediate energies with plasma fluctuations, two plasma immersible lithium ion sources, based on solid-state thermionic emitters ͑Li aluminosilicate͒ were developed. Compared to discharge based ion sources, they are compact, have zero gas load, small energy dispersion, and can be operated at any angle with respect to an ambient magnetic field of up to 4.0 kG. Beam energies range from 400 eV to 2.0 keV with typical beam current densities in the 1 mA/cm2 range. Because of the low ion mass, beam velocities of 100–300 km/s are in the range of Alfvén speeds in typical helium plasmas in the large plasma device. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2431086͔ I. INTRODUCTION source has to be immersed in the plasma puts severe con- straints on the properties of the ion gun. An ideal source for Fast ions ͑FI͒ with energies large compared to those of this research should have these features ͑Table I͒: the background plasma ions play a key role in space plasmas as well as in controlled fusion related laboratory plasmas.
    [Show full text]
  • Dependence of Fast-Ion Transport on the Nature of the Turbulence in the Large Plasma Device Shu Zhou,1 W
    PHYSICS OF PLASMAS 18, 082104 (2011) Dependence of fast-ion transport on the nature of the turbulence in the Large Plasma Device Shu Zhou,1 W. W. Heidbrink,1 H. Boehmer,1 R. McWilliams,1 T. A. Carter,2 S. Vincena,2 and S. K. P. Tripathi 2 1Department of Physics and Astronomy, University of California, Irvine, California 92697, USA 2Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA (Received 19 June 2011; accepted 14 July 2011; published online 11 August 2011) Strong turbulent waves (dn=n 0.5, f 5-40 kHz) are observed in the upgraded Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] on density gradients produced by an annular obstacle. Energetic lithium ions (Efast= Ti 300, qfast=qs 10) orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating wave fields. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon and by modifying the bias on the obstacle. Different spatial structure sizes (Ls) and correlation lengths (Lcorr) of the wave potential fields alter the fast ion transport. The effects of electrostatic fluctuations are reduced due to gyro-averaging, which explains the difference in the fast-ion transport. A transition from super-diffusive to sub-diffusive transport is observed when the fast ion interacts with the waves for most of a wave period, which agrees with theoretical predictions.
    [Show full text]
  • 2017-2018 by Walter Gekelman
    Department of Physics & Astronomy 2017 — 2018 CONTENTS Chair’s Message 3 FEATURE ARTICLE Science and Technology Research Building 8 DONOR RECOGNITION • Matching Funds • The Impact of Giving • Donor Highlights • List of Special Donors 12 RESEARCH HIGHLIGHTS 25 FACULTY NEWS • New Faculty Welcome to this year’s “Reflections” newsletter, as we have renamed the An- nual Report of the Department of Physics and Astronomy. It’s our hope this • Remembering Rubin Braunstein is useful to our alumni – but I use the word broadly. Yes, we want to keep con- • Professor Wright receives the nected to those who have participated in and graduated from our many pro- NASA Distinguished Public Service grams. But also I include our staff, researchers, benefactors, and others who Medal became part of the P&A Department at some point in our lives. I very much include our future alumni as our target reader, too; the feature article on the 26 STUDENT INFORMATION Science and Technology Research Building, and the many pages of Research • Astronomy Live Highlights will help prospective students see some of what UCLA has to offer. • Science for Kids • UCLA Internal Research I want to thank Professor Turner who was Chair during the period of this Experience (REU) for Undergraduates year’s newsletter. Under her leadership and that of the vice chairs, the depart- ment has moved forward enormously. We’ve welcomed many wonderful new faculty. Newly created committees on diversity for physics and astronomy have made concrete impacts. A new introductory physics series for life sciences majors propels us into 21st century teaching and benefits thousands of UCLA undergraduates.
    [Show full text]
  • Propagation of Shear Alfvén Waves in a Two-Ion Plasma and Application As a Diagnostic for the Ion Density Ratio
    J. Plasma Phys. (2020), vol. 86, 905860613 © The Author(s), 2020. 1 Published by Cambridge University Press This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. doi:10.1017/S0022377820001403 Propagation of shear Alfvén waves in a two-ion plasma and application as a diagnostic for the ion density ratio J. Robertson 1,†,T.A.Carter1 and S. Vincena 1 1Department of Physics and Astronomy, University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90034, USA (Received 11 February 2020; revised 11 October 2020; accepted 12 October 2020) In this paper, we propose an efficient diagnostic technique for determining spatially resolved measurements of the ion density ratio in a magnetized two-ion species plasma. Shear Alfvén waves were injected into a mixed helium–neon plasma using a magnetic loop antenna, for frequencies spanning the ion cyclotron regime. Two distinct propagation bands are observed, bounded by ω<ΩNe and ωii <ω<ΩHe,whereωii is the ion–ion hybrid cutoff frequency and ΩHe and ΩNe are the helium and neon cyclotron frequencies, respectively. A theoretical analysis of the cutoff frequency was performed and shows it to be largely unaffected by kinetic electron effects and collisionality, although it can deviate significantly from ωii in the presence of warm ions due to ion finite Larmor radius effects. A new diagnostic technique and accompanying algorithm was developed in which the measured parallel wavenumber k is numerically fit to the predicted inertial Alfvén wave dispersion in order to resolve the local ion density ratio.
    [Show full text]
  • Study of Flow, Turbulence and Transport on the Large Plasma Device
    University of California Los Angeles Study of Flow, Turbulence and Transport on the Large Plasma Device A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Physics by David Andrew Schaffner 2013 c Copyright by David Andrew Schaffner 2013 Abstract of the Dissertation Study of Flow, Turbulence and Transport on the Large Plasma Device by David Andrew Schaffner Doctor of Philosophy in Physics University of California, Los Angeles, 2013 Professor Troy A. Carter, Chair The relationships amongst azimuthal flow, radial particle transport and turbulence on the Large Plasma Device (LAPD) are explored through the use of biasable limiters which con- tinuously modify the rotation of the plasma column. Four quarter annulus plates serve as an iris-like boundary between the cathode source and the main plasma chamber. Application of a voltage to the plates using a capacitor bank drives cross-field current which rotates the plasma azimuthally in the electron diamagnetic direction (EDD). With the limiters inserted, a spontaneous rotation in the ion diamagnetic direction is observed; thus, increasing biasing tends to first slow rotation, null it out, then reverse it. This experiment builds on previous LAPD biasing experiments which used the chamber wall as the biasing electrode rather than inserted limiter plates. The use of inserted limiter biasing rather than chamber wall biasing allows for better cross-field current penetration between the plasma source and the electrodes which in turn allow for a finer variation of applied torque on the plasma. The modification of plasma parameter profiles, turbulent characteristics, and radial trans- port are tracked through these varying flow states.
    [Show full text]