DOCSLIB.ORG

A Possible Mechanism for the Generation and Motion of Blobs in Tokamaks V

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Possible Mechanism for the Generation and Motion of Blobs in Tokamaks V Plasma Physics Reports, Vol. 29, No. 10, 2003, pp. 803–815. Translated from Fizika Plazmy, Vol. 29, No. 10, 2003, pp. 867–879. Original Russian Text Copyright © 2003 by Vlasov, Trubnikov. TOKAMAKS A Possible Mechanism for the Generation and Motion of Blobs in Tokamaks V. P. Vlasov and B. A. Trubnikov Nuclear Fusion Institute, Russian Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia Received January 15, 2003; in final form, March 7, 2003 Abstract—A possible mechanism for the generation and motion of so-called blobs—peculiar perturbations that are observed in a tokamak edge plasma—is proposed. It is suggested that blobs are self-contracting plasma filaments generated either by the thermal-radiative instability of a plasma with impurities or by the nonradiative resonant charge-exchange instability resulting from the presence of neutral hydrogen atoms near the tokamak wall. Instability occurs in a narrow temperature range in which pressure is a decreasing function of density. Under these conditions, the most typical perturbations are the local ones that originate spontaneously in the form of separate growing hills and wells in the density. The temperature at the centers of the hills is lower than that in the surrounding plasma, but they are denser and, consequently, brighter than the background. The (denser) hills should move (“sink”) toward the separatrix, while the (less dense) wells should “rise” in the oppo- site direction, as is observed in experiments. It may even be said that they behave in accordance with a peculiar Archimedes’ principle. © 2003 MAIK “Nauka/Interperiodica”. 1. INTRODUCTION some papers, it was pointed out that the temperature at Observations in some tokamaks have revealed fila- the center of a blob is close to 20 eV, which seems to be ments—commonly referred to as “blobs”—that more than mere coincidence. The fact that a blob appeared sporadically in the edge plasma, were divides into two parts in crossing the separatrix likely stretched along the main magnetic field, and moved provides evidence for its double structure. toward the chamber wall. Figure 1, borrowed from the The mechanism by which blobs move was consid- paper by Marmar [1], presents six successive film ered by Krasheninnikov [2], who supposed that a blob frames of an individual blob that moved at a speed of is a magnetic tube that becomes polarized in a nonuni- 2 km/s toward the edge of the plasma column in the form peripheral tokamak magnetic field by the differ- Alcator C-Mod tokamak (the frames were taken with µ ence between the gradient drifts of the electrons and an exposure time of 4 s). Blobs have also been ions and then continues to move with the velocity V = observed in the DIII-D tokamak, whose cross section is cE/B toward the wall, while at the same time being shown in Fig. 2, in which the arrow indicates the obser- spread out by diffusion. However, in [2], nothing was vation region. said about the mechanism by which blobs originate. From Fig. 1, we can see that, as a blob crosses the separatrix magnetic surface, it breaks into two parts, In the present paper, we consider possible causes of one of which stays inside the separatrix and the other the generation of blobs and the mechanism for their passes through the separatrix and continues to move motion. Although the mechanism of motion to be con- toward the wall. Blobs originate in the edge plasma, in sidered here differs somewhat from that proposed in which neutral impurities play an important role. In [2], it yields the same motion picture of the blobs. 2 cm ∆t = 4 µs Fig. 1. Six successive frames of a blob in the Alcator C-Mod tokamak. The dashed curve shows the separatrix. 1063-780X/03/2910-0803 $24.00 © 2003 MAIK “Nauka/Interperiodica” 804 VLASOV, TRUBNIKOV z, m 2. THERMAL-RADIATIVE INSTABILITY We think that one of the possible mechanisms for 1 the generation of blobs is thermal-radiative instability, during which the plasma heating power W is balanced by the power Wrad of radiative losses from impurities arriving from the chamber wall. In this case, the pres- sure p, as a rule, becomes a decreasing function of den- sity, thereby giving rise to the instability. It is important to note that, in such specific unstable 0 media (in [3, 4], they were called “quasi-Chaplygin media”), there are no running waves that causally con- nect the neighboring regions. Consequently, more typi- cal disturbances in these media are individual local per- turbations that are spontaneously generated and grow until they reach their saturation level. These perturba- tions qualitatively resemble blobs. In addition, the Ð1 blobs observed in experiments originate in a rather nar- row temperature range around a value of ~20 eV. It is noteworthy that the model based on the thermal-radia- tive instability gives the same temperature value. Note that thermal-radiative instability is also referred to as radiative condensational instability and, in the particu- lar case of Joule heating, is called thermal-ionizational instability [5]. Let us discuss this hypothesis in more detail. The inductive voltage around the circumference of the torus is approximately equal to V [V] ≈ 3.6/B|| [T] [6], so that 021 the longitudinal electric field can be assumed to be con- R, m stant during the discharge, E|| = const. The Joule heating 2η power WJ = E is deposited in the central plasma and Fig. 2. Cross section of the DIII-D tokamak. The arrow indi- heats it. However, blobs originate in the scrape-off cates the region where the blobs are observed. layer (SOL) plasma, in which an important role is played by impurities arriving from the tokamak wall. This is why, in considering the first illustrative Q, W cm3 example, we assume that the electrical conductivity in the peripheral plasma is created by collisions of elec- trons with neutral atoms and is described by the formu- W las 10Ð25 η 2 ν ν σ ==e ne/me ea, ea na eav Te, Mo (2.1) Ð26 σ π 2 10 Fe ea ==a , v Te T e/me, σ where ea is the cross section for collisions and vTe is 10Ð27 the electron thermal velocity. In the SOL plasma, impurity atoms are ionized and O become ions with a certain density nZ. The electrons 10Ð28 C recombine with impurity ions, emitting radiation with the specific power Wrad = nenZQ. The dependence of the factor Q on the electron temperature Te for typical 10Ð29 10Ð3 10Ð2 10Ð1 110 impurities (such as C, O, Fe, Mo, and W) is shown in Fig. 3, borrowed from [7]. Te, keV We can see that, for heavy impurities, this factor is nearly constant and is approximately equal to Q ≈ − Fig. 3. Factor Q(T) for C, O, Fe, Mo, and W impurities. 10 17 [cm3 erg/s]. In the simplest model at hand, the PLASMA PHYSICS REPORTS Vol. 29 No. 10 2003 A POSSIBLE MECHANISM FOR THE GENERATION AND MOTION 805 ρ * equality WJ = Wrad yields the dependence nZ T e = C1 = 2 2 (‡) E|| e /n σ Qm = const. a ea e 2 If we introduce the ratio of the density of impurity 3 α ions to the electron density, nZ/ne = , and take into 1 1 account the electron pressure p = n T , then we arrive at e e 2 the following inverse dependence of the pressure of the electrons on their density: Ð3π/2 3π/2 x ρ 2 * C2 C1 (b) p ===------, C2 -----α- const. (2.2) ne 3 It is this inverse dependence that leads to a peculiar 2 kind of quasi-Chaplygin instability, which will be ana- lyzed below. 1 1 Ð3π/8 3π/8 x 3. THEORY OF QUASI-CHAPLYGIN INSTABILITIES Fig. 4. Density profiles in an individual well and an individ- Here, the theory of quasi-Chaplygin instabilities, ual hill that develop spontaneously against the background of an initially homogeneous medium (borrowed from [3, which was presented in detail in [3, 4], is described 4]). Curves 1 refer to t = Ð∞. The evolution proceeds from only briefly. We begin with the conventional hydrody- curves 2 to curves 3. namic equations ∂ -----ρ +0,— ⋅ ()ρv = The simplest solutions to Eqs. (3.3) are those describ- ∂t ing spatially periodic standing perturbations that grow (3.1) ∂ exponentially in time: Ψ(t, r) ~ exp(γt + ikr). However, ()⋅ 1 ∂-----vv+ — v = – ρ---—p, these perturbations can only originate from spatially t periodic seeds, which, in turn, cannot appear for no rea- but supplement them with an unusual equation of state son whatever because, in such media, there are no run- in which the pressure decreases according to a power ning waves that causally connect the neighboring ρ ρ Ð|s| regions. That is why the most interesting solutions are law as the density increases, p = p0( / 0) , where p0 and ρ are the unperturbed pressure and density of a those corresponding to spontaneous local perturba- 0 tions. We require that these solutions vanish at an infi- homogeneous background medium, respectively. Intro- ∞ ducing the dimensionless density ρ = ρ/ρ , we find it nitely distant past (t Ð), thereby modeling the ∗ 0 property of perturbations to originate spontaneously expedient to rewrite the equations as and grow progressively. ∂ Thus, in three-dimensional spherical geometry, in -----ρ +0,— ⋅ ()ρ v = ∂t * * which Ψ(t, x, y, z) = ψ(R)exp(γt) (where R = (3.2) 2 2 2 ∂ 2 1/µ x ++y z ), we obtain the following equation and -----vv+ ()⋅ — v = µc —ρ , ∂t 0 * local solution for ψ(R): where c = sp/ρ is the growth rate of the perturba- ∆ ψ 1 ()ψ 2ψ ψ sinkR 0 0 0 3 ==--- R RR'' –k , =A-------------- , (3.4) tions and the parameter µ = Ð1/(1 + |s|) will be referred R kR to as the azimuthal number.
Load more

Recommended publications
  • Pro.Ffress D &Dentsdc Raddo
    Pro.ffress d_ &dentSdc Raddo FIFTEENTH GENERAL ASSEMBLY OF THE INTERNATIONAL SCIENTIFIC RADIO UNION September 5-15, 1966 Munich, Germany REPORT OF THE U.S.A. NATIONAL COMMITTEE OF THE INTERNATIONAL SCIENTIFIC RADIO UNION Publication 1468 NATIONAL ACADEMY OF SCIENCES NATIONAL RESEARCH COUNCIL Washington, D.C. 1966 Library of Congress Catalog Card No. 55-31605 Available from Printing and Publishing Office National Academy of Sciences 2101 Constitution Avenue Washington, D.C. 20418 Price: $10.00 October28,1966 Dear Dr. Seitz: I ampleasedto transmitherewitha full report to the NationalAcademy of Sciences--NationalResearchCouncil,onthe 15thGeneralAssemblyof URSIwhichwasheldin Munich,September5-15, 1966. TheUnitedStatesNationalCommitteeof URSIhasparticipatedin the affairs of the Unionfor forty-five years. It hashadmuchinfluenceonthe Unionas,.for example,in therecent creationof a Commissiononthe Mag- netosphere.ThisnewCommission,whichis nowvery strong,demonstrates the ability of theUnion,oneof ICSU'sthree oldest,to respondto the changingneedsof its field. AlthoughtheUnitedStatessendsthelargest delegationsof anycountry to the GeneralAssembliesof URSI,theyare neverthelessrelatively small becauseof thestrict mannerin whichURSIcontrolsthe size of its Assem- blies. This is donein order to preventineffectivenessthroughuncontrolled participationbyvery largenumbersof delegates.Accordingly,our delega- tions are carefully selected,andcomprisepeoplequalifiedto prepareand presentour NationalReportto the Assembly.Thepre-Assemblyreport is a report of progressin
    [Show full text]
  • Mighty Eagle: the Development and Flight Testing of an Autonomous Robotic Lander Test Bed
    Mighty Eagle: The Development and Flight Testing of an Autonomous Robotic Lander Test Bed Timothy G. McGee, David A. Artis, Timothy J. Cole, Douglas A. Eng, Cheryl L. B. Reed, Michael R. Hannan, D. Greg Chavers, Logan D. Kennedy, Joshua M. Moore, and Cynthia D. Stemple PL and the Marshall Space Flight Center have been work- ing together since 2005 to develop technologies and mission concepts for a new generation of small, versa- tile robotic landers to land on airless bodies, including the moon and asteroids, in our solar system. As part of this larger effort, APL and the Marshall Space Flight Center worked with the Von Braun Center for Science and Innovation to construct a prototype monopropellant-fueled robotic lander that has been given the name Mighty Eagle. This article provides an overview of the lander’s architecture; describes the guidance, navi- gation, and control system that was developed at APL; and summarizes the flight test program of this autonomous vehicle. INTRODUCTION/PROJECT BACKGROUND APL and the Marshall Space Flight Center (MSFC) technology risk-reduction efforts, illustrated in Fig. 1, have been working together since 2005 to develop have been performed to explore technologies to enable technologies and mission concepts for a new genera- low-cost missions. tion of small, autonomous robotic landers to land on As part of this larger effort, MSFC and APL also airless bodies, including the moon and asteroids, in our worked with the Von Braun Center for Science and solar system.1–9 This risk-reduction effort is part of the Innovation (VCSI) and several subcontractors to con- Robotic Lunar Lander Development Project (RLLDP) struct the Mighty Eagle, a prototype monopropellant- that is directed by NASA’s Planetary Science Division, fueled robotic lander.
    [Show full text]
  • PROJECT PENGUIN Robotic Lunar Crater Resource Prospecting VIRGINIA POLYTECHNIC INSTITUTE & STATE UNIVERSITY Kevin T
    PROJECT PENGUIN Robotic Lunar Crater Resource Prospecting VIRGINIA POLYTECHNIC INSTITUTE & STATE UNIVERSITY Kevin T. Crofton Department of Aerospace & Ocean Engineering TEAM LEAD Allison Quinn STUDENT MEMBERS Ethan LeBoeuf Brian McLemore Peter Bradley Smith Amanda Swanson Michael Valosin III Vidya Vishwanathan FACULTY SUPERVISOR AIAA 2018 Undergraduate Spacecraft Design Dr. Kevin Shinpaugh Competition Submission i AIAA Member Numbers and Signatures Ethan LeBoeuf Brian McLemore Member Number: 918782 Member Number: 908372 Allison Quinn Peter Bradley Smith Member Number: 920552 Member Number: 530342 Amanda Swanson Michael Valosin III Member Number: 920793 Member Number: 908465 Vidya Vishwanathan Dr. Kevin Shinpaugh Member Number: 608701 Member Number: 25807 ii Table of Contents List of Figures ................................................................................................................................................................ v List of Tables ................................................................................................................................................................vi List of Symbols ........................................................................................................................................................... vii I. Team Structure ........................................................................................................................................................... 1 II. Introduction ..............................................................................................................................................................
    [Show full text]
  • Evidence for Crater Ejecta on Venus Tessera Terrain from Earth-Based Radar Images ⇑ Bruce A
    Icarus 250 (2015) 123–130 Contents lists available at ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus Evidence for crater ejecta on Venus tessera terrain from Earth-based radar images ⇑ Bruce A. Campbell a, , Donald B. Campbell b, Gareth A. Morgan a, Lynn M. Carter c, Michael C. Nolan d, John F. Chandler e a Smithsonian Institution, MRC 315, PO Box 37012, Washington, DC 20013-7012, United States b Cornell University, Department of Astronomy, Ithaca, NY 14853-6801, United States c NASA Goddard Space Flight Center, Mail Code 698, Greenbelt, MD 20771, United States d Arecibo Observatory, HC3 Box 53995, Arecibo 00612, Puerto Rico e Smithsonian Astrophysical Observatory, MS-63, 60 Garden St., Cambridge, MA 02138, United States article info abstract Article history: We combine Earth-based radar maps of Venus from the 1988 and 2012 inferior conjunctions, which had Received 12 June 2014 similar viewing geometries. Processing of both datasets with better image focusing and co-registration Revised 14 November 2014 techniques, and summing over multiple looks, yields maps with 1–2 km spatial resolution and improved Accepted 24 November 2014 signal to noise ratio, especially in the weaker same-sense circular (SC) polarization. The SC maps are Available online 5 December 2014 unique to Earth-based observations, and offer a different view of surface properties from orbital mapping using same-sense linear (HH or VV) polarization. Highland or tessera terrains on Venus, which may retain Keywords: a record of crustal differentiation and processes occurring prior to the loss of water, are of great interest Venus, surface for future spacecraft landings.
    [Show full text]
  • GRAIL Gravity Observations of the Transition from Complex Crater to Peak-Ring Basin on the Moon: Implications for Crustal Structure and Impact Basin Formation
    Icarus 292 (2017) 54–73 Contents lists available at ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus GRAIL gravity observations of the transition from complex crater to peak-ring basin on the Moon: Implications for crustal structure and impact basin formation ∗ David M.H. Baker a,b, , James W. Head a, Roger J. Phillips c, Gregory A. Neumann b, Carver J. Bierson d, David E. Smith e, Maria T. Zuber e a Department of Geological Sciences, Brown University, Providence, RI 02912, USA b NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA c Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130, USA d Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA e Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139, USA a r t i c l e i n f o a b s t r a c t Article history: High-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission provide Received 14 September 2016 the opportunity to analyze the detailed gravity and crustal structure of impact features in the morpho- Revised 1 March 2017 logical transition from complex craters to peak-ring basins on the Moon. We calculate average radial Accepted 21 March 2017 profiles of free-air anomalies and Bouguer anomalies for peak-ring basins, protobasins, and the largest Available online 22 March 2017 complex craters. Complex craters and protobasins have free-air anomalies that are positively correlated with surface topography, unlike the prominent lunar mascons (positive free-air anomalies in areas of low elevation) associated with large basins.
    [Show full text]
  • The Earth As an Extrasolar Transiting Planet II
    A&A 564, A58 (2014) Astronomy DOI: 10.1051/0004-6361/201323041 & c ESO 2014 Astrophysics The Earth as an extrasolar transiting planet II. HARPS and UVES detection of water vapour, biogenic O2,andO3 L. Arnold1, D. Ehrenreich2, A. Vidal-Madjar3, X. Dumusque4, C. Nitschelm5,R.R.Querel6,7,P.Hedelt8, J. Berthier9, C. Lovis2, C. Moutou10,11,R.Ferlet3, and D. Crooker12 1 Aix Marseille Université, CNRS, OHP (Observatoire de Haute Provence), Institut Pythéas (UMS 3470), 04870 Saint-Michel-l’Observatoire, France e-mail: [email protected] 2 Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland 3 Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Boulevard Arago, 75014 Paris, France 4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, 02138 Cambridge, USA 5 Unidad de Astronomía, Facultad de Ciencias Básicas, Universidad de Antofagasta, 601 Avenida Angamos, Antofagasta, Chile 6 University of Chile, Department of Electrical Engineering, 2007 Tupper Avenue, Santiago, Chile 7 National Institute of Water and Atmospheric Research (NIWA), 1010 Auchland, Lauder, New Zealand 8 Deutsches Zentrum für Luft und Raumfahrt e.V. (DLR), Oberpfaffenhofen, 82234 Wessling, Germany 9 Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, Avenue Denfert-Rochereau, 75014 Paris, France 10 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France 11 CFHT Corporation, 65-1238 Mamalahoa Hwy Kamuela, Hawaii 96743, USA 12 Astronomy Department, Universidad de Chile, Casilla 36-D Santiago, Chile Received 7 November 2013 / Accepted 3 February 2014 ABSTRACT Context. The atmospheric composition of transiting exoplanets can be characterized during transit by spectroscopy.
    [Show full text]
  • Introduction to Astronomy from Darkness to Blazing Glory
    Introduction to Astronomy From Darkness to Blazing Glory Homework DVD This is a spiral galaxy. There are billions of this type in the Universe. The cloudy areas are a mix of gas, dust and stars. The center has a black hole as well as millions upon millions of closely packed stars systems. Jeff Scott JAS EP SpiralGalaxy M81 1 This DVD contains : •Your semester’s homework assignments. •Your generic homework sheet. •The textbook glossary. •Website suggestions. Comet Tempel 1 A special thank you to NASA, NOAA and USGS for the images, photographs and diagrams. Earthrise photo taken by an Apollo Astronaut. On the Moon. JAS EP 2 This DVD provides instruction for student homework assignments. Each chapter has its own assignments. The teacher will assign due dates. You may use the generic homework page at the end of the DVD by printing out a copy. The picture on the right is of a nebula. It is a cloud in space made of dust and gas. These clouds can be enormous. Credit: NASA, H.Ford (JHU), G. Cone Nebula (NG2264) Illingsworth (USCC?LO), Mclampin (STScl), G.HARtwig (STScl), the ACS 3 Science Team and ESA Table Of Contents Reports Pg. 7 Chapter 1 Astronomy Basics Pg. 8 Chapter 2 Time Pg. 10 Chapter 3 Solar System Overview Pg. 13 Chapter 4 Our Sun Pg. 15 Chapter 5 Terrestrial Planets Pg. 17 Chapter 6 Outer and Exoplanets Pg. 29 Chapter 7 The Moons Pg. 37 Chapter 8 Rocks N’ Ice Pg. 43 Chapter 9 The Stars Pg. 49 Stephan’s Quintet Galaxy Grouping Chapter 10 Galaxies Pg.
    [Show full text]
  • Apollo 16 Press
    .. Arii . cLyI( ’ JOHN F . KENNEDY Si ACE GENTEb @@C€ i!AM LIB XRY cJ- / NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Washington, D . C . 20546 202-755-8370 I FOR RELEASE: THURSDAY A .M . RELEASE NO: 12-64X April 6. 1972 PRO IFCT. APOLLO 16 (To be launched no earlier than April 16) E GENERAL RELEASE ..................... .1-5 COUNTDOWN ........................ 6-10 Launch Windows ................... .9 Ground Elapsed Time Update ............. .10 LAUNCH AND MISSION PROFILE ............... 11-39 Launch Events .................... 15-16 Mission Events .............. ..... 19-24 EVA Mission Events ................. 29-39 APOLLO 16 MISSION OBJECTIVES .............. 40-41 SCIENTIFIC RESULTS OF APOLLO 11, 12. 14 AND 15 MISSIONS . 42-44 APOLLO 16 LANDING SITE ................. 45-47 LUNAR SURFACE SCIENCE .................. 48-85 Passive Seismic Experiment ............. 48-52 ALSEP to Impact Distance Table ...... ..... 52-55 Lunar Surface Magnetometer ............. 55-58 Magnetic Lunar sample Returned to the Moon ..... .59 K Lunar Heat Flow Experiment ............. 60-65 ALSEP Central Station ................ .65 SNAP-27 .. Power Source for ALSEP .......... 66-67 Soil Mechanics ................... .68 I Lunar Portable Magnetometer ............. 68-71 Far Ultraviolet Camera/Spectroscope ......... 71-73 Solar Wind Composition Experiment .......... .73 Cosmic Ray Detector ................. .74 T Lunar Geology Investigation........ ..... 75-78 Apollo Lunar Geology Hand Tools ........... 79-85 LUNAR ORBITAL SCIENCE ............. ...... 86-98 Gamma-Ray
    [Show full text]
  • Science Concept 2: the Structure and Composition of the Lunar Interior Provide Fundamental Information on the Evolution of a Differentiated Planetary Body
    Science Concept 2: The Structure and Composition of the Lunar Interior Provide Fundamental Information on the Evolution of a Differentiated Planetary Body Science Concept 2: The Structure and Composition of the Lunar Interior Provide Fundamental Information on the Evolution of a Differentiated Planetary Body Science Goals: a. Determine the thickness of the lunar crust (upper and lower) and characterize its lateral variability on regional and global scales. b. Characterize the chemical/physical stratification in the mantle, particularly the nature of the putative 500-km discontinuity and the composition of the lower mantle. c. Determine the size, composition, and state (solid/liquid) of the core of the Moon. d. Characterize the thermal state of the interior and elucidate the workings of the planetary heat engine. INTRODUCTION Each of the Science Goals addressed by Science Concept 2 is linked: data regarding the crust, mantle, and core must be obtained in order to understand the thermal state of the interior and the planetary heat engine. Much about these Science Goals is currently unknown: crustal thickness and lateral variability are constrained by gravity and seismic models which suffer from non-uniqueness and a lack of control points; mantle composition is ambiguously estimated from seismic velocity profiles and assumed lunar bulk compositions; mantle structure is obtained through seismic velocity profiles, but fine-scale structure is not resolved and any structure outside the Apollo network and below 1000 kilometers depth is unknown; the size, composition and state of the core are obtained through models with few constraints, where the size and state are dependent on an unknown composition, making any core characteristic estimates highly variable; and the thermal state of the interior is constrained by heat flow measurements and characteristics of the core, but current heat flow data are not representative of the global heat flux and core models are non-unique.
    [Show full text]
  • The Messenger
    THE MESSENGER ( , New Meteorite Finds At Imilac No. 47 - March 1987 H. PEDERSEN, ESO, and F. GARe/A, elo ESO Introduction hand, depend more on the preserving some 7,500 meteorites were recovered Stones falling from the sky have been conditions of the terrain, and the extent by Japanese and American expeditions. collected since prehistoric times. They to which it allows meteorites to be spot­ They come from a smaller, but yet un­ were, until recently, the only source of ted. Most meteorites are found by known number of independent falls. The extraterrestrial material available for chance. Active searching is, in general, meteorites appear where glaciers are laboratory studies and they remain, too time consuming to be of interest. pressed up towards a mountain range, even in our space age, a valuable However, the blue-ice fields of Antarctis allowing the ice to evaporate. Some source for investigation of the solar sys­ have proven to be a happy hunting have been Iying in the ice for as much as tem's early history. ground. During the last two decades 700,000 years. It is estimated that, on the average, each square kilometre of the Earth's surface is hit once every million years by a meteorite heavier than 500 grammes. Most are lost in the oceans, or fall in sparsely populated regions. As a result, museums around the world receive as few as about 6 meteorites annually from witnessed falls. Others are due to acci­ dental finds. These have most often fallen in prehistoric times. Each of the two groups, 'falls' and 'finds', consists of material from about one thousand catalogued, individual meteorites.
    [Show full text]
  • Understanding the Lunar Surface and Space-Moon Interactions Paul Lucey1, Randy L
    Reviews in Mineralogy & Geochemistry Vol. 60, pp. 83-219, 2006 2 Copyright © Mineralogical Society of America Understanding the Lunar Surface and Space-Moon Interactions Paul Lucey1, Randy L. Korotev2, Jeffrey J. Gillis1, Larry A. Taylor3, David Lawrence4, Bruce A. Campbell5, Rick Elphic4, Bill Feldman4, Lon L. Hood6, Donald Hunten7, Michael Mendillo8, Sarah Noble9, James J. Papike10, Robert C. Reedy10, Stefanie Lawson11, Tom Prettyman4, Olivier Gasnault12, Sylvestre Maurice12 1University of Hawaii at Manoa, Honolulu, Hawaii, U.S.A. 2Washington University, St. Louis, Missouri, U.S.A. 3University of Tennessee, Knoxville, Tennessee, U.S.A. 4Los Alamos National Laboratory, Los Alamos, New Mexico, U.S.A. 5Smithsonian Institution, Washington D.C., U.S.A. 6Lunar and Planetary Laboratory, Univ. of Arizona, Tucson, Arizona, U.S.A. 7University of Arizona, Tucson, Arizona, U.S.A. 8Boston University, Cambridge, Massachusetts, U.S.A. 9Brown University, Providence, Rhode Island, U.S.A. 10University of New Mexico, Albuquerque, New Mexico, U.S.A. 11 Northrop Grumman, Van Nuys, California, U.S.A. 12Centre d’Etude Spatiale des Rayonnements, Toulouse, France Corresponding authors e-mail: Paul Lucey <[email protected]> Randy Korotev <[email protected]> 1. INTRODUCTION The surface of the Moon is a critical boundary that shapes our understanding of the Moon as a whole. All geologic mapping and remote sensing techniques utilize only the outermost portion of the Moon. Before leaving the Moon for study in our laboratories, all lunar samples that have been studied existed at or very near the surface. With the exception of the deeply probing geophysical techniques, our understanding of the interior of the Moon is derived from surficial, but not superficial, information, coupled with geologic reasoning.
    [Show full text]
  • Design of a Direct-Detection Wind and Aerosol Lidar for Mars Orbit
    CEAS Space Journal https://doi.org/10.1007/s12567-020-00301-z ORIGINAL PAPER Design of a direct‑detection wind and aerosol lidar for mars orbit Daniel R. Cremons1 · James B. Abshire1,2 · Xiaoli Sun1 · Graham Allan1,3 · Haris Riris1 · Michael D. Smith1 · Scott Guzewich1 · Anthony Yu1 · Floyd Hovis4 Received: 10 April 2019 / Revised: 31 January 2020 / Accepted: 2 February 2020 © The Author(s) 2020 Abstract The present knowledge of the Mars atmosphere is greatly limited by a lack of global measurements of winds and aerosols. Hence, measurements of height-resolved wind and aerosol profles are a priority for new Mars orbiting missions. We have designed a direct-detection lidar (MARLI) to provide global measurements of dust, winds and water ice profles from Mars orbit. From a 400-km polar orbit, the instrument is designed to provide wind and backscatter measurements with a vertical resolution of 2 km and with resolution of 2° in latitude along track. The instrument uses a single-frequency, seeded Nd:YAG laser that emits 4 mJ pulses at 1064 nm at a 250 Hz pulse rate. The receiver utilizes a 50-cm diameter telescope and a double- edge Fabry-Pérot etalon as a frequency discriminator to measure the Doppler shift of the aerosol-backscatter profles. The receiver also includes a polarization-sensitive channel to detect the cross-polarized backscatter profles from water ice. The receiver uses a sensitive 4 × 4 pixel HgCdTe avalanche photodiode array as a detector for all signals. Here we describe the measurement concept, instrument design, and calculate its performance for several cases of Mars atmospheric conditions.
    [Show full text]