alfonso-tarditi (1)

Plasma Technologies for Aerospace Applications Alfonso G. Tarditi Engineering and Science Contract Group NASA Johnson Space Center and University of Houston, Clear Lake Outline •Plasmas •Main Thrust for Plasma Research: Fusion Energy •Aerospace Applications •Research at UHCL Plasmas The “Fourth State” of the Matter •The matter in “ordinary” conditions presents itself in three fundamental states of aggregation: solid, liquid and gas. •These different states are characterized by different levels of bondingamong the molecules. •In general, by increasing the temperature(=average molecular kinetic energy) a phase transitionoccurs, from solid, to liquid, to gas. •A further increase of temperatureincreases the collisional rate and then the degree of ionization of the gas. The “Fourth State” of the Matter (II) •The ionized gas could then become a plasma if the proper conditions for density, temperature and characteristic length are met (quasineutrality, collective behavior). •The plasma state does not exhibit a different state of aggregationbut it is characterized by a different behavior when subjected to electromagnetic fields. The “Fourth State” of the Matter (III) Plasmas (V) •An ionized gas has a certain amount of free charges that can move in presence of electric forces Debye Shielding •Shielding effect: the free charges move towards a perturbing charge to produce, at a large enough distance l D , (almost) a neutralizationof the electric field. E~0 E Debye Shielding (II) l D •The quantity is called the (electron) Debye lengthof the plasma •The Debye length is a measure of the effective shielding length beyond which the electron motions are shielding charge density fluctuations in the plasma 0 2 B De e k T nq  l Debye Shielding (IV) •Typical values of the Debye Lengthunder different conditions: n [m -3 ] T[e V] Debye Length [m] Interstellar 10 6 10 -1 1 Solar Wind 10 7 10 10 Solar Corona 10 12 10 2 10 -1 Solar atmosphere 10 20 1 10 -6 Magnetosphere 10 7 10 3 10 2 Ionosphere 10 12 10 -1 10 -3 Debye Shielding (IV) •An ionized gasis characterized, in general, by a mixture of neutrals, (positive) ions and electrons. •For a gas in thermal equilibriumthe Saha equationgives the expected amount of ionization: •The Saha equationdescribes an equilibrium situation between ionization and (ion-electron) recombination rates. From Ionized Gas to Plasma / 2213 / 2 2.4 10 i B U k T in nn Te   From Ionized Gas to Plasma (II) •(Long range) Coulomb force between two charged particles q 1 and q 2 at distance r: r 12 2 0 4 qq F r  q 2 q 1 From Ionized Gas to Plasma (III) •(Short range) force between two neutral atoms (e.g.from Lenard-Jones interatomic potential model) attractive repulsive r •If Lis the typical dimension of the ionized gas, a condition for an ionized gas to be “quasineutral” is: •The “collective effects” are dominant in an ionized gas if the number of particles in a volume of characteristic length equal to the Debye length (Debye sphere) is large: •N D is called “plasma parameter” 3 4 1 3 DD Nnl D Ll From Ionized Gas to Plasma •A plasma is an ionized gas that is “quasineutral” and is dominated by “collective effects” is called a plasma: D Ll 3 4 1 3 DD Nnl From Ionized Gas to Plasma (II) From Ionized Gas to Plasma (III) •An ionized gasis not necessarily a plasma •An ionized gas can exhibit a “collective behavior” when the long-range electric forces are sufficient to maintain overall neutrality •An ionized gas could appear quasineutralif the charge density fluctuations are contained in a limited region of space •A plasmais an ionized gas that exhibits a collective behavior andis quasineutral Plasma Confinement: the Lorentz Force Force on a charged particle in a magnetic field F= q vx B Magnetic Mirror: charged particles (protons and electrons) move in helical orbits at their cyclotron frequency Plasma Confinement: the Magnetic Mirror Main Thrust for Plasma Research: Fusion Energy The Bad Stuff The Bad Stuff [Ref: Fusion Power Associates, http://fusionpower.org] The Bad Stuff [Ref: US Do E, 1999] U.S. Fusion Budget Vs. the Price of Crude Oil The Bad Stuff [Ref: US Do E, 1999] World Magnetic Fusion Effort (1999) The Fusion Energy Hope The Fusion Energy Hope [Ref: Fusion Power Associates, http://fusionpower.org] The Fusion Energy Hope [Ref: US Do E, 1999] The Advantages of Fusion Energy The Fusion Process Deuterium Tritium Fusion How to Achieve Nuclear Fusion Fusion Works The Sun: a very old fusion reactor Fusion Works Controlled Fusion Experiments Joint European Torus (JET), Culham, UK Controlled Fusion Experiments Inertial confinement: the 192 laser beams in the National Ignition Facility(LLNL) heat the inside surface of a hohlraumwith high uniformity Controlled Fusion Experiments Inertial confinement: the target chamber in the National Ignition Facility(LLNL) Controlled Fusion Experiments Aerospace Applications -Lightning Protection -Airfoils for Super/Hypersonic Flight -MHD/Chemical Plasma Propulsion -Plasma Spacecraft Interactions -Electric Propulsion Lightning Plasma Channel •Lightning affect spacecrafts: Lightning Plasma Channel Apollo 12 Space Shuttle •Objective: improve current fluid dynamic models [1-3] with prescribed current waveforms to a self-consistent plasma channel in a neutral background Lightning Plasma Channel (II) Idealized lightning current waveform [1] S. I. Braginskii, Sov. Phys. JETP 7, 1068 (1958). [2] M. N. Plooster, Phys. Fluids 14, 2111 (1971) [3] A. H. Paxton, R. L. Gardner, and L. Baker, Phys. Fluids 29, 2736 (1986) Lightning Plasma Channel (III) “Stuff” happens: Current Interest: Constellation Program Lightning Protection Design Lightning Plasma Channel (IV) Plasma Airfoils for Super/Hypersonic Flight a)Plasma off.b) Plasma on Subsonic Plasma Aerodynamics for Flight Control of Aircraft: Surface plasma induced flow re-attachment of an airfoil at an angle to the oncoming free-stream (University of Tennessee). Plasma Airfoils/Actuators General Test Bed Arrangement for Wedge Model MHD Flow Interaction Experiments Plasma Airfoils/Actuators MHD HYPERSONIC FLOW CONTROL (Russian Academy of Sciences, Moscow, Russia A concept of On-Board surface MHD Generator on a Re-Entry vehicle. Plasma Airfoils/Actuators Experimental Photographs of Wedge Model Test (Right Side Photo Images –Left Side Spectral Enhanced Images) Plasma Airfoils/Actuators Plasma Actuators for Super/Hypersonic Flight Conceptual Scheme of Airframe Embedded Magnetized Plasma Actuator WING MAGNETIC FIELD AND PLASMA SOURCE COILS ENGINE AIR INLET AIRFLOW OUTLET AIRFLOW Fig. 1 -Conceptual Scheme of the Airframe-Embedded Magnetized Plasma Actuator AIRFLOW + PLASMA MHD/Chemical Plasma Propulsion MHD/Chemical Plasma Propulsion NASA-Langley Seeded Plasma Accelerator for enhanced propulsion experiment (1965) MHD/Chemical Plasma Propulsion MHD Plasma Accelerator for wind tunnel experiment (USAF, 1999) MHD/Chemical Plasma Propulsion System study on the efficiency of an MHD Augmented Atmospheric Propulsion System MHD Generator Optimized SCRAMJET MHD Accelerator Magnetic Nozzle De Laval Nozzle General scheme of an MHD Augmented propulsion system MHD/Chemical Plasma Propulsion Scramjet-Driven Air Borne MHD Generator Concept (US Air Force) MHD/Chemical Plasma Propulsion Assembled Scramjet MHD Test Bed Plasma-Spacecraft Interactions Spacecraft Charging Hazard Spacecraft Charging Hazard (II) •The ISShaslargesurfaces(MMODshields)coveredbyathin (1.3mm)anodizedaluminumasadielectricinsulator •Voltagesaslowas70Vhavebeenfoundtoproducearcingon thedielectriccoating •Long-termexposureofthedielectricsurfacetothespace environmentcanproducelocaldamages(duetomicro- meteoritesordebris)ofthedielectricandenablearcingateven lowervoltages Spacecraft Plasma Hazard (III) •EVAspacesuitshaveasafetythresholdof40V(Marshall Space Flight Centertestshowedarcingthroughthesuitat68 Vwithnewfabric) •Beyondthe40Vvalueitispossiblethatacircuitclose throughtheastronaut’sthoraxcavitywithacurrentinexcess of1m A •Thiscurrentlimitisgenerallyacceptedassafetythresholdto preventheartfibrillation. ISS Floating Potential Probe FPP Spacecraft Plasma Hazard (IV) •Plasmacontactorsaredevicesthatallowtocontrolthe maximumfloatingpotentialofaspacecraftbyprovidinga dischargepathtotheionospherefortheexcesselectrons •Essentially,theplasmacontactorisaplasmasourcethat establishesanelectricallyconductingpath(theplasma) betweenthespacecraftgroundandtheionosphere. •Thefloatingpotentialofthespacecraftisthen“clamped down”tosafevalues(intheorderof-10Vforthecurrent ISS implementation) •ISSplasmacontactorsare Xenonsources(hollow-cathode design,maximumcurrentof4A,muchlargerthanthepresent requirements) Plasma Contactors •Insteady-stateconditionsaplasmasheathisformedbetween thecontactorplasmaandthespacecraftconductingsurface •Forlargevaluesofthespacecraftfloatingpotentialthecurrent inthesheathcanbecomputedthroughthe Childlawandis independentonthespacecraftfloatingpotential •Correctionstothe Childlawcanbeintroducedforcollisional sheaths:inthiscasethereisadependenceofthecurrentonthe potential. •Forexamplea(ion)plasmacurrentofabout12Acanbe sustainedina Hydrogenplasmawithdensityof10 18 and temperatureof1e Vwithaplasmaradiusof5cm. Plasma Contactors •Iftransientsoccur(forexampleasuddenvariationofthe spacecraftpotentialatorbitalsunrise)thesheaththickness adjustitselftonewthevalueofthepotentialcausingvariations ofthecurrentthatarealsodependentonthepotential. •Iftheplasmacontactoriseffectivelyloweringthefloating potentialtosmallvalues(comparedtotheionosphericplasma temperature)thesheathbecomesmuchsmaller(few Debye lengths)andacalculationoftheequilibriumconditions accordingtothe Bohmsheathcriterionshouldbeperformed. Plasma Contactors •Ifahigh-densityplasmaisproducednearaconductingsurface ofaspacecraftinthe Earthorbitanadditionalcurrentpathto theionospherewillbeestablished(inadditiontothepath representedbytheinterfacebetweentheionosphericplasma andthespacecraftexposedconductingsurfaces). •Onthe ISS,thechargingduetothesolarpanelsproducesan electronexcessonthestationstructureandbringsittoa potentialenergythatissignificantlylargerthanthethermal energyoftheionosphericplasma. •Thisisoftenexpressedinlessrigoroustermsbysayingthat the“floatingpotentialismuchhigherthantheplasma temperature”. Plasma Contactors i s :currentthroughthesheathsupportedbythe ISSfloatingpotentialthat dischargesplasmaelectronstotheionosphere Plasma Source Plasma Contactors Outline •Plasmas •Main Thrust for Plasma Research: Fusion Energy •Aerospace Applications -Airfoils for Super/Hypersonic Flight -MHD/Chemical Plasma Propulsion -Plasma Contactors -Electric Propulsion Limitations of Chemical Rockets •Chemicalrocket:exhaustejectionvelocityintrinsicallylimited bythepropellant-oxidizerreaction •Largervelocityincrementofthespacecraftcouldbeobtained onlywithalargerejectedmassflow. •Missionpracticallimitation:exceedinglylargeamountof propellantthatneedstobestoredaboard The Rocket Equation Understanding the motion of a spacecraft The Rocket Equation (II) •Therocketequationlinksthemassofexhaustedpropellant DM,therelativeexhaustvelocityu ex andthevelocity incrementofthespacecraft Dv: 0 1 exp ex v m M u   D D      •Foragiven Dv,thelargeru ex ,thesmaller DM,andviceversa •Alarge DMrequiresthestorageofalargeamountof propellantonboard,reducingtheusefulpayload Advanced (Electric) Propulsion The Concept: •Definition -Electric propulsion: A way to accelerate a propellant through electro(magnetic) fields •There is no intrinsic limitation(other than the relativistic one) to the speed to which the propellant can be accelerated •Energy available on board is the only practical limitation Advanced (Electric) Propulsion (II) Understanding what’s behind it: •Tradeoff 1: more energy available, less propellant mass required •Tradeoff 2: more time allowed for a maneuver, less power needed Advanced (Electric) Propulsion (III) Features: •High exhaust speed (i.e.high specific impulse), much greater than in conventional (chemical) rockets •Much less propellant consumption(much higher efficiency in the fuel utilization) •Continuous propulsion: apply a smaller thrust for a longer time •Mission flexibility(Interplanetary travel, defense) •Endurance (commercial satellites) Electric Propulsion Concepts •Variety of designs to accelerate ions or plasmas •Most concepts utilize grids or electrodes: power and endurance limitations •Ion Engine •Hall Thruster •RF Plasma Thrusters (ECR, VASIMR, Helicon Double Layer) •Magnetoplasma Dynamic (MPD) Thrusters •Plasmoid Accelerated Thrusters Ion Engine •Scheme of a gridded ion engine with neutralization Ion Engine NASA’s Deep Space One Ion Engine Ion Engine NASA’s Evolutionary Xenon Thruster (NEXT) at NASA’s JPL Hall Thruster The Hall effect Hall Thruster (II) The Hall thruster scheme Hall Thruster (III) The Hall thruster: the Hall effect confines electrons Hall Thruster (III) High Voltage Hall Accelerator (Hi VHAC) Thruster -Hall Thruster (NASA Glenn R.C.) Magneto Plasma Dynamic Thruster The MPD thruster Helicon Double Layer Thruster Experiment Artists rendering of a Helicon Double Layer Thruster concept (Australian National University) Helicon Double Layer Thruster Experiment 2003 Helicon Double Layer Thruster Experiment (Australian National University) 2005 Helicon Double Layer Thruster Experiment (European Space Agency, EPFL, Switzerland) Plasmoid Thruster Experiment (PTX) PTX Schematic (NASA MSFC/U. Alabama) Plasmoid Thruster Experiment (PTX) PTX Plasmoid Images with Coil Current Electric Propulsion Applications 1.ISS 2.Interplanetary Missions 3.Commercial/Defense •ISS meeds drag compensation •Currently ISS is “reboosted” periodically •Presently Shuttle(or Soyuz) perform this operation •Very high cost: 9000 lbs/yr propellant at $5,000/lbs = 45M$/yr! ISS Electric Propulsion Boosting Future Perspectives: Fusion Propulsion The Field Reversed Configurationis a plasma confinement scheme very appealing also for propulsion applications Fusion Propulsion Fusion Propulsion FRC plasma simulated with the MHD-2 Fluid NIMRODcode Fusion Propulsion Plasma and power production scheme for a FRCfusion (still to be demonstrated...) indirectpropulsion rocket Plasma Accelerator Magnets FRC Electric Power Magnetic Nozzle Exhaust Fusion Propulsion Plasma and power production scheme for a FRCfusion (still to be demonstrated...) directpropulsion rocket Magnets FRC Electric Power Magnetic Nozzle Exhaust FRC Direct Propulsion •The Field Reversed Configuration (FRC) is an attractive concept for plasma propulsion because its intrinsically high plasma beta and the formation of magnetically detached plasmoids. •Direct FRC fusion-propulsionschemes (that is, besides the basic concept of a reactor producing electricity to power a thruster) have been previously discussed (e.g.[1]), with the plasma exhaust accelerated directly from the fusion core or collected from the FRC scrape-off layer and channeled through a magnetic nozzle [1] M.J. Schaffer, Proc. NASA Advanced Propulsion Workshop in Fusion Propulsion, Huntsville, AL, Nov. 2000 and General Atomics report GA- A23579, Dec. 2000 FRC Fusion Plasma Thruster Concept •The plasma detachmentin the nozzle is then induced in a controlled way, through the formation of a sequence of FRC plasmoids FRC Ignited Plasmoid Plasma Generation FRC Plasmoid Confinement Coils FRC Formation Coil Confined plasma column Fusion Product Energy Direct Converter Short-term: Sub-critical FRC’s •Thecaseofasub-critical(withoutfusionyield)FRCisalso interestingforthepossibilityofincreasingtheoverallnozzle performanceviaacontrolleddetachmentandofimplementing plasmoidpre-accelerationschemes. Long-term: FRC Fusion Propulsion •Foran FRCplasmoidabletosustainfusionconditions,the energyofthefusionproductscanbecollectedinthenozzle, whiletheplasmoidisleavingtherocket(ideallyviadirect conversionfromneutron-freereactions)withtransittimeinthe nozzlelongerthantheignited FRClifetime. •Onlythefusionproductsthatareescapingradiallythedetached plasma(plasmoid)areinteractingwiththerocketandarenot expectedtoproduceappreciablenetback-thrust. Long-term: FRC Fusion Propulsion (II) •Assuming that the plasmoidsare formed in a 1msand have the lifetimeof 100 msand that they travel at 5∙10 4 m/sthe direct conversion system should be 5 mlong (if the fusion conditions are maintained for the lifetime of the FRC). •The fusion power can be collected in the nozzle during the lifetime of the plasmoid. •A D-Tplasmoid with density of 1∙10 20 and T=10 ke Vwill produce a power density of about 3MW/m 3 . For plasmoids of a 1 m 3 volume, e.g.,r=0.22 m, R=1 m, P=3 MW •The mass of one of these plasmoids will be: m pmd =2 ∙10 20 ∙2.5∙1.67∙10 -27 =8.77∙10 -7 kg •The thrustfor 1 plasmoid per msejected at 5∙10 4 m/swill be T=5∙10 4 (m/s)∙8.77∙10 -7 kg/(1∙10∙10 -3 s)=43 Nand the specific impulsewill be about 5000 s. Research at UHCL -Current Application Focus •MHD Augmented Propulsion (UHCL) •RF Magnetized Plasma Sources, Atmospheric Plasma Torches (Propulsion, Re-entry plasma) (UHCL/JSC) •Plasma Actuator/Airfoil for Hypersonic Flight (UHCL) •FRC-based Electric Propulsion (Fusion/Propulsion) •Lightning Stroke Simulation (JSC) •Magnetic Reconnection (UHCL) -Some applications require neutrals: •Development 0-D Plasma-Neutral model Simulation Studies 1.Fluid (MHD) Plasma Simulation 2.Particle Simulation 3.Computer Science: Massively Parallel Processing Theory Simulation Experiments 1.Pre-Maxwell Equations: 2.Continuity Equation: 3.Momentum Equation 4.Energy Equation 5.Ohm’s Law(resistive MHD) , pp j E B , n n t   u , , , , , ,p t      u j Buu ,, , , , T n T p Q t   uq , , , p u Bj E MHD Plasma Simulation 0 , p pp t  m     B EBj 1.Pre-Maxwell Equations: 2.Continuity Equation: 3.Momentum Equation: 4.Energy Equation: 5.Ohm’s Law(resistive MHD): () 0 n n t    u ()p t              u uuj Bu 1 n T Tp Q t             uuq 0 , p      p Eu Bj BBB MHD Plasma Simulation Physical Model: Legenda =m e /m i isthemassratio m 0 and 0 arethepermeabilityandpermittivityoffreespace nisthenumberdensity isthemassdensity visthecenterofmassvelocity Bisthemagneticfluxdensity Eistheelectricfield Jisthecurrentdensity pisthescalarpressure Qistheheatflux istheelectricalresistivity P’=p I+P,Iistheunittensor Pis the symmetric, traceless part of the stress tensor MHD Plasma Simulation Magnetic Reconnection Leading to Detachment Field line perturbedby the plasma current stretches and eventually reconnectsproducing a detached plasmoid (ring-like) structure Reconnection Studies: Magnetic Nozzle Perturbation NIMROD MHD Simulation: Step 450000 = 425 ms FRC-based Plasma Thruster •The plasma detachmentin the nozzle is induced in a controlled way, through the formation of a sequence of FRC plasmoids. Plasma Accelerator FRC Formation Coil Accelerated Plasma FRC Plasmoid Simulation Hardware •“Columbia” at NASA-Ames: 20 SGI® Altix™ 3700 superclusters, each with 512 Itaniunm processors = 10240 processors •In-house Linux Clusters MHD Accelerator MHD Generator Coil Power Supply Magnetic Nozzle Coils RF Generator Automatic RF Matching Networks Mass Flow Controller Argon RF Plasma Torch Building the UHCL Plasma Lab High-Voltage Power Supply and Capacitor Bank Formation and Confinement Coils Mass Flow Controller Argon Plasma Toroid Experiment Vacuum Chamber High-Vacuum Pump Coil Power Supply Building the UHCL Plasma Lab The Field Reversed Configuration(FRC) is a well studied plasma confinement scheme that is very appealing also for propulsion applications Fusion and Plasma Propulsion A conceptual scheme for a FRC Rocket Plasma and power production scheme for a FRCfusion (still to be demonstrated...) directpropulsion rocket Magnets FRC Electric Power Magnetic Nozzle Exhaust Fusion and Plasma Propulsion FRC Plasmoid Fusion-Propulsion Concept A sequence of FRC plasmoidsis formed from an accelerated plasma column FRC Ignited Plasmoid Plasma Generation FRC Plasmoid Confinement and Plasma Acceeration FRC Formation and Acceleration Confined plasma column Fusion Product Energy Direct Converter