An Overview Of Fundamental R&D Problems In Space Propulsion (and .
An Overview of Fundamental R&DProblems in Space Propulsion(and Related Environment)4rd Divisional (RQR) 6.1 Review20-21 January 2015Jean-Luc Cambier,Technical Advisor,AFRL/RQRS15005, 16 January2015Distribution A: ApprDoivsetrdbcArepleparosen ruenlleiamsiete;dd.isAtrFiTbCelaimraitnecdeNo. XXXXX, XX January 2014i foutriopnubAli–v;edisfotrribputibloicu/tPioAn culn1
TOC The problems1.2.3.4.5.6.7.What are we trying to solve? (challenge)Why? (relevance)How do we solve them? (approach)How well do we solve them? (status)How else do we solve them? (alternatives)What did we not solve? (future work)SummaryDistribution A – Approved for public release; distribution unlimited2
1: Problems to solve Problems being solved (now):– Complex (multiscale) plasma chemistry: Collisional-Radiative: 1F, multi-F, non-Maxwellian– Multiscale dynamics: me/M 1, ωceΔt 1, cΔt “v”, ωpeΔt 1– Multiscale density: Impact on: statistics, EOS, models .Problems remaining:– Radiation transport– Instabilities, Turbulence– Physical models (XS, rates, EOS.)Problems defined by complexity of interactions.Found elsewhere, but dealing with unique aspects.Distribution A – Approved for public release; distribution unlimited3
2: Why these problems? Core applications:– Plasma thruster M&S: HET and FRC– Plasma spacecraft environment: plumes, SSA,contamination, damage– Plasma diagnostics: LIBS, absorption tomography Q: How well are we solving these core issues? Core Extension:– Laser plasma interactions (LPI): hyper-spectraldiagnostics, weapon effectiveness, propagation – Space weather?: solar and geomagnetic flowsQ: How are the prospects for contributing to these problems?Distribution A – Approved for public release; distribution unlimited4
2: Core Applications HET– Performance– Instabilities– Contamination/damage– Signature (SSA)FRC– Performance– Instabilities– Diagnostics– DesignDistribution A – Approved for public release; distribution unlimited100o50o5
2: Core Extension LPI– RQ experiment (target liquid)– Interaction with density profile– Conditions favorable to RT instability?– Ponderomotive forces important! Space weather?– Similar problems to Core: multiscale dynamics andchemistry, instabilities, magnetized plasma Synergy between Core Extension. Room for expansion if resources available.Distribution A – Approved for public release; distribution unlimited6
3: Scope of R&D1)Multiscale Collisional-Radiative Kinetics (“chemistry”)– Hierarchy of complexity: Single-fluid / MHD Multi-fluid / MHD / Maxwell Non-Maxwellian (discrete & MC)2)Multiscale Transport (“dynamics”)– LHS of FP/Boltzmann streaming operator– Different directions: PIC, Vlasov, Hybrid– Anisotropic effects (magnetized)3)Multiscale Couplings (additional physics)– How to integrate sub-scale physics: MD MC Cont.– Fluid/Solid coupling (LPI, HET), non-ideal properties– Electromagnetic phenomenaFocusing on most important issues (1,2) basis of M&S capability.Distribution A – Approved for public release; distribution unlimited7
3: Multiscale CR Past:– 1D and 2D coupled 1F-CR– Complexity Reduction– Non-Maxwellian discrete model Kapper, Cambier, JAP 109 (2011)Present– Multi-Fluid CR model development– Non-Maxwellian stochastic model Future– Multi-species & dynamic reduction– RHS to Vlasov– PIC integration– Radiation transportLe, Karagozian, Cambier, PoP 20 (2013)Distribution A – Approved for public release; distribution unlimited8
3: Multiscale Transport Past– PIC development: GPU-implemented PICImplicit PIC (Lapenta, Brackbill)– Time-parallel acceleration Present– Vlasov: basics being implemented/tested– PIC: complexity reduction (merging)– MHD: introduction of DG/FE Future– CR coupling: CR-PIC, CR-Vlasov-FP– Hybrid: Vlasov-Fluid, PIC-Vlasov-Fluid, δfDistribution A – Approved for public release; distribution unlimited9
3: Multiscale Physics Past:– XS databases for Ar, Xe, Kr– CR complexity reduction Present:– Working with collaborators to extend CR to molecular plasma– Some introduction to MD-based sputtering Future:– Micro-physics averaging: MD sputtering database, SEE, CR cross-sections / rates Sub-grid turbulence (MHD)– Non-ideal properties: Fermi statistics (CR), Debye-Hückel, Thomas-Fermi Distribution A – Approved for public release; distribution unlimited10
4: Status Discussed in more detail by accompanying talks – Col-Rad: –Transport: –Fluid: 1F done, MF in progress – needs more dataDiscrete: found instability – needs limiter / FP term?MC: particle merging OK – see also UCLA work (Caflisch-Yan)Molecular CR: collaborationRT: planning stage CFD: 1F, MF implemented – need GPU optimizationPIC: implicit scheme not integrated yet – needs more thoughtTP acceleration: ambiguous results – switch to other approachesVlasov: basic schemes tested, working – needs FP, GPU accel., improvedaccuracy, robustness to magnetized conditions Hybrid: still mostly on drawing board Coupling: Need consistent XS-rates database (diagnostics, signature ) Need MD-based models integrated (“averaging” operators UQ ?) Need extension of physical regimes (e.g. Fermi-CR, EOS)Last item less urgent ( 6.2). Some resource limitations.Distribution A – Approved for public release; distribution unlimited11
5: Alternatives Chemistry:– Similar work in EU: Variable quality / focus Leverage? Possible in certain areas integration effort– DOE work: higher energy (useful for LPI) - TBDTransport:– Implicit PIC at LANL –Lots of Vlasov work (US, EU universities) –Mostly fusion (tokamak) related Possible collaboration with U-MichiganRecent Hybrid Vlasov-Fluid (Germany) But still need integration effortWe are on the right track .Coupling:– Looking for leverage in most areas– Focus on integration ( 6.2)Be aware! If integration effort development effort, no leverage.Still evaluating best options.Distribution A – Approved for public release; distribution unlimited12
6: Remaining Work Lots to do, besides completing started efforts:– Need to couple/integrate CR and MHD solvers at ALL levels Multi-D, Multi-Species, Radiation transportPIC – Vlasov – MultiF – MHD(1F)– Need to improve accuracy/efficiency of some solvers Ensure conservations (variational, projection integrators?)Magnetized transport stiffness (PIC and MHD)– Need to increase effort on modeling instabilities HET/magnetron: drift-waves, ionization FRC: Rayleigh-Taylor (RT), Kelvin-HelmholtzBoeuf, Front. Phys. 2 (2014)Distribution A – Approved for public release; distribution unlimited13
6: Remaining Work – Ex: instabilities Relevance/Specialization:– FRC propulsion: Current sheet development (shear at FRC interface) Stability and mass capture efficiency– Important Characteristics & Differences: Collisionality with neutrals (partially ionized) Tangential B-field (orientation-dependent) Also found in laser fusion and solar prominences– e.g.:Srinivasan & Tang, PoP 20 (3013)Khomenko et al., arXiv:1403.4530v1 (2014) Potentially relevant to upper-atmospheric physicsMahalov, Phys. Scr. 89 (2014)Distribution A – Approved for public release; distribution unlimited14
6: Remaining Work – Ex: instabilities RT Example: Crab NebulaPorth, Komissarov, Keppens, arXiv:1405.4029v2 (2014) Growth of filamentary structures Generation/concentration of EM fields Mixing of elements/chemistryDistribution A – Approved for public release; distribution unlimited15
6: Remaining Work – Ex: instabilities Previous FRC modeling––––B2NiImplicit PICme x 10Theta-Pinch configurationFlute (RT) instability𝑔𝑔 𝑃𝑃VDBEVH𝑉𝑉𝐷𝐷 𝐹𝐹 𝐵𝐵 𝑀𝑀 𝑔𝑔 𝐵𝐵 𝑒𝑒𝐵𝐵2𝑒𝑒 𝐵𝐵2𝑉𝑉𝐻𝐻 𝐸𝐸 𝐵𝐵𝐵𝐵 2Ion drift charge separation Hall drift–Unstable !Is it real? (given enough time) me/M still small enough Assumed fully ionized Assumed no initial shear Distribution A – Approved for public release; distribution unlimited16
6: Remaining Work – Ex: instabilities KH example: instability– Relevant to current sheet stability?– Suppressed/Enhanced by B fieldKarimabadi, PoP 20 (2013)Hamlin, Newman, Phys Rev E87 (2013)– Similar effect was previously studied (RT)Fundamental studies compatible with development &application of M&S capability for Core Extension projects.L. Cole, PhD dissertation (2012)Distribution A – Approved for public release; distribution unlimited17
7: Summary Several projects at the forefront of modern physics andmathematical methodsSupports overall R&D objectives in plasma propulsionProgress made in various areas:– Moving towards Big-Challenge project in CR– Various (promising) options for transport actively pursued– Need more algorithm work (accuracy/stiffness)– Need additional physics: databases, properties and models ( 6.2)Fundamental work, can be applied to other areas– rev: work in other areas can be leveraged)Challenging and exciting projects .Stretched resources Distribution A – Approved for public release; distribution unlimited18
BACKUP/EXTRADistribution A – Approved for public release; distribution unlimited19
6: Remaining Work Multiple: drift-wave, Rayleigh-Taylor (RT) and KelvinHelmholtz (KH)– RT: Driven by forces normal to interface (gravity,pressure)– KH: Driven by forces tangential to interface (shear)– Prelude to turbulence– Critically important for: Astrophysics (Supernovae, Nebulae, Solar prominences) Inertial Fusion (mixing)Distribution A – Approved for public release; distribution unlimited20
FRC modeling– Implicit PIC– me x 100– Theta-Pinch configuration– Flute (RT) instability– Is it real?𝑔𝑔 𝑃𝑃VDBEVH𝑉𝑉𝐷𝐷 𝐹𝐹 𝐵𝐵 𝑀𝑀 𝑔𝑔 𝐵𝐵 𝑒𝑒𝐵𝐵2𝑒𝑒 𝐵𝐵2𝑉𝑉𝐻𝐻 𝐸𝐸 𝐵𝐵𝐵𝐵 2Ion drift charge separation Hall driftUnstable !Distribution A – Approved for public release; distribution unlimited21
FRC modeling– Implicit PIC– me x 10– Theta-Pinch configuration– Flute (RT) instability– Is it real?𝑔𝑔 UVDB2NiBEVH𝑉𝑉𝐷𝐷 𝐹𝐹 𝐵𝐵 𝑀𝑀 𝑔𝑔 𝐵𝐵 𝑒𝑒𝐵𝐵2𝑒𝑒 𝐵𝐵2𝑉𝑉𝐻𝐻 𝐸𝐸 𝐵𝐵𝐵𝐵 2Ion drift charge separation Hall driftstable !Distribution A – Approved for public release; distribution unlimited22
FRC modeling– Implicit PIC– me x 100– Theta-Pinch configuration– Flute (RT) instability– Is it real?𝑔𝑔 𝑃𝑃VDBEVH𝑉𝑉𝐷𝐷 𝐹𝐹 𝐵𝐵 𝑀𝑀 𝑔𝑔 𝐵𝐵 𝑒𝑒𝐵𝐵2𝑒𝑒 𝐵𝐵2𝑉𝑉𝐻𝐻 𝐸𝐸 𝐵𝐵𝐵𝐵 2Ion drift charge separation Hall driftUnstable !Distribution A – Approved for public release; distribution unlimited23
Distribution A – Approved for public release; distribution unlimited24
FRC modeling– Wait! Remember that me is not physical𝑉𝑉𝐷𝐷 𝑀𝑀 𝑔𝑔 𝐵𝐵 𝑃𝑃1 𝑘𝑘𝑘𝑘 𝑒𝑒 𝐵𝐵2𝑒𝑒𝑒𝑒𝑒𝑒𝐿𝐿 𝑒𝑒𝑒𝑒– T unchanged: VD does not depend on M OK– Other drift? Field curvature .–𝑉𝑉𝐷𝐷 2𝑀𝑀 𝑣𝑣 𝑒𝑒 2 𝑣𝑣 2𝑅𝑅𝑐𝑐 𝐵𝐵𝑅𝑅𝑐𝑐2 𝐵𝐵2 𝑃𝑃𝑒𝑒𝑁𝑁𝑅𝑅𝑐𝑐 𝐵𝐵 1 𝑘𝑘𝑘𝑘𝑅𝑅𝑐𝑐 𝑒𝑒𝑒𝑒Distribution A – Approved for public release; distribution unlimited OK25
Nature of Multiscale Problems Traditional approach: projection operator– Scale separation: when ε 0, solve Use "relaxed" solution forFine-scaletrajectoriesCoarse-scaletrajectory Works best if– Implies eigen-decomposition ( ) If dynamics become constained on MsSlow manifold Invariant manifoldDistribution A – Approved for public release; distribution unlimitedµMsϕ(m)26
Nature of Multiscale Problems– Works if slow manifold is "attractive" Negative real eigenvalues– Could work if basin of attraction Allows for some imaginary eigenvalues (bounded) Ex: electron trajectories in PIC– Need to model plasma oscillations? In most cases, no.Distribution A – Approved for public release; distribution unlimited27
Nature of Multiscale Problems Complications:– Positive eigenvalues: invariant manifold repulsive fixed point (saddle) Ex: instability, inverse cascade – Chaotic regime: no invariant manifold (not of interest)– Stochastic fine scales: Need statistical model Ex: e- trajectories collisions– Non-separation of scales:Distribution A – Approved for public release; distribution unlimited28
Nature of Multiscale Problems Complications:– Positive eigenvalues: invariant manifold repulsive fixed point (saddle) Ex: instability, inverse cascade – Chaotic regime: no invariant manifold (not of interest)– Stochastic fine scales: Need statistical modelFast structures Ex: e- trajectories collisions– Non-separation of scales:Slow manifoldsReal structure can be very complex Distribution A – Approved for public release; distribution unlimited29
1) Multiscale Collisional-Radiative Kinetics ("chemistry") - Hierarchy of complexity: Single-fluid / MHD Multi-fluid / MHD / Maxwell Non-Maxwellian (discrete & MC) 2) Multiscale Transport ("dynamics") - LHS of FP/Boltzmann streaming operator - Different directions: PIC, Vlasov, Hybrid - Anisotropic effects (magnetized) 3) Multiscale Couplings (additional physics)
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