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Tokamak and Stellarator Require Doubly Connected Blanket => Very Tokamak and Stellarator require doubly connected blanket => Very complex & large systems Tokamak Stellarator Tokamak and Stellarator require doubly connected blanket => Very complex & large systems Tokamak Stellarator Study of Magnetic Reconnection and Merging of Compact Toroids Russell Kulsrud and Masaaki Yamada Norman Rostoker Memorial Symposium August 24, 2015 Magnetic Reconnection Experiment Magnetic reconnection = Fundamental Process Local view of reconnection: filed line reconnection＝＞ Topology Change Conversion of magnetic energy to particle heating and acceleration How do we study magnetic reconnection in dedicated lab experiments? 1. We create a proto-typical reconnection layer in a controlled manner and study the fundamental plasma dynamics 2. Cross-validation of experiment and numerical modeling The primary issues/questions; • Why does reconnection occur so fast? • Dynamics of electrons and ions • How does local reconnection determine global phenomena? • How is magnetic energy converted to plasma flows and thermal energy? Experimental Setup and Formation of Current Sheet Experimentally measured flux evolution 13 -3 ne= 1-10 x10 cm , Te~5-15 eV, B~100-500 G, Local Reconnection Physics 1. MHD analysis 2. Two-fluid analysis Particle dynamics of the two-fluid reconnection layer Normalized with Erec +Vin × Brec = 0 Hall term Electron inertia Electron Ideal MHD region term pressure term B (G) Y 44 42 Ion Flow 40 Electron Flow 40 Separatrix 20 38 Magnetic Field Line R (cm) 0 36 Electron Diffusion Region −20 34 Ion Diffusion Region 32 −40 −9 −6 −3 0 3 6 9 Z (cm) MRX with fine probe arrays Linear probe arrays • Five fine structure probe arrays with resolution up to ∆x= 2.5 mm in radial direction are placed with separation of ∆z= 2-3 cm Evolution of magnetic field lines during reconnection in MRX e Measured region Experimental Setup for Energetics Study Magnetic Probe Array Equilibrium Field Coil Magnetic Field Lines 3 7 . 5 c m Flux Core R Current Sheet Y Z • Helium discharge 13 3 • ne: 2-8×10 /cm • Te~Ti: 6-15eV • λmfp,e ≥ c/ωpi > δCS (~2cm) • No guide field. • IDSP to measure Ti Electron dynamics and strong electron heating observed in the broad exhaust region of MRX AB3−D View of Fig.a Z (cm) ABMagnetic Field Lines and Electron Flow Vectors 3−D View of Fig.a Z (cm) Magnetic Field Lines and Electron Flow Vectors 0 0 j = Curl B, V = j /ne 44 5 5 e e 44 10 10 15 15 45 4242 45 4040 40 40 3838 R (cm)R (cm) R (cm) R (cm) 3636 35 35 3434 30 −305 −5 3232 0 0 5 5 10 10 Y (cm)Y (cm) 0 0 5 5 10 10 15 15 Z (cm)Z (cm) CDCDT (eV)T (eV) 3 3 2−D2− ElectronD Electron Temperature Temperature Profile Profile e e j ⋅E Profilej E Profile (W/cm(W/cm) ) e e 12 12 - Electron gain energy mostly near the 4242 42 42 11 11 150 150 X-point. 4040 40 40 10 10 100 100 - The energy transported via heat 3838 38 38 9 9 conduction R (cm) R (cm) R (cm) R (cm) 50 3636 36 36 50 8 8 3434 34 34 0 7 7 0 3232 32 32 6 6 0 0 5 5 10 10 15 15 0 0 5 5 10 10 15 15 Z (cm)Z (cm) Z (cm)Z (cm) Ion acceleration and heating in the reconnection layer Ion heating is attributed to re-magnetization of accelerated ions We note collisions play a role in ion heating in the exhaust Inventory of Energy Magnetic energy inflow rate! 1.0±0.1! Magnetic energy Energy deposition Energy deposition outflow rate! rate to electrons! rate to ions! 0.49±0.05! 0.18±0.04! 0.37±0.07! MHD Change of Change of flow component! thermal energy! energy! 0.22±0.02! 0.14±0.05! 0.07±0.02! Hall-field Energy loss rate Change of component! (Conduction, thermal energy! radiation) 0.27±0.03! radiation) 0.17±0.05! 0.08±0.04! Energy loss rate (Conduction, neutrals) ≤ 0.16! Nature Communications (2014) Energy conversion during magnetic reconnection - Significant particle heating and acceleration observed in reconnection events in the magnetosphere, solar flares and laboratory experiments. - It is generally difficult to identify the inventory and partitioning of energy - Our findings on energy partitioning in a reconnection layer is remarkably consistent with the recent space results J. Eastwood et al, 2013 Summary of findings on MRX reconnection research MRX has been very productive; 15 plus PRL, Science, Nature papers et al. • Verified experimentally the two-fluid (collision-less) reconnection physics – Verification of Hall effects – Validation and verification of numerical simulation codes – Identification electron diffusion layer => NASA’s MMS Project • Identified the in-plane electric field which plays a key role for ion acceleration and heating – Ions are accelerated electrostatically near the separatrices. – Ions are heated downstream by re-magnetization and collisions. • Conversion magnetic energy and partitioning is quantitatively analyzed in the reconnection layer - Substantial component of outgoing magnetic energy (~ 50%) - 50+% of incoming magnetic energy goes to plasma particles 2/3: to ions 1/3: to electrons SPIRIT (Self-organized Plasma by Induction, Reconnection, Injection Techniques) Attempts for simpler reactor core design => Compact Toroid Reactor Core Spherical Torus Spheromak Field Reversed Configuration SPIRIT Concepts (1997 -) “Self-organized Plasma with Induction, Reconnection, and Injection Techniques” • Formation of FRC by reconnection of spheromaks • Sustained FRC plasmas with the use of inductive drive • Sustainment of FRC by 10-20 kV NB Injection • <=> N. Rostoker <=> TAE Spheromak Merging Experiments in MRX (Toroidal Energy => Plasma Kinetic Energy) Plasma Initiation Spheromak Formation (1) - + Speromak Merging Final CT (1) Spheromak Merging Experiments in U. Tokyo (Toroidal Energy => Plasma Kinetic Energy) TS-3; Yamada et al PRL (1990) Ono et al PRL(1996) Norman’s 70 year Symposium (1995) Strong ion heating occurs while toroidal field is annihilated Strongest ion Temperature Rise During Merging Phase (285µs-300µs) Strong Elimination of Toroidal Field Energy During Merging (285µs-300µs) Spheromak Merging is provide a promising option for the TAE project CT Sustainment Campaign on MRX • 68 turn Ohmic solenoid, Inconel liner • Three capacitor banks for 4 coils (TF, PF, SF, Ohmic) New 2D Probe Array Surface Voltage Current Density Trapped Flux Solenoid Current (V) (A/m2) (mWb) (kA) MoreFlux, Drive Generates Inductive Longer Sustainment Longer Input Powers: Input Powers: OH Voltages OH Voltages 300-800kW 300-800kW 5kV-9kV 5kV-9kV Ohmic Sustainment for ~300µs Demonstrated 275 µs 325 µs 375 µs 450 µs 550 µs Summary Notes 1) Compact toroid plasma concept to achieve a small, simple, high efficiency, and economical reactor core. • Simple geometry • High power density • High beta ( FRC has highest equilibrium beta) • Can lead to advanced fuel reactor (P-B11, D-He3) 2) Major challenges remain: • Obtain good confinement of plasma • Control of magnetic self-organization 3) To understand magnetic reconnection is a key 4) TAE is in the forefront to solve these major issues => M. Binderbauer’s talk .
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