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 and Merging of Compact Toroids

Russell Kulsrud and Masaaki Yamada 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 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 CD AB R (cm) R (cm) CD AB 32 34 36 R (cm)38 40 42 32 34 36 R (cm)38 40 42 44 32 34 36 38 40 42 44 32 34 36 38 40 42

Magnetic FieldLinesandElectronFlowVectors Electron dynamics Electron anddynamics strong electron heating observed

Magnetic FieldLinesandElectronFlowVectors 2 − D ElectronTemperatureProfile 2 0 0 − D ElectronTemperatureProfile 0 0 Z (cm) 5 Z (cm) 5 5 Z (cm) 5 Z (cm) 10 10 10 10 in the broad regionexhaust of MRX 15

15

T 15 e (eV) T 6 7 8 9 10 11 12 15 e (eV) 6 7 8 9 10 11 12 R (cm) 32 34 36 38 40 42

R (cm) 3 32 34 36 38 40 42 − D ViewofFig.a 0

3 − D ViewofFig.a 0 5 Z (cm) j e 5 ⋅ E Z (cm) 0 Profile j e 10 E 0 Profile 10 5 10 5 Z (cm) 10 10 5 Y (cm) 5 Z (cm) 0 10 Y (cm) 15 15 0

− 15 45 40 35 (W/cm 30 5 15

R (cm) − 45 40 35 (W/cm 30 0 50 100 150 5 3 R (cm) ) 0 50 100 150 3 ) - -

conduction X-point. The energy transported via heat heat via transported The energy the mostly near energy gain Electron j = Curl B, V e =

j e

/ne 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

Field Reversed Configuration SPIRIT Concepts (1997 -) “Self-organized Plasma with Induction, Reconnection, and Injection Techniques”

• Formation of FRC by reconnection of

• 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 Inductive Drive Generates More Flux, Longer Sustainment

(mWb) OH Voltages

Trapped Flux Flux Trapped 5kV-9kV Input Powers:

300-800kW (V) Surface Voltage SurfaceVoltage

) 2 (A/m CurrentDensity

(kA) SolenoidCurrent 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