Gota_APS-DPP2020_Poster

Overview of the C-2W Field-Reversed Configuration Experimental Program
H. Gota, A. Smirnov, M.W. Binderbauer, T. Tajima, S. Putvinski, M. Tuszewski, R. Magee, T. Roche, E. Trask, P. Yushmanov and the TAE Team
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
Contact: hgota@tae.com Company website: www.tae.com
62nd APS-DPP Meeting (virtual), November 9–13, 2020
Abstract
TAE Technologies, Inc. (TAE) is a privately-funded company pursuing an alternative approach to magnetic confinement fusion, which relies on field-reversed configuration (FRC) plasmas composed of mostly energetic and well-confined particles via neutral-beam injection (NBI). TAE’s current experimental device, C-2W (also called “Norman”) [1], is the world’s largest compact-toroid device which has the following key features: linear and axisymmetric configuration; NBI with high injection power (up to 20 MW) and intra-discharge variable energy (15–40 keV) functionality; flexible edge-biasing systems in divertors; external magnetic field fast control capabilities, such as ramp-up, and active feedback control of the FRC plasma. In C-2W, record breaking, advanced beam-driven FRC plasmas dominated by fast particles are produced, achieving total plasma temperature of >3 keV and sustained in steady state up to 30 ms that is only limited by energy storage. Dedicated experimental campaigns have been conducted to further optimize and also characterize FRC plasmas. This paper reviews the highlights of the C-2W experimental program and newly obtained experimental results.
The C
-
2W Device (a.k.a. Norman)
Achieved Steady
-
State FRC Discharge
Inner divertors:
high vacuum pumping
Neutral beams: ~21 MW, ~30 ms Formation sections:
C-2W Parameters
NBs terminated
• Advanced beam-driven FRC sustained in steady state – duration up to 30 ms limited by energy storage
• Plasma heating and ramp-up clearly observed • Neutron signal indicates fast-ion accumulation
~15 mWb trapped flux
Outer divertors:
high vacuum pumping
Key Systems on C
Parameter
Bext (T)
rs (cm)
Ls (m)
ne (m-3)
Ttot =Ti +Te (keV) Pulse length (ms)
Value
~0.1–0.3 ~40 ~2–3 ~1–3×1019 upto3 up to 30
Steady state discharge
Field ramped
Plasma heating
Fast-ion accumulation
Equilibrium coils
Standard Mirror coils current
Actively controlled current
[1] H. Gota et al., Nucl. Fusion 59, 112009 (2019).
Plasmagunand biasing electrodes: high voltage & long pulse capability
C
r􏰀􏰁 (normalized)
Neutron (105 s-1)
-
Reversed Configurations and TAE’s Approach
-
2W Goals:
2W (upgrade from C
-
2U):
Confinement vessel:
skin time <3 ms
Magnet system:
field ramp & active control
Details can be found in:
H. Gota et al., Nucl. Fusion 59, 112009 (2019)
-
Field
• Field-reversedconfiguration(FRC):highlyelongatedcompact toroid (CT) which has a closed poloidal field with zero or small self- generated toroidal field, an axisymmetric structure with a natural divertor, and an extremely high beta value (β~1)
• FRC offers an ideal configuration for an economic reactor and may allow use of aneutronic fuels, such as D-3He and p-11B
• Tangential neutral beam injection (NBI): large orbit ion population, increased stability, and improved transport property
• Fast ions: decoupled from micro turbulence, slow down at near classical rates
TAE’s Research History (until C
Magnets
Example of active control: current waveforms and measured flux on CV wall
• Demonstration of active feedback control
• External field actively controlled as plasma pressure builds up
• Electrode biasing and gas puffing can also be actively controlled
FRC
• Demonstrate plasma parameter ramp up by NB heating and current drive
• Improve performance of the plasma edge / divertor to achieve high electron temperature at the plasma edge and core
• Develop plasma control on the time scale significantly longer than L/R vessel time and plasma confinement times
• Exploreawiderangeofplasmaparameterssuch as plasma temperature, magnetic field and plasma size to confirm TAE energy confinement scaling
• Diagnostic suite – extensive coverage using 50+ diagnostics • Domestic–Google,UCI,UCLA,PPPL,LLNL,ORNL,LBNL,ANL,MIT,UW-Madison,SwarthmoreCollege,GeneralAtomics
• NB injectors – 8 injectors, 4 out of 8 NBs w/ tunable beam energy at 15–40 keV during a shot, up to ~21 MW for ~30 ms
• Edge biasing – plasma guns and biasing electrodes in inner/outer divertors, high-voltage (up to 4 kV) and long-pulse (>30 ms) operation
• Confinement vessel – short skin time for field ramp-up / plasma control
• Magnets – field ramp-up, active plasma control, fast-switching coils inside inner divertors, independently controlled power supplies
• Divertors – additional divertors in between confinement and formation sections, higher vacuum pumping capability
• Pulsed-power formation – more stored energy, improved gas pre-ionization, improved system reliability
Typical steady-state discharge with field ramp
Characteristics of Advanced Beam
-
2
Driven FRC Plasma
hg20150827.tae.2b
NB injection
Collaborators:
3
1.1 1.0
0.9 0.8
0.7 0.6
NBs terminated
no term.
1 NB term.
2 NBs term.
4 NBs term.
15 20 25 30 t (ms)
NB termination study
Bias Voltage (kV)
-
2U)
C-2U – Sustainment 5+ ms
n 1 kG, 1 keV
n neutral beams, Wb ~100 kJ
* HPF – High Performance FRC regime
•
1
0 2 4 6 8 10 12 NB Power (MW)
• C-2/2Usummarypapers:
• M.W. Binderbauer et al., Phys. Plasmas
22, 056110 (2015)
• H. Gota et al., Nucl. Fusion 57, 116021 (2017)
• More can be found at www.tae.com
• Establishedhigh-performanceFRC/
International – Budker Institute (Russia), Nihon U. (Japan), ASIPP (China), U. of Pisa (Italy), Pelin (Russia)
A & B – Basic FRC core
n 100-800 G, 5-10 eV
n ion beams, Wb ~0.1 kJ
C-1 – Enhanced lifetime
n 400G,10eV
n ion beams, Wb ~1 kJ
C-2 – HPF* w/ 2 guns, Ti getter
n 1 kG, 1 keV
n neutral beams, Wb ~12 kJ
Edge Control / Electrode Biasing from Divertors
Fast-framing camera image (confinement vessel)
• Oxygen (O 4+ line) emission well correlates with magnetic measurement
• Line filters (e.g. O, C, D𝝰) can be changed every shot
Correlation of FRC performance with NBI and biasing
• Strong synergy between edge biasing and NBI leads to good plasma performance
Example set of bias voltage scans for
T & T measurements ie
• Both ion and electron temperatures clearly correlate with bias voltage
• Plasma radius shrinks when NBs are terminated
• The more NBs terminated, the larger drop in radius as expected
beam-driven FRC plasma states
10ximprovedparticleconfinement; global energy confinement time improved via various key subsystem operations and optimizations
Strongpositivecorrelationbetween energy confinement time and electron temperature
è New scaling law emerged
Electron energy confinement time vs. electron temperature in C-2/2U
+
•
•
Langmuir probe
Electrodes
Outer Divertor
Energy analyzers
Pyro bolometers
C-2 – HPF* w/ 2 guns, Li getter
n 1kG,1keV
n neutral beams, Wb ~20 kJ
Fast-framing camera image (Out. divertor)
Features of Divertor Region:
• High pumping speed (~2x106 L/s in hydrogen per divertor) to reduce gas recycling
• Ti-gettering / wall conditioning in between shots
• Independently-controlled electrode biasing (with voltage /
current regulation) to stabilize plasma as well as for auxiliary heating
• Voltage up to ~4 kV; Current up to ~8 kA
• Operation in “feedforward” or “feedback” control mode
• Field expanders to minimize electron cooling from ionization and secondary emission
• Well diagnosed axial energy flow on each electrode
Relative
Particle confinement time in C-2 (vs others)
Global energy confinement time in C-2/2U
Edge Control and Electron Confinement:
• Biasing drives plasma rotation via 𝑗!×𝐵 force
• Plasma spins up until drag (neutrals, viscosity)
balances azimuthal torque
• Plasma rotation is indication of 𝐸
• Electron energy lost per ion at divertors (with adequate field expansion) is near ideal level
è ηe ~ 6–7 in C-2W (while, ηe ~25 in C-2U)
Density reconstruction and mode analysis
Electron energy confinement time vs. electron temperature in C-2/2U/2W
• C-2W regime shows same trend at >3x Te of C-2/2U
• Transport rates inferred from 0-D model with experimental inputs and constraints
• Further analysis is underway
!
• High fidelity holistic plasma reconstruction in collaboration with Google
• Internal dynamics of plasma perturbations – toroidal mode number n up to 5