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Overview and Recent Achievements in the C-2W Field-Reversed Configuration Experiment
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 stable particles. 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: neutral beam injection with high power (up to 21 MW) and intra- discharge variable energy (15–40 keV) functionality; flexible edge-biasing systems in both inner and outer 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 (total Te+Ti exceeding 3 keV, based on a pressure balance) are produced and sustained in steady state (up to 30 ms, limited by the energy storage).Dedicatedexperimentalcampaignshavebeenconductedtofurtheroptimizeandimproveperformanceand characterize the plasma. This paper will review the highlights of the C-2W experimental program as well as the newly obtained high-performance operating regime.
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2W Device (a.k.a. Norman)
Improvements in Initial FRC Condition
• Ti-gettering systems in confinement vessel / divertors have reduced impurity content and wall recycling (i.e. improved pumping capability)
• FRC performance – commensurate increase with vacuum/wall conditioning as well as effective optimization processes (collaboration with Google)
• Total temperature (ion + electron; from pressure balance) consistently increased; early Ttot up to 2 keV
[1] H. Gota et al., Nucl. Fusion 59, 112009 (2019).
Field
• Afield-reversedconfiguration(FRC)plasmaisahighlyelongated compact toroid (CT) which has a closed poloidal field with zero or small self-generated toroidal field, an axisymmetric structure with a natural divertor, and a 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
Confinement vessel:
skin time <3 ms
Magnet system:
field ramp & active control
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Reversed Configurations and TAE’s Approach
Key Systems on C
2W:
TAE’s Research History (until C
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2U)
C-2U – Sustainment 5+ ms
n 1kG,1keV
n neutral beams, Wb ~100 kJ
* HPF – High Performance FRC regime
• Domestic–Google,UCI,UCLA,PPPL,LLNL,ORNL,UW-Madison,SwarthmoreCollege,GeneralAtomics... • International–BudkerInstitute(Russia),NihonU.(Japan),ASIPP(China),U.ofPisa(Italy)...
A & B – Basic FRC core
n 100-800G,5-10eV
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 1kG,1keV
n neutral beams, Wb ~12 kJ
Edge Control / Electrode Biasing from Divertors
• Ttot inferred through an interpretive equilibrium reconstruction
• Field-ramp experiments tend to produce hotter plasmas
• Peak Ttot exceeding 3 keV
Particle confinement time in C-2 (vs others)
Global energy confinement time in C-2/2U
Electron energy confinement time vs. electron temperature in C-2/2U
See V. Sokolov (UP10.00142) and M. Griswold (UP10.00141)
Outer Divertor
(end view)
Energy analyzers
Pyro bolometers
Electron energy confinement time vs. electron temperature in C-2/2U/2W
• C-2W regime shows same trend up to 3x Te of C-2/2U
• Transport rates inferred from 0-D model with experimental
C-2 – HPF* w/ 2 guns, Li getter
n 1kG,1keV
n neutral beams, Wb ~20 kJ
H. Gota, A. Smirnov, M.W. Binderbauer, T. Tajima, S. Putvinski, M. Tuszewski, S.A. Dettrick, 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
61st APS-DPP Meeting, Fort Lauderdale, FL, October 21–25, 2019
NBI
• C-2/2Usummarypapers:
• M.W. Binderbauer et al., Phys. Plasmas 22,
056110 (2015)
• H. Gota et al., Nucl. Fusion 57, 116021 (2017)
• Establishedhigh-performanceFRC/ beam-driven FRC plasma states
• 10x improved particle confinement; global energy confinement time
improved via various key subsystem operations and optimizations
• Strongpositivecorrelationbetween energy confinement time and electron temperature
è New scaling law emerged
Collaborators:
Steady state discharge
Field ramped
Plasma heating Fast-ion accumulation
Example of current waveforms and measured flux on CV wall
• First demonstration of active feedback control on FRC •Externalfieldactivelycontrolledasplasmapressurebuild-up
C
•
•
•
•
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2W Goals:
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102900 103100 103300 103500 103700 103900 104100 104300
Shot Number
Improvement in FRC lifetime with wall conditioning
103400 103500 103600 103700 103800 103900 104000 104100 104200
Shot Number
Improvement in Ttot (estimated from Thomson ne)
The C
Plasma guns and biasing electrodes: high voltage & long pulse capability
Inner divertors:
high vacuum pumping
Neutral beams: ~21 MW, ~30 ms Formation sections:
Designed C-2W Parameters
+
E.A. Baltz et al., Scientific Reports 7, 6425 (2017)
Much higher initial temperature
C-2W
C-2/2U
0 10 20 30 40 50 60 Radius (cm)
Temperature profiles right after FRC collision/merging (t~0.05 ms)
Actively controlled current
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
Explore a wide range of plasma parameters such as plasma temperature, magnetic field
and plasma size to confirm TAE energy confinement scaling
• 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, higher voltage and longer pulse operation (>30 ms)
• 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
• Formation pulsed powers – a lot higher stored energy, improved gas pre-ionization, improved system reliability
• Extensive diagnostic suite – see T. Roche (UP10.00125)
Breakthrough in FRC Performance
~15 mWb trapped flux
Outer divertors:
high vacuum pumping
Parameter
n (m-3) e
Ttot = Ti + Te (keV) Ip (MA) Pulse length (ms)
Value
~0.1–0.3 ~40
~3 ~3–5􏰀1019 ~1.2–3.0 ~1
up to 30
(T) rs (cm) Ls (m)
B ext
Features of Divertor Region:
• High pumping speed (~2x106 L/s in hydrogen) to reduce gas recycling
• Ti-gettering / wall conditioning between shots as needed
• Independently-controlled electrode biasing to stabilize plasma and for auxiliary heating
• Field expanders to minimize electron cooling from ionization and secondary emission
• Well diagnosed axial energy flow on each electrode
Edge Control and Electron Confinement:
• Biasing drives plasma rotation via !"×$ force
• Plasma spins up until drag (neutrals, viscosity)
balances azimuthal torque
• Plasma rotation is indication of %"
• 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)
Typical steady-state discharge with field ramp
• 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
+
Density reconstruction
• High fidelity holistic plasma reconstruction
• Internal dynamics of plasma perturbations now visible
Peak Te (eV)
Peak total and electron temperatures at quiescent time
PlasmaLifetime_T5History
Ti getter in Out-DIVs
Ti getter in CV
00
Total Temperature History/Trend
9
8
7
6
5
4
3
2
1
Ti getter in 2
w/o Ti getter
hg20150827.tae.2b
See E. Trask (UP10.00126)
See P. Norgaard (UP10.00129)
See E. Trask (UP10.00126)
(2) Inner divertor operating mode
(1) Outer divertor operating mode
Peak Ttot (keV)
See S. Gupta (UP10.00150)
See J. Romero (UP10.00128)
See K. Zhai (UP10.00130)
hg20180120.tae.1b
Plasma Lifetime, T5 (ms)
Ti gettering started
Total Temperature (keV)
Te (eV)
for first time – toroidal mode number n up to 5
inputs and constraints
In-DIVs
1.8 1.6 1.4 1.2
1 0.8 0.6 0.4 0.2
Ttot_TS@50us Ttot_TS@100us Ttot_TS@200us
NBs terminated
Equilibrium coils
Standard Mirror coils current