High Time Resolution Reconstruction of Electron Temperature Profiles with a Neural Network in C-2U
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Field-Reversed Configurations and TAE’s Approach
•  A field-reversed configuration (FRC) plasma is a highly elongated 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 beam injection: large orbit ion population, increased stability, and improved transport property
•  Fast ions: decoupled from micro turbulence, slow down at near classical rates
Plasma guns and biasing electrodes: high voltage & long pulse capability
Parameter
Bext, T rs, cm
Value
~0.1–0.3 ~40
~3 ~3–5×1019 ~1–2 ~0.2–1 ~1
up to 30
Overview of C-2W Field-Reversed Configuration Experimental Program
H. Gota,1 M.W. Binderbauer,1 T. Tajima,1 S. Putvinski,1 M. Tuszewski,1 S. Dettrick,1 S. Korepanov,1 J. Romero,1 A. Smirnov,1 Y. Song,1 M.C. Thompson,1 A. Van Drie,1 X. Yang,1 A.A. Ivanov,2 and the TAE Team1 1TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
Abstract
Tri Alpha Energy’s research has been devoted to producing a high temperature, stable, long-lived field-reversed configuration (FRC) plasma state by neutral-beam injection (NBI) and edge biasing/control. C-2U experiments have demonstrated drastic improvements in particle and energy confinement properties of FRC’s, and the plasma performance obtained via ~10 MW NBI has achieved plasma sustainment of up to 5 ms and plasma (diamagnetism) lifetimes of 10+ ms. The emerging confinement scaling, whereby electron energy confinement time is proportional to a positive power of the electron temperature, is very attractive for higher energy plasma confinement; accordingly, verification of the observed Te scaling law will be a key future research objective. The new experimental device, C-2W (now also called “Norman”), has the following key subsystem upgrades from C-2U: (i) higher injected power, optimum energies, and extended pulse duration of the NBI system; (ii) installation of inner divertors with upgraded edge-biasing systems; (iii) fast external equilibrium/mirror-coil current ramp-up capability; and (iv) installation of trim/saddle coils for active feedback control of the FRC plasma.
2Budker Institute of Nuclear Physics, Novosibirsk, 630090, Russia The C-2W Device (a.k.a. Norman)
59th APS-DPP Meeting, Milwaukee, WI, October 23–27, 2017 FRC Formation / Translation (single-sided experiment vs. simulation)
Inner divertor:
high vacuum pumping
Upgraded NB’s: ~13 MW, ~30 ms (~19 MW in Phase 2)
•  • 
The C-2W device is the world’s largest CT device, upgraded from C-2U, that produces high temperature, stable, long- lived FRC plasma state.
Upgraded NB injection and edge-biasing systems (end-on plasma guns, electrodes) mitigate FRC global instabilities and improve its performance such as confinement and transport properties.
Experiment
S. Inner Divertor
Simulation
2D MHD simulation by LamyRidge code
New confinement vessel:
skin time <3 ms
Experiment: Excluded-flux radius time evolution in S. formation & confinement sections (1) FRC is generated and ejected out from the formation section
(2) CT enters the confinement vessel and reflects off of the north mirror section:
Axial translation speed ~150 km/s (can be >400 km/s)
(see T. Roche’s poster)
Fast-Framing Camera Images
Simulation: Excluded-flux radius time evolution in S. formation & confinement sections
•  LamyRidge simulation with actual experimental setup indicates
similar FRC formation and translation characteristics
"  FRC plasma has been successfully translated through the inner divertor and entered into the CV in both experiment and simulation
Density / Temperature Measurements
Upgraded formation sections: ~15 mWb trapped flux
Outer divertor
Designed C-2W Parameters
S. Formation
(1)
Confinement
(2)
S. Inner Divertor
S. Formation
Confinement
hg20150827.tae.2b
w/ Field Expansion w/ Straight Field
(at inner divertor) (at inner divertor)
in confinement vessel in inner divertor
TAE’s Research Progress
Inner divertor camera:
•  Radial view at center of divertor •  FRC translation thru inner
divertor has been observed
Confinementvesselcamera:
•  Radial view at z=-0.7 m
•  Dynamics of FRC translation
and reflection (back and forth) has been observed
Inner divertor
Confinement vessel (CV)
A & B – Basic FRC core 
!  100-800 G, 5-10 eV
!  ion beams, Wb ~0.1 kJ
C-1 – Enhanced lifetime 
!  400 G, 10 eV
!  ion beams, Wb ~1 kJ
C-2 – HPF* w/ 2 guns, Ti getter  !  1 kG, 1 keV
!  neutral beams, Wb ~12 kJ
C-2 – HPF* w/ 2 guns, Li getter 
!  1 kG, 1 keV
!  neutral beams, Wb ~20 kJ
C-2U – Sustainment 5+ ms 
!  1 kG, 1 keV
!  neutral beams, Wb ~100 kJ
* HPF – High Performance FRC regime
•  •  •  • 
C-2W Goals (focus towards “hot enough”)
DemonstrateplasmaparameterrampupbyNBheatingand current drive
Improve performance of the plasma edge/divertor to achieve high electron temperature at the plasma edge
Develop plasma control on the time scale significantly longer thanL/Rvesseltimeandplasmaconfinementtimes
Explore a wide range of plasma parameters such as plasma temperature,magneticfieldandplasmasizetoconfirmTAE energy confinement scaling
Inner Divertor Configuration
New / Upgraded Key Subsystems on C-2W
•  NBinjectors–8injectors,4outof8NBsw/tunablebeam energy at 15–40 keV during a shot, up to ~19 MW for ~30 ms
•  Enhancement of edge biasing – plasma guns (see A. DuBois’ poster) and biasing electrodes in inner/outer divertors, higher voltage and longer pulse operation (>30 ms)
•  Newconfinementvesselandmagnets–fieldramp-upand active plasma control
•  New/upgradeddivertors–additionaldivertorsinbetween confinement and formation sections, higher vacuum pumping capability
•  Formationpulsedpowers–alothigherstoredenergy, improved gas pre-ionization (see E. Trask’s poster)
•  Extensive diagnostics upgrade – see M.C. Thompson’s poster
C-2W Equilibrium Calculation
After settled, t~0.9 ms
•  Thomson Scattering (initial data):
Radial profile of electron temperature & density (midplane)
•  C-2 experiments in 2008–2014:
o  Summary paper by M. Binderbauer, Phys. Plasmas 22, 056110 (2015)
•  High pumping speed (~2x106 L/s) to reduce gas recycling •  Field expanders to minimize electron cooling from
ionization and secondary emission
•  Concentric electrodes to stabilize plasma position
Research Collaborations with TAE
•  Budker Institute (Russia) – Neutral beams, Plasma guns, Diagnostics, Divertor physics, etc.
•  UCI – Simulation
•  UCLA – Diagnostics, Edge biasing, RF heating
•  PPPL – Diagnostics, Neutral beams, Simulation, RF heating
•  LLNL – Divertor physics
•  ORNL – Diagnostics, Computation
Summary
•  UW-Madison – Material, Diagnostics, CT injector, Theory •  Swarthmore College – Pulsed powers
•  Google – Machine operation/optimization, Data mining
•  Univ. of Pisa (Italy) – Diagnostics
•  Nihon Univ. (Japan) – CT injector, Magnetic pumping •  Pelin, llc. (Russia) – Pellet injector
•  Many more...
•  C-2U experiments in 2015–2016 (13 months OPS, >55,000 shots in C-2/2U):
o  Plasma sustainment (flat top) for 5+ ms was achieved in 3 months of experiment; diamagnetism lifetime reached up to 11 ms
o  Plasma lifetime is limited by equipment/system constraints (e.g. NBs and edge-biasing power supplies and its durations) o  Papers by M. Binderbauer, AIP Conf. proceedings 1721, 030003 (2016); by H. Gota, Nucl. Fusion 57, 116021 (2017)
Cryo panels
Fast switching coils
Coaxial Electrodes
Field profile at t=0 (straight field for FRC translation)
Field profile at t=5 ms (flared field for edge biasing)
Density Contours
S. Outer S. Inner Divertor S. Formation Divertor
Edge biasing (Out-Div.)
Edge biasing (In-Div.)
Magnetic Field Contours
N. Inner N. Outer Divertor N. Formation Divertor
Strong field
Weak field (thus expanded)
Particle confinement time in C-2 (vs others)
Global energy confinement time in C-2/C-2U
Electron energy confinement time vs. electron temperature in C-2/C-2U
•  • 
2D simulations successfully reproduced characteristics of FRC formation/translation observed in experiments FRC collision / merging experiments have just begun
NBI
Radial Te & ne Profile Evolution in C-2U
Te profile by Thomson Scattering
ne profile by FIR/CO2 interferometer
Ti, keV
Te, keV
Ip, MA Pulse length, ms
During FRC translation
(See E. Granstedt’s poster) During FRC translation
•  Dispersion interferometers: Line-integrated densities in inner divertor and CV show 2 strong peaks, indicating good FRC translation
New magnet system:
field ramp & active control
NB injection
L , m
s
ne, m-3
Confinement
• 
setup to study initial FRC formation and translation
C-2W major subsystems have been constructed/installed, and experiments have commenced with single-sided
• 
confinement vessel, followed by a reflection off the end mirrors (bounced back-and-forth)
FRC plasma has been successfully produced in formation section as well as translated through inner divertor and
Temperature (t~0.1ms)
Density (t~0.1ms)


































































































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