Page 1 - Simulation of drift wave instability in field-reversed configurations using global magnetic geometry

Field-ReversedConfigurations
§ 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
C-2U Project Goals
Improvements in Confinement / Transport
FRC Correlates with NB Duration
§ Key plasma parameters maintained until end of NB duration
§ Diamagnetism persists ~1.5–2.5 ms after NB termination due to accumulated fast ions
Overview of C-2U FRC Experimental Program and Plans for C-2W
H. Gota,1 M.W. Binderbauer,1 T. Tajima,1 S. Putvinski,1 M. Tuszewski,1 S. Dettrick,1 S. Korepanov,1 A. Smirnov,1 M.C. Thompson,1 E. Trask,1 X. Yang,1 M. Cappello,1 A.A. Ivanov,2 and the TAE Team1
Abstract
Tri Alpha Energy’s experimental program has been focused on a demonstration of reliable field-reversed configuration (FRC) formation and sustainment, driven by fast ions via high-power neutral-beam (NB) injection. The world’s largest compact-toroid experimental devices, C-2 and C-2U, have successfully produced a well-stabilized, sustainable FRC plasma state with NB injection (input power, PNB ~10+ MW; 15 keV hydrogen) and end-on coaxial plasma guns. Remarkable improvements in confinement and stability of FRC plasmas have led to further improved fast-ion build up; thereby, an advanced beam-driven FRC state has been produced and sustained for up to 5+ ms (longer than all characteristic system time scales), limited by hardware and electric supply constraints such as NB and plasma-gun power supplies. To further improve the FRC performance the C-2U device is being replaced by C-2W featuring higher injected NB power, longer pulse duration as well as enhanced edge-biasing systems and substantially upgraded divertors. Main C-2U experimental results and key features of C-2W will be presented.
Coupled Core to Scrape-Off-Layer Confinement
Divertor Magnets ON: Regular field
NBI
HPF* and Advanced Beam-Driven FRC
Towards Further FRC Improvement
(1) Dynamic FRC formation
èSuitable target for NB injection
(2) Wall conditioning (Titanium gettering)
è Reduce background neutrals (3) Plasma guns and Plugs
èBoundary/edge control (stabilization) (4) Neutral beam injection
è Improve stability and confinement
è Current drive and plasma sustainment
(5) Flux conserver (external)
èFRC length/shape control (6) Particle refueling via
è Compact-toroid (CT) injection èPellet injection
1TRI ALPHA ENERGY, INC., P.O. Box 7010, Rancho Santa Margarita, CA 92688-7010 2Budker Institute of Nuclear Physics, Novosibirsk, 630090, Russia
Overall Progress and Achievements on C-2 / C-2U: Towards Plasma Sustainment
58th APS-DPP Meeting, San Jose, CA, October 31 – November 4, 2016
1.0
0.8
0.6
0.4
0.2
C-2U (06-2015)
#43833
§ Improving open-field-line plasmas is a key for better core FRC confinement
§ Core T increased by 20–30% with flaring 160 e 140 divertor magnetic field 120
80 § Flaring divertor magnetic field effectively 100
Necking
Divertor Plasma gun
Radius (m)
hg20150803.tae.1b
Plasma Radius
FRC Radius
hg20150812.tae.1
mb20150917.tae.1.pdf
Te (eV)
FRC only (2008) #2519
HPF w/ 1 gun (04-2011) #16758
Divertor Magnets OFF: Flare field
Divertor-magnet / field configurations
Key Approaches to C-2U Achievements
Research Collaboration
§ Budker Institute (Russia) – Neutral beams, Plasma guns, Diagnostics, Divertor physics, etc.
§ UCI – Simulation
§ UCLA – Diagnostics, Edge biasing
§ PPPL – Diagnostics, Simulation
§ LLNL – Divertor physics
§ ORNL – Diagnostics, Computation
§ UW-Madison – Material, Diagnostics, CT injector
§ Univ. of Pisa (Italy) – Diagnostics § Nihon Univ. (Japan) – CT injector § Pelin, llc. (Russia) – Pellet injector § And more collaborators
§ 0-D global power-balance analysis indicates substantial improvements in equilibrium and transport parameters
§ Regression gives electron energy confinement time, τE,e ~Te1.8; more heating power, better confinement
§ Details in E. Trask’s poster (CP10.00064)
FRC w/ gun (03-2011) #15741
HPF12 (07-2012)
#25968
Flare field Regular field
8 9
HPF14 (01-2014)
#34913
HPF w/ 2 guns (09-2011) #20408
Core Te Evolution
0 60
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 *Radius normalized Time (ms) *HPF – High Performance FRC regime
§ C-2 experiments in 2008–2014 (over 40000 shots obtained): summary paper by M. Binderbauer, Phys. Plasmas 22, 056110 (2015) § C-2U experiments started in March 2015:
Ø Plasma sustainment (flat top) for 5+ ms was achieved in 3 months of experiment; diamagnetism lifetime reached up to 11 ms Ø Plasma lifetime is limited by equipment/system constraints (e.g. NBs and edge-biasing power supplies and its durations)
Ø Paper by M. Binderbauer, AIP conference proceedings 1721, 030003 (2016)
increases Er in the edge of FRC 40 20
Ø EffectivecoreheatingbyNBI(possiblyby shearing as well)
Ø Enhance ExB shearing – Improve transport/ 00 confinement
1
2
3
4 5
Time (ms)
6 7
hg20150827.tae.2b
1.0 0.8 0.6 0.4 0.2
Plasma-guns and biasing electrodes (in both inner
and end divertors)
S. Divertor
Electrodes
0 -10
Plasma gun
S. Formation
DC-magnets
Con nement
NB injection
N. Formation
N. Divertor
Electrodes
10
Plasma gun
n Centered, angled and tangential NB injection
§ Beams aimed at mid-plane to reduce plasma shape impact
§ Simulations suggest optimized injection angle in range of 15o–25o
§ Injection in ion-diamagnetic direction to drive current n High current at low beam energy
§ Reduces peripheral fast-ion losses
§ Increases core heating
§ Rapidly establishes dominant fast-ion pressure
C-2U diagnostic suite
*Radius normalized Time (ms)
§ This is now called “Advanced Beam-Driven FRC” state
Features of Advanced Beam-Driven FRCs
§ C-2U’s advanced beam-driven FRC regime is far better than C-2 HPF: Ø In the best operating condition – FRCs are maintained for 5+ ms
Ø In longer-pulsed operations – FRCs can last up to and beyond 10 ms § Diamagnetism maintained – showcases ability to drive current by
beams
§ Electron and ion temperatures maintained (Te up to 150 eV at ~6 ms,
Ti ~500 eV)
§ Total plasma pressure maintained – post transient evolution, over 60% of initial thermal particle pressure replaced by fast particle pressure
§ Energetic fast ions – near classical confinement, double-humped density profile, largely define FRC dimension, beam-driven micro- bursts (staircase)
§ Sustained plasma well correlated with NB pulse duration
§ Demonstrate current drive and plasma sustainment in excess of characteristics of confinement times § Correlate FRC lifetime with neutral-beam pulse duration
The C-2U Device
C-2U Neutral Beam System Specification
*HPF – High Performance FRC (initially obtained in C-2)
-5
Mirror plug
0
Axial distance (m)
5
Mirror plug
Scrape-o layer
FRC
Separatrix
§ The C-2U device is the world’s largest compact toroid device, upgraded from C-2, that produces high temperature, stable, long-lived FRCs.
New confinement vessel, skin time <3 ms
§ Upgraded neutral-beam (NB) injection (15 keV hydrogen, co-injection) and end-on plasma guns mitigate FRC global instabilities and improve its performance such as confinement and transport properties.
§ Improvements of plasma performance in both core and open-field-line (scrape-off layer) regions are equally important to produce advanced beam-driven FRCs and demonstrate plasma sustainment.
Te profile by Thomson Scattering
Dependence of fast-ion pressure on NB power
ne profile by FIR/CO2 interferometer
ne profile from Q2D simulation
n n
n
Advanced beam-driven FRCs correlate with NB duration and have the following features
drive, (ii) double-humped density profile, (iii) FRC dimensions largely defined by accumulated fast ions, (iv) high temperatures overall, (v) near classical fast-ion confinement, etc.
Parameter
Beam energy Total power in neutrals # of injectors Pulse duration
Beam radial e-fold. size Beam divergence Ion current per source
Value
15 keV 10+ MW
6
8 ms flat-top < 10 cm
< 28 mrad 145 A
Effect of NB Injection on C-2U
1.0 hg20150813.tae.2b 0.5
P
>10 MW
C-2 Data
Electron energy confinement time vs. temperature
• 60+ diagnostics
Details in M. Thompson’s poster (CP10.00063)
: (i) showcasing current FRC performance in C-2U is limited by equipment constraints, which will be upgraded in the next device, C-2W
• 1000+ channels acquired
• 1+ GB data per shot
Dynamic FormaAon
(1)
(3)
Boundary Control via Edge Biasing
Wall CondiAoning
(2)
(4)
Neutral Beam InjecAon
FRC Length/ Shape Control
ParAcle Refueling
NB termination
C-2U Synergetic effect
(5) (6)
Global energy confinement time in C-2/C-2U
Pinj ~1.7 MW 001234567891011
Upgraded NB’s: up to 20 MW, ~30 ms
Upgraded formation sections, ~15 mWb trapped flux
End divertor
New magnet
system for field
ramp & active control
C-2U has successfully demonstrated plasma sustainment for 5+ ms as well as produced long-lived FRCs (~11 ms) by ~10 MW NB injection and plasma-gun edge biasing
Pinj ~5 MW
§ Higher NB injection power clearly improves decay rate of diamagnetism as well as extends plasma lifetime
inj
6 NBs 5 NBs 4 NBs 3 NBs 2 NBs 1 NB
*All quantities normalized
Inner divertor
Next Experimental Device, C-2W
§ C-2W is being constructed at TAE facility
§ C-2W experiments will be focused on demonstration of plasma ramp up and higher plasma temperature
§ New / upgraded systems in C-2W:
Ø NB injectors – 8 injectors, switchable beam
energy at 15–40 keV, up to ~20 MW for ~30 ms,
details in A. Dunaevsky’s poster (CP10.00065)
Ø Enhancement of edge-biasing – plasma guns and biasing electrodes in inner/outer divertors, longer pulse duration
Ø New confinement vessel and magnets – field ramp-up and active control
Ø New/upgraded divertors – additional divertors in between confinement and formation sections, higher vacuum pumping capability
Ø Extensive diagnostics upgrade Summary