Sep 20, 2017 - Overview of the PEGASUS. Non-Solenoidal Startup Research Program. M.W. Bongard. G.M. Bodner, M.G. Burke, R.J. Fonck, J.L. Pachicano,Β ...
Overview of the PEGASUS Non-Solenoidal Startup Research Program M.W. Bongard G.M. Bodner, M.G. Burke, R.J. Fonck, J.L. Pachicano, J.M. Perry, C. Pierren, N.J. Richner, C. Rodriguez Sanchez, D.J. Schlossberg, J.A. Reusch, J.D. Weberski
17th International ST Workshop Seoul National University Seoul, South Korea University of Wisconsin-Madison
20 September 2017
PEGASUS Toroidal Experiment
The π΄π΄ ~ 1 PEGASUS ST is Evolving To Become The US Center for Non-Solenoidal Startup
High-stress Ohmic Heating Solenoid
LHI Phase
OH Phase
H-mode
2m
Time [ms]
Local Helicity Injectors
PEGASUS Program: Divertor Coils
π΄π΄ π
π
[m] πΌπΌππ [MA] π΅π΅ππ [T] Ξπ‘π‘π π π π π π π [s]
1.15 β 1.3 0.2 β 0.45 β€ 0.25 < 0.15 β€ 0.025
M.W. Bongard, ISTW 2017
β’
Local Helicity Injection (LHI) for Non-Solenoidal ST Startup
β’
H-mode Physics at Ultralow-π΄π΄ (recently concluded)*
β’
Access to high πΌπΌππ > 10 and High π½π½π‘π‘
β’
Proposed Facility Enhancements and New Program Directions
* K.E. Thome, Phys. Rev. Lett. 116, 175001 (2016) M.W. Bongard, IAEA FEC 2016 EX/P4-51 R.J. Fonck, IAEA FEC 2016 OV/5-4 K.E. Thome, Nucl. Fusion 57, 022018 (2017)
2
Local Helicity Injection is a Promising Non-Solenoidal Startup Technique Injected Current Stream
Non-Solenoidal, High πΌπΌππ β€ 0.2 MA (πΌπΌππππππ β€ 8 kA)
LFS System HFS System
Local Helicity Injectors
β’
Edge current extracted from injectors
β’
Relaxation to tokamak-like state via helicity-conserving instabilities
β’
Used routinely for startup on PEGASUS
M.W. Bongard, ISTW 2017
β’
Current drive quantified by
πππΏπΏπΏπΏπΏπΏ
π΄π΄ππππππ π΅π΅ππ,ππππππ β ππππππππ Ξ¨ 3
Local Plasma Sources Inject Current Streams that Reconnect to Form Tokamak-like Plasma
Phase:
1
Injectors
33
2
4
77139
Local source:
Instability:
Reconnection:
Bias shutdown:
Helical plasma streams
Current driven along streams
Relaxation to tokamak-like state, current growth
High-πΌπΌππ tokamak
M.W. Bongard, ISTW 2017
4
Injector Location in LHI Emphasizes Different CD Mechanisms
Low-Field-Side (LFS) Injection: β’
Injectors near outboard midplane
M.W. Bongard, ISTW 2017
High-Field-Side (HFS) Injection: β’
Injectors in lower divertor 5
LFS Injection Dominated by Inductive Current Drive β’ β’
Injector location: tradeoff between HI driven and inductively driven current Power balance relation:
πΌπΌππ πππΏπΏπΏπΏπΏπΏ + πππΌπΌπΌπΌ + πππΌπΌπΌπΌπΌπΌ = 0 β’
β’
Radial compression β large πππΌπΌπΌπΌπΌπΌ
β’
Net induction voltage dominates current drive
Shape Evolution
Confinement behavior may be affected by dominant current drive type VIND VLHI
β’
LFS injection maximizes inductive drive, πππΌπΌπΌπΌπΌπΌ
M.W. Bongard, ISTW 2017
VIR
J.L. Barr, UW-Madison PhD Thesis (2016)
6
In Contrast, HFS Injection Dominated by Helicity Drive β’
Low π
π
ππππππ β high πππΏπΏπΏπΏπΏπΏ
πππΏπΏπΏπΏπΏπΏ = β’
β’
ππππππππ π΄π΄ππππππ π΅π΅ππππππ 1 ~ Ξ¨ππππ π
π
ππππππ
HFS injection minimizes πππΌπΌπΌπΌπΌπΌ Fully HI-driven system may have different transport properties
M.W. Bongard, ISTW 2017
β’
Static plasma shape β low πππΌπΌπΌπΌπΌπΌ
β’
HI dominates current drive
VLHI
VIR
VIND
7
Since Last ST Workshop, HFS Divertor Injectors Installed to Study HI-Dominant Regime Tokamak Plasma Edge ππππ β 1019 mβ3
Current Stream ππππ β 1019 m-3
Injection Cathode (βππππππππ)
β’
2 injectors in lower divertor
β’
4Γ VLHI over LFS injection
β’
π΄π΄ππππππ = 8 cm2; ππππππππ β€ 1.5 kV; πΌπΌππππππ β€ 8 kA (8β12 MW total power)
Arc Plasma
ππππ β 1021 m-3 Shield Rings (floating)
Local Plasma Limiters (ground)
8
Injector Alignment, Local Limiters Critical to PMI Mitigation Injector Schematic and Field Line Alignment
Fast Visible Imaging
β’ Proper
Proper alignment: β
Injector shadowed
β
High voltage standoff in tokamak SOL
Improper
β’
β’
Improper limiter placement: β
Injector immersed in plasma
β
Cathode spots on injector
Improper alignment to local field: β
β’ M.W. Bongard, ISTW 2017
Arc-back to limiter
Local limiters, shield plates needed to minimize DIV plate interactions 9
Relaxation Challenges with HFS Injection Addressed Injected current weakens vacuum π΅π΅ππ
Unstable current streams attract, reconnect
Tokamak-like plasma; rapid πΌπΌππ growth
πΌπΌππ ~ πππ‘π‘π‘π‘π‘π‘π‘π‘π‘π‘ πΌπΌππππππ
πΌπΌππ β³ πππ‘π‘π‘π‘π‘π‘π‘π‘π‘π‘ πΌπΌππππππ
πΌπΌππ β« πππ‘π‘π‘π‘π‘π‘π‘π‘π‘π‘ πΌπΌππππππ
M.W. Bongard, ISTW 2017
10
Initial Relaxation to Tokamak State Requires Strong Deformation of Vacuum Field β’
Injector geometry sets minimum pitch (π΅π΅ππ /π΅π΅ππ ) for stream clearance
β’
HFS injection: β β
β’
Lower π
π
ππππππ β more π΅π΅ππ for clearance
Relaxation impeded for fixed π΅π΅ππ, πΌπΌππππππ
Deformed π΅π΅π£π£π£π£π£π£ Aids Relaxation
β’
Relaxation achieved at full Pegasus π΅π΅ππ
Solution: poloidal field shaping β β
π΅π΅ππ strong in divertor; weak at midplane Increased πΌπΌππππππ required at increased π΅π΅ππ
M.W. Bongard, ISTW 2017
11
β’
β’
Target πΌπΌππ of 0.2 MA Without Solenoidal Induction Achieved
Non-solenoidal πΌπΌππ = 0.2 MA scenarios at full π΅π΅ππ β
Static plasma geometry
β
Current multiplication ~ 40 Γ πΌπΌππππππ
πππΏπΏπΏπΏπΏπΏ increased 4Γ over LFS injection β
Access to high πΌπΌππ with πππΏπΏπΏπΏπΏπΏ dominant
β
First test of HFS injectors with modern technology
β
β’
High πΌπΌππ = 0.2 MA Driven Predominantly by πππΏπΏπΏπΏπΏπΏ
High πππΏπΏπΏπΏπΏπΏ aided by active cathode spot detection
Facilitates studies of LHI confinement β
Example: ππππ / π΅π΅ππ / πΌπΌππ scalings under present study
M.W. Bongard, ISTW 2017
12
Thomson Scattering Indicates Range of ππππ π
π
Realized During LHI β’ ππππ (π
π
) profiles vary with discharge evolution, ππππ , shape, and π΅π΅ππ
πΌπΌππ = 0.08 MA π΅π΅ππ = 0.15 T
πποΏ½ππ ~ 1β2 Γ 1019 m-3
LFS Injectors
πΌπΌππ = 0.10 MA π΅π΅ππ = 0.05 T
HFS Injectors
πποΏ½ππ ~ 1β2 Γ 1019 m-3
β’ Issues under study: β Core vs. edge transport M.W. Bongard, ISTW 2017
β ππππππππ , ππππππππ
πΌπΌππ = 0.15 MA π΅π΅ππ = 0.15 T
HFS Injectors
πππππ ~ 0.5 Γ 1019 m-3
β Pulse length β π΅π΅ππ, ππππ effects
D.J. Schlossberg, Rev. Sci. Instrum. 87, 11E403 (2016); UW-Madison PhD Thesis (2016)
13
Projecting Forward: Dissipation of Helicity is a Main Issue β’
β’
Helicity input balanced by resistive dissipation β
Simplistic global interpretation of helicity balance
β
Plasma resistivity influenced by confinement properties
Crude estimates of confinement inform operation space, assuming: β β β
β’
Confinement Scaling Estimates
ππππππ = πππΏπΏπΏπΏπΏπΏ πΌπΌππ ππππππππ = 1
Fixed plasma geometry, π΅π΅ππ
Understanding how πΌπΌππ depends on HI rate is critical to predictive capability
M.W. Bongard, ISTW 2017
Geometrically Normalized HI Rate ~ π΄π΄ππππππ ππππππππ/π
π
ππππππ [V-m]
14
β’
To Date, Maximum Achieved Current Increases with πππΏπΏπΏπΏπΏπΏ
πΌπΌππ generally increases with ππππππππ β β
β’
e.g. scaling with ππππππππ , πππΊπΊπΊπΊ , π΅π΅ππ, plasma geometry, β¦
Electron behavior is a point of emphasis for present work β β
High π©π©π»π»
Low π©π©π»π» π΅π΅ππ = 0.05 T Constant Shape
Volume average ππ Profile effects β’
β
π΅π΅ππ [T] β [0.113, 0.150]
Fixed geometry ππππππππ scans suggest linear scaling
Predictive understanding requires more detailed knowledge β
β’
Achieved πΌπΌππ varies with π΅π΅ππ , MHD levels
Experimental HFS LHI π΅π΅ππ [T] β πΌπΌππβπππΏπΏπΏπΏπΏπΏ Operating Spaces: [0.038, 0.075]
ππππ , ππππππππ , π½π½(π
π
), ππππππππ
Radiation losses
M.W. Bongard, ISTW 2017
Low π©π©π»π» No PF Induction
15
Hierarchy of Physics Models Contribute Towards Predictive Understanding of LHI Startup Taylor Relaxation
1. Taylor relaxation, helicity conservation β Steady-state maximum πΌπΌππ limits
2. 0-D power-balance πΌπΌππ(π‘π‘)
πΌπΌππππ πΌπΌππππππ πΌπΌππ β€ πΌπΌππππ ~ π€π€
Helicity Conservation
πππΏπΏπΏπΏπΏπΏ
π΄π΄ππππππ π΅π΅ππ,ππππππ ππππππππ β Ξ¨
πΌπΌππ πππΏπΏπΏπΏπΏπΏ + πππΌπΌπΌπΌ + πππΌπΌπΌπΌπΌπΌ = 0 ; πΌπΌππ β€ πΌπΌππππ
β πππΏπΏπΏπΏπΏπΏ for effective LHI current drive
Reconnecting LHI Current Stream
3. 3D Resistive MHD (NIMROD) β Physics of LHI current drive mechanism
M.W. Bongard, ISTW 2017
D.J. Battaglia, et al. Nucl. Fusion 51 073029 (2011) N.W. Eidietis, Ph.D. Thesis, UW-Madison (2007) J. OβBryan, Ph.D. Thesis, UW-Madison (2014) J. OβBryan, C.R. Sovinec, Plasma Phys. Control. Fusion 56 064005 (2014)
16
NIMROD Simulations Indicate Helical Current Stream Reconnection as a Current Drive Mechanism NIMROD: Early Relaxation Phase in Divertor LHI Geometry
Early Formation Phase
Current Ring
1. Streams follow field lines
2. Adjacent passes attract
3. Reconnection forms current rings
NIMROD Simulation [OβBryan PhD 2014]
2016 PEGASUS High-speed Imaging Fonck, IAEA FEC 2016 OV/5-4
β’ Divertor LHI startup shows suggestive commonality between NIMROD simulations and experiment
M.W. Bongard, ISTW 2017
OβBryan et al., Phys. Plasmas 19 080701 (2012) OβBryan and Sovinec, Plasma Phys. Control. Fusion 56 064005 (2014)
17
Current Stream Interaction Manifests as Edge-Localized MHD Burst
Consistent with line-tied kink instability
β’ Internal magnetic measurements localize coherent streams in LFS edge
Ip [kA]
Ip [kA]
Internal π΅π΅π§π§ Measurements
External π΅π΅π§π§ Phase Correlation
0. 4
Inferred Stream Location
Z [m]
β
Low frequency: 20β80 kHz, ππ = 1
~b [mT]
β
NIMROD
PEGASUS
~bΜ [T/s]
β’ LFS injection: MHD bursts and ion heating support presence of outboard stream reconnection
β’ Suggests any stochastic reconnection region may be localized to edge
-0.4 0. 0
M.W. Bongard, ISTW 2017
J.L. Barr, UW-Madison PhD Thesis (2016) J.B. OβBryan, UW-Madison PhD Thesis (2014) E.T. Hinson, UW-Madison PhD Thesis (2015)
R [m]
18
0.8 5
β’
Reconnection-driven Ion Heating Gives ππππ > ππππ During LHI
Anisoptropic ion heating in injector streams consistent with two-fluid reconnection β
Channel ππππ,β₯ > ππππ
ππππ,β₯ ~ πππ΄π΄2 of injected current streams
He-II Ti [eV]
β
Ion heating correlated with high-f MHD fluctuations, not discrete reconnection between helical streams
VA2 ~ IinjVinj1/2
β’
ππππ(π‘π‘) correlated with continuous, high frequency activity β
Suggests considering short wavelength reconnection as another CD mechanism
M.W. Bongard, ISTW 2017
M.G. Burke, et al. Nucl. Fusion 57 076010 (2017)
19
β’
HFS Injection: Reduction in Large-Scale MHD and Increased πΌπΌππ Indicates More Complex Current Drive Mechanism
HFS injection: initially similar to LFS β β
β’
β
Plasma Current LFS Mirnov Coil π΅π΅οΏ½
Low-f ππ = 1 activity reduced by over 10Γ Extremely sensitive to π΅π΅ππ, π΅π΅ππ, πΌπΌππ, fueling
Bifurcation in πΌπΌππ evolution following transition β
Current growth continues after transition
β
ππππ rises, edge sharpens visibly
β
β’
Consistent with line-tied kink
Abrupt MHD transition can occur: β
β’
Large scale ππ = 1 at 20β80 kHz
HFS Injectors
High MHD
Reduced MHD
Preliminary indications of πΈπΈπ
π
shear at edge via probes
MHD evolution indicates strong CD mechanism independent of MHD bursts
M.W. Bongard, ISTW 2017
20
β’
Long-pulse, Non-inductive HFS LHI Discharges Sustained Without Low-Frequency ππ = 1 Activity
Current sustained in reduced MHD regime β β
β’
ππ = 1 activity suppressed during πΌπΌππ flattop
Pulse length limited by power supplies
πΌπΌππ = 0.1 MA non-inductive scenario β Constant shape
β Zero measured PF induction
M.W. Bongard, ISTW 2017
21
Transition Coincident with Shift of MHD From Low to High Frequency β’
Reduction in low-frequency activity presently interpreted as stabilization of kinked injector streams β
β’
R = 85 cm (outside LCFS)
Mechanism of stabilization under investigation
New high-frequency insertable probes deployed β
First results indicate high-frequency content near plasma edge
β
High-frequency content unobservable on outboard sensors R = 56.6 cm (inside LCFS)
β’
Correlated with additional CD mechanism β β
Link to short ππ turbulence?
Reconnection on inboard, high-field side (NIMROD)?
M.W. Bongard, ISTW 2017
22
HFS LHI Provides High-Performance Operation at Extremely Low π΅π΅ππ β’ β’
Access to highly-shaped, high π½π½π‘π‘ plasmas HFS LHI: unique operation space β β β
β’ β’
Low πΌπΌππππ ~ 0.6 πΌπΌππ πΌπΌππ = 5π΄π΄
πΌπΌππ
πΌπΌππππ
> 10 accessible
Naturally high π
π
, low βππ
Reconnection-driven ππππ > ππππ
Ramped π΅π΅ππ discharges terminate disruptively at ideal no-wall stability limit β
Consistent with DCON analysis
M.W. Bongard, ISTW 2017
D.J. Schlossberg et al., PRL 119 035001 (2017)
23
β’
LHI at π΄π΄ ~ 1 Expands the Operating Space for the ST to Ξ²π‘π‘ ~1
World record Ξ²π‘π‘ ~ 1 achieved β
β’
β
β’
Facilitated by π΄π΄ ~ 1 and LHI
π΄π΄ ~ 1: β
β’
Troyon Stability Diagram for Tokamaks, STs
LHI:
Naturally high π
π
High πΌπΌππ stability limit
β
Strong ion auxiliary heating
β
Edge current drive β low βi
Low βππ at low-π΄π΄: high π½π½ππ,ππππππ
M.W. Bongard, ISTW 2017
R.J. Fonck, IAEA FEC 2016 OV/5-4 D.J. Schlossberg et al., Phys. Rev. Lett. 119 035001 (2017) J.E. Menard et al., Phys. Plasmas 11, 639 (2004) 24
LHI Provides Access to Desirable ST Operating Space β’
Non-solenoidal sustained plasmas with high-π½π½ t, low βππ , high π
π
, high πΌπΌππ, are ST research goal β
Target operating space of NSTX-U at high performance
β
PEGASUS reaches much of this space, albeit through different mechanisms
ST Target
β’
NSTX, NSTX-U Low π΄π΄
PEGASUS π΄π΄ = 1.15 β π
π
β 2.5
High π
π
Low βππ
Bootstrap, Off-axis NBI, RF
High πΌπΌππ
High π½π½π‘π‘ , π½π½ππ
High πΌπΌππ, low π΄π΄, wall stabilization NBI, RF Heating
Low π΅π΅ππ, π΄π΄ ~ 1, no-wall limit
Non-solenoidal sustainment
Bootstrap, NBI, RF
LHI
Collisionality
Very low
Modest
LHI edge CD β βππ β 0.2
Reconnection Ion Heating
LHI facilitates near-term access and stability studies
M.W. Bongard, ISTW 2017
J.E. Menard et al., Nucl. Fusion 56 106023 (2016)
25
β’
Unique Feature of High-π½π½π‘π‘ LHI Plasmas: Sustained min π΅π΅ Region
High-Ξ²t equilibrium contains large minimum π΅π΅ region β
Up to 47% of plasma volume
β
Well deepens and broadens as π½π½π‘π‘ increases
β
β’
Persists for several energy confinement times
Minimum π΅π΅ regime arises from 3 major influences β β β
β’
High-π½π½π‘π‘ equilibrium flux surfaces (blue), π΅π΅ (black), and min- π΅π΅ region (red)
π΅π΅ππ ~ π΅π΅ππ at π΄π΄ ~ 1 Hollow π½π½(π
π
)
Pressure-driven diamagnetism (although π½π½ππ < 1)
Potentially favorable for stabilization of drift modes, reduction of stochastic transport β
Presently under investigation
M.W. Bongard, ISTW 2017
D.J. Schlossberg et al., Phys. Rev. Lett. 119 035001 (2017) 26
PEGASUS-E: US Non-Solenoidal Development Station β’
Compare / contrast / combine reactor-relevant startup techniques β β
β’
PEGASUS-E (Enhanced) β β β β β β β
β’
LHI, CHI, RF/EBW Heating & CD Goal: guidance for ~1 MA startup on NSTX-U, beyond
No solenoid magnet Increase π΅π΅ππ 4Γ: 0.15 β 0.6 T Longer pulse Active shape control Kinetic and impurity diagnostics RF Heating & CD (w/ ORNL) Transient, Sustained CHI (w/ Univ. Washington, PPPL)
PEGASUS
PEGASUS-E
High-Stress OH Solenoid 12-turn TF Bundle
Solenoid-free 24-turn TF Bundle
Proposals submitted to US DOE β
Decisions expected late 2017
M.W. Bongard, ISTW 2017
27
LHI Research Activities on PEGASUS-E Will Test Scaling to High π΅π΅ππ
β’ Physics Issues β β β β β β
Taylor limit πΌπΌππ scaling Efficiency / confinement scaling Relaxation accessibility MHD behavior & CD mechanisms PMI and impurities Advanced injector technology β’
Increased HI drive with high Taylor limit
β’ Facility Enhancements β 24-turn TF rod; power system β Programmable ππππππππ (π‘π‘) control β PF coils and power systems β’
X-point, shape control
β DNB spectroscopy β’
οΏ½ π΅π΅(π
π
, π‘π‘), π½π½(π
π
, π‘π‘), ππππ (π
π
, π‘π‘), ππππ (π
π
, π‘π‘), ππππ (π
π
, π‘π‘)
β Impurity diagnostics β’
SPRED, VB, bolometry
M.W. Bongard, ISTW 2017
Parameter
PEGASUS
PEGASUS-E
Non-circular, High-π΄π΄ππππππ Helicity Injector Renderings
Mo Frustum Shield, Rings
π
π
π π π π π π [cm]
4.9
N/A
πΌπΌπ π π π π π [kA]
Β± 24
0
40
0
ππππππ
12
24
πππ π π π π π (mWb) ππππππ Γ πΌπΌππππ
0.288 MA
1.15 MA
0.15
0.60
π΄π΄
1.15
1.22
50
100
13.2
151
0.2
0.3
π΅π΅ππ,ππππππ [T] at π
π
0 ~0.4 m π΅π΅ππ Flattop [ms]
TF Conductor Area [cm2] πΌπΌππ Target [MA]
High-voltage Ignition Electrode
Annular Anode Gas Feed
Distributed Gas Manifold
High Ainj = 6 cm2, Low winj = 1.6 cm Aperture
Refurbished PBX-M DNB
28
High-π΅π΅ππ of PEGASUS-E Facilitates RF/EBW and CHI Studies
β’ EBW heating and CD; synergy with HI startup β β β β
GENRAY, CQL3D Modeling Indicates Core Absorption for EBW Heating, CD
ππππ increase for compatibility with non-inductive sustainment (e.g. NBCD) Potential for direct RF startup Initial concept: ~ 400 kW EBW RF, 9 GHz (TBD) ORNL collaboration
β’ Deploy βsimpleβ CHI systems β Flexible, segmented floating anode and cathode structures β Transient and/or Sustained CHI β Univ. Washington, PPPL collaboration
Support Ring Vacuum Vessel Tab
Pre-Conceptual Segmented CHI Electrode Concept Divertor Plate
β’ LHI β CHI β RF Experiments β Generate significant closed-flux πΌπΌππ with CHI β Compare ππππ , ππππ , ππππππππ , π½π½(π
π
), usable πΌπΌππ β Coupling to consequent CD mechanism M.W. Bongard, ISTW 2017
29
Broadening Studies of Non-Solenoidal Startup on PEGASUS and PEGASUS-E β’
Local Helicity Injection provides non-solenoidal startup and sustainment β β
β’
Appears scalable to large scale; open questions on confinement, reconnection dynamics and π΅π΅ππ scaling
New high-field-side injector systems exploring strong VLHI limit β
Relaxation to tokamak demonstrated with HFS system
β
πΌπΌππ up to 0.2 MA with πΌπΌππππππ β€ 8 kA
β
New reduced-MHD regime discovered
β
πΌπΌππ,ππππππ scales with helicity injection rate
β
β’
Flexible injection geometry balances πππΏπΏπΏπΏπΏπΏ and πππΌπΌπΌπΌπΌπΌ drive, engineering constraints
Focus increasing on electron dynamics and πΌπΌππ scaling
LHI and π΄π΄ ~ 1 enable access to high-πΌπΌππ , high-π½π½π‘π‘ regime β Stability tests at extreme toroidicity
β’
PEGASUS-E: Proposed US non-solenoidal R&D facility β β
LHI, RF, CHI startup at π΅π΅ππ > 0.5 T Projection to NSTX-U and beyond
M.W. Bongard, ISTW 2017
30