A Mission to Discover the Plasma Solutions
for Future Fusion Reactors
presented by

RJ Buttery

with thanks to the DIII-D teamfor theNational Academies Committee
for a Strategic Plan for U.S.
Burning Plasma ResearchFeb 26th 2018

Work supported by US DOE under DE-FC02-04ER54698.

1 - Buttery/NAS/Feb 2018

Fusion Reactors Encounter
New Physics Challenges

Turbulence

GYRO δTe/Te0

2 - Buttery/NAS/Feb 2018

Turbulence

GYRO δTe/Te0

3 - Buttery/NAS/Feb 2018

Simulation

Fluctuations
(Te)

Z (m)

Frequency /kHz

Fusion Reactors Encounter
New Physics Challenges

Energetic particles
drive Alfvénic resonances

Turbulence

GYRO δTe/Te0

Simulation

Fluctuations
(Te)

Z (m)

Frequency /kHz

Fusion Reactors Encounter
New Physics Challenges

Energetic particles
drive Alfvénic resonances
Radiated
Cold
partially ionizedradiative
power plasma

174272 @ 2745 ms
4 - Buttery/NAS/Feb 2018

Turbulence

GYRO δTe/Te0

Simulation

Fluctuations
(Te)

Z (m)

Frequency /kHz

Fusion Reactors Encounter
New Physics Challenges

Energetic particles
drive Alfvénic resonances
Radiated
Cold
partially ionizedradiative
power plasma

US Strength

Science ! Solutions
174272 @ 2745 ms
5 - Buttery/NAS/Feb 2018

U.S. Missions in Fusion Energy• Make ITER better– U.S. learning from ITER

• Path to a steady state reactor– U.S. should have a path
– Establish physics & technical basis

6 - Buttery/NAS/Feb 2018

Our Vision is to Transform DIII-D to Meet theUnique Challenges of Burning Plasma Regimes
Address in D-D so that we can proceed with D-T• Develop integrated core-edge solution:– Performance, transients, steady state, divertor-PMI𝜿↑𝟐 )/𝟐​𝜷↓𝑻 /(𝟏+​Fusion Power index

Performance

4

3• DIII-D is the right scale toexecute this mission

DIII-D
Pilot
Plant

2

βN=5
βN=4

1

βN=3
βN=2
0

0

1

2

Self-driven Current, βP

Sustainment

3– Can access relevant parametersand physics mechanisms– High flexibility & diagnosis– Meaningful integration ofcore and edge

• Explore how to configure plasma
to make fusion solutions• Enable scientific breakthroughs to discover fusion solutions– Make ITER better and enable U.S. to benefit from ITER
– Basis to proceed with steadystate fusion reactor
7 - Buttery/NAS/Feb 2018

Contents" New physics challenges• Strategic needs for
U.S. fusion path
• DIII-D plan to meetcritical challenges• Conclusions

8 - Buttery/NAS/Feb 2018• Demonstrate and explore
physics of the self-heatedburning plasma stateτexp sThe World Program is Focused on theTokamak Path to Fusion Energy– Based on enormous bodyof work to project solution
τH98(y,2) s

ARIES-AT

ITER• Sustain the burning plasma non-inductively andbreed tritium in high flux environment– High bootstrap & RF replace inductive current– Detached divertor to handle heat flux

An Integrated Path to Fusion Energy
9 - Buttery/NAS/Feb 2018

EU DEMO

CFETR

K-DEMO

ARC

SlimCS

ACT1

Steady StateITER Provides Vital Learning for Path to a Fusion Reactor• Exploration of the burning plasma concept !
• Testing physics & techniques at reactor scale• Development of validated predicted models• Test steady state configurations• How to build and operate a large scale nuclear
fusion facility
ARIES-AT

ITER

ITER participation is vital if the U.S. is serious
about fusion energy• Crucially informs U.S. approach to a D-T reactor• Know-how you don’t get from just reading the papers

EU DEMO

CFETR

K-DEMO

ARC

SlimCS

ACT1

Steady State10 - Buttery/NAS/Feb 2018

How does the U.S. get to fusion energy
and what is DIII-D’s role?
– Enable U.S. ITER success & learning– Establish plasma basis to specify and decideon progression to U.S. D-T reactor

11 - Buttery/NAS/Feb 2018

• Make ITER work – Make ITER better– Physics to raise performance– Stable, ELM controlled regimes– Disruption mitigation

ITER design
point• Validate simulation to design discharges– Gain U.S. leadership on ITER
– Provide predictive tools for U.S. reactor

Snyder NF 2015

DIII-D can

DIII-D is The Vital Tool for U.S. ITER Engagement –to Enable ITER’s Success and Bring Back Learning to U.S.

Improvedpedestal
may raise
ITER Q• Resolve ITER issues when it is running– High flexibility: can be rapidly configured & deployed
DIII-D• DIII-D is the U.S.’s ITER simulator– Relevant collisionality, ω, Te/Ti, β, q95, shape, aspect ratio & control– Gaps on core-edge understanding & pedestal addressed here
Tight DIII-D–ITER coupling levers U.S. programand provides unique opportunities for U.S. in ITER
12 - Buttery/NAS/Feb 2018

DIII-D is The Vital Tool for U.S. ITER Engagement –Without ITER Path?
to Enable ITER’s Success and Bring Back Learning to U.S.
• Make ITER work – Make ITER better

ITER designmodels
These
topicalissues and this need for validated– Physics
to raise
performancepoint– Stable,
controlled
are allELM
also
crucialregimes
needs for a steady state tokamak reactor– Disruption mitigation– Provide predictive tools for U.S. reactor

Snyder NF 2015

Improvedpedestal• Validate simulation to design discharges
Without ITER, the DIII-D program would pivot to address these issues in
may raise– Gain U.S. leadership on ITER
ITER Qthe context of steady state reactor scenarios(we are already looking at these issues for steady state scenarios,
but would accelerate this)• Resolve ITER issues when it is running– High flexibility: can be rapidly configured & deployed

DIII-DThe loss of ITER participation
be asimulator
huge blow to the U.S.,• DIII-D is thewould
U.S.’s ITER
eliminating access to theworld’s
first serious– Relevant
collisionality,
ω, Tnuclear
shape, reactor
aspect ratio & control
e/Ti, β, q95,fusion– Gaps on core-edge understanding & pedestal addressed here
# Sets back U.S. ability
to construct & operate a D-T device,
and would likely add Tighta generation
the U.S.levers
pathU.S. program
DIII-D–ITERto
coupling
and provides unique opportunities for U.S. in ITER
13 - Buttery/NAS/Feb 2018

Tokamak Provides Promising Path
to Steady State Fusion
Per-shot disruptivityper(%) shotDisruptivity
is low at reactor q95• High q95 raises stability• Strong shaping raises performance

ReactorShaping raises limits
345

q95 (at peak b )6N-.%/'0)1"+&%'+)2*&

1

Predicted Stability Limit
for given profiles

5

goal

Stability
improved

4
3
2

DIII-D
2

1

On axis

qmin
qmin

3

Off axis

Current Deposition

Thermal Conductivity

6

Ratio to Gyro-Bohm
Scaling
Normalized
Pressure

6.7"%&80'#$&
Steady-state

Normalized Pressure34/)!&+%)5"&"+,"&!"#$"%&'()*&

92%%"#$&+"#*)$:&• Favorable synergy of broad current profile, stability & transport:
65PredictedStability
Transport
Predicted
Limit
for given profiles

Electrons

goal

Ions

4
3
2

Electron heated regime
at q=2 surface
DIII-D
DIII-D
12

Magnetic2Shear0
Magneticshear
q qminOn axis
On
axis

min

-1
3
Off axis

Off axis

Current
CurrentDeposition
Deposition

How can the U.S. accelerate this path to fusion energy?
14 - Buttery/NAS/Feb 2018

Stability
Transport
improvedlowerFull Physics Simulations Show Potential of Steady State
Tokamak as an Efficient Compact Reactor– Converged self-consistent fully non-inductive plasmas

FASTRAN 4m 7T fully non-inductive plasmas
stationary TGLF-EPED-CD-EFIT solutions

MW

PNET

• Trade-offs & optimizations:

PH/CD– Shaping is key: Q~shaping2– Higher density reduces H&CD needs

Fix βN = 3.5– Higher βN raises fusion performance

PNET
PH/CD

​𝜂↓𝑇𝐻 =​𝜂↓𝐶𝐷 =0.4

• Projects H98~1.3-1.5 leading to solutions at 4m 6-7T

Fix neped/nGW = 0.9​𝑛↓𝑒𝑝𝑒𝑑 /​𝑛↓𝐺𝑊​𝛽↓𝑁
7T​𝜼↓𝑪𝑫 =𝟎.4 ​6T𝜼↓𝑻𝑯 =𝟎.𝟑𝟑​𝜼↓𝑻𝑯 =𝟎.𝟒

– Higher BT improves confinement– Higher efficiencies raise Pnet-electric– Dissipative divertor vs core radiation– Transients must be controlled$ Important to develop and validate these solutions

Fixed IP & density

PH/CD (MW)Improved physics & technology reduces
required scale, fusion power, fluxes and cost
15 - Buttery/NAS/Feb 2018

​𝜼↓𝑪𝑫 =𝟎.𝟐𝟓,​𝜼↓𝑻𝑯 =𝟎.𝟑𝟑
PH/CD (MW)Powerplants• Should address these in a compact ‘pilot plant’ test facility

SlimCS

Rm

6.3

5.5

6.8

7.9

IP MA

11

17

17

14

Pfus GW

1.8

3

2.9

2

Pnet GW

1

1

0.5

0.5

– Combine missions to remove a generation ! more compelling– Low capital cost so affordable to go forward– Do not need to be at large, low-COE scale to prove
approach for that scale

Korea
DEMO
EU
DEMO

• Key challenges for self-sustaining reactor:– Breeding– Nuclear materials– Net electricity

ACT1

U.S. Should Innovate to Enable
Low Capital Cost Net Electric Pilot Plant• U.S. proposals for ARC, Compact-AT and ST-pilot– All at scale 100-200MWe, R~3-4m, A~2-3 & benefit from high temperature superconductors• A pilot plant would lever U.S. ITER participation• But requires additional ‘enabling research’– To raise fusion performance & provide required technologies

Distinctive window of opportunity for U.S.
16 - Buttery/NAS/Feb 2018

Powerplants• Should address these in a compact ‘pilot plant’ test facility

SlimCS

Rm

6.3

5.5

6.8

7.9

IP MA

11

17

17

14

Pfus GW

1.8

3

2.9

2

Pnet GW

1

1

0.5

0.5

– Combine missions to remove a generation ! more compelling– Low capital cost so affordable to go forward– Do not need to be at large, low-COE scale to prove
approach for that scale

Korea
DEMO
EU
DEMO

• Key challenges for self-sustaining reactor:– Breeding– Nuclear materials– Net electricity

ACT1

U.S. Should Innovate to Enable
Low Capital Cost Net Electric Pilot Plant• U.S. proposals for ARC, Compact-AT and ST-pilot– All at scale 100-200MWe, R~3-4m, A~2-3 & benefit from high temperature superconductors• A pilot plant would lever U.S. ITER participation % U.S. would not have the expertise to proceed• But requires additional ‘enabling research’without its ITER participation

May need additional facility & time to– To raise fusion performance & provide required technologies
develop skills and physics basis

Distinctive window of opportunity for U.S.
17 - Buttery/NAS/Feb 2018

Research Required in Seven Areas
to Enable Low Capital Cost Pilot Plant
1. ITER participation– Validated physics models& reactor knowhow

2. Stable high performance
fully noninductive core
3. Dissipative Divertor
4. Efficient current drive

Tokamak research enables ITER
& pilot plant missions• DIII-D provides key opportunity
to advance ITER and pilot plantresearch agendas

5. Reactor materials
6. Demountable high temp
superconducting magnets
7. Engineering design &breeding concepts

Work on engineering &technologies to advancepilot plant approach

These 7 missions provide opportunities for breakthroughs inunderstanding & performance that transform fusion prospects
18 - Buttery/NAS/Feb 2018

Contents" New physics challenges" Strategic needs for
U.S. fusion path
• DIII-D plan to meetcritical challenges• Conclusions

19 - Buttery/NAS/Feb 2018

Understanding an Integrated Solution Requires Improved Performance• Core and divertor physics are governed by different parameters:
core

Pedestal

Divertor

Separatrix

Pressure

Collisionality, ​n↓𝒑𝒆𝒅↑∗ ~​𝒏↓𝒑𝒆𝒅↑𝟑 /​𝑷↓𝒑𝒆𝒅↑𝟐
Pedestal​𝛽↓𝑁𝑝𝑒𝑑 ~𝑆ℎ𝑎𝑝𝑖𝑛𝑔.​𝑓↓𝐺𝑊
physics

nsep

Core

PedestalEdgetransport
barrier

Radius20 - Buttery/NAS/Feb 2018

Closure &neutrals

ndiv

q||

Understanding an Integrated Solution Requires Improved Performance• Core and divertor physics are governed by different parameters:
core

Pedestal

Divertor

Separatrix

Collisionality, ​n↓𝒑𝒆𝒅↑∗ ~​𝒏↓𝒑𝒆𝒅↑𝟑 /​𝑷↓𝒑𝒆𝒅↑𝟐
Pedestal​𝛽↓𝑁𝑝𝑒𝑑 ~𝑆ℎ𝑎𝑝𝑖𝑛𝑔.​𝑓↓𝐺𝑊
physics

nsep

Closure &neutrals

ndiv

Pressure

Radiated
power

Core

PedestalEdgetransport
barrier

Radius21 - Buttery/NAS/Feb 2018174272 @ 2745 ms

q||Understanding an Integrated Solution Requires Improved Performance• Core and divertor physics are governed by different parameters:
core

Pedestal

Collisionality, ​n↓𝒑𝒆𝒅↑∗ ~​𝒏↓𝒑𝒆𝒅↑𝟑 /​𝑷↓𝒑𝒆𝒅↑𝟐
Pedestal​𝛽↓𝑁𝑝𝑒𝑑 ~𝑆ℎ𝑎𝑝𝑖𝑛𝑔.​𝑓↓𝐺𝑊
physics

nsep

Pressure

Low​[Maggi, NF2015]

Closure &neutralsndiv

Radiatedpower

JET pedestaln↓𝒑𝒆𝒅↑
BallooningHigh∗ ​n↓𝒑𝒆𝒅↑∗ pressure gradient)(Normalized

Divertor

Separatrix

Core

PedestalEdgetransport
barrier

Radius22 - Buttery/NAS/Feb 2018174272 @ 2745 ms

q||Understanding an Integrated Solution Requires Improved Performance• Core and divertor physics are governed by different parameters:
core

Pedestal

Divertor

Separatrix

Collisionality, ​n↓𝒑𝒆𝒅↑∗ ~​𝒏↓𝒑𝒆𝒅↑𝟑 /​𝑷↓𝒑𝒆𝒅↑𝟐
Pedestal​𝛽↓𝑁𝑝𝑒𝑑 ~𝑆ℎ𝑎𝑝𝑖𝑛𝑔.​𝑓↓𝐺𝑊
physics

nsep

Closure &neutrals• Core-edge solution depends on progress in each region– Improved pedestal (nsep:nped) and divertor (ndiv:nsep) solutions play a key role

23 - Buttery/NAS/Feb 2018

ndiv

q||

Understanding an Integrated Solution Requires Improved Performance• Core and divertor physics are governed by different parameters:
core

Pedestal

Divertor

Separatrix

Collisionality, ​n↓𝒑𝒆𝒅↑∗ ~​𝒏↓𝒑𝒆𝒅↑𝟑 /​𝑷↓𝒑𝒆𝒅↑𝟐
Pedestal​𝛽↓𝑁𝑝𝑒𝑑 ~𝑆ℎ𝑎𝑝𝑖𝑛𝑔.​𝑓↓𝐺𝑊
physics

nsep

Closure &neutrals

q||

ndiv

• Core-edge solution depends on progress in each region

Pedestal vs divertor closure– Improved pedestal (nsep:nped) and divertor (ndiv:nsep) solutions play a key role

• Strong interaction
between these regionsTe– Depends on opacityne24 - Buttery/NAS/Feb 2018

High density an important
governing parameter

Understanding an Integrated Solution Requires Improved Performance• Core and divertor physics are governed by different parameters:
core

Pedestal

Divertor

Separatrix

Collisionality, ​n↓𝒑𝒆𝒅↑∗ ~​𝒏↓𝒑𝒆𝒅↑𝟑 /​𝑷↓𝒑𝒆𝒅↑𝟐
Pedestal​𝛽↓𝑁𝑝𝑒𝑑 ~𝑆ℎ𝑎𝑝𝑖𝑛𝑔.​𝑓↓𝐺𝑊
physics

nsep

Closure &neutrals

q||

ndiv

• Core-edge solution depends on progress in each region– Improved pedestal (nsep:nped) and divertor (ndiv:nsep) solutions play a key role

• Progress in underlying parameters is important​𝒏↓𝒑𝒆𝒅 ~​(𝑺𝒉𝒂𝒑𝒊𝒏𝒈 ​𝒇↓𝑮𝑾 𝑰 𝑩 /𝒂)↑𝟑/𝟐(fixed ​n↓𝑝𝑒𝑑↑∗ )Shaping, field, current & power are key levers to get to reactor-like physics regimes
Need to increase flexibility and performance
25 - Buttery/NAS/Feb 2018

A Performance Upgrade Provides an Opportunity
to Explore Integrated Core-Edge Solutions
Key elements:• Shaping increase – raises pedestal height,
volume & current carrying capacity

Present

δ=0.9:

Volume& IP rise

26 - Buttery/NAS/Feb 2018

A Performance Upgrade Provides an Opportunity
to Explore Integrated Core-Edge Solutions
Key elements:• Shaping increase – raises pedestal height,
volume & current carrying capacity

250
200

• Heating & current drive upgrade – exploit shaping
rise to higher pressure & high density steady state– 28MW balanced beam + 12.5MW helicon (750MHz)
fully non-inductive solution at 2.2T
• ~3x pedestal height & stored energy in steady state• ITER-like ​n↓𝐩𝐞𝐝↑∗ with much higher density

27 - Buttery/NAS/Feb 2018

FASTRAN 2.17T 2MA<J||> (A/cm2)
Tot

150
100
50
0.0
0.0

Helicon
or LH

BS

NB
0.2

0.4

0.6 0.8 1.0
ρ
q95=5.5 3.8MJ Pped=41kPa βN=4.1(limit 10) ​n↓𝑝𝑒𝑑↑∗ ~0.14 nped=8.7E19 Te>Ti
Ω~21krad/s
11% fast ions 61% bootstrap

A Performance Upgrade Provides an Opportunity
to Explore Integrated Core-Edge Solutions
Key elements:• Shaping increase – raises pedestal height,

Pedestal Collisionality
vs DIII-D/D-IV
Density for and
DIII-D/D-IV
Pedestal Collisionality
vs Density for
ITER and ITErise to higher pressure & high density steady state• Higher field – higher density & power flux at low ν*– Extend existing TF!~2.5T or replacement !4T– Increases opacity

ITER like pedestal at 2.5T

DIII-D
Ip=1.8MA,
Bt=2.1T (Measured)
DIII-D Ip=1.8MA,
Bt=2.1T(Measured)
DIII-D
Ip=1.8MA,
Bt=2.1T (EPED)
DIII-D Ip=1.8MA,
Bt=2.1T(EPED)
D-IV
Ip=2.6MA,
Bt=3T (EPED)
D-IV Ip=2.2MA,
Bt=2.5T(EPED)
D-IV Ip=3MA,D-IV
Bt=4TIp=3MA,(EPED)Bt=4T (EPED)
DIII-Dbaseline(EPED)ITER baselineITER(EPED)

Pedestal
Collisionality
Pedestal Collisionality (ν*)ν*• Heating & current drive upgrade – exploit shaping

Pedestal Collisionality (ν*)

volume & current carrying capacity

0.1

2.1T

0.1

2.5T ITER
4T
EPED

0.01

0.01
0

0

5

10

5

10

Pedestal
Density
19m/2)-3
Pedestal Pedestal
Density[nDensity,10[n191/2(Ze,ped(Z0.5
eff/2)e,ped
eff ]1/2,1019m-3]-3[nped (Zeff/2)*present steady state

28 - Buttery/NAS/Feb 2018

10

m ]

A Performance Upgrade Provides an Opportunity
to Explore Integrated Core-Edge Solutions
Key elements:• Shaping increase – raises pedestal height,
volume & current carrying capacity• Heating & current drive upgrade – exploit shaping
rise to higher pressure & high density steady state

Optimized divertor• Higher field – higher density & power flux at low ν*– Extend existing TF!~2.5T or replacement !4T• Double null closed divertor – isolate dense

detached divertor from high performance coreDirects neutrals toimprove detachment

29 - Buttery/NAS/Feb 2018

A Performance Upgrade Provides an Opportunity
to Explore Integrated Core-Edge Solutions
Key elements:• Shaping increase – raises pedestal height,
volume & current carrying capacity• Heating & current drive upgrade – exploit shaping
rise to higher pressure & high density steady state• Higher field – higher density & power flux at low ν*– Extend existing TF!~2.5T or replacement !4T• Double null closed divertor – isolate dense

detached divertor from high performance core

Supporting research elements establish basis for high performance stable core & dissipative divertor:– Low ν* ‘burning plasma’ core regimes– Steady state sustainment– Transients– Divertor science, PMI & core interactions

30 - Buttery/NAS/Feb 2018

A Performance Upgrade Provides an Opportunity
to Explore Integrated Core-Edge Solutions
Key elements:• Shaping increase – raises pedestal height,
volume & current carrying capacity• Heating & current drive upgrade – exploit shaping
rise to higher pressure & high density steady state• Higher field – higher density & power flux at low ν*

D IV?

– Extend existing TF!~2.5T or replacement !4T• Double null closed divertor – isolate dense

detached divertor from high performance core

Supporting research elements establish basis for high performance stable core & dissipative divertor:– Low ν* ‘burning plasma’ core regimes– Steady state sustainment– Transients– Divertor science, PMI & core interactions

Provide the plasma physics basis to decide on a D-T device
and to lead on & learn from ITER
31 - Buttery/NAS/Feb 2018

Plan Provides Distinctive & Needed Capability in World Context• Core-edge interaction with closed divertors• Low ν* & rotation with reactor-like core conditions

DIII-D• 3-D optimization of the tokamak• Steady state configuration & current drive

Larger scale

Superconducting
EAST

KSTAR

• Material &PFC evolution• Projection toreactor• Long pulse
control• Operational
techniques

Metal walls

JT-60SANSTX-U

JET• High Z
behavior• Bulk W
influx• RF

Key physics
MAST-U

Flexibility & diagnosis
to explore physics
and develop
candidate solutions• Aspect ratio effects• Divertor magnetic geometry• Super Alfvénic ions & high β
32 - Buttery/NAS/Feb 2018

Innovative Diagnostics and Modeling Enable
Tests of State-of-the-Art Theoretical Models• Comprehensive, high resolution diagnostics• High speed computing & cutting edge simulation• Strong collaborative approach – e.g.:– Turbulence: GA, UCLA, Wisconsin, MIT, UCSD
– Alfvén eigenmodes: UCI, PPPL, GA– ELMs: UCSD, LLNL, ORNL, SNL, GA

Heart of our approach:
Understanding to develop predictive
capability & better solutions

33 - Buttery/NAS/Feb 2018

Example of Science Leading to Solutions: Pedestal Improvement• DIII-D research validated a model of thepedestal based on two instabilities

Peeling-Ballooning
limits pressure

Kinetic-Ballooning
limits gradient34 - Buttery/NAS/Feb 2018

Example of Science Leading to Solutions: Pedestal Improvement• DIII-D research validated a model of thepedestal based on two instabilities

Peeling-Ballooning
limits pressure

Kinetic-Ballooning
limits gradientAccounts forbehavior on
6 devices

35 - Buttery/NAS/Feb 2018

Example of Science Leading to Solutions: Pedestal Improvement• DIII-D research validated a model of thepedestal based on two instabilities

Peeling-Ballooning
limits pressure

Kinetic-Ballooning
limits gradientAccounts forbehavior on
6 devices

Unstable• Used model to predict access toimproved pedestals

Unstable– Shaping decouples modes ! stability

36 - Buttery/NAS/Feb 2018

Stablepath

Example of Science Leading to Solutions: Pedestal Improvement• DIII-D research validated a model of thepedestal based on two instabilities

Peeling-Ballooning
limits pressure

Kinetic-Ballooning
limits gradientAccounts forbehavior on
6 devices• Used model to predict access toimproved pedestals– Shaping decouples modes ! stability– Leads to record DIII-D pedestal pressureand highest QDD/IaB in a tokamak

Pedestal Pressure [2*pe,ped, kPa]

Access to High Performance Super H-Mode Regime on DIII-D
35
30

Unstable25

t=2.4st=2.2s

Unstable20
15

t=1.9s

10
5
0

3

4

5

Stablepath
67

H-ModeNear Super H
Super H
8

9

10

11

Pedestal Density [ne,ped(Zeff/2)1/2,1019m-3]

DIII-D has relevant flexibility, parameter space& diagnostics to develop pioneering solutions
37 - Buttery/NAS/Feb 2018

12

DIII-D Benefits from a Diverse and Broad Community Engagement• 623 Users• 108 Institutions• 71 PhD students• 64 Postdocs• Hosts collaborative partners from across community– High level of run time and broad research capabilities– Center for theory collaboration & simulation validation– Strong international & ITER engagement• Integrated scientific organization– Opportunities for leadership across the program– 100 onsite scientists: 1/3 Universities 1/3 Labs 1/3 GA• Hundreds more visiting/remote• Training next generation of scientists
40– Hands on access

PhD

Postdocs

30
20

Collaboration is key to DIII-D’s success
38 - Buttery/NAS/Feb 2018

10
0
2007

2009

2012

2014

2016

Supporting Research Elements– Burning Plasma performance– Transients– Steady State– Divertor/PMI
All these issues require progress for a steady state reactor,
with or without ITER
39 - Buttery/NAS/Feb 2018

• Research plan addresses the key elements:– Changes with low ν*, rotation & Te~Ti throughelectron heating & balanced beams• Study multi-field interactions between flows, particles & energies– Coupling of ions & electrons through performance (density) upgrade– New diagnostics to simultaneously measure multi-scale interactions– Electromagnetic (β) and magnetic shear with current drive upgrades

−3

m
10

19

ECH
T e = Ti

2

ECH power
density

ETG
0

0

0.2

7

Density fluctuation power– Need to access underlying phenomena, understanddependencies and interactions between themno ECH
Te = 0.5 Ti

4

ITG-TEM 0

ρ 0.6

0.4

0.8

1.0

r = 0.30

Rise in TEM turbulence3080 mswithelectron heating

6
5

ECH

4

1.2

3

GYRO
1.0

DBS

H98y
2980 ms
no ECH

0.8

2

0.6

1
0

4

W/cm 3– Strong nonlinear coupling across scales & fields

Density

TEM
ETG

155161 2980/3080• Turbulence driving instabilities change as burning
plasma parameters approached

DBS Fluctuations

6[Gyro, Candy]

DIII-D Plans to Understand How to Project &Improve Turbulent Transport for Low ν* Burning Plasma

0.4
00.2100
0.0
0
2.0
1.5

200

300

400

500

600

Frequency (kHz)

5

10

>
T<T
e>/<T
e/T
i: i

15

Baseline
βN=1.71.0

AT βN=3.7

0.5
0.0
0
2.5
2.0

GLF23

5

10

15

Electronheating /MW
T /T
e0

i0

1.5

1.0
Achieve predictive capability to design & optimize ITER discharges
0.5(confinement, L-H access, rotation, isotope effect) and fusion reactor
0.0

40 - Buttery/NAS/Feb 2018

0

5

10
PEC (MW)15

A 3-D Upgrade Provides Unique Basis to
Optimize ELMs & Stability for ITER & Reactor Design• DIII-D discovered multi-mode plasma response to 3-D fields

Edge current
driven mode
! ELM
suppression– Accounts for ELM suppression$ Affords selective control: ELMs, Rotation profile, Error fields– But ELMs & rotation control most effective with n=3,4 fields(more edge resonant)

41 - Buttery/NAS/Feb 2018

n=2

Global pressure
driven kinkn=2

A 3-D Upgrade Provides Unique Basis to
Optimize ELMs & Stability for ITER & Reactor Design• DIII-D discovered multi-mode plasma response to 3-D fields

Edge current
driven mode
! ELM
suppression– Accounts for ELM suppression$ Affords selective control: ELMs, Rotation profile, Error fields– But ELMs & rotation control most effective with n=3,4 fields(more edge resonant)– Tune for ELM suppression & rotation profile control– More efficient coupling for ELMs
– ITER-like coil set

ITER

DIII-Dn=2
NTV torque a.u.

• New 12 coil midplane array will provide first ability
to vary n=3 & 4 spectrum

Global pressure
driven kink

GPEC MHD response
6kA coils

n=2

Edge resonant

Core resonant
00High Bmn – low response
1

Radius (n’rm flux)
Midplane array:higher edge couplingx5
42 - Buttery/NAS/Feb 2018

Achieving Robust Disruption Mitigation Remains Critical for
the Viability Of Tokamak Reactors
Challenge: Radiate thermal & magnetic energy

Runaway phase space

Gamma Ray
Camerawhile avoiding runaway electron damage

Key Development Paths
1. Linking modeling & experiment to understandrunaway evolution using novel diagnostics– Image real and phase space
2. Optimize ITER shattered pellet injection (SPI)– Pioneered & developed on DIII_D
3. Core impurity deposition to simultaneously
mitigate thermal, magnetic, & RE needs– “Inside-out” mitigation with
low-Z shell pellets

3. SPI on
DIII-D43 - Buttery/NAS/Feb 2018

NIMROD: shell pellet stochastization

Flexible Heating and Current Drive Systems will
Enable DIII-D to Discover Path to High β Steady State• Potential solutions from broad to peaked current profiles

High ℓi– With high bootstrap or efficiently drive on-axis
RegimeStrength

N=5 potential;
High qmin βLow
disruptivity

HybridChallenge

High qmin

Fast ion transport
Resistive wall mode

HybridHigh
confinement

Current evolution
βN limit

High ℓiβN=5 without
RWM

Sustainment;
Tearing

Current
Density0

Normalized radius• Need to find a self-consistent solution– Need high βN: βT for performance, βP for bootstrap– Transport & stability dependence on profiles & β• Device flexibility is key– Assess physics in reactor relevant regimes$ Requirement for off-axis current drive in DIII-D
44 - Buttery/NAS/Feb 2018

Current profile
set by transportand stability
Transport and stability
depend on current &pressure distributions

1

DIII-D Heating and Current Drive Upgrades Will Provide
the Range to Explore Path to Steady State
Assess ideal MHD &Energetic Particle transport
vs. current profile
at high βN

Assess core-edge
integration & coupledelectron-ion scenarios
at high density

Assess turbulent
transport & ideal MHD
kinetic resonances
at low rotation& Toroidally steerable beams !

Basis to Project Steady States to Reactors
45 - Buttery/NAS/Feb 2018

DIII-D Will Test Advanced Current Drive Methods For
Reactors That Will Expand Steady State Research• Challenges: Efficient reactor current drive– Good coupling – Harsh reactor environment

Top EC

28kA/MW10• DIII-D will test 3 promising concepts
0– Top launch ECCD
Doubles off-axis efficiency

Helicon

80kA/MW– High harmonic fast wave (helicon)
2-4x greater efficiency at high βe– High-field side lower hybrid wave
HFS SOL more quiescent: Reduces flux to antenna& improves wave penetration

HFS
LHCD

120kA
/MW

Extends scenarios to higher βN,
broader J, lower Ω & higher density.
Develops potential reactor technologies.
46 - Buttery/NAS/Feb 2018rResearch Will Explore How to Combine Core & Edge Solutions
Pedestal vs divertor closure• Understand overall configurationand shape optimization– High DIII-D flexibility & double null divertor• Test influence of divertor closureon pedestal and coreTene

– Particle dynamics & pedestal turbulence• Develop radiative mantle techniques– & understand impact of radiators on PMI• A SiC wall will provide a low carbon backgroundto conduct radiative, PMI and impurity studies– C impacts radiative mantle and PFC erosion

SiC wall to assess behavior
without strong C radiation

Understand physics of core-edge interaction
47 - Buttery/NAS/Feb 2018

SiC wallDIII-D Will Develop Physics of Dissipative Detached State
and Configurations to Project Reactor Solutions
2D Thomson scattering• Key challenges– Understand physics processes of dissipative divertor– Develop concepts for improved divertor:
full detachment compatible with low ν* reactor corenene

• Tightly coupled processes– Atomic, molecular and neutral dissipation– Plasma drifts and parallel flows– Turbulent transport• Address critical physics– Increased 2D diagnostics, especially Ti and neutrals– High density, high power, closed configurations• Assess role of closure and magnetic geometry
in containing neutrals and detachment– Close coupling to model validation & development

Eθ×B Er×B Eθ×B Eθ×B Er×B Eθ

Flows(eV)play key rolein detachment(1e20 m-3)

Basis to develop validated models of detachment
48 - Buttery/NAS/Feb 2018

FlaringDIII-D Will Develop Innovative Closed Divertor Concepts inHigh Power Conditions• Goal: Minimize divertor volume needed
for steady state operation

SOLPS Te– Low plasma temperature across target– Compatibility with high performance core

• Approach– Close divertor– Direct neutrals to detach on all surfaces– Manipulate magnetic geometry to keep
detachment front in divertor• Plan– Explore closure geometry– Assess in high power main pumped divertors– Develop innovative particle and heat exhaust scenarios(gas & impurity injection; magnetic geometry)
Key contributions to the ‘Divertor Test Tokamak’ mission
49 - Buttery/NAS/Feb 2018

Smallangle slot

DIII-D Can Provide Unique Insights in Plasma-Materials
Interaction Solutions for a Fusion Reactor• Focus on mixed material solution:high Z divertor with low Z wall
• DIII-D strength: perturbative measurement of
impurity dynamics against low Z backgroundSAS 1-W– Laser blow off & spectroscopy techniques tounderstand impurity transport– SiC wall will provide low C source backgroundto remove low Z induced sputtering

Wall Interaction
Tile Station(proposed)• Assess high-Z interaction with closed divertors– Sources. Role in dissipation. Leakage• Test PMI & innovative materials in wall & divertor– Flexible sample facilities & region tests– Heated tile testing
Unique opportunity to resolve physics basiswith relevant materials and conditions
50 - Buttery/NAS/Feb 2018

DiMES
(existing)

WITS
Face-on
View

~60cm

Upgraded DIII-D Addresses the Critical Challenges
the U.S. Needs to Pursue for Fusion Energy+⇒
Core-Edge
UpgradeDIII-D

U.S. leadershipon ITER
Basis to proceedwith U.S. D-T pilot• Redevelopment of facility transforms access to new physics regimes & behaviors– Explore new frontiers in plasma science to meet critical challenges for fusion energy• Provides state of the art tool to U.S. community to enable research excellence & leadership• Resolve science & solutions in D-D in DIII-D so we can succeed with D-T– DIII-D 5 Year Proposal is an important first step & should be fully funded

If we didn’t have a DIII-D, we would build one to addressthese exciting & important scientific challenges
51 - Buttery/NAS/Feb 2018

REFERENCE SLIDES

52 - Buttery/NAS/Feb 2018

U.S. Pilot Plant Strategy Levers ITER Role with
Distinctive Science & Technology Innovations
Construct

Ops

D-T

Steady State

ITER

e.g. ARIES

Private sector
ENABLING RESEARCHNSTX-U, DIII-D!D IV
International
Technologies& test beds

e.g. ARC/C-AT/ST-PP

Decision

Pilot Plant –FNSF facility
Phased mission:
Net
Materials
elec.
Breeding

Provides key insights in world path to fusion energy

53 - Buttery/NAS/Feb 2018

Low COE
Power Plant
or additional
test devices byprivate industry

U.S. Pilot Plant Strategy Levers ITER Role with
Distinctive Science & Technology Innovations
Construct

Ops

D-T

Steady State

ITER

e.g. ARIES

Private sector
ENABLING RESEARCHNSTX-U, DIII-D!D IV
International
Technologies& test beds

e.g. ARC/C-AT/ST-PP

Decision

Pilot Plant –FNSF facility
Phased mission:
Net
Materials
elec.
Breeding

Provides key insights in world path to fusion energy
Without ITER : Add short pulse low Q facility to gain expertise
54 - Buttery/NAS/Feb 2018

Low COE
Power Plant
or additional
test devices byprivate industry

GA Vision and Strategy from
Scientific Excellence to Fusion Energy
Cost-Attractive Pilot-FNSF

Fully Fund DIII-D
5-Year Proposal
to Inform US Path

This
talk

Advance Core-Edge
Integration withMajor Upgrades

DIII-DUS enabling research
program for fusionenergy (materials,
magnets, blankets)

Theory andComputation
Develop Foundation
for Tokamak
Approach to Fusion

Ensure Success of ITER
55 - Buttery/NAS/Feb 2018Play Leading
Role inInternational
Fusion Effort

Steady State Projections with H&CD Upgrades:
Co-injected beam cases• High qmin with 9MW ECCD &half beam power off axis #
On-Ax
NBI
(MW)

Off-Ax
NBI
(MW)

ECH
(MW)

Transport
Limit in bN

Ideal
Stability
bN Limit

7.5

3.3

3.2
(FY16)

3.5(qmin=1.5,
fNI=0.75)

3.7

9.5

10.7

9
(FY24)

5.1

4.9(qmin>2,
fNI=1)High qmin• High li with 9MW ECCD & beam
upgrade:(see next)

projected

56 - Buttery/NAS/Feb 2018

We Will Also Develop the High-li Scenario as an Alternative
Solution for βN~4 Without Need for Wall Stabilization•••

Peaked current gives high no-wall limit &good confinement
No need for n>0 active feedback
stabilization
Requires more driven current•

Research items:- Must learn to deal with sawteeth and2/1 tearing modes- Benefits from reduced pedestal height•

FASTRAN predicts same NBI & ECH
upgrades enable fNI=1 high-li at βN=4- Below no-wall limit- 9 MW near-axis ECCD required
9 MW gyrotrons, off-axis NBI,
3D coils & power supplies
57 - Buttery/NAS/Feb 2018

Helicon or Lower Hybrid Can Raise βN limits& provide access to high density steady states• Co-injected beams
βN limit raised #• High density solutions
without ECH and coinjected beams #J||(A / m )2

βN-limit
4.6!5.3

Jtot

J||(A / m )2

Jtotn ||=3βN-limit
4.6!5.9

JHC

JLH

(1MW)

(1MW)

FASTRAN: fNI=1, fBS≈0.7, βN≈5, fGW=0.9,
9.6 MW off-axis NBI, 0 MW ECH, B=1.6 T, q95=6.5
2MW

58 - Buttery/NAS/Feb 20182MW

High density higher volume ‘core-edge’ solution15

8

ne(1019/m3)

12Present9

δ=0.9:

6

Volume& IP rise

6

4

ni

0
100

0.0

0.2

0.4

0.6

0.8

Ω(krad/s)

1.0

0
0.0
2.0

80

1.6

60

1.2

Fully non-inductive, 65% bootstrap,40
2T, 3MJ, ffast ion~15% , βN=4, βN-limit=10​n↓𝒑𝒆𝒅↑∗ ~0.24, nped=7.5E19, Te>Ti, Ω~20krad/s
20
25MW balanced NBI +10MW helicon
0

Ti

2

3

FASTRAN integrated simulation:

Te(keV)

0.0

0.2

0.4

Tot

0.6

0.2

59 - Buttery/NAS/Feb 2018

0.4

ρ

0.6

0.8

1.0 0.00.0

1.0<J||> (A/cm2)
Helicon
BS

0.8
0.4

0.8

NB
0.2

0.4

ρ

0.6

0.8

1.0

FASTRAN Validation vs DIII-D• FASTRAN routinely used in DIII-D
program to interpret results, test
underlying models and guidedevelopment– Combines TGLF, EPED, H&CD
source models and equilibria–

60 - Buttery/NAS/Feb 2018