review of st panel activity - us doe fusion research needs workshop

ISTW 2009: Review of ST Panel Activity – Fusion Research Needs Workshop (S.A. Sabbagh) October 22nd – 24th, 2009

Review of ST Panel Activity - US DoE Fusion Research Needs Workshop

S.A. Sabbagh1, N. Gorelenkov2, C.C. Hegna3, M. Kotschenreuther4, D. Majeski2, J.E. Menard2, Y.-K. M. Peng5, A.C. Sontag5, V.

Soukhanovskii6, D. Stutman7

1Department of Applied Physics and Applied Mathematics, Columbia University2Princeton Plasma Physics Laboratory

3University of Wisconsin, Madison4University of Texas, Austin

5Oak Ridge National Laboratory5Lawrence Livermore National Laboratory

5Johns Hopkins University

International Spherical Torus Workshop

October 22 - 24, 2009

UW Madison, Madison, WI

V1.2

Supported byOffice ofScience


Review of ReNeW ST Panel Activity - Outline

• ReNeW Purpose and Product

• ReNeW Structure in Brief

• ReNeW ST Panel and approach

• ReNeW Report ST Research Theme Chapter ST Research “Thrust”

• Comments re: guiding ST research forward


DOE ReNeW process to aid in defining the “ITER-era” (20 yr) research program

• ReNeW: Research Needs Workshop To inform the Office of Fusion Energy Sciences (OFES) in preparing

a strategic plan for research in each major area of the Fusion Energy Sciences Program

To allow U.S. fusion community to explain research goals, methods to achieve them

• Including communication to new administration

• Six month process (January – June 2009)

• Document (419 pages) http://burningplasma.org/renew.html Part 1: Defines scientific research issues and requirements needed

to fill “gaps” in present understanding

• Guidance from Greenwald report, FESAC TAP and EPA reports

• Divided into 5 “themes” comprising magnetic fusion research Part 2: Defines 18 “research thrusts” to carry out this research Basis for detailed program plan to be constructed by OFES


ReNeW organized into 5 fusion research themes

Structure/gapsFESAC Toroidal Alternates Panel

Report

Structure/gapsPriorities, Gaps, and Opportunities Panel Report

(“Greenwald Report”)

Structure/gaps Energy Policy Act task group report

Reports available at: http://burningplasma.org/renew.html

Spherical Torus sub-theme


The ReNeW Spherical Torus Panel had broad expertise and institutional base

• In addition, more than 30 advisors agreed to help Special thanks to Brian Lloyd, Ray Fonck, Dick Majeski (as Thrust 16 coordinator)

• Special thanks to Theme 5 ExCom leaders J. Sarff, M. Zarnstorff, S. Barish

Member Institution telephone emailSteve Sabbagh Columbia U. (609) 243-2645 [email protected] Sontag ORNL (865) 574-1179 [email protected] Soukhanovskii LLNL (609) 243-2064 [email protected]. Kotschenreuther U. Texas (512) 471-4367 [email protected] Stutman Johns Hopkins U.(410) 516-7929 [email protected] Majeski PPPL (609) 243-3112 [email protected] Menard PPPL (609) 243-2037 [email protected] Gorelenkov PPPL (609) 243-2552 [email protected] Hegna U. Wisconsin (608) 263-0810 [email protected] Peng ORNL (865) 368-0917 [email protected]

ReNeW ST Panel membership


ReNeW tasks and ST panel approach to them had many positive elements

• Communication Numerous conference calls, individual calls, small meetings,

two large ReNeW group meetings over a 6 month process

• Community outreach ST panel was prolific in extending drafts to the community;

posting to ReNeW web page

• Open process All were invited to participate

• Identification of cross-cutting research ST topic perhaps best situated


ReNeW theme chapter addresses ST research goals

• ReNeW ST panel largely adheres to TAP ITER-Era Goal

• Some important clarifications of emphasis, and alterations “properly informing the design of a demonstration fusion power plant

requires that research extend past the needs of an ST fusion nuclear science component testing facility”

“Important that research examine a high level of plasma control flexibility and performance beyond baseline ST-CTF design needs to minimize performance risk for ST-CTF”

ST Panel further suggests that during the ITER-era: “research aggressively pursue improvements to the ST concept that advance an ST-based DEMO”

Goal: “Establish the ST knowledge base to be ready to construct a low aspect-ratio fusion component testing facility that provides high heat flux, neutron flux, and duty factor needed to inform the design of a demonstration fusion power plant.”


ReNeW theme chapter refocuses TAP research needs

• Physics of twelve TAP report critical research issues retained Issues re-grouped and slightly redefined

• For more logical arrangement of topics; smaller number of areas (12 6)

• To better emphasize required research in all areas; avoid a perception that one can choose one or two areas out of 12

• To align with the proposed actions in Research Thrust 16

• Six topical research areas (focus on ST specific components) Plasma initiation and ramp-up (difficulties due to compact ST geometry) Plasma-material interface (uniquely high ST heat loads) Electron energy, ion scale transport (low A differences; EM turbulence)

Stability and steady-state control (unique low li, high N regime) Technological development (unique ST challenges, eg. magnets) Integration at high (self-consistent, low A physics: ST-CTF, Hybrid,

DEMO)


Sub-division of ST panel research requirements

• Further detail of research needs comprises the majority of the ST section See full document

• This talk: research needs will be addressed in the Thrust 16 actions


ST available means for research - general timeline

• Address research needs in existing international devices when possible

• Upgrades to existing devices to fill “near-term” research

• ST physics at long pulse/high field: Open question does this step require a new device? what capabilities would such a device need to have?

ITER era

NSTX NSTX-U

Lower , , Sustained plasma

MAST MAST-U

High Ip Startup, GrowthPegasus Peg-HIRF

ST-CTF, Hybrid

ST Physics Validation at Long-Pulse and

High-Field

LowRecycling

Alternative non-SolenoidalFormationCore fueling, Low-

LTX LTX-NBI

TF, Magnet DevelopIntegrated power supply

Fusion Nuclear Science

ITER era

NSTX NSTX-U

Lower , , Sustained plasma

MAST MAST-U

High Ip Startup, GrowthPegasus Peg-HIRF

ST-CTF, Hybrid

ST Physics Validation at Long-Pulse and

High-Field

LowRecycling

Alternative non-SolenoidalFormationCore fueling, Low-

LTX LTX-NBI

TF, Magnet DevelopIntegrated power supplyTF, Magnet DevelopIntegrated power supply

Fusion Nuclear Science

• Subject of extensive discussion at June meeting

• Guidance / decision to keep timeline general and qualitative


ST research requirements summarized in one page

• Gives some quantitative guidance on ST research next steps


ReNeW Thrust 16 suggests ST research actions to address research needs

• Thrust 16: “Develop the spherical torus to advance fusion nuclear science”

• Elements of thrust aim to: Leverage extensive knowledge-base of higher-A tokamak

Extend understanding to unique ST high- + low operation regime

Advance ST as reduced size and cost configuration for fusion


Proposed actions for Thrust 16: Develop the ST to advance fusion nuclear science

1. Exploit and understand magnetic turbulence, electromagnetic waves, and energetic particles for megampere plasma current formation and ramp-up.

2. Develop innovative magnetic geometries and first-wall solutions such as liquid metals to accommodate multi-megawatt per square meter heat loads.

3. Utilize upgraded facilities to increase plasma temperature and magnetic field to test the understanding of ST confinement and stability at fusion-relevant parameters.

4. Implement and understand active and passive control techniques to enable long-pulse disruption-free operation in plasmas with very broad current profiles.

5. Employ energetic particle beams, plasma waves, particle control, and core fueling techniques to maintain the current and control the plasma profiles.

6. Develop normally conducting radiation-tolerant magnets for low-A applications.

7. Extend the ST to near-burning plasma conditions in a new or further upgraded device.


(16.1) Develop plasma startup and ramp-up with no, or very low transformer flux

Non-solenoidal startup withHI and PF induction

• Develop reliable plasma initiation and growth schemes Establish science basis for helicity injection

• Current limiting mechanisms, resulting plasma characteristics

Implement EBW/ECH/ECCD coupling to startup plasma

• Demonstrate ramp-up to full current Effective coupling to RF/NBI

• Develop predictive modeling capability Validate transport-based CD modeling

against ST database

• Effects of fast-particle transport on NBCD

• Assess feasibility of central induction Mineral insulated conductor Retractable solenoid technology Modeling & engineering assessment of iron-core

• Demonstrate integrated test at ST-CTF relevant level of performance Similar transport regime, magnetic field, Ip, etc.


(16.2.1) Demonstrate and understand a viable plasma-material interface at high heat flux and low density

ST presents the opportunity to push to higher neutron wall loading

Common to other compact alternates (spheromak, FRC, RFP)

• Develop divertor and wall power reduction and handling solutions Innovative divertors, flux expansion, stochastic edge Divertor targets: liquid metals, moving “pebbles” as PFCs Develop edge transport and turbulence models for predictive capability

• Reduce divertor heat flux from 20-60 MW/m2 to <10 MW/m2

Transient loads to < 0.5 MJ/m2

Nuclear environment, long pulse

• Develop particle control for continuous, low density H-mode operation Cryo-pumping and/or liquid metals for impurity, helium, density control

Achieve steady-state ne/nG ~ 0.2-0.3

• Demonstrate integration with high-performance pedestal and core high- plasma in upgraded and scaled ST configurations

Compact geometry drives need for high power handling PFCs


(16.2.2) Deploy liquid metal, especially lithium, PFCs in the ST

• Validate models for the core, edge, and PMI, for arbitrary global recycling

Determine optimum global recycling coefficient for the ST

• Construct an “optimized”, reduced recycling liquid metal-walled DD ST

• Implement full liquid lithium wall in an ST, with NB core fueling

Does performance continuously improve in the ST as recycling is reduced?

• Implement a full liquid lithium divertor in an ST, with core fueling

Is a low recycling divertor sufficient?

Characterize PMI, transport in a low recycling ST

Electron confinement improves with reduced recycling - NSTX

150

100

50

00 100 200 300

WMHD<EFIT> (kJ)

We (

kJ)

Average std. dev.

DeuteriumBT = 0.45 TIp = 0.9 MAPNBI = 4.0 ± 0.2 MW

With LithiumWithout Lithium

+20%

+44%

Wel

ectr

on (k

J)

Total stored energy (WMHD, kJ)

ST provides rapid, cost-effective test of flowing liquid metal PFCs discussed in Thrust 11

Integration of PMI, confinement in the ST


(16.3) Understand electron and fast/thermal ion confinement in high , low ST plasmas

BT scaling of E in NSTX

Modeling of Alfven eigenmode - induced electron transport

• Does stronger BTT, scaling of E in present STs

lead to improved fusion performance at low-A? Study transport in upgraded (x2) and new (x4) STs

(near term focus: electrons) Measure high and low-k EM turbulence (n.t.

focus: ETG ‘streamers’+ -tearing islands) Develop predictive understanding (models+control)

• Will large population of super-Alfvenic energetic

particles affect heating/current drive in a ST reactor? Study EP transport over extended range of *

(n.t. focus: intermediate *) Study EP interaction with background plasma via AEs

(n.t. focus: ion heating/alpha channeling,

electron transport)

~BT0.91


(16.4) Understand stability and develop control of low li, high ST plasmas

• Achieve, understand global mode stability near low li current-driven kink

limit, over full range of N, with controlled broad pressure, V profiles

Steady-state current profiles; near-burning plasma conditions

• Explore/validate key stability science for low A at reduced collisionality

(~order of magnitude; near burning plasma levels), at increased field Extend capability to alter V and shear (e.g. expanded NBI, 3-D fields)

Understand stability at intermediate V; effects of V shear on NTMs

Characterize disruptions at low A and li

• Demonstrate/study high N with minimal disruptivity or transients using

multiple controls - compatible with a high neutron fluence environment Active and passive RWM and ELM control, q0 > 2 for NTM control

Operate continuous high N beyond CTF (N > 5.8), approaching ST-DEMO levels (N > 7), with flexible controls


(16.5) Employ beams, plasma waves, particle control, core fueling to maintain the current and control plasma profiles

• Reduce collisionality 1 - 2 orders of magnitude at high beta Toroidal field, current, heating power increase by ~ 2 - 4 Pumping to reduce recycling, density, collisionality

Assess impact on ST transport and stability

• 100% sustained non-inductive current-drive, at 50% bootstrap

Non-inductive ramp-up to MA, or multi-MA, level in the ST Control of core safety factor profile; optimize stability, confinement

• Mitigate steady-state, high heat and particle exhaust in the ST

• Increase plasma pulse length by 1 - 3 orders of magnitude Control fully-non-inductive ST for many current relaxation times Develop disruption avoidance, mitigation for integrated ST conditions

Sustained high performance with equilibrated first-wall conditions


(16.6) Develop normally-conducting radiation-tolerant magnets

• Design, evaluate single-turn centerpost magnet

Evaluate candidate multi-turn designs

Develop matching low impedance power supplies

• Construct, test candidate TF magnet + PS

High field (2-3T); ~10 sec. pulse

• Design, test radiation-tolerant OH solenoids

Backup for non-inductive approach

• Implement a testing program for radiation tolerance

DPA limits, tritium migration, joints, electrical, mechanical degradation

Thrust element can provide the core of a high field, moderate pulse-length ST

Rotor

LiquidMetal

ST-CTF ExampleST-CTF Example


(16.7) Extend ST performance to near-burning-plasma conditions

• Potential need for new (large) device(s) Device upgrades advance knowledge base for ST fusion nuclear science

applications• Factor of 5- 10 reduction in collisionality, increase in pulse duration by doubling of

the field, current, and heating and current drive power in upgraded ST facilities Depending on upgrade results and worldwide tokamak program, a new ST

device with increased performance and capabilities may be needed • Demonstrate and understand physics insufficiently addressed at that point

• Configuration and control flexibility to reduce risk before moving to goal device

• Actions Reduce collisionality to near-burning-plasma conditions to assess

• Current drive for ramp-up / sustainment at high current, core and pedestal transport, MHD stability, PMI solutions.

Operate a high-performance ST for very long pulse lengths with actuators relevant to a high neutron fluence environment to assess:

• Sustained plasma current drive and profile control, reliable disruption prediction, avoidance, and mitigation for integrated ST conditions

• Compatibility of sustained high-performance with high power and particle exhaust mitigation techniques, with equilibrated divertor and first-wall conditions and low hydrogenic retention.

Test high-field, long pulse magnets under conditions directly relevant to ST applications


Some suggestions to guide ST research forward in the next several years

• Quantification of ReNeW goals Advantage: ST milestone of an ST fusion nuclear science facility

(CTF) is arguably closer than “standard” tokamak goal of DEMO ReNeW process didn’t aim at detailed quantification of physics goals The STCC is suggesting quantification of physics goals as next step

• Creation/adoption of design for next-step device(s) Would have been useful many times during ReNeW

• New assessments of ST for fusion burn applications ARIES-ST study somewhat outdated Re-assessment of the relative cost of low vs. high aspect ratio device

• Increase ST constituency Entire process should be open, engaging innovative physics / ideas

review of st panel activity - us doe fusion research needs workshop

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