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NCSX Research

M.C. ZarnstorffPrinceton Plasma Physics Laboratory

NCSX PAC-7

13 July 2004

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Outline

• NCSX mission and research issues

• Expected research phases & topics

• Required capabilities and R&D

• Team Preparation

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NCSX Design Goals: Combine Best Features of Stellarators & Tokamaks

Use flexibility of 3D plasma shaping to combine best features of stellarators and tokamaks, synergistically, to advance our understanding of both

Stellarators: Externally-generated helical fields; steady-state compatible; robust stability, generally disruption free.

Tokamaks: Excellent confinement; low aspect ratio – affordable; self-generated bootstrap current and flows

Transport Optimization: Quasi-axisymmetry (Boozer,1983) Orbits & collisional transport depends on variation of |B|

within flux surface, not the vector components of B ! (Nührenberg) If |B| is symmetric in flux coordinates, get confined orbits

like tokamak

transport very similar to tokamaks, undamped rotation

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NCSX Research MissionAcquire the physics data needed to assess the attractiveness of

compact stellarators; advance understanding of 3D fusion science. (FESAC-99 Goal)

Understand…• Pressure limits and limiting mechanisms in a strongly shaped 3D plasma

• Effect of 3D magnetic fields on disruptions

• Reduction of neoclassical transport by quasi-symmetric design.

• Confinement scaling with quasi-symmetry; transport barrier formation and reduction of turbulent transport by flow shear control with 3D field.

• Equilibrium islands and tearing-modes, including effects of magnetic shear, seed perturbations and ion-kinetics

• Effect of stochasticity and 3D shaping on the SOL plasma and power and particle exhaust methods. Compatibility with good core confinement.

• Energetic-ion stability and confinement in 3D magnetic fields

Demonstrate…• Conditions for high- disruption-free operation• High pressure, good confinement, compatible with steady state

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NCSX Will Have Broad ImpactNCSX will make strong contributions to the scientific issues facing MFE:

(in terms of the Priorities Panel’s Topical Questions)

T1.How does magnetic structure impact confinement? What is the effect of 3D shaping on confinement? Shear? Is quasi-axisymmetry effective? How does it differ from axisymmetry?

T2.What limits maximum pressure? Can 3D shaping increase the limit? Is reversed shear beneficial? What are the limiting mechanisms with 3D fields and how can they be controlled?

T3.External control and self organization How does 3D shaping affect self-organization of profiles? How high a bootstrap fraction is controllable? Under what conditions are disruptions eliminated?

T4.Turbulent transport How is turbulent transport affected by 3D shaping? Does reversed shear help stabilize turbulence in 3D? How does electron transport depend on local shear and curvature?

T5 Electromagnetic fields and mass flow generation How does flow damping affect zonal flows and turbulence stabilization? Can transport barriers be accessed with quasi-symmetry?

T6.Magnetic field rearrange and dissipate How do shear, pressure, seed perturbations, and ion kinetics affect NTM onset and saturation,in detail?

T9.How to interface to room temperature surroundings? How is the SOL and interface affected by stochasticity and 3D shaping? Can the interface and exhaust be improved using 3D effects?

T11.Electromagnetic waves interacting with plasma How do RF waves interact with plasma in 3D?

T12.High-energy particles interacting with plasma How does 3D shaping affect energetic-ion instabilities? Can they be stabilized? Can orbit losses of energetic ions be controlled in 3D?

T15.How to heat, fuel, confine steady-state or pulsed plasmas? How can we control and fuel a 3D plasma? How much control is required? How can we diagnose the plasma state in 3D?

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NCSX Has Many Unique Physics PropertiesNeed to explore experimentally

• R/a=4.4

• Strong shaping ~1.8, ~1

• No need for external current drive

• Designed to have good flux surfaces

at high- and low-

• ‘Reversed shear’ for stability

• Passively stable at =4.1% to kink,

ballooning, vertical, Mercier,

neoclassical-tearing modes

• Stable for 6% by adjusting coil currents

• LHD & W7AS operate well above their linear instability threshold• What will be the limit for NCSX ?

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Normalized Minor Radius ( r / a )

Very good Quasi-Axisymmetry: Very Low effective ripple

New stellarator global scaling finds E ~ [eff(=2/3)]–0.4! NCSX eff(=2/3) ~ 0.002!

Low eff gives low flow-damping; control of Er , flow-shear stabilization; persistent zonal flows

Reversed shear should stabilize turbulent transport, via drift precession reversal Does NCSX confinement act like historical stellarators or tokamaks or ?? Local transport mechanisms?

-H.Yamada, J.Harris et al EPS 2004

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HSX Quasi-helical symmetry: Less flow damping, Goes faster for Less Drive

• Flow driven by biased probe• Quasi-symmetry can be spoiled by powering auxiliary coils (Mirror mode)

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Variations from coil currents

NCSX will be a Flexible Experiment• Wide range of 3D shaping flexibility, for control

of physics properties• 9 independent field coil currents • B 2 T• Separate trim coils for control of resonant

islands and edge shape• Solenoid for control of toroidal current

• NBI power up to 6MW (1.5MW initial)

• ICRF power up to 6MW• ECH power up to 3MW

• Robust divertor configuration, using flux expansion in elongated cross-section

• Full set of diagnostics planned

Shear scan

increased & reduced

iota

eff

(%

)

• ref•

eff scan

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First Plasma, CD4

FY-06 FY-07 FY-08 FY-09

1. Initial operation - warm field map, first plasma

2. Magnetic Configuration Mapping (cryogenic)

3. 1.5MW Initial Experiments

4. 3MW Heating

5. Confinement and High Beta - (~6 MW)

6. Long Pulse – (pumped divertor)

– Diagnostic & facility upgrades throughout to match research goals– Phases 3 - 5 may last multiple years.– Expect 18 run weeks in FY09

NCSX Research will proceed in Phases

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Research Goals of the Initial Phases

2. Magnetic Configuration Mapping – Document vacuum flux surface characteristics– Document control of vacuum field characteristics using coil current

3. 1.5MW Initial Experiments– Explore and establish plasma operating space– Characterize low-power confinement, stability, and operating limits

4. 3MW Heating– Characterize confinement and stability at moderate power, and their dependence on plasma

3D shape– Test plasma stability at moderate , dependence on 3D shape– Investigate local transport and effects of quasi-symmetry– Characterize SOL properties for different 3D geometries, prepare for the first divertor design.– Explore ability to generate transport barriers and enhanced confinement regimes.

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Initial Phases(1) Initial Testing (pre-CD4) Capabilities Measurement Requirements

Map flux surfaces (room temperature)

- Assess alignment of coils

Electron-beam mapping apparatus

First plasma; exercise coil set & supplies

- Ip > 25 kA (cryogenic)

Ohmic Plasma current

External Magnetic diagnostics

Checkout initial magnetic diagnostics 150 bake Plasma / wall imaging

Checkout vacuum diagnostics

Initial wall conditioning

(2) Magnetic Configuration Mapping

Map flux surfaces (cryogenic) Electron-beam mapping apparatus

Verify coil-flexibility characteristics

Verify iota and QA

Test trim coils

[ Indicates high priority ]

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Research Areas for

(3) 1.5MW Initial ExperimentsTopic Heating Measurement Requirements

Plasma control, plasma evolution control B=1.2 T Plasma shape and position

1.5MW NBI

Global confinement & scaling, effect of 3D shaping

Effect of plasma current

Partial PFCs Plasma stored energy

Core Te, Ti

Density limit & mechanisms GDC Ne profile

Total Prad

Impurity sources &concentrations

Current-driven kink stability Low (m,n) MHD (< 50kHz)

Vertical stability

Alfvenic mode stability

Effect of low-order rational surfaces on flux-surface topology

Effect of shear on NTM stability

Flux surface topology

Effect of contact location on plasma plasma performance Control of plasma contact location

PFC temperature

Hydrogen recycling

[ Indicates high priority ]

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Research Areas for

(4) 3MW HeatingTopic Capabilities Measurement Req.

Plasma and shape control, diagnostic validation B = 2T Core Te, Ti, Prad profiles

Test of kink & ballooning stability at moderate beta 3MW NBI Tor. & pol. rotation profiles

Effect of shaping on MHD stability & disruptions Full liner Iota profile

Initial study of Alfvenic modes with NB ions 350 bake Er profile

Confinement scaling Fast ion losses

Local transport & perturbative transport measurements Ion energy distribution

Effect of quasi-symmetry on confinement and transport First wall surf. temperature

Density limits and control with auxiliary heating High frequency MHD

Use of trim coils to minimize rotation damping & islands Edge neutral pressure

Blip meas. of fast ion confinement and slowing down SOL temp. & density

Initial attempts to access enhanced confinement Zeff, Impurity profiles

Pressure effects on surface quality Flux surface structure

Controlled study of NTMs using shear variation & trim coils

Wall coatings with aux. Heating

Plasma edge and exhaust characterization, w/ aux. heating

Attempts to control wall neutral influx

Wall biasing effects on edge and confinement

Low power RF loading and coupling studies (possible)[ Indicates high priority ]

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Diagnostic Upgrades Provide Needed Measurements

Upgrading the diagnostics will continue throughout Research Program

• Initial (MIE) diagnostics:– Ex-vessel magnetic diagnostics (trapped in structure)– Diagnostics needed for initial research phases:

Rogowskii loopFast Camerae-beam mapping apparatus

– Design integration for all planned diagnostics included

• See B. Stratton’s talk for diagnostics development plan

• Details of development plan (and research plan) will evolve– as NCSX research team assembles– as collaboration opportunities are developed

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Equipment Upgrades are Also NecessaryMajor elements Phase• Plasma facing components and divertors

– partial liner 3 Oct. 08– full liner, with some plates 4 Aug. 09– divertor 5 Aug. 10

• Heating systems– second NB-line 4 Aug. 09– RF or further NBI 5 Aug. 10

• Power supplies– all 9 field-coil circuits + trim coils 3 Oct. 08– full field 4 Aug. 09

• Data acquisition and control– acquisition upgrades along with diagnostics– pre-programmed WFs 3 Oct. 08– initial feedback control 4 Aug. 09

– Priorities will be set in response to research results

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Long-term developments preparing for researchOngoing:• Assembly of NCSX Research Team• Physics design and requirements for diagnostics (Stratton, Lazarus)• Edge Modeling; Physics design and requirements for PFCs

(Mioduszewski)• Preparation for field mapping (e-beam) (Fredrickson)

To start later:• Equilibrium reconstruction analysis• Development of feedback control strategies• Development of comprehensive analysis capability (similar to TRANSP).• Pre-conceptual design of RF test antenna.

NCSX Research Preparation

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NCSX will be operated as a National & International Collaboration, similar to NSTX

• Integrated team, including members from many institutions

• Open participation by members, open access to data.

Will hold Research Forums in FY2005/06 to

• Identify groups interested in developing needed diagnostics

• Nucleate the research team

• Form initial working groups (4 – 6)

• Develop prioritized research plans– Opportunities for collaboration

• Plan required resources

• Diagnostics, equipment upgrades, researchers

Preparatory activities (early FY05)

• Work to attract best people to participate

• Ensure participation of adequate expertise to achieve goals

Preparation of NCSX Research Team

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DOE funding of collaborations on NCSX will be similar to NSTX

• Independently reviewed proposals

• 3-year proposal cycle

• Input via Program Priorities letter, identifying– Research topics expected to have high priority, and– Topics thought to be most appropriate for new collaboration

e.g. not duplicating existing hardware or ongoing work– However, all topics will be open for collaboration proposals

Expect call for first round of diagnostic proposals in FY06

• For funding starting in FY06/07

• Additional calls for diagnostic and participation proposals in FY07 and FY08

Participation by Reviewed Proposals

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Conclusions• NCSX is an exciting opportunity for unique fusion-science research.

Have developed outline plans for

– Research program

– Required diagnostic and equipment upgrades

– Preparatory research

– Preparation of the research team

• Ask your advice on

– Research priorities

– Pace of research and upgrades

– Preparatory activities and Research Forum

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4. Confinement and High BetaTopic Upgrade Measurement Requirements

Stability tests at >~ 4% 6 MW Core fluctuations & turbulence

Detailed study of limit scaling total Core helium density

Detailed studies of beta limiting mechanisms Divertor Divertor Radiated power profile

Disruption-free operating region at high beta Divertor recycling

Active mapping of Alfvenic mode stability (with antenna) Divertor target Te, ne profiles

Enhanced Conf.: H-mode; Hot ion regimes; RI mode; pellets

Divertor target temperature

Scaling of local transport and confinement

Turbulence studies Divertor impurity concentration

Scaling of thresholds for enhanced confinement

ICRF wave propagation, damping, and heating (possible)

Perturbative RF measurements of transport (possible)

Divertor operation optimized for power handling and neutral control

Trace helium exhaust and confinement

Scaling of power to divertor

Control of high beta plasmas and their evolution

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5. Long Pulse

Topic Upgrades Measurement Requirements

Long pulse plasma evolution control Long pulse More detailed divertor profiles

Equilibration of current profile Divertor pumping

Beta limits with ~ equilibrated profiles 12 MW?

Edge studies with 3rd generation PFC design, pumping

Long-pulse power and particle exhaust handling with divertor pumping

Compatibility of high confinement, high beta, and divertor operation