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NCSX Research Plan

Revisited

M.C. Zarnstorff

NCSX Physics Meeting

16 October 2003

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MotivationSeveral things have changed since the CDR

(when we last discussed the research plan as a group)

• Scope changes in MIE Project

– initial plasma and ebeam mapping at room temperature

– one NB line prepared

– fewer diagnostics installed

• Experience on a high-beta stellarator with current: W7AS

Better understanding of stellarator device operation

– importance of separating current from heating

– importance of heating

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NCSX Research Mission

Acquire 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 low-A current carrying stellarator

• Effect of 3D magnetic fields on disruptions

• Reduction of neoclassical transport by quasi-axisymmetric design.

• Confinement scaling; reduction of turbulent transport by flow shear control.

• Equilibrium islands and tearing-mode stabilization by design of magnetic shear.

• Compatibility between power and particle exhaust methods and good core performance in a compact stellarator.

• Energetic-ion instabilities stability in compact stellarators

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

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Planned as:

I. Initial operation - shake down systemsII. Field Line MappingIII. 1.5MW Initial Experiments - (1.5MW NBI, partial PFCs)IV. 3MW Heating - (3MW NBI, PFC liner)V. Confinement and High Beta - (~6 MW, 3rd gen. PFCs)VI. Long Pulse – (pumped divertor)

– Diagnostic upgrades throughout to match research goals– Phases IV – VI may last multiple years.

(equipment included in MIE project cost)

Research will Proceed in Phases

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• Initial Plasma– Engineering measurements and tests.

• e-Beam mapping– Characterize magnetic field for research.

• 1.5MW Initial Experiments– Global confinement scaling, with and without current; Density limits; Plasma evolution– Effect of low-order rational surfaces; vertical and current-driven mode stability– Initial plasma-wall interaction

• 3MW Heating– Control of shape during evolution– Moderate pressure tests of stability; effect of 3D fields on disruptions– Confinement scaling; local transport; rot. damping; effects of trim coils; enhanced conf.– Effect of plasma on surface quality; neoclassical tearing– Wall coatings; characterization of wall interaction; attempts to control influx

Fabrication Project I eB 1.5MW 3MW

Diagnostics 1.5 MW NBI > 1.2 T Partial PFCs Plasma Control

Diags 3 MW NBI 2 T Full PFCs 350C Bake

FY-04 FY-05 FY-06 FY-07 FY-08 FY-09

Overview of Initial Research Phases

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Checkout Phases

I. Initial Operation Heating Measurement Requirements

Initiate plasma; exercise coil set & supplies Ohmic Plasma current

Ip > 25 kA External Magnetic diagnostics

Checkout initial magnetic diagnostics 150 bake Plasma / wall imaging

Checkout vacuum diagnostics

Initial wall conditioning

II. Field Line Mapping

Map flux surfaces (cold & room temperature) Electron-beam mapping apparatus

Verify iota and QA

Verify coil-flexibility characteristics

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III. 1.5MW Initial Experiments

Topic Heating Measurement Requirements

Plasma control, plasma evolution control 1.5MW Plasma shape and position

Global confinement & scaling, effect of 3D shaping, effect of plasma current

NBI Plasma stored energy

Core Te, Ti

Density limit & mechanisms Partial PFCs

Ne profile

Total Prad

Vertical stability GDC Low (m,n) MHD (< 50kHz)

Current-driven kink stability Cryo-op Flux surface topology

Impurity sources &concentrations

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

Hydrogen recycling

PFC temperature

Effect of contact location on plasma plasma performance

Control of plasma contact location

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IV. Auxiliary HeatingTopic Upgrades Measurement Requirements

Plasma and shape control with NB heating, CD 3MW NBI Core Te, Ti, Prad profiles

Test of kink & ballooning stability at moderate beta PFC liner Tor. & pol. rotation profiles

Effect of shaping on MHD stability & disruptions 350 bake Iota profile

Initial study of Alfvenic modes with NB ions 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 neoclassical tearing using 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)

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V. 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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VI. Long PulseTopic 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

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Before operation (FY2004-07), need to do long-term development to prepare for operation (similar to NSTX)

• Design and begin fabrication of diagnostic upgrades for Phase III and IV.

• Stellarator Edge Modeling; Design and begin fabrication of PFCs for Phase III and IV

• Development of discharge control strategy, modeling.• Design of internal trim coils for Phase IV.• Design of low-power RF loading study, for Phase IV.

Research Preparation

Program Funding ($M) FY04 FY05 FY06 FY07

Research Preparation 0.8 1.7 2.1 9.9

Consistent with Acquisition Execution Plan