1

Boundary Physics Five Year Plan

R. Maingi, H. Kugel* and the NSTX Team

Oak Ridge National Laboratory

* Princeton Plasma Physics Laboratory

Five Year Planning WorkshopPrinceton Plasma Physics Laboratory

12-13 Dec. 2002

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Boundary physics activities have enabling technology goals and science goals

• Enabling technology - tailor edge plasma to optimize discharges– evaluate power handling needs and solutions– assess fueling and particle pumping needs– develop and evaluate wall conditioning techniques

• Science goals– characterize edge power and particle transport regimes

• parallel vs. cross-field• do conventional aspect ratio models fit?

– understand effect of ST features on boundary physics, e.g.• large in/out Bt ratio

– pedestal asymmetry– target heat flux profiles

• large SOL mirror ratio and short connection length

3

Boundary goals are linked to IPPA goals

• 5-Year Objective: Make preliminary determination of the attractiveness of the spherical torus (ST), by assessing high-T stability, confinement, self-consistent high bootstrap operation, and acceptable divertor heat flux, for pulse lengths much greater than energy confinement times.

• Implementing Approach 3.2.1.5:

– Disperse Edge Heat Flux at Acceptable Levels

– Study ST specific effects

• high mirror ratio

• high flux expansion

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Boundary physics talk outline

• Fuel and impurity particle control– sources and sinks

– wall conditioning techniques

• Power handling and mitigation– heat flux scaling and power balance

– steady heat flux mitigation and off-normal event study

• H-mode, pedestal and ELM physics– profile shapes, gradients and widths

– ELM characterization and control

• Edge, SOL, divertor and wall conditioning physics– nature of cross-field transport and “classical” parallel transport

– ST kinetic effects

5

Fuel and impurity particle control issues

• Center stack gas injection enabled routine H-mode access– higher due to lower pressure peaking factor

– long pulse due to low volt-second consumption rate, owing to high bootstrap fraction from edge pressure gradient

• Limited control leads to uncontrolled density rise

• Location of gas fueling source affects H-mode access

• Goal: make density independent of time

• Staged plan– improve control of sources, aiming toward higher efficiency

– improve control of sinks via wall conditioning and active pumping

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Uncontrolled (non-disruptive) density rise in long pulse H-modes

Ip [MA]

PNBI/10 [MW]

ne [1019 m-3]

D [au]

WMHD*10 [MJ]

H98pby2

0

2

4

6

8

10

20 40 60 80 100 120 140 160Radius [cm]

nem sec

sec

sec

sec

•Inner and outer ‘pedestal’ ne show similar trends•Profile requires ~ 300-500 msec to flatten out

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• Improved source control– more poloidal locations for gas

(FY03-04)

– supersonic gas nozzle (FY03-04)

– Lithium pellets (FY03)

– D2 pellet injection (FY05)

– CT injection? (FY07 )

• New diagnostics– D cameras for core fueling

– pellet diagnostics

– more edge Thomson channels

– divertor Langmuir probe upgrade

Fuel and impurity source control plan

?

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Fuel and impurity sink control plan

• Improved sink (density) control– improved boronization (FY03)

• high temp. boronization• morning boronization• between shots TMB

– lithium pellets (FY03)– in-vessel cryopumps (FY06,FY04 )– lithium module(FY08, FY06 )

• New diagnostics– D cameras for core fueling

– divertor SPRED– upgraded Langmuir probe array– fast pressure gauges

?

?

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Power handling and mitigation background

• ST’s can have high heat flux because of high Pheat/R

– NSTX: PNBI ~ 7 MW, PRF ~ 6 MW, Pheat/R ~ 15.3

• Highest qpeak in NSTX ~ 10 MW/m2

– Tdiv ~ 300 0C in LSN

– extrapolates to ~ 3 sec. pulse length limit (Tdiv ~ 1200 0C)

• For Te < 2 keV, current diffusion time << 3 sec.

– If Te increases, current diffusion time could approach few seconds

• Goal: assess power balance and survey heat flux in many scenarios (vs. shape, input parameters, etc.)

• Staged plan– quasi-steady power balance over next few years

– transient events in future

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Peak heat flux increased with NBI power in lower-single null configuration

• Good power accountability:Pdivin+out ~ 70% of PSOL

0

2

4

6

8

10

12

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Heat Flux [MW/m 2]

Target Radius [m]

InboardDivertor

OutboardDivertor

In/Out Gap

4.9 MW

4.1 MW

#109063: 4.9 NBI#109053: 4.1 MW#109034: 2.0 MW

2 MW

0

1

2

3

4

5

6

7

8

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Heat Flux [MW/m 2]

Target Radius [m]

InboardDivertorTarget

OutboardDivertorTarget

In/Out Gap

4.1 MW LSN ( L~0.40)δ

. (MW DNDL~.)δ

#: .DND@ s#5: .LSN@ s

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Peak heat flux increased decreased in double-null0

2

4

6

8

10

12

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Heat Flux [MW/m 2]

Target Radius [m]

InboardDivertor

OutboardDivertor

In/Out Gap

4.9 MW

4.1 MW

#109063: 4.9 NBI#109053: 4.1 MW#109034: 2.0 MW

2 MW

0

1

2

3

4

5

6

7

8

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Heat Flux [MW/m 2]

Target Radius [m]

InboardDivertorTarget

OutboardDivertorTarget

In/Out Gap

4.1 MW LSN ( L~0.40)δ

. (MW DNDL~.)δ

#: .DND@ s#5: .LSN@ s

(outer strike point)

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Power handling and mitigation plan

• Experimental plan– Power balance studies (FY02+)

• divertor heat flux vs core and divertor radiation

• parallel vs perpendicular transport

– Detailed comparison between single-nulls and double-nulls (FY03+)

– Heat flux reduction studies (FY03+)

– Impact of fast events, e.g. ELMs, IREs, and disruptions (FY05)

• New Diagnostics– Cross-calibrate core bolometry with platinum-foils (FY03)

– Add and optimize divertor bolometer channels (FY03-04)

– Add two slow and one fast infrared cameras (FY04, FY05, FY07)

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H-mode, pedestal and ELM physics background

• L-H transition physics (common with transport group)– PLH higher than scalings - trapped particles, poloidal damping?

– Ip and maybe Bt dependence of PLH appears different

– role of E X B shear?

• Pedestal: profile shapes, gradients and widths– density pedestal high and in/out asymmetry

– pedestal Te < 400 eV, below predictions

• ELMs– Tokamak-like ELMs in double-null

– Usually ELM-free or very large events in single-null

– Fueling affects ELM type strongly

• Plan: characterization studies over next few years and optimization studies over longer term

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0

2

4

6

8

10

20 40 60 80 100 120 140 160

ne [1013 cm-3]

Radius [cm]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

20 40 60 80 100 120 140 160Radius (cm)

Te [keV]0.710 sec

0.460 sec

0.260 sec

0.227 sec

sec

0.260 sec

0.710 sec

High ne and relatively low Te pedestal observed

• ne profile hollow after transition and fills in 300-500 ms

• Moderate in/out ne asymmetry usually observed

• Te profile flattens initially and peaks later in time

0.460 sec

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135 Hz

LSN

LSN

DN

W/W0: 5-25%

W/W0: 1-4%

7830

108015

0.0 0.2 0.4 0.6Time (s)

2

1

01

1

0

0

D (

arb.

)D (

arb.

)D (

arb.

)

ELM behavior depends on operating conditions

Higher Fueling

Lower Fueling

Bush (ORNL)

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H-mode, pedestal and ELM physics plan

• Continue L-H mode transition parametric studies

• Pedestal studies– height, width, and maximum gradient scalings

– role of fueling profile in setting density width

• ELM studies– role of shape and fueling

– conductive vs. convective losses

– optimization for density and impurity control

• New Diagnostics– extra edge Thomson channels

– improved time resolution in CHERs

– edge Helium line ratio being considered

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Edge, SOL, divertor and wall conditioning physics background

• Classical divertor heat flow regimes applicable?– high divertor Te, sheath-limited heat flow

– low divertor Te, conduction-limited heat flow

– detachment

• Impact of unique ST features– high SOL mirror ratio, short connection length, high flux expansion

– in/out Bt ratio and target; E X B flows

• Cross-field transport: diffusive vs. intermittent– intermittent transport appears strong in both L and H-modes

– any cross-correlation with ELMs?

• Wall conditioning technique assessment

• Plan: near-term focus on nature of cross-field transport, and longer term on ST kinetic effects

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=I DL >

• Density is intermittent• Rate of bursts is 2E3• Poloidal field is much less intermittent• Instantaneous particle flux ~1019 m-2s-1

DL >

H-mode#109052

L-mode#109033

Intermittent behavior observed in L and H-mode

Boedo, UCSD

Time [sec]

ne [cm-3] ne [cm-3]

Time [sec]

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#105710

GPIview

Gas Puff Imaging shows a narrower , more quiescent emission pattern in H-mode than L-mode

Radial vs. poloidal imaging

Gas manifold

Side-viewing re-entrant window

• Image distributed gas puff of Helium (or Deuterium)

• View looks directly at field lines

Zweben (PPPL), Maqueda (LANL)

0.230 sec (L)0.215 sec (H)

12 cm

core

SOL

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UEDGE modeling needed to estimate transport rates

D = 1 m2/sec, = 3 m2/s

Porter (LLNL)

• LLNL using diffusive cross-field transport

• UCSD examining convective cross-field transport

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Edge, SOL, and divertor physics plan

• Do classic divertor heat flow models apply? (FY03-04)– need UEDGE simulations for interpretation

• Continue GPI studies (FY03+)– simulation and coupling with theory crucial (e.g. BOUT, DEGAS-2)

• Cross-field transport and SOL scaling with reciprocating probe (FY03+)

• Experiments to test ST kinetic effects (FY05+)

• New Diagnostics– divertor Langmuir probe array with improved spatial resolution (FY04)– divertor Thomson scattering (FY06)– X-point reciprocating probe (FY06)– energy extract analyzer (FY06)– imaging spectrometer (FY07)

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Wall conditioning physics plan

• Wall conditioning technique assessment (FY03+)– how does boronization change wall physics?

– how do those changes improve the core plasma?

• New Diagnostics– quartz crystal deposition monitors for real time flux

– divertor SPRED for impurities

– divertor materials probes (like DiMES on DIII-D)

– plus all other divertor diagnostics...

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Power Handling

FY02 03 04 05 06 07 08 0921 weeks/year

IPPA: 5 year

IPPA: 10 yr

Fast CHERs

Power balance, heat flux scaling

Divertor swept Langmuir <------- Upgrade ---------------------->probes

X-point Reciprocating probe

Helium Line ratio?

MPTS upgrades

ST Edge Physics

Improved TMB

Divertor SPRED

Particle Controland Fueling

Li/B pellets

Cryopumps and baffles

Liquid li

module?Fast pressure

gauges

D camerasMulti-pulse CT

injector?Fueling studies

Supersonic gas

injectors

D pellets

Divertor bolometer, upgrade

Add’l IR camera

Fast IR cameraPFC

upgrade?

Energy Extract Analyzer

DiMES probe

Imaging Spectrometer

Add’l IR camera

Pedestal and ELM characterization Edge Optimization Studies

Heat flux reduction scenarios

Off-normal event studies

Cryo-pumps?

MPTS divertor chans

Particle balance

Long pulse with density control

Long pulse with power handling

Comprehensive edge physics studies