# Presentation: 170354

## Boundary Physics Five Year Plan 

**Boundary Physics Five Year Plan**

- R. Maingi, H. Kugel* and the NSTX Team
- Oak Ridge National Laboratory
- * Princeton Plasma Physics Laboratory

**Five Year Planning Workshop**
**Princeton Plasma Physics Laboratory**
**12-13 Dec. 2002**

## 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 B**t** ratio*
*pedestal asymmetry*
*target heat flux profiles*
*large SOL mirror ratio and short connection length*

## 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

## 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

## Fuel and impurity particle control background

- 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

## 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

****

- nem

- sec

- sec

- sec

- sec

****

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

## Density rise in long pulse H-modes may be reduced with improved gas injector control 

- Ip [MA]

- PNBI/10 [MW]

- ne [1019 m-3]

- D [au]

- WMHD*10 [MJ]

- H98pby2

****

- Center stack injector has a long tube and pumpout time
- “Shoulder” injector should have better control (FY03)

## 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

- 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**

- ?

## Fuel and impurity sink control plan

**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
- nC(r) f/CHERs, Zeff f/MPTS (FY03)
- D cameras for core fueling
- divertor SPRED
- upgraded Langmuir probe array
- fast pressure gauges

- ?

- ?

## Preliminary neutral transport studies show possible plenum pressure sensitivity to strike point 

- Same model and ne, Te, Pe profiles for DIII-D as in Maingi, et. al., *Nucl. Fusion* **39** (1999) 1190
- Ion current = 5kA, used for normalization
- Leakage conductance = 20 m^3/sec

**Menon, ORNL**

## 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

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

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

## Peak heat flux increased decreased in double-null

**(outer strike point)**

## 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)

## 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

## High ne and relatively low Te pedestal observed

**High n****e**** and relatively low T****e ****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

## ELM behavior depends on operating conditions 

- 135 Hz

- LSN

- LSN

- DN

- W/W0: 5-25%

- W/W0: 1-4%

- 

- 7830

- 108015

- 0.0

- 0.2

- 0.4

- 0.6

- Time (s)

- 2

- 1

- 0

- 1

- 1

- 0

- 0

- D (arb.)

- D (arb.)

- D (arb.)

**ELM behavior depends on operating conditions**** **

- Higher
- Fueling

- Lower
- Fueling

**Bush (ORNL)**

## 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

## 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

## Intermittent behavior observed in L and H-mode

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

**H-mode**
**#109052**

**L-mode**
**#109033**

**Intermittent behavior observed in L and H-mode**

**Boedo, UCSD**

**Time [sec]**

**n****e**** [cm****-3****]**

**n****e**** [cm****-3****]**

**Time [sec]**

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

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

- Image distributed gas puff of Helium (or Deuterium)
- View looks directly at field lines

**Zweben (PPPL), Maqueda (LANL)**

**core**

**SOL**

## 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

## Progress made in 2-D modeling of L-modes

**Pigarov (UCSD)**

- UEDGE with convective cross-field transport model
- Able to match L-mode well
- Concluded that main chamber recycling plays role in NSTX

## 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)

## 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...

## Power Handling

*Power Handling*

***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 Control*
*and Fueling *

- Li/B
- pellets

- Cryopumps and baffles

- Liquid
- li
- module?

- Fast pressure gauges

- D cameras

- Multi-pulse CT
- injector?

- Fueling studies

- Supersonic gas injectors

- D pellets

-  Divertor bolometer, upgrade

- Add’l IR camera

- Fast IR camera

- PFC
- 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

## High-Field Side Gas Injector Fueling Allows Early L-H Transition and Longer H-mode Duration

**High-Field Side Gas Injector Fueling Allows Early L-H Transition and Longer H-mode Duration**