# Presentation: 321601

## The 2001 NSTX Research Program and Progress

- E.J. Synakowski
- for the NSTX Research Team
- Presentation to the
- NSTX Program Advisory Committee
- Princeton Plasma Physics Laboratory
- October 4, 2001

*Lodestar *
*NYU *
*Princeton Sci. Instruments*
*UC Irvine*
*UKAEA*
*Tokyo U *
*Kyushu Tokai U *
*Himeji Inst. Science Tech Hiroshima*
*Niigata U*
*Tsukuba U*
*Ioffe Inst*
*Triniti (RF)*
*KBSI (Korea)*

## NSTX research is uncovering high beta, low aspect ratio physics central to the ST mission 

- In this talk: discussion of run plan, execution, and topical science, framed by the milestones we are pursuing
- Outline
- Overview of goals, plan, and usage
- Core transport
- HHFW
- MHD
- Boundary physics
- Non-inductive startup
- Summary

## Increase in range of operating scenarios enabled topical research

- Reproducible operating scenarios underly all of the research
- 25% T achieved
- Routine and effective HHFW heating
- Topical studies
**MHD**: characterizing -limiting and pulse-length-limiting modes
**Transport** with NBI and HHFW, core and edge
**HHFW**: heating, wave-particle and initial CD studies
**CHI**: MHD activity generated that is needed for flux closure
**Boundary**: Heat fluxes. Wall prep tools
- Cross-discipline studies
- Beam-induced MHD and heating
- H mode access requirements, expanded operating space

- Ip

- T

- p = 0.6

## NSTX milestones and decision points are derived from its proof-of-principle mission

- Milestones are checkpoints towards this assessment
- FY ‘01 Milestones:
- Measure confinement properties with auxiliary heating
- Assess HHFW heating; achieve 6 MW
- Progress reports on FY ‘02 Milestones:
- MHD: Global stability without external control
- Transport: Role of high beta and flow shear on confinement
- CHI, EBW: Innovative startup techniques
- HHFW CD physics & effectiveness
- Upcoming decision points:
- MHD
- FY ‘02: Mode stabilization: scientific assessment
- FY ‘03: Mode stabilization: technical assessment
- Advanced particle pumping/fueling, FY ‘03

*Recall IPPA 2.1: Assess the attractiveness of the ST concept*

## We planned an emphasis on topical research, with some time for enabling activity

- Division of experimental time, FY ‘01.
- 	_ET Group, Leaders__	__	__	_                  _Plan_                            _Actual_
- MHD (Sabbagh, Menard)				15%		21%
- Transport and Turbulence (Kaye, LeBlanc)			15%		17%
- HHFW (Wilson, Swain)				13%		24%
- CHI (Raman, Gates)				13%		8%
- Boundary Physics (Maingi, Skinner): heat flux		6%		2%
- 	_Program Enabling/cross-cutting_
- e.g. 1st NBI, control commissioning, boron, calibration 		18%		28%
- _	__Scientific Contingency_				20%		-----
- Highlights	_	_
- HHFW: success and broad impact resulted in giving significant contingency time
- Program enabling/cross cutting work also received additional time
- •	CHI: ~ 2x more days attempted; system setbacks (TF water leak, gas programming)
- •	Boundary: IR camera repair delayed start

## Activities supporting a broad portion of the program are high priority 

- NBI long-pulse work
- Startup optimization
- Diagnostic development & cross-checking
- Ti(R,t), V(R,t): Background array installation and calibration for CHERS.
- Te from 3 different techniques
- H mode search: dedicated run days to explore operating space
- HHFW & early heating in the pulse
- Modify the current profile; use as a control tool
- Boronization
- TMB established; plasma boronization being developed

## Diagnostics are maturing and being confirmed

- Ti, V: development of direct background measurement
- Required for time-dependent measurements
- Required cross-calibrations performed; analysis techniques being developed

- Observed

- Background

*LeBlanc, R. Bell; Bitter, Hill*

*R. Bell*

- Fitted line

## Diagnostics are maturing and are being confirmed (2)

- TS high throughput, small error bars. ne consistent with reflectometry
- Ti: CHERS, NPA consistent with each other

## Outline 

- Overview of plan, usage, and goals
- Core transport
- NBI heating,E scaling, and power balance; puzzles
- Possible role of fast-ion MHD
- Perturbative particle transport
- Microstability analysis
- HHFW
- MHD
- Boundary physics
- Non-inductive startup
- Summary

## Profile measurements give first indication that favorable confinement with NBI may be due to ion channel

- Broad Ti profile (compared to Te), even though ~2/3 of beam energy expected to go to electrons
- Large Ti - Te seen routinely
- High V in core & edge

*B. LeBlanc, R. Bell*

- T(EFIT) ~ 20%

## Power balance analysis reveals puzzles

*S. Kaye*

- With NBI: apparent anomalous source of heat to ions, or a heat pinch
- New heating physics?
- Small A changes in basics?
- Requires vigilence in diagnostic calibration

## Astrophysics and observed MHD may hold one clue to the power balance puzzle

*Fredrickson (PRL 2001)*

- Time (sec)

- 103932/103936

- TF

- TF

- neL (1015 cm2)

- Frequency (MHz)

- ne

- Tesla

- •  Being investigated:
-     Compressional
-     Alfven
-     Eigenmodes
- •  Modes excited
-     by fast ions;
-     waves transfer
-     energy to
-     thermal ions

## Beam-driven Compressional Alfven Waves may heat ions on NSTX

- Simulations of compressional Alfven modes give stochastic ion heating.
- e.g.-- with 20 modes centered at half Alfven frequency
- Possible relevance to interpretation of ion-heating on NSTX

*D. Gates, N. Gorelenkov, R. White*
*(PRL, 2001)*

- (keV/s)

## Impurity transport rates are small in the core

- After puff, almost no neon penetrates the core until MHD event near 260 ms
- Modelling suggests core diffusivity < 1 m2/s, rivaling neoclassical theory
- Low ion particle transport consistent with low ion thermal transport

*Stutman, JHU*

*Signals from difference of*
*similar plasmas w/ and w/o neon*

## Theory: short wavelength modes may dominate transport; long wavelength modes may be suppressed 

- Theory: short wavelength modes may dominate transport; long wavelength modes may be suppressed

- Long wavelengths: growth rate lower than **E**x**B** shear rate
- Large associated with ion thermal transport
- Short wavelengths: growth rates large
- Responsible for electron thermal transport?
- Non-linear simulations begun

**=0.31**

*C. Bourdelle (PPPL), W. Dorland (U. MD)*

- ExB s

- Growth rates,

- (Short 

- (Long 

## Overview of plan, usage, and goals

Transport

HHFW
Heating results
Source calculations & electron thermal transport
_x001d_Fast ion interactions and early current drive studies

MHD

Boundary physics

Non-inductive startup

Summary

- Transport
- HHFW
- Heating results
- Source calculations & electron thermal transport
- _x001d_Fast ion interactions and early current drive studies
- MHD
- Boundary physics
- Non-inductive startup
- Summary

- Outline

## HFFW heating observed in a wide variety of conditions

- Pe

- Pe

- Fast phasing nearly as good as slow

- Pe

- Fast
- phasing

- Slow
- phasing

- Modulated rf used to measure deposition profile
- Complicated by electron energy transport physics

## Strong central peaking of Te observed in some cases

- Strong central peaking of Te observed in some cases

- Te

- ne

- Pressure

## Power balance analysis reveals that reduced electron transport correlated with high Te

- Core e drops as high Te develops
- Steep gradients due to transport changes, not source
- Conductivity still very high!
- Heating source from HPRT ray tracing (Rosenberg)

*LeBlanc*

- 105830a03

- Preliminary

- 0.1

- 0.3

- 0.5

- 0.7

- 0.9

- r/a

- 1

- 10

- 100

- 1000

- m2/s

- Conduct a theory experiment: vary Ti/Te, keeping other profiles constant

- ETG

- ITG

- Turbulence theory suggests testable trend for transport experiments

*C. Bourdelle*

- Shearing rate

- Growth rates

- measured

- Theory indicates:
- high Ti/Te stabilizes ion modes
- high Te/Ti *stabilizes* *electron modes*
- _	_*Do we see signatures of this in measured confinement trends?*

## Recent data is the foundation of important tests ofwave-particle interactions theory

-  Tail saturates in time during HHFW

-  HHFW turns off at t=200ms
-  NBI Source A on throughout

- Recent data is the foundation of important tests ofwave-particle interactions theory

*Rosenberg, Medley, Menard*

- HPRT code: 50% of rf power absorbed on beam ions
- May explain reduction in effective electron heating when NBI is combined with early HHFW

## HHFW-driven H modes found

- LSN
- Lower current (350 - 500 kA)
- He and D
- ELMy, ELM-free
- p = 1 observed
- Large bootstrap?
- Large dip in surface voltage

- N

*Starting scenario for future CD work?*

## High power phasing tests for current drive begun

- Co, counter, balanced fast phasing investigated (7 m-1)
- Similar heating, reproducible matching for all phasings
- Not obvious differences in loop voltage evolution
- Difficult to obtain a long steady shot: H mode target a possibility
- Need MSE
- Closed loop phase feedback from antenna started
- Two transmitters in vacuum
- Fast particle interactions studies key part of CD assessment

## Overview of plan, usage, and goals

Transport

HHFW

MHD: beta-limiting
Range of operations
Towards assessing physics of RWM’s
Locked mode coils/error field detection 
NTM’s
Current driven kinks
Boundary physics

Non-inductive startup

Summary

- Transport
- HHFW
- MHD: beta-limiting
- Range of operations
- Towards assessing physics of RWM’s
- Locked mode coils/error field detection
- NTM’s
- Current driven kinks
- Boundary physics
- Non-inductive startup
- Summary

- Outline

## Profile variations have been performed to map out operational space for stability studies

- Maximum N increases, then saturates with increased current profile peaking
- Fast beta collapses observed at all values of li
- High pressure peaking
- Beta saturation coincident with tearing activity at higher N, p ~ 0.45

- N = 4*l**i*

## Taking a step towards an MHD control strategy: identifying the Resistive Wall Mode

- Dedicated experiments; continued active discussion
- Goals
- Operate at or above the ideal no-wall beta limit: candidate plasmas have ideal kink-driven collapses
- Critical rotation frequency test: measure the plasma rotation leading up to the instability
- Plasma/wall coupling test: Vary the outer gap: determine variation of mode stability
- Techniques
- Operate with *l**i* ~ 0.6, N > 3
- Operate clear of sawteeth and low n islands

*Sabbagh, Columbia U.*

## USXR data shows a mode structure resembling a global kink in RWM candidate shots

- RWM Candidate
- Fast collapse
- No core islands  and no 1/1 mode before reconnection event (RE)
- More likely a kink mode onset

- D. Stutman

- 1/1

*midplane*

*down*

- RE

*up*

- t (s)

- t (s)

- Plasma with island activity
- Reconnection event leads to 1/1 mode at 237 ms
- Less likely a kink mode onset

- 106168

- 106169

## Candidates for RWM have a fast collapse when rotation frequency is below a small value

- “Critical” rotation frequency < 2 kHz at the plasma core at time of collapse, consistent with DIII-D observations of RWM and theory
- Rotation decrease occurs across the entire plasma (preliminary CHERS analysis)

## Locked mode coils have been installed, calibrated, and used

**6 large B****r ****sensors**
- Opposing sensors are differenced in analog, then integrated
- MDS+ tree archives uncompensated Br
- J/K-D/E, A/L-F/G, B/C-H/I
- Remaining calibration done in software (IDL)
- Br sensors are mounted on PF5 coils
- PF5 generates large apparent Br caused by:
- Sensor misalignment
- PF5 non-circularity

- Vessel wall

- CS

- PF5 coil

*J. Menard*

## RWM candidate driven unstable by greater NBI heating

- Control plasma: small outer gap, 1 NB
- Plasma stable until q(0) = 1 (sawtooth)
- Fast increase of locked mode signal

- Pressure-driven mode: small gap, 3 NB’s
- Beta collapse observed 15 ms afer Br excursion

## Wall-plasma gap scan, B r and rotation measurements reveal clues regarding RWM

- Smaller gap
- 	 longer time between start of rapid growth phase of Br and beta collapse
-  stronger wall mode interaction
- With clear tearing activity, no observed Br precursor to collapse

*At least two possible complications*
- Theory suggests Br largest on inboard side for these N’s,  weaker wall interactions compared to DIII-D
-  Locked mode coils  large field error from PF 5

## Error field is localized to lower PF5 coil

30-50 Gauss n=1 error field for typical PF5 current and 0 cm gap

20-30 Gauss peak error field for 10cm gap

- 30-50 Gauss *n*=1 error field for typical PF5 current and 0 cm gap
- 20-30 Gauss peak error field for 10cm gap

- 10cm gap

- 0 cm gap

******=1.8 plasma**
** ****boundary**

**Gauss**

- PF5 is apparently responsible for a large *n*=1 field error

## Ohmic shots: often early and prolonged locking

- “Reconnection event” collapse occurs near t=220ms
- Mode growth starts near t=160ms
- Mode persists for 100ms after collapse event

## Slow-growing, -limiting internal modes are likely NTM’s

- Slow-growing, -limiting internal modes are likely NTM’s

- Coincident with saturation of beta
- Limits p ~ 0.4
- Modes appear near crit
- Further analysis required

*D. Gates, E. Fredrickson*

## Current-driven kinks observed on NSTX

- BT ramp-down, Ip ramp-up key elements of XP
- SXR array shows growth of edge kink structure

- Edge
- kink

- Internal,
- possible
- external kink

*Manickam, Fredrickson, Okabayashi*

*106004*

*106004*

*106007*

## Overview of plan, usage, and goals

Transport

HHFW

MHD

Boundary physics
H modes and turbulence characteristics
Heat and particle flux measurements
Wall preparations

Non-inductive startup

Summary

- Transport
- HHFW
- MHD
- Boundary physics
- H modes and turbulence characteristics
- Heat and particle flux measurements
- Wall preparations
- Non-inductive startup
- Summary

- Outline

## Both ELM-free and ELMy H-modes have been observed in NSTX  

- HHFW and NBI
- Exploration for scenario development, transport, and boundary physics

- ELMing

- ELM-free

- 0

- 100

## Transitions to H mode state exhibit typical signatures but high power thresholds

*Visible light, false color*

*Maingi, Bush (ORNL); LeBlanc; PRL (to be published)*

*Fast camera: Maqueda (LANL)*

- NBI: Power required > 10x that predicted from empircal scaling laws:
- Strong magnetic shear?
- Poloidal damping? Wall neutrals?

*Movie not available*

## Helium puffed; emission viewed along a field line
He0 emission observed with a fast-framing, digital, visible camera
1000 frames/sec, 10 s exposure each frame

- He0 emission observed with a fast-framing, digital, visible camera
- 1000 frames/sec, 10 s exposure each frame

- Imaging of edge reveals qualitative differences in H- and L-mode turbulence

**Los Alamos**
- NATIONAL LABORATORY

*Maqueda, LANL; Zweben*

*Movie not available*

## BOUT code: turbulence modeling
2-fluid,3D Braginskii equation code

- 2-fluid,3D Braginskii equation code

- Theory indicates complex turbulent structures may exist in NSTX edge

*Xu (LLNL)*

## Influx data being obtained with 1-D CCD arrays

*Soukhanovskii; Maingi (ORNL)*

## IR camera being used for heat flux studies

*Heat flux peaks during auxiliary heating*

- IR camera view

*Maingi (ORNL)*

## Boronization consistently reduced impurity influxes, improved performance

- TMB

- O III

- C III

- B III

- Ip flattop

- Stored energy

- Prad

- Loop voltage

- TMB Boronization now a routinely used tool

*Na (KBSI); Maingi (ORNL), Skinner, Kugel*

## Overview of plan, usage, and goals

Transport

HHFW

MHD

Boundary physics

Non-inductive startup
Higher currents; n = 1 activity
Spectroscopy
EBW

Summary

- Transport
- HHFW
- MHD
- Boundary physics
- Non-inductive startup
- Higher currents; *n* = 1 activity
- Spectroscopy
- EBW
- Summary

- Outline

## High currents, strong MHD observed in CHI start-up studies

- Up to 390 kA of toroidal current was produced, with 14 times current multiplication
- Discharges sustained for 330 ms
- Strong *n* = 1 oscillations observed

## Spectroscopy used to measure Ti and edge plasma rotation in CHI plasmas

- Direction of rotation is clockwise (same as HIT-II)
- Ti ~ 30 - 50 eV, midplane view
- V ~ -10 to -20 km/s

## Flux closure is being assessed via further analysis of magnetics and spectroscopy

- MFIT consistently shows modest closed flux regions when CHI-driven current is sufficiently high
- Not seen in absence of n=1 MHD
- Encouraging, but is not proof of closed mean-field surfaces

- USXR emission increases at the higher CHI currents

*Schaffer, GA*

*Stutman, JHU*

## A next step for CHI on NSTX is feedback control & handoff with other current drive mechanisms

- Control challenge: currents not on flux surfaces play a role in the equilibrium
- Absorber arcs reduced, but still limit experiment efficiency
- EFIT analysis with Iinj fitting required
- Likely an increase in the 	fraction of run time     		required for CHI and 		control system work

- CHI injector current

- OH current

- Ip

## EBW mode conversion efficiency increases at L-H transition when edge density increases

- Mode conversion of EBW from core occurs in scrapeoff in H mode
- Measured EBW conversion efficiency agrees relatively well with calculated values
- On CDX-U, limiter inserted to control Ln demonstrates conversion efficiency can be controlled
- Possible tool for plasma startup, island healing
- Joint research with U. Wisconsin

## Physics central to the ST mission is being investigated

- Transport: confinement picture intriguing and potentially important
- New heating physics specific to the ST?
- Electron thermal channel may dominate
- Edge turbulence measurements made; comparison to modelling begun
- HHFW: effective heating in all regimes
- Fast ion interactions observed
- CD studies begun; no obvious signatures of HHFW-CD yet
- MHD: Beta-limiting modes being investigated
- RWM studies underway: well along towards ‘02 Milestone
- Importance of locked mode uncovered
- NTM’s, current-driven kinks both being studied

## Physics central to the ST mission is being investigated (con’t)

- Boundary physics extended to heat and particle flux studies
- Comparisons to modelling begun
- Enabling techniques extended: plasma boronization
- H mode power threshold established for one condition: ~ 10x usual scaling
- CHI research produced record toroidal current, observed critical MHD activity
- Ti of 30 - 50 eV measured
- MFIT analysis consistent with closed flux, not conclusive
- Absorber arcs reduced, but continue to be an issue
- First CHI-to-ohmic, ohmic-to-CHI experiments performed; technical exploration stage

## This was an exciting run for the NSTX Team

- The group worked well in a limited amount of time
- For FY ‘02: day-to-day run coordination duties are handed over to Rajesh Maingi
- The run scheduling is in good hands!

##   not conserved 

EIGOL: full orbit, including model of wall

Ions from each source expected to have different confinement

- EIGOL: full orbit, including model of wall
- Ions from each source expected to have different confinement

*D. Darrow*

- Detailed orbit calculations being performed to benchmark heat source models

## NSTX has achieved t025% plasmas

**Data shown below:**
**EFIT reconstructions using external magnetics only**
-  N  3-4 ***at peak W******TOT***

- IP/aBt0 = 2-6
-  P  0.55  paramagnetic
- Original Troyon definition of  better fit to present data

**EFIT - S. Sabbagh**

**Shot numbers ******** 106451**

*Menard*