# Presentation: 419785

## Transport Studies in NCSX 

**Transport Studies in NCSX**** **
**D. R. Mikkelsen**
- For the NCSX Research Team
- NCSX Research Forum
- PPPL, December 7, 2006

- Phys of ST

## Overview

- Goals
- Transport experiments in FY11
- Diagnostics needed
- Upgrades to enhance transport studies
- Transport analysis tools
- Summary

- Phys of ST

## FY11 Transport-related Goals

- Characterize confinement and stability
- 	Variation with global parameters, e.g. iota, shear, Ip, density, rotation...
- 	Comparison of very low ripple stellarator confinement with scalings
- 	Sensitivity to low-order resonances
- 	Operating limits
- Quantify the effects of quasi-symmetry:
- 	Effect of quasi-axisymmetry on plasma confinement
- 	Effect of quasi-axisymmetry on rotation damping
- 	Search for transport barriers and enhanced confinement regimes
- Investigate local ion, electron, and momentum transport

- Phys of ST

## FY11 Priorities: Global Confinement

- Characterize global E dependence on:
- 	iota
- 	magnetic shear
- 	heating power
- 	density
- 	beta
- 	bulk ion isotope (H,D,He)
- Compare to ISS-04 scaling:
- Also compare to tokamak
- L-mode scaling: ITER-97P

- NCSX

- Phys of ST

## Explore E  Dependence on Iota & Shear

- Iota and magnetic shear can be varied independently by adjusting coil currents.
- Low-shear iota scan is also possible at full current.

- Vacuum

- Ip=150 kA

- Full current

- Phys of ST

## Will NCSX Confinement be Sensitive to iota?

- Search for similar behavior with low shear in NCSX.
-     Will this also occur with large shear?
- Will H-modes occur at special iota values, as in W7-AS?

**W7-AS**

- Phys of ST

## eff

**Effective Helical Ripple can be Scanned**** by Adjusting Coil Currents**

- Vary effective helical ripple,
- look for strong changes in:
- 	momentum confinement
- 	particle pinch
- Also look for changes in:
- 	ExB flow shear
- 	energy confinement
- 	profile stiffness
- 	transport barriers
- Similar to HSX studies

- eff

- Phys of ST

## Effective Ripple Should Control Rotation in NCSX 

- Modulate NBI torque in NCSX; measure v with CHERS.
- DNB will decouple CHERS from torque input.

**HSX **
**biased probe drives flow**

- low ripple

- high ripple

- Phys of ST

## High Ripple can Affect Heat Transport

- Ion-root 1/ regime:
- Qhel-neo  eff1.5 T4.5
- Negligible for the standard configuration.
- Large ripple should cause noticeable effect.
- More easily seen at high temperature.

**NCSX**

- Phys of ST

## Local Transport studies in FY11

- Will begin studies of heat and particle diffusivities as profile diagnostics become available; look for effect of magnetic configuration changes.
- Identify regimes with impurity accumulation.
- Use gas-puff source for impurity transport studies.
- Compare total bootstrap current with expected magnitude
- 	Profile information will come from external loops.

- Phys of ST

## Diagnostics for Transport Studies

- Magnetic diagnostics provides global energy confinement, and total bootstrap current.
- CHERS (Ti) and Thomson scattering (Te, ne) : local heat- and particle-transport.
- CHERS toroidal rotation for momentum transport;
- 	also used to infer radial electric field.
- CHERS impurity density, SXR, and filtered cameras will be used for impurity transport.
- VUV spectrometer, bolometer and SXR will monitor impurity accumulation.

- Phys of ST

## Upgrades to Enhance Transport StudiesCollaboration Opportunities

- ECH (IPP collaboration) would enable:
- 	Local electron heating, separate ion &electron channels
- 	No fast-ion driven current or MHD
- 	Modulated heating -> derive diffusivity (heat pinch?)
- 	Test profile consistency - profile stiffness
- 	Electron-root studies
- HIBP (possible NIFS/RPI collaboration) would enable:
- 	Direct determination of Er
- 	Fluctuation studies
- 		Potential and density fluctuations
- 		Spatial correlation lengths

- Phys of ST

## Transport Analysis Tools

- Magnetic analysis for Wtot and profile mapping;
- 	provides input to other analysis tools.
- D. Spong’s neoclassical transport module will be used;
- 	benchmarking of neoclassical modules maturing now.
- Must develop standalone neutral beam heating module;
- 	several candidates exist; all need added features.
- Prepare for development of a transport analysis code.
-   find potential modules (ORNL, PPPL, IPP, NIFS)
-   identify additional features needed for NCSX
- Collaborative gyrokinetic studies (IPP, NIFS, U. Md., U. Wisc., PPPL)
- 	Coordinate work to facilitate configuration comparisons.

- Phys of ST

## FY11 results will guide NCSX’s future

- Characterize confinement and stability over broad operating space.
- Compare NCSX confinement with stellarator and tokamak scalings.
- Quantify the effects of quasi-symmetry on E and rotation.
- Check magnitude of bootstrap current.
- Investigate local ion, electron, and momentum transport.

- Phys of ST