Ion Heating and Velocity Fluctuation Measurements in MST Sanjay Gangadhara, Darren Craig, David Ennis, Gennady Fiskel and the MST team University of Wisconsin-Madison.

Ion Heating and Velocity Fluctuation Measurements in

MST

Sanjay Gangadhara, Darren Craig, David Ennis, Gennady Fiskel and the MST team

University of Wisconsin-Madison

General CMSO meeting, Princeton, NJOctober 5-7, 2005

Motivation for Impurity Ion Measurement

Anomalous Ion Heating Ti(r,t)

MHD Dynamo

Momentum Transport v(r,t)

Energy and Particle Transport

bv ~~×

n rv~ p rv~

Outline

CHERS Experimental Setup

First Spatially Resolved Measurement of Ion Heating at a Sawtooth Crash

First Spatially Resolved Measurement of Velocity Fluctuations in the Core

Ion Doppler Spectroscopy (IDS)

For any Doppler shifted and broadened spectral line:

Width Ion Temperature

Centroid Shift Ion Velocity

Area Relative Ion

Density

Charge Exchange Recombination Spectroscopy

(CHERS)

Stimulated emission of the impurity ions due to charge exchange recombination with neutral beam atoms

Charge exchange measurement is localized to the intersection of the line of sight and the beam path (~ 2 cm)

CHERS on MST

Two fiber bundles allow for a simultaneous measurement of the charge exchange component and the background

Measure the spectrum of the n=7 to n=6 transition of C+5 (~ 343.4 nm) with a 100 kHz bandwidth

A Higher Energy and Longer Pulse DNB Installed on MST

Neutral particle energy increase from 30 keV to 50 keV

Longer duration of the pulse from 3 ms to 20 ms

Outline

CHERS Experimental Setup

First Spatially Resolved Measurement of Ion Heating at a Sawtooth Crash

First Spatially Resolved Measurement of Velocity Fluctuations in the Core

Localized Heating On-Axis is Observed During a Sawtooth

Crash

Heating occurs on a fast time scale (~ 100 s) Cooling time scale is much longer (~ 1 ms)

Temperature Profile Evolution During the Crash Suggests

Global Heating

Temperature Profile Evolution During the Crash Suggests

Global Heating

Temperature Profile Evolution During the Crash Suggests

Global Heating

Temperature Profile Evolution During the Crash Suggests

Global Heating

Temperature Profile Evolution During the Crash Suggests

Global Heating

Ion heating is strongest in the center and edge but active throughout the entire plasma volume

Non-uniform heating of different radial positions

Cooling fastest in the edge

Comparison with Bulk Ions Indicates Larger Impurity

Heating during Crash

Comparable temperatures for bulk and impurity ions away from sawteeth

Impurity heating at the sawtooth crash stronger than for the bulk

Impurity Ion Heating appears to

be localized during m=0 bursts

An increase in Ti during burst is only observed outside of mid-radius

200

400

600

800

1000Ion Temperature (eV)

13 14 15 16 17

time (ms)

20

40

60

80

m=0 amplitude (G)r/a = 0.00r/a = 0.37r/a = 0.55r/a = 0.75

Outline

CHERS Experimental Setup

First Spatially Resolved Measurement of Ion Heating at a Sawtooth Crash

First Spatially Resolved Measurement of Velocity Fluctuations in the Core

Ensembles of similar plasmas are generated to reduce measurement noise levels

0.5 ms time windows were selected away from sawtooth crashes

Method for Computing Coherence of Velocity Fluctuations with

Magnetic Modes

Summary of Coherence Between Velocity Fluctuations and

Magnetic Modes

Strong coherence with high n mode numbers at the mid-radius

Modest coherence with the dominant n=6 magnetic mode

Velocity fluctuations are much less global than magnetic fluctuations

MHD Dynamo

The dynamo term depends on the magnitude of the fluctuating parameters along with their coherence () and phase difference ()

Within the error bars, the sum of the on-axis dynamo could encompass the prediction

Future Work

Collect more data with the new diagnostic neutral beam to improve error bars on all measurements

Adding toroidal & radial measurement capability gives:Tvs T

vs Examine the dynamo during a sawtooth crash Simultaneous measurement of the Hall dynamo spatial structure during and away from sawteeth

vè~ vr

~

Summary

First localized measurement of impurity ion temperatureHeating at the sawtooth crash is globalImpurity ions heated stronger than the bulk

First localized measurement of impurity ion velocity fluctuations in the coreVelocity fluctuations not as global as magnetic fluctuations

Small dynamo in the core possibly consistent with expectations between sawteeth