NSTX High-k Scattering System on NSTX: Status and Plan*

H.K. Park1, W. Lee1, E. Mazzucato1, D.R. Smith1, C.W. Domier2, W. Horton3, S. Kaye1, J. Kim3,N.C. Luhmann,Jr.2,NSTX

Team

European Physical Society Conference

July 1-6, 2007

Warsaw, Poland

1 PPPL, Princeton University, NJ2 UCD, CA3 U. Texas, TX

Supported byOffice ofScience

2

National Spherical Torus Experiment

Major Radius, R 0.85 m

Minor Radius, a 0.67 m

Aspect Radio, A ≥ 1.27

Elongation, ≤ 2.6

Triangularity, ≤ 0.8

Plasma Current, IP 1.5 A

Toroidal Field at R0, BT .3-.45 T

NB Power, PNB 7 MW

HHFW Power, PHHFW 6 MW

Toroidal Beta, T ≤ 40%

Normalized Beta, N ≤ 9

Pulse Length 1 s

3

0.1 ks 1.0 10.0

1.0 10 k [cm-1] 100

ITGTEM

ETG

Hennequin et al. PPCF 46, 2004

NSTX plays a key role in extending fluctuation measurements beyond the present data base

Scale length andTurbulence type

→NSTX

Full exploitation of turbulence based transport physics is the goal Capability of investigating turbulence

physics up to k┴ρe~0.7 Multi-channel NSTX scattering

system → k-space turbulence continuum through simultaneous measurement of five wavenumbers Various operating regimes were

studied – H/L modes, RS regime, High Te/Ti regime, confinement dependence on BT, Alfvén wave study

4

BWO millimeter wave source and power supply

Thomson CSF BWOModel CO 10-1 O-type backward wave

oscillator (BWO) High power

~200 mW Frequency tunable

275-290 GHz ~15 MHz/V

Lifetime: ~2000 hrs

Siemel Power Supply High voltage: 12 kV Low ripple: < 15 mV Anode current controls

BWO power output Cathode voltage

controls BWO frequency

Configured to lower BWO filament current between shots to conserve BWO lifetime

F-bandWaveguide

Output

CoolingLines

High Voltage LinesThomson CSF BWO

Siemel Power Supply

5

Probe beam launching hardware arrangement

Launcher system has three mirrors Microwave power is piped through corrugated

waveguide system

Motorized Linear Slide

From

Input Beam

Splitter

Translation AcrossEntrance Window

Spherical FocusingMirror

6

Detection system hardware arrangement

Detection system is piped through corrugated waveguides Detection array is located in the test cell base

To detector array

From

Input Beam

Splitter

Windows for the Scattered signals

Spherical FocusingMirror

Scatteredsignals

To the wave-guideArray

7

Characteristics of the scattering system on NSTX

Inboard ρ = 0.05k┴ρe up to 0.7

Outboard ρ = 0.75k┴ρe up to 0.4

Tangential multi-channel (5) scattering system: Po ~100 mW

~1 mm (280 GHz)

System NF ~ 5000oK

System resolution k= a/2 ~1.0 cm-1

Scattering length (Lv)

8

Calibration of the System with A/O cell

Possible source of errors Emissions from the

plasma at the probe beam wavelength is negligible

Cross talk between channels is minimized by optical isolation

Calibration of the scattering system Verification of the

scattering length, relative efficiency curvature effect, magnetic shear effect and k-matching condition

Verification of the direction of waves

9

Verification of the propagation direction of the wave

Heterodyne detection system Edge region – outward propagation direction is Positive frequency Core region – outward propagation direction is Negative frequency

InwardPropagating

wave

outwardPropagating

wave

Frequency response from the probe beam

at the edge region

10

Fluctuation of the Ohmic discharge (He)

Monotonically decreasing power spectra as a function of wave-numbers in OH plasma

Plasma parameters ne (0) ~ 2.5x1013cm-3

Te (0) ~ 200eV r/a ~0.85

k┴ρe~0.1

11

Characteristics of H-mode edge plasma (pedestal)

Monotonically decreasing power spectra during L-mode phase

Non-monotonic power spectra during H-mode phase

ETG?

12

Reduction of fluctuation is well correlated with improved confinement

Reduction of fluctuation at upper ITG/TEM and moderate changes at ETG during H-mode

Bursts of the scattered signal at the highest k is noted.

Ion transport is close to new classical in H-mode

Electron transport is reduced from L- to H-mode

13

Theoretical calculations Indicate ITG,TEM and ETG are possible candidates for electron transport

GS2 calculations indicate lower growth rate at lower k during H-mode phase and higher growth rates for all wavenumber during L-mode

Non-linear GTC results indicate ITG modes are stable during H-mode phase

ETG mode is unstable in L-mode and marginal in H-mode

lin >> ExB during L-phase for all ks

lin << ExB during H-phase for ITG/TEMlin ~ ExB during H-phase for ETG

Experimental results areConsistent with

the growth rate of ETG mode

Other types of fluctuations???

14

Electron confinement dependence on BT

Confinement is improved at higher BT due to the improved electron transport at the edge region

The core electron thermal diffusivity increases at higher BT

15

Core experimental results

Asymmetric spectral feature increases at higher field.

16

Edge experimental results

Asymmetric spectral feature decreases at higher field.

17

Highly shifted frequency spectra (inside the pedestal of the H-mode)

Highly shifted (inward propagating) turbulence spectra was observed during H-mode phase (inward propagating?)For the poloidal component: Negative frequency is electron diamagnetic direction

r/a ~ 0.75

k┴ ~ 9.3 cm-1

k┴e ~ 0.22

18

Frequency broadening during RF heating phase where Te is peaked at ~3 keV while Ti is at 1 keV

L-mode discharge (high Te/Ti) by RF

19

L-mode discharge (Te ~Ti) by RF+NBI

Te is comparable to Ti

and no spectral broadening during RF +NBI heating

20

Alfvén wave study using scattering system

21

Electrostatic component of the Alfvén wave

Beta-induced Alfvén Acoustic Eigenmode (BAAE)

AVR

nm

2

22

Summary

L-mode (k-) and OH (k-) plasmas - Monotonically decreasing fluctuation level extends the previous data base up to k┴ρe ~ 0.2

H-mode plasmas Reduction of fluctuations below k┴ρe << 0.1 (ITG/TEM) at the edge of

the H-mode plasma is consistent with the improved confinement (k-) Enhanced fluctuations at higher k (above k┴ρe ~ 0.15) is observed in H-

mode plasma (suppression of ETG in L-mode?)

Electron transport dependence on toroidal field strength Enhanced fluctuation at the lower field at the edge and at the higher

field at the core Highly shifted frequency spectra inside the pedestal region but not in

the core

Alfvén wave studies BAAE mode was detected by scattering system

Highly broadened spectra at high Te/Ti ratio Comparison study of discharges with RF alone and RF+NBI