J. Boedo, UCSD

Fast Probe Results and Plans

By J. Boedo

For the UCSD and NSTX Teams

J. Boedo, UCSD

Probe Installed and Commissioned

11 deg angle

6.8”

Location is 6/8” below midplane

J. Boedo, UCSD

New head and tips to accommodate curvature and heat flux

Thermal ConductivityThermalgraph Tips (parallel) 800 W/mKCopper 401 W/mKPOCO graphite 72 W/mK

J. Boedo, UCSD

IsatVf1

Vf2Epol

DoubleProbe

Vf3

Mach1

Mach2

Er

Vf4

Te fluct

Existing Probe Head has 10 Tips

•Tips in blue will be active on day one, the rest implemented as upgrades (if funded)•Fluctuations to 1 MHz•Two Vf tips used for Epol (and fluctuations)•Two Vf tips used as Er (and fluctuations) >> Reynolds Stress•One tip as Isat >> ne•Two tips as double probe (Te and Ne profiles)

J. Boedo, UCSD

Data Taken at High Spatial and Temporal Resolution

-5.0 100

0.0 100

5.0 100

1.0 101

1.5 101

2.0 101

0.05 0.1 0.15 0.2 0.25

sp109033

Radius

Time

~ 100 ms

~ 30 ms

Insertion completed in 100 ms. ~30 ms in plasma

Time resolution for Te and Ne is 1 ms

Time resolution for fluctuations is 1 micro sec

Spatial resolution is 1.5-2 mm (tip size + probe motion)

J. Boedo, UCSD

0.0 100

1.0 1012

2.0 1012

3.0 1012

4.0 1012

5.0 1012

-2 0 2 4 6 8 10 12

109052 H 4.2 MW λ=1.51 cm109035 2.0 H MW λ=2.55 cm109033 2.0 L MW λ=3.25 cm

Radius

Within the limited shot space, density and power were varied. So scaling is inconclusive

So far:

decreases in H mode with power 2.5>1.5 cm

Will obtain wider operating space in the future and produce scalings

€

λn

J. Boedo, UCSD

H-mode Radial Electric Field Flat in SOL

-80

-60

-40

-20

0

20

40

-5 0 5 10 15

Er

(V/cm)

R-Rsep

(cm)

H-Mode

L-Mode

J. Boedo, UCSD

Fluctuation Quantities to Characterize in NSTX

density fluctuations:

€

n

~

n

=

Isat

~

Isat

+

Te

~

2 Te

plasma potential fluctuations

€

φpl

~

= φfl

~

+ α Te

~

cross-field particle flux:

€

Γturb

= ⟨ n

~

Eθ

~

⟩ Bφ

convective heat flux:

€

Qconv

=

5

2

Te

Γturb

conductive heat flux:

€

Qcond

=

3

2

⟨ Te

~

Eθ

~

⟩ Bθ

− Te

Γturb

Need to add Te fluct capability

J. Boedo, UCSD

Harmonic Diganostic

250 WRF amp

Pearsoncoil

Probe

AmpR1

V_fast

V

Ifdrive= 400 kHz

AmpAmp

Amp

400 kHzBandpass

filter

800 kHzBandpass

filter

Ampli-tude

detector

I2

I_fast

Te_slow

TunableLPF

Compa-rator

Analogmultiplier

Analogdivider

Ampli-tude

detector

Ampli-tude

detector

I /I2

Amp

Analogmultiplier

Compa-ratorAdder

RefRef

V_min I_minDummy

transmissionline

R2C3C1

C2

J. Boedo, UCSD

Harmonics Technique

Current to a DC-floating probe driven by sinusoidal voltage

can be expressed as a series of sinusoidal harmonics [1]:

where - amplitude of mth harmonic

- Bessel functions of integer order k

For eU0/kTe << 1:

Thus Te can be determined from the ratio

of the amplitudes of 1st and 2nd harmonics

The error of this approximation for eU0/kTe= 1 is only about 5% [1]

ekT

eU

ekTeU

2I 01

0 ≈⎟⎠⎞⎜

⎝⎛

20

2 81

I 0⎟⎟⎠

⎞⎜⎜⎝

⎛≈⎟

⎠⎞⎜

⎝⎛

ekTeU

ekTeU

2

0

2

104I

I4 I

IeUeUkTe =≈

[1] Boedo et al, Rev. Sci. Instrum. 70 (1999), 2997

)cos()cos(II

2 00

0 110

tmItmI

IekT

eU

ekTeU

ekTeU m

mm

msi

pr ⎟⎠⎞⎜

⎝⎛∑=∑ ⎟

⎠⎞⎜

⎝⎛

⎟⎠⎞⎜

⎝⎛

=∞

=

∞

=

⎟⎠⎞⎜

⎝⎛⎟

⎠⎞⎜

⎝⎛=⎟

⎠⎞⎜

⎝⎛

ekTeU

ekTeU

ekTeU

msim II 0000II2ω

)(I zk

J. Boedo, UCSD

Need to Include Magnetic component

⎟⎟⎠

⎞⎜⎜⎝

⎛ ×∇−⎟⎟

⎠

⎞⎜⎜⎝

⎛ ×∇−=

22

~~

BBnm

BBì

φφt

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡+

×≡

B

q

B

p BBEQ

~~~~

2

3~ ||

2

B

vn

B

n BBÃ

~~~~~ ||

2+

×∇−=⊥

φParticle Flux

Reynolds Stress(neglecting ion pressure

fluctuations)

Heat Flux

B

p

B

j r

J

BBÃ

~~~~~ ||

2

||

|| +×∇

−=φParallel

Current Flux

⊥= BÃ~~~

φKHelicity Flux

J. Boedo, UCSD

Normalized N fluctuations very large

0.0

0.5

1.0

1.5

-1 0 1 2 3 4 5 6 7

Position

J. Boedo, UCSD

Radial Turbulent Flux Lower in H-mode

-7.0 1017

-6.0 1017

-5.0 1017

-4.0 1017

-3.0 1017

-2.0 1017

-1.0 1017

0.0 100

1.0 1017

-5 0 5 10 15 20

-Γr (cm-2 s -1 )

- H mode-L mode

Position

Value is ~3-5 1017 cm-2 s-1

J. Boedo, UCSD

Intermittent Plasma Events Pervasive

J. Boedo, UCSD

Power Spectrum Comparison

10-5

0.0001

0.001

0.01

0.1

1

0 20 40 60 80 100

Power spectrum vs f (in kHz) from probe data during gas injection (solid circles) and without(x) and comparison to that obtained form the GPI system (open circles). Note that the power spans y 4 orders of magnitude indicating excellent S/N ratio.

J. Boedo, UCSD

Intermittency (Radial Convective Transport) Lower in H-Mode

L-Mode 109033 H-Mode 109052

Intermittency is very strong in NSTX!

J. Boedo, UCSD

Intermittency (Radial Convective Transport) Lower in H-Mode

L-Mode 109033 H-Mode 109052

Intermittency is very strong in NSTX!

J. Boedo, UCSD

L-Mode 109033DL >

DL >

=I DL >

Density is highly intermittentRate of bursts is ~1E4Poloidal field is much less intermittentCoherent modes show in EthetaInstantaneous flux is 1-3E15 cm-2s-1

J. Boedo, UCSD

H-Mode 109052=I DL >

=I DL >

=I DL >

Density is intermittent (ELMs?)Rate of bursts is 2E3Poloidal field is much less intermittentCoherent modes show in EthetaInstantaneous flux is ~2E15 cm-2s-1

J. Boedo, UCSD

Initial Reynolds Stress and Bicoherency Measurements

€

∂uθ∂t

+∂uruθ∂r

=−μuθ

Codes Written and Tested

H-Mode

L-Mode

J. Boedo, UCSD

Bispectrum

H-mode L-Mode

f3=f1+f2

f3=f1-f2

J. Boedo, UCSD

Bicoherency

H-mode L-Mode

J. Boedo, UCSD

Profile Conclusions

Edge/SOL profiles available with high spatial (2-2.5 mm) resolutionLimited to 1086xx, 1089xx, 109032-109062Fully calibrated data for 109032-xxx062

NSTX profiles seem different from larger aspect ratio devicesTe profile in the edge/SOL is flat at 25-30 eVNe profile has a very long decay length. Reduced by power!H-mode Er profile flat in SOL

How do flat Te profiles are maintained?Do we have (more) anomalous radial transport? (intermittency)Adding fast Te diagnostic

J. Boedo, UCSD

Future Work and Goals

Data obtained in L and H-mode. SOL length scales with power. Ongoing

Many puzzles need addressingFeatures usually associated with LCFS vicinity are different in NSTX, such as a potential well, steep H-mode profiles, etc Ongoing

Intermittency is quite strong in NSTX (very strong radial transport?)

Need to quantify electrostatic turbulence and Intermittency (enough to explain strong transport?) Codes just ported for electrostatic turbulence, ongoing for intermittency!

Bicoherency and Reynolds Stress codes just finished. Investigate energy cascading and self-organized flows

Need to quantify electromagnetic components of transportUpgraded head partially designed and to be built in FY04

J. Boedo, UCSD

J. Boedo, UCSD

J. Boedo, UCSD