v. vershkov nuclear fusion institute of russian research centre “kurchatov institute

"Comparison of the confinement ofdifferent plasma components and

turbulence rotation with [ExB]velosity in OH and ECRH T-10 plasmas"

•V. VershkovV. Vershkov

•NUCLEAR FUSION INSTITUTE OF RUSSIAN RESEARCH CENTRE “KURCHATOV INSTITUTE

•9th ITPA Transport Physics meeting, St. Petersburg, Russia, October 3-6, 2005

RUSSIAN RESEARCH CENTRE “KURTCHATOV INSTITUTE”


OUTLINE

1. Comparison of the confinement of the different plasma components in OH and ECRH plasmas

1. New measurements of the radial electrical field by HIBP and comparison with turbulence rotation


Schematic comparison of the results for the impurity decay and short gas puffing

0,0 0,1 0,2 0,3 0,4 0,5 0,60

2

4

6

8

10

120

5

10

15-8

-6

-4

-2

0

2

n e(r =

0)

[a.u

.]

Time [s]

Devia

tion f

rom

exponent

law

[%

]

Diffusive rise and decay examples

Vpinch

= 8 m/s; D = 0.5 m2/s; a=0.3 m

Ln(n e(r

= 0

)) [

a.u

.]

1.The time of the approaching the steady state are equal for impurity decay with zero recycling and short gas puffing with 100 % recycling


Comparison of k+17 decay times with the energy confinement times/1.5 in OH plasma

1. The K+17 data from 10th IAEA (1984) 200 kA

2. Energy confinement from Lion EX/P3-01 paper 200 kA,

3. Both values and density dependence are in agreement

0 1 2 3 4 5 6 70

10

20

30

40

50

n eGre

enw

ald

OH discharges

energy conf./1.5 200 kA old K+17 decays 220 kA new K+17 decay 250 kA ITER scaling for OH/1.5

E, m

s

ne, 1019 m-3


Comparison of the energy confinement/1.5 with impurity decay and characteristic times of

density evolution after short gas puff in ECRH1. Good overlapping the

values and density dependence for all components

2. Degradation of confinement in two times in accordance with rise the turbulence level

3. Question: energy – only heat conduction;Density and impurity - Diffusion + convection. How they can coincide functionally at al densities?

0 1 2 3 4 5 6 7 80

5

10

15

20

25

nGr

ECRH plasma. Energy and K+17 decays

Energy conf. time diveded by 1.5 K+17 decay reduced to 200 kA Density rise to 0.7 reduced to 200 kA ITER scaling

L-96

[m

s]

ne [1019 m-3]


The relative level of the density fluctuation in OH and ECRH

0,0 0,2 0,4 0,6 0,8 1,00,0

0,5

1,0

OH

n/n [%

]

ne/n

Gr

ECRH

The relative level of density fluctuation in ECRH increases in two times with respect to OH in accordance with confinement degradation in “L” mode, practically without dependence on density


Discussion of the physical mechanisms determining the functional dependence of confinement on density

1. Instead of the question about saturation at high densities, more important – Why confinement rises at low densities?

2. One reason – The gradual transfer from the dangerous long-wave ITG to less dangerous shorter-wave TEM (see next slide)

3. In that way the rise up to 0.5 Greenwald is reasonable and the constancy after establishing of the TEM also understandable.

4. The other important feature is the strong Te/Ti ratio decrease with density rise. As theory predict the confinement should be bad at high Te at low Ne (see second slide)


Turbulence spectrum variation versus density in OH (top row) and ECRH (bottom row)

0,0

0,2

0,4

0,6

-400 -200 0 2000,0

0,5

1,0

-400 -200 0 200 -400 -200 0 200

I-a) LF QC

ne/n

Gr=0.17

Ampl

itude

[a.u

.]

II-a)HF QC

LF QC

ne/n

Gr=0.35

III-a)HF QC

ne/n

Gr=0.44

Ampl

itude

[a.u

.]

I-b)n

e/n

Gr=0.25

BB

II-b)

Frequency [kHz]

ne/n

Gr=0.32

III-b)

ne/n

Gr=0.53

1.In both cases low frequency (long-wave) ITG? Gradually substituted for the short-wave TEM? Up to 0.5 Greenwald. This may lead to increase of confinement2. After establishing of the TEM no confinement rise is expected.


Variations of Te(0) and Ti(o) with average density in OH and ECR heated discharges

1. Te(0) measured by ECE and SXR

2. Ti(0) was measured by NPA analysis and modeling with “ASTRA”, normalized on neutron emission

3. The ratio is strongest in ECRH case

0 1 2 3 4 5 6 70

1

2

3

40,0

0,5

1,0

1,5

ECRH

T [k

eV]

ne [1019 m-3]

OH

Central electron temperatureCentral ion temperature

T [k

eV]


The map of the primary Tl+1 and secondary Tl+2 beams of T-10 HIBP

B=2.4 TE=180-250 keV

13 < r < 32 cm


-7000 -6000 -5000 -4000 -3000 -2000 -1000 0-100

0

100

200

300

400

500

600

700

800

900

1000N40345

, V

Uscan

t531 t613 t724 t827

Double radial pass of potential value in OH and ECRH

450 500 550 600 650 700 750 800 850-100

0

100

200

300

400

OHECRHOH

, V

t, ms

1. Potential well is symmetric2. It has negative value in plasma center3. It greatly decreases in ECRH phase


Core potential evolves with Te variations

500 600 700 800 900

0

100

200

300

400

0.10

0.15

0.20

, V

r

~ 20

cm

t, ms

#40202 B = 2.33T I = 180kA

Te, a

.u.,

ECE0

5, 2

0cm

•Potential follows the local Te with lower increment•The characteristic time of the potential evolution is ~ 50 ms, higher than E •ECRH power is deposited closer to the plasma center


Comparison of rotation velocities of density perturbations with plasma, [ExB] and electron drift waves rotation in OH and ECRH deuterium core plasma

0 1 2 3 4 5

r = 18 cm

turb40396 EC

[104 rad/s]

ExB

+e

drift

ExB

-i

dia

ExB

r = 18 cm

turb 40396 OH

ExB

+e

drift

ExB

-i

dia

ExB

r = 14 cm

turb 40342 EC

ExB

+e

drift

ExB

-i

dia

ExB

r = 14 cm

turb

40342 OH

ExB

+e

drift

ExB

-i

dia

ExB

1. In core deuterium plasma both turbulence and EB rotation decrease in ECRH2. The uncertainties of calculated velocities are determined by the uncertainties in estimations of Er

3. In spite of the scattering the EB rotation seems fit better to turb

4. More work should be done, especially at different BT


Comparison of the turbulence rotation TURB with

EB in OH and ECRH helium edge plasma

0 1 2

ExB

r = 27 cm

turb

40932 EC

[104 rad/s]

ExB

+e

drift

ExB

-i

dia

ExB

ExB

r = 27 cm

turb

40931 OH

ExB

+e

drift

ExB

-i

dia

ExB

Clear disagreement between two rotations was observed at the outer half of plasma radius* TURB increases, while EB decreases in ECRH

v. vershkov nuclear fusion institute of russian research centre “kurchatov institute

Documents

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density dependence

density rise

confinement degradation

ka energy confinement

average density

density discussion

energy confinement times1