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Density Modulation Experiments to Determine Particle Transport Coefficients in HT-7 Tokamak

HT-7

ASIPP

Y.X.Jie, X.Gao, K.TanakaY.X.Jie, X.Gao, K.Tanaka**, and HT-7 team, and HT-7 team

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HT-7

OutlineOutline

1.1. AbstractAbstract

2.2. PrinciplePrinciple of the measurementof the measurement

3.3. ExperimentsExperiments and and resultsresults

4.4. SummarySummary

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HT-7AbstractAbstract

Particle confinement study is a very important issue for magnetically confined plasmas. However, only less number of the studies is reported, compared with energy transport study. This is due to the technical difficulty of the estimation of the particle source and existence of the convection term. Density modulation is a powerful approach to solve these experimental difficulties. Periodic gas fueling induces periodic density modulation. The induced density modulation propagates from edge region to core region. The propagation tells us particle confinement characteristics. From the radial propagation of the modulation, it is possible to estimate D and V separately. It should be noted that the absolute value of particle source is not necessary for this analysis, and the shape of particle source is required.

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HT-7

The particle diffusion coefficient D and the convection velocity V in different plasma of HT-7 tokamak were evaluated based on density modulation using D2 gas-puffing.

D and V were compared at different density background. D was smaller and V changed from outward to inward at high density background.

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HT-7

OutlineOutline

1.1. AbstractAbstract

2.2. PrinciplePrinciple of the measurement of the measurement

3.3. ExperimentsExperiments and and resultsresults

4.4. SummarySummary

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HT-7

The particle balance equation :

1 (1),

nS r S

t r r

(2) nD Vn

r

where n, Γ, S, D and V are electron density, particle where n, Γ, S, D and V are electron density, particle flux, particle source rate, particle diffusion co-flux, particle source rate, particle diffusion co-efficient and convection velocity, respectively.efficient and convection velocity, respectively.

Principle of measurementPrinciple of measurement

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Here, we assume the equilibrium and modulated components are independent,

and separate these two components as follows,

(3) ~

SS ,~

,~eq Snnn eqeq

(4) ~~ ,~~ , ~~

nitnenneSS titi where where ωω is the modulation angular frequency. is the modulation angular frequency.

Then, the following particle balance equations for Then, the following particle balance equations for modulated components are obtained from eq.(1),modulated components are obtained from eq.(1),

(5) 0~

~~1~11~2

2

D

Sn

Din

r

V

DrD

V

r

n

D

V

r

D

Drr

n

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ASIPP

Because of the limit of the interferometer chord number, simple model is used for the analysis. Diffusion coefficient D is assumed to be spatially constant. Convection velocity is assumed to be zero at plasma center and

increase proportionally to minor radius: V(r) = (r/a)V0

Since an interferometer measures path integration of modulated density propagation, the integration of and in eq. (5) are compared with the measured one, changing model of D and V so that the calculated amplitude and phase should agree well with the measured ones. The value of D and V0 are scanned. For each D and V0, NL in eq. (5) are

calculated. Then, the difference between the experimental and calculated values is calculated to minimize the following equation,

chord

IcalcIRcalcxp NLNLNLNL 2

exp

2

Re

2 )()(

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HT-7

OutlineOutline

1.1. AbstractAbstract

2.2. PrinciplePrinciple of the measurementof the measurement

3.3. ExperimentsExperiments and and resultsresults

4.4. SummarySummary

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HT-7

Waveform with/without density modulation

statusIp~130kANe3~1.5,3.0It~3800AModulation frenquency:10Hz

amplitude:

10%

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HT-7Modulation at

(a) low density (1.5x1019m-3 ) and (b) high density (3.0x1019m-

3 )

0

1

2

3

0 0.2 0.4 0.6 0.8 1

n e_

ba

r(x1

019m

-3)

t(sec)

(a)

0 0.2 0.4 0.6 0.8 1t(sec)

(b)

Time trace of the line averaged density in a typical ohmic discharge at (a) low density (1.5x1019m-3 ) shot 67938 and (b) high density (3.0x1019m-3 ) shot 67941 , where Bt=1.8T, Ip=130kA, . From upper to down traces correspond to R=0, 0.1, and 0.2m, respectively.

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67941 ne=3.0x1019m-367938 ne=1.5x1019m-3

D(0.05~0.6m2/sec)

V(-

10~1

0m/s

ec)

D(0.05~0.6m2/sec)

V(-

10~1

0m/s

ec)

The minimum point is indicated with a cross symbol.

Contour plot of 2 for (left) low density

and (right) high density discharges

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HT-7

Shot Ne_bar(0)

(x1019m-3)

D (m2/sec) V(m/sec)

67398 1.5 0.42 4.7

67941 3.0 0.17 -1.6

Estimated D and V in low and high density background

The lower diffusion at higher density is observed, as The lower diffusion at higher density is observed, as similar similar to the results to the results on other tokamaks(TEXT,ASDEX,JT60U). on other tokamaks(TEXT,ASDEX,JT60U).

Positive and negative V indicate outward and inward convection, respectively.

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HT-7(D,V) vs Ne

1.0 1.5 2.0 2.5 3.0 3.50.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

D (

m2 /s

ec)

Ne_bar(0)(x1019m-3)

D vs NeD vs Ne

1.0 1.5 2.0 2.5 3.0 3.5

-2

0

2

4

6

8

V(m

/sec

)Ne_bar(0)(x1019m-3)

V vs NeV vs Ne

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HT-7

Ne profile at high density (3.0x1019m-3 )

-1.0 -0.5 0.0 0.5 1.0

0

1

2

3

4

5

6

Ne(

x1013

m-3)

r

No:67946 450ms

-1.0 -0.5 0.0 0.5 1.0

0

1

2

3

4

5

Ne(

x1013

m-3)

r

No; 67941 B640ms C655ms D670ms E690ms F715ms

Without modulationWithout modulation With modulationWith modulation

The shape is similarThe shape is similar

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HT-7

Total stored energy (kJ)

0.0 0.2 0.4 0.6 0.8 1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

w(k

J)

t(s)

67908#

0.0 0.2 0.4 0.6 0.8 1.0-1

0

1

2

3

4

w(k

J)

t(s)

67938#

0.0 0.2 0.4 0.6 0.8 1.0-1

0

1

2

3

4

5

6

w(k

J)

t(s)

67941#

0.0 0.2 0.4-1

0

1

2

3

4

5

6

w(k

J)

t(s)

67946#

Ne=1.5Ne=1.5

Ne=3.0Ne=3.0

The difference is less than 5%

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HT-7

Te by sxs(Ne=1.5x1019m-3 )

67908#,no modulation67908#,no modulation 67938#,modulation67938#,modulation

The difference is about 0.2kevThe difference is about 0.2kev

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HT-7

OutlineOutline

1.1. AbstractAbstract

2.2. PrinciplePrinciple of the measurementof the measurement

3.3. ExperimentsExperiments and and resultsresults

4.4. SummarySummary

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HT-7SummarySummary

1. Density modulation experiments have been done first time on HT-7 tokamak to estimate particle transport coefficients.

2. Results show clear difference of particle transport in low (ne_bar=1.5x1019m-3) and high density (ne_bar=3.0x1019m-3) cases.

3. No or very weak influence in plasma with density modulation.

4. This technique can be used for the analysis of LHW and IBW heating in the future experiments on HT7.

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THANK YOU!