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Feature of Energy Transport in NSTX plasma

Siye Ding

under instruction of Stanley Kaye

05/04/09

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Outline

• Data selection

• dependence at constant Bt

• The influence of plasma current profile on

• The ‘pivot’ phenomenon in profile

• The influence of lithium on energy transport

• Conclusion

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Data selection

• 2008 Data: 04/21---07/14• Quasi-steady plasma state

– A least discharge length of 500ms– Flat top of at least 80ms in total stored energy during the flat top of

plasma current– No transients in the loop voltage– Quiet MHD activities

• There lithium states– Pre-lithium: e.g. 128584– With-lithium: e.g. 129021– No-lithium: e.g. 130187

• TRANSP analysis– Data used: equilibrium data, temperature and density profile, visible

bremsstrahlung radiation, beam power, etc.– Match neutron emission rate by adjusting the neutral density bound

ary condition to values between 1010 and 1013 cm-3

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dependence on Bp (or q)

• Parameters: Ip(900kA),

Bt (0.48T), Pheat(5.6MW), and

<ne> (4.6~5.61013cm-3),

<Te> (490~608eV)• A significant influence of ngTx i

n the relation between s and B

p (or q)– ngTx: the abbreviation of ‘local -n

e*Ti/e’ value– units: Bp in T, ne in 1013cm-3, Ti/e in

eV, r is normalized magnetic surface

• The proportional relation between and Bp (or the inversely proportional relation between and q )

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The dependence of local heating on Pheat

• Parameters: Ip(900kA), Bt (0.48T)

• Pb i/e x, Pheat i/e x, Pcond i/e x

• Qie x

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Relation between ngTx and current profile

• Equilibrium– – –

• Ipx: the area integral of j from zero to the local position, i.e. the plasma current generated from core to the local position

• Validity– Equilibrium

• could not be met. The other terms in the motion equation?

– Tn• The relation fails if two plasma states have too different Tn (the discreteness becomes too large)

• Current profile has an important impact on

BjBjnTTnBjp

1401~,3.02.0~ jjBB

pxIjBjTn ~~

Bjp

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dependence on plasma current

• Pcond vs ngTx and q at constant Bt and different Ip

– No obvious dependence on Ip

– Plasma current profile• Constant ngTx

–

–

• Constant q• Peaky and flat

(hollow) profile

pxIjngTx pxIq 1

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Multiple Linear Regression Analysis (1)

• pxp IjBjTn

The fit using jBp instead of ngTx

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Multiple Linear Regression Analysis (2)

• The result without using local Pheat, -T as independent variables– The dependence on Bp is inconsistent with data observed– Low R2

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Support from recent theoretical work

• Reference– Phys. Plasmas 10(2003)2881 C. Bourdelle et al.– Nucl. Fusion 45(2005)110 C. Bourdelle et al.

• Conclusion of their theory and simulation work– High |'|~|p| reduce the drive of the B and curvature drifts

responsible for the interchange instability.• The -stabilization while using ballooning formulism

– The stabilizing effect of high |'| can induce enhanced temperature and density peaking leading to even higher values of |'|, i.e. a positive feedback loop with respect to turbulence suppression and enhanced confinement.

• It can be responsible for part of the ITB sustainment.

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The ‘pivot’ phenomenon in eprofile

• Governed by local current density (or current profile) – Data at constant Bt (2008)

– Data at different Bt (2006) Ip=900kA Ip=1100kA

Data at different Bt (2006 )

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The influence of lithium on energy transport

• Energy confinement time– Parameters:

• Ip (kA): 800, 900

• Bt (T): 0.54(max), 0.51(avg), 0.48(min)

• Pheat (MW): 4.3(max), 3.7(avg), 3.2(min)

– E increases

– 0mg: without-lithium data

• Radiated power– Local e decreases

– Large percentage of radiated power

– No obvious improvement on i

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The influence of lithium on energy transport

•

298,)2,(98

yth

thyHH

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The influence of lithium on energy transport

• e (direct comparison)– More than 50% reduction

• i (indirect comparison)– Effective

• The third lithium stateIp: 900kABt: 0.47TPheat: 5MW

Ip: 900kABt: 0.49TPheat: 3.6MW

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Conclusion

• The local energy transport properties of the NSTX plasmas both with and without lithium were investigated.

• The significant influence of ‘local -ne*Ti/e’ (ngTx) value was discovered, as well as a proportional relation between and Bp.

• Plasma current profile affects values via ngTx.• The ‘pivot’ phenomenon w/o Bt varying is the consequen

ce of different current profile.• Lithium can improve energy confinement time and enha

nce radiation.• Lithium can reduce e more than 50% when large quanti

ties are injected. For i, it is effective, but not quantitative investigated.

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Work plan for the extended month

• The purpose of my visit– Analysis: TRANSP – Prediction: pTRANSP

• The key issue: learn the technique of doing pTRANSP predictive run

• Learn the skill of using the some auxiliary heating packages for pTRANSP and build EAST launcher model.

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Thank you for your attention !