托卡馬克剪切流和內(nèi)部輸運壘觸發(fā)機制初探

1、托卡馬克剪切流和內(nèi)部輸運壘觸發(fā)機制初探    托卡馬克剪切流和內(nèi)部輸運壘觸發(fā)機制初探董家齊 龍永興 牟宗澤 張錦華核工業(yè)西南物理研究院成都432信箱托卡馬克輸運壘的特征輸運壘Internal Transport Barrier or External Transport Barrier (ITB或ETB)是先進托卡馬克放電的特征;托卡馬克內(nèi)部輸運壘的定義1)regions where the gradient length is reduced with respect to the L- and H-mode values:托卡馬克內(nèi)部輸運壘的定義2)

2、 regions where 托卡馬克內(nèi)部輸運壘的判據(jù)=0.014for JET discharges 托卡馬克內(nèi)部輸運壘的形成條件形成ITB或ETB的外部條件是非歐姆加熱(即中性束或波)功率要高于一定的閾值;這種閾值隨非歐姆加熱功率輸入時等離子體的狀態(tài)而變;實驗發(fā)現(xiàn),ITB比較傾向于在低q的有理面附近形成;實驗發(fā)現(xiàn),輸運壘的形成與MHD不穩(wěn)定性有密切的關(guān)系;同時,理論和實驗研究還發(fā)現(xiàn),輸運壘的形成總是伴隨著剪切流;托卡馬克內(nèi)部輸運壘觸發(fā)機制的現(xiàn)有理論這些實驗現(xiàn)象已經(jīng)在世界各大裝置上普遍觀察到.但是,對剪切流和輸運壘的觸發(fā)機制,目前還沒有比較統(tǒng)一的理論.The plasma poloidal

3、rotation shear stabilises the drift-type plasma turbulence,either by reducing/suppressing the mode amplitude (predominantly ITGs & TEMs)or by altering the radial correlation lengths (breaking up turbulence eddies)There was a reminder of the central role of rotational shearJ. Connor et al., sub t

4、o NFErTS Hahm, KH Burrell, Phys. Plasmas 2 (1995)1648pressure gradient - poloidal flow - toroidal flowRole of plasma current profileHighlights complexity, and also points to transport control possibilitiescurrent profileexternal flow shear generationH-mode workshop, San Diego, 26-28 sept 03 A. B

5、3;couletCoupling of external and internal MHD modes magnetic braking of plasma rotation at inner q surface;Fishbone instability: expulsion of fast resonant particle sheared plasma flow equivalent to a radial electric field;Double internal transport barrier triggering mechanismin tokamak plasmas _1,

6、IntroductionNon-monotonic q profiles are desirable for advanced tokamak (AT) operation with internal transport barriers (ITBs)Such configurations are prone to excitation of double tearing modes (DTMs) Possible causal relationship between DTMs and the experimentally observed Double ITBs around qmin s

7、urfaces is one important research topic in tokamak physicsE. Joffrin et al., PPCF 2002H-mode workshop, San Diego, 26-28 sept 03 A. Bécoulet2, Equilibrium and MHD equationWe consider the standard sheared slab configuration, , (1)where equals zero at ,The plasma sheet is of scale length a in x-di

8、rection, has a current in z-direction,The equilibrium flow velocity ,The resistivity and the viscosity are bothassumed to be constantNon-linear reduced MHD equations1) Ohm's law+Faraday's law2) Plasma vorticity equationSpectrum method is adopted3, Non-linear simulation Quasi-linear Equations

9、Non-linear EquationsQuasi-linear simulation without ion viscosity dissipation_parametersQuasi-linear simulations,xs=0.25, k=0.25, R=105, S=9.4e5Quasi-linear simulation with ion viscosity dissipation5, SummaryNarrow layers with strongly sheared flows exist in tokamak discharges with ITBsThe mechanism

10、s for the creation of such flows is far from being under-stoodOne of the principal aims of thisinvestigation is the search for an engine for the creation of transport barriersThe double tearing mode studied in this work may provide a possible trigger for the formation of ITBsA quasi-linear simulation demons-trates that the sheared flow