托卡马克剪切流和内部输运垒触发机制初探

1、托卡马克剪切流和内部输运垒触发机制初探    托卡马克剪切流和内部输运垒触发机制初探董家齐 龙永兴 牟宗泽 张锦华核工业西南物理研究院成都432信箱托卡马克输运垒的特征输运垒Internal Transport Barrier or External Transport Barrier (ITB或ETB)是先进托卡马克放电的特征;托卡马克内部输运垒的定义1)regions where the gradient length is reduced with respect to the L- and H-mode values:托卡马克内部输运垒的定义2)

2、 regions where 托卡马克内部输运垒的判据=0.014for JET discharges 托卡马克内部输运垒的形成条件形成ITB或ETB的外部条件是非欧姆加热(即中性束或波)功率要高于一定的阈值;这种阈值随非欧姆加热功率输入时等离子体的状态而变;实验发现,ITB比较倾向于在低q的有理面附近形成;实验发现,输运垒的形成与MHD不稳定性有密切的关系;同时,理论和实验研究还发现,输运垒的形成总是伴随着剪切流;托卡马克内部输运垒触发机制的现有理论这些实验现象已经在世界各大装置上普遍观察到.但是,对剪切流和输运垒的触发机制,目前还没有比较统一的理论.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