Sains Malaysiana 46(9)(2017): 1385–1392

http://dx.doi.org/10.17576/jsm-2017-4609-05

 

Formation and Sustainability of H-mode Regime in Tokamak Plasma via Source Perturbations Based on Two-Field Bifurcation Concept

(Pembentukan dan Kelestarian Rejim H-mod pada Plasma Tokamak melalui Pengusikan

Sumber Berdasarkan Konsep Dua-Bidang Dwicabang)

 

 

B. CHATTHONG^1* & T. ONJUN²

 

¹Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai,

Songkla, 90110, Thailand

 

²School of Manufacturing Systems and Mechanical Engineering, Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani, Thailand

 

Received: 31 August 2016/Accepted: 10 November 2016

 

 

ABSTRACT

A set of coupled particle and thermal transport equations is used to study a formation and sustainability of an edge transport barrier (ETB) in tokamak plasmas based on two-field bifurcation. The two transport equations are numerically solved for spatio-temporal profiles of plasma pressure and density. The plasma core transport includes both neoclassical and turbulent effects, where the latter can be suppressed by flow shear mechanism. The flow shear, approximated from the force balance equation, is proportional to the product of pressure and density gradients, resulting in non-linearity behaviors in this calculation. The main thermal and particle sources are assumed to be localized near plasma center and edge, respectively. It is found that the fluxes versus gradients regime illustrates bifurcation nature of the plasma. This picture of the plasma implies hysteresis properties in fluxes versus gradients space. Hence, near marginal point, the perturbation in thermal or particle sources can trigger an L-H transition. Due to hysteresis, the triggered H-mode can be sustained and the central plasma pressure and density can be enhanced.

 

Keywords: ETB; fusion; L-H transition; plasma; tokamak

 

ABSTRAK

Satu set gandingan zarah dan persamaan angkutan terma digunakan untuk mengkaji pembentukan dan kelestarian halangan angkutan pinggiran (ETB) dalam plasma tokamak berdasarkan dua medan dwicabang. Dua persamaan angkutan diselesaikan secara berangka untuk profil ruang-masa tekanan plasma dan ketumpatan. Teras plasma mengangkut kedua-dua kesan neoklasik dan turbulens, dengan turbulens boleh disekat melalui mekanisme aliran ricih. Aliran ricih, penghampiran daripada persamaan keseimbangan daya, adalah berkadaran dengan produk tekanan dan kecerunan ketumpatan yang mengakibatkan tingkah-laku yang tak linear dalam pengiraan ini. Sumber utama terma dan zarah masing-masing adalah diandaikan setempat berhampiran pusat plasma dan pinggiran. Didapati bahawa rejim kecerunan menggambarkan dwicabang semula jadi plasma. Gambaran plasma ini membayangkan sifat histeresis dalam fluks berbanding ruang kecerunan. Oleh yang demikian, berhampiran titik marginal, pengusikan di dalam sumber terma atau zarah boleh mencetuskan peralihan L-H. Oleh sebab histeresis, pencetus H-mod dapat dikekalkan dan ketumpatan tekanan tengah plasma boleh dipertingkatkan.

 

Kata kunci: ETB; lakuran; plasma; peralihan L-H; tokamak

 

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*Corresponding author; email: boonyarit.ch@psu.ac.th