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A full radius gyrokinetic stability analysis for large aspect ratio finite-beta tokamaks

Linear, fully gyrokinetic, full radius (global), large aspect ratio studies of Alfven-ion temperature gradient mode (AITG) or kinetic ballooning modes or beta-induced Alfven eigenmodes considering only "passing" species is presented. Effects hitherto completely neglected in a full radius approach such as B-parallel to-fluctuations and the ones which have been treated partly [Phys. Plasmas 10, 1424 (2003)] such as Shafranov shifts are included. To this end, an existing code EM-GLOGYSTO has been upgraded to incorporate these effects. Among others, the most interesting results include: (i) For relatively large positive magnetic shear (s) over cap [1.25<(s) over cap <4.25, (s) over cap =d ln q(s)/d ln rho, where q(s)(rho) is safety factor and rho minor radius], B-parallel to fluctuations have a benign effect on AITG growth rates and for positive but small shear (0.0<s<2.7), B-parallel to fluctuations are too weak to play any crucial role. (ii) In the later case, inclusion of Shafranov shift leads to the following: (a) Growth rates without Shafranov shift effects are in general larger than those including Shafranov shift; (b) nonmonotonous dependence of growth rates and frequencies on beta=2mu(0)NT(i)/B-0(2); (c) the presence of multiple eigenmodes with competing growth rates for same values of beta; (d) no sign of complete stabilization with increasing beta. Finally eigenmode structures [phi,A(parallel to),A(theta)] with and without Shafranov shift are reported. The growth rates and frequencies thus obtained may serve as estimates of transport coefficients and for future bench marking of the (then) global electromagnetic, gyrokinetic, time evolution codes (particle-in-cell or otherwise). (C) 2004 American Institute of Physics.

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