Intrinsic momentum transport in tokamaks with tilted elliptical flux surfaces*

Recent work demonstrated that breaking the up-down symmetry of tokamaks removes a constraint limiting intrinsic momentum transport, and hence toroidal rotation, to be small.\footnote{F.I. Parra, M. Barnes, and A.G. Peeters. Phys. Plasmas, 18(6):062501, 2011.} We show, through MHD analysis, that ellipticity is most effective at introducing up-down asymmetry throughout the plasma. Using GS2, a local $\delta f$ gyrokinetic code that self-consistently calculates momentum transport, we simulate tokamaks with tilted elliptical poloidal cross-sections and a Shafranov shift. These simulations show both the magnitude and poloidal dependence of nonlinear momentum transport. The results are consistent with TCV experimental measurements\footnote{Y. Camenen, A. Bortolon, B.P. Duval, et al. Phys. Rev. Lett., 105(13):135003, 2010.} and suggest that this mechanism can generate rotation with an Alfven Mach number of several percent in a tilted elliptical ITER-like machine. It appears that rotation generated with up-down asymmetry may be sufficient to stabilize the resistive wall mode in reactor-sized devices.