Helical flow in RFX-mod tokamak plasmas

Helical flow in RFX-mod tokamak plasmas

Helical flow in RFX-mod tokamak plasmas 150 150 Mathew

This work presents the first evidence of helical flow in RFX-mod q(a) < 2 tokamak plasmas. The flow pattern is characterized by the presence of convective cells with m = 1 and n = 1 periodicity in the poloidal and toroidal direction, respectively. A similar helical flow deformation has been observed in the same device when operatedfas a Reversed Field Pinch (RFP). In RFP plasmas, the flow dynamic is tailored by the innermost resonant m = 1, n = 7 tearing mode, which sustains the magnetic field configuration through the dynamo mechanism [Bonomo F. et al 2011 Nucl. Fusion 51 123007 ]. By contrast, in the tokamak experiments presented here, it is strongly correlated with the m = 1, n = 1 MHD activity. A helical deformation of the flow pattern, associated with the deformation of the magnetic flux surfaces, is predicted by several codes, such as Specyl [Bon glio D. et al. 2005 Phys. Rev. Lett. 94 145001 ], PIXIE3D [Chac on L. et al 2008 Phys. Plasmas 15 056103 ], NIMROD [King J.R. et al. 2012 Phys. Plasmas 19 055905 ] and M3D-C1 [Jardin S.C. et al. 2015 Phys. Rev. Lett. 115 215001 ]. Among them, the 3D fully non-linear PIXIE3D has been used to calculate synthetic flow measurements, using a 2D flow modelling code. Inputs to the code are the PIXIE3D flow maps, the ion emission profiles as calculated by a 1D collisional radiative impurity transport code [Carraro L. et al 2000 Plasma Phys. Control. Fusion 42 731 ] and a synthetic diagnostic with the same geometry installed in RFX-mod. Good agreement between the synthetic flow behavior and the experimental one has been obtained, confirming that the observed flow oscillations with the associated convective cells are a signature of helical flow.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IAEA
Published date:
21/09/2018