RT Journal Article
T1 Bootstrap current control studies in the Wendelstein 7-X stellarator using the free-plasma-boundary version of the SIESTA MHD equilibrium code
A1 Peraza Rodríguez, Hugo Alberto
A1 Reynolds Barredo, José Miguel
A1 Sánchez Fernández, Luis Raúl
A1 Tribaldos Macía, Víctor
A1 Geiger, John F.
AB The recently developed free-plasma-boundary version of the SIESTA MHD equilibrium code (Hirshman et al 2011 Phys. Plasmas 18 062504; Peraza-Rodriguez et al 2017 Phys. Plasmas 24 082516) is used for the first time to study scenarios with considerable bootstrap currents for the Wendelstein 7-X (W7-X) stellarator. Bootstrap currents in the range of tens of kAs can lead to the formation of unwanted magnetic island chains or stochastic regions within the plasma and alter the boundary rotational transform due to the small shear in W7-X. The latter issue is of relevance since the island divertor operation of W7-X relies on a proper positioning of magnetic island chains at the plasma edge to control the particle and energy exhaust towards the divertor plates. Two scenarios are examined with the new free-plasma-boundary capabilities of SIESTA: a freely evolving bootstrap current one that illustrates the difficulties arising from the dislocation of the boundary islands, and a second one in which off-axis electron cyclotron current drive (ECCD) is applied to compensate the effects of the bootstrap current and keep the island divertor configuration intact. SIESTA finds that off-axis ECCD is indeed able to keep the location and phase of the edge magnetic island chain unchanged, but it may also lead to an undesired stochastization of parts of the confined plasma if the EC deposition radial profile becomes too narrow.
PB IOP Publishing
SN 0741-3335
YR 2018
FD 2018-02
LK https://hdl.handle.net/10016/35749
UL https://hdl.handle.net/10016/35749
LA eng
NO Research was funded in part by the Spanish National Project No.ENE2015-68265. Research carried in part at the Max-PlanckInstitute for Plasma Physics in Greifswald (Germany), whosehospitality is gratefully acknowledged. SIESTA free-boundaryruns have been carried out in Uranus, a supercomputer clusterlocated at Universidad Carlos III de Madrid and funded jointlyby EU-FEDER funds and by the Spanish Government via theNational Projects No. UNC313-4E-2361, No. ENE2009-12213-C03-03, No. ENE2012-33219, and No. ENE2012-31753.
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RD 18 may. 2024