Physics of forced magnetic reconnection in coaxial helicity injection experiments in National Spherical Torus Experiment

F. Ebrahimi, R. Raman, E. B. Hooper, C. R. Sovinec, A. Bhattacharjee

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

We numerically examine the physics of fast flux closure in transient coaxial helicity injection (CHI) experiments in National Spherical Torus Experiment (NSTX). By performing resistive Magnetohydrodynamics (MHD) simulations with poloidal injector coil currents held constant in time, we find that closed flux surfaces are formed through forced magnetic reconnection. Through a local Sweet-Parker type reconnection with an elongated current sheet in the injector region, closed flux surfaces expand in the NSTX global domain. Simulations demonstrate outflows approaching poloidally Alfvénic flows and reconnection times consistent with the Sweet-Parker model. Critical requirements for magnetic reconnection and flux closure are studied in detail. These primary effects, which are magnetic diffusivity, injector flux, injector flux footprint width, and rate of injector voltage reduction, are simulated for transient CHI experiments. The relevant time scales for effective reconnection are τV<τ rec τ AS(1+Pm)1/4<τR, where τV is the time for the injector voltage reduction, τA is the poloidal Alfvén transit time, τR is the global resistive diffusion time, and Pm and S are Prandtl and Lundquist numbers.

Original languageEnglish (US)
Article number056109
JournalPhysics of Plasmas
Volume21
Issue number5
DOIs
StatePublished - May 2014

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

Fingerprint Dive into the research topics of 'Physics of forced magnetic reconnection in coaxial helicity injection experiments in National Spherical Torus Experiment'. Together they form a unique fingerprint.

  • Cite this