Title: The locking and unlocking thresholds for tearing modes in a cylindrical tokamak

Abstract

The locking and unlocking thresholds for tearing modes are in general different. Here, the physics origin for this difference is illustrated from theory analysis, and a numerical procedure is developed to find both locking and unlocking thresholds. In particular, a new scaling law for the unlocking threshold that is valid in both weak and strong rotation regimes has been derived from the lowest amplitude of the RMP (resonant magnetic perturbation) allowed for the locked-mode solution. Above the unlocking threshold, the criterion for the phase-flip instability is extended to identify the entire locked-mode states. Two different regimes of the RMP amplitude in terms of the accessibility of the locked-mode states have been found. In the first regime, the locked-mode state may or may not be accessible depending on the initial conditions of an evolving island. In the second regime, the locked-mode state can always be reached regardless of the initial conditions of the tearing mode. The lowest RMP amplitude for the second regime is determined to be the modelocking threshold. The different characteristics of the two regimes above the unlocking threshold reveal the underlying physics for the gap between the locking and unlocking thresholds and provide an explanation for the closelymore » related and widely observed hysteresis phenomena in island evolution during the sweeping process of the RMP amplitude up and down across that threshold gap.« less

Authors:

Huang, Wenlong ^[1]; Zhu, Ping ^[2]

---

+ Show Author Affiliations

1. Univ. of Science and Technology of China, Hefei (China). Key Lab. of Geospace Environment and Dept. of Modern Physics
2. Univ. of Science and Technology of China, Hefei (China). Key Lab. of Geospace Environment and Dept. of Modern Physics; Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics

Publication Date:

Thu Mar 10 00:00:00 EST 2016

Research Org.:

Univ. of Wisconsin, Madison, WI (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division; National Magnetic Confinement Fusion Science Program of China; Chinese Academy of Sciences (CAS)

Contributing Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)

OSTI Identifier:

1468532

Alternate Identifier(s):

OSTI ID: 1241440

Grant/Contract Number:  

FG02-86ER53218; FC02-08ER54975; AC02-05CH11231; 2014GB124002; 2015GB101004; 2015GB120005

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 23; Journal Issue: 3; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 42 ENGINEERING; magnetohydrodynamics; plasma confinement; laser physics; electron density; magnetic ordering; tokamaks; dynamical systems; oscillators; non linear dynamics; plasma instabilities