Model for Incomplete Reconnection in Sawtooth Crashes

TL;DR

This paper presents a model explaining incomplete magnetic reconnection during sawtooth crashes in tokamaks, supported by simulations and data, with implications for future fusion devices like ITER.

Contribution

The paper introduces a self-consistent model linking reconnection dynamics, pressure gradients, and diamagnetic effects to incomplete reconnection in sawtooth crashes.

Findings

Model predictions align with experimental data from Mega Ampere Spherical Tokamak.

Simulations confirm the role of diamagnetic drift speed in shutting off reconnection.

The model's applicability extends to future tokamaks, including ITER.

Abstract

A model for incomplete reconnection in sawtooth crashes is presented. The reconnection inflow during the crash phase of sawteeth self-consistently convects the high pressure core toward the reconnection site, raising the pressure gradient there. Reconnection shuts off if the diamagnetic drift speed at the reconnection site exceeds a threshold, which may explain incomplete reconnection. The relaxation of magnetic shear after reconnection stops may explain the destabilization of ideal interchange instabilities reported previously. Proof-of-principle two-fluid simulations confirm this basic picture. Predictions of the model compare favorably to data from the Mega Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are discussed. The results should apply across tokamaks, including ITER.