Comparison between resistive and collisionless double tearing modes for nearby resonant surfaces

Bierwage, Andreas; Yu, Q.

doi:10.1088/0741-3335/49/5/008

Cited by 19 publications

(16 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The estimate for m peak is valid only for resistive DTMs. Nevertheless, broad spectra and high values m peak are also found when reconnection is mediated by electron inertia instead of resistivity, as is shown in a separate paper [21]. Also, Eq.…”

Section: Discussionmentioning

confidence: 54%

See 1 more Smart Citation

Dynamics of resistive double tearing modes with broad linear spectra

et al. 2007

View full text Add to dashboard Cite

The nonlinear evolution of resistive double tearing modes (DTMs) with safety factor values q = 1 and q = 3 is studied with a reduced cylindrical model of a tokamak plasma. We focus on cases where the resonant surfaces are a small distance apart. Recent numerical studies have shown that in such configurations high-m modes are strongly unstable and may peak around m = m peak ∼ 10. In this paper, it is first demonstrated that this result agrees with existing linear theory for DTMs. Based on this theory, a semi-empirical formula for the dependence of m peak on the system parameters is proposed. Second, with the use of nonlinear simulations, it is shown that the presence of fast growing high-m modes leads to a rapid turbulent collapse in an annular region, where small magnetic island structures form. Furthermore, consideration is given to the evolution of low-m modes, in particular the global m = 1 internal kink, which can undergo nonlinear driving through coupling to fast growing linear high-m DTMs. Factors influencing the details of the dynamics are discussed. These results may be relevant to the understanding of the magnetohydrodynamic (MHD) activity near the minimum of q and may thus be of interest for studies on stability and confinement of advanced tokamaks.

show abstract

Section: Discussionmentioning

confidence: 54%

“…The stabilization of high-m modes seems to depend on other factors, including the mechanism breaking the ideal-MHD constraint. For instance, collisionless DTMs due to electron inertia tend to have a broader spectrum of unstable modes than resistive DTMs for the same q profile [21].…”

Section: Comparison With Linear Theorymentioning

confidence: 99%

Dynamics of resistive double tearing modes with broad linear spectra

et al. 2007

View full text Add to dashboard Cite

show abstract

“…The simulation code is based on that used in [7,[18][19][20], which solves the normalized and Fourier-analysed reduced MHD equations in the form…”

Section: Normalization and Numerical Methodsmentioning

confidence: 99%

Dynamics of multiple flux tubes in sawtoothing KSTAR plasmas heated by electron cyclotron waves: II. Theoretical and numerical analysis

et al. 2014

View full text Add to dashboard Cite

The dynamics of multiple closed flux tubes in the core of a sawtoothing tokamak plasma are studied using nonlinear simulations. This is motivated by recent observations of long-lived hot spots in the electron cyclotron emission (ECE) images of KSTAR plasmas with electron cyclotron heating (ECH) (Yun et al 2012 Phys. Rev. Lett. 109 145003). Using an empirical source term in a reduced set of MHD equations, it is shown that flux tubes with helicity h = 1 are easily produced and survive for the observed time intervals only if the safety factor is close to unity (|q − 1| 0.5%) and the magnetic shear is small (|s| 1). This suggests that sawteeth in KSTAR leave behind wide regions where q ≈ 1. On the basis of the relevant time scales, we discuss how this magnetic geometry and the spatial localization of the EC resonance may allow ECH to actively induce the formation of flux tubes. Using simulations with q profiles that possess a wide q = 1 region inside the sawtooth inversion radius, we examine how the flux tubes merge and annihilate, and how their dynamics depend on the strength of the drive. The phenomena seen in the simulations and experiments lead us to conclude that, during the sawtooth ramp phase, there is a dynamic competition between sources and sinks of thermal and magnetic energy, where the flux tubes may play an important role; both as carriers of and channels for energy. The development of self-consistent simulation models is motivated and directions for future experiments are given.

show abstract

“…[19][20][21][22][23][24][25][26][27][28][29][30][31] Thus, the magnetic field can be expressed by the magnetic flux function w as B ¼ B ff þ rw Âf, where the toroidal field B f is assumed to be a constant,f Àẑ=R 0 qðaÞ is the unit vector in the toroidal direction, and a and R 0 are, respectively, the minor and major radius of the tokamak plasma. Under the assumption of incompressibility, the velocity can be represented as v ¼ Àr/ Âf, where / is the stream function.…”

Section: Modeling Equationsmentioning

confidence: 99%

The q-profile effect on high-order harmonic q = 1 tearing mode generation during sawtooth crashes

2012

View full text Add to dashboard Cite

The effect of q-profiles on the excitation of high-order harmonic q ¼ 1 tearing modes during sawtooth crashes is investigated by a collisionless fluid model with the electron inertia term in Ohm's law. It is found that for a flat q-profile in the core region, the high-order harmonics, such as m=n ¼ 2=2 and/or m=n ¼ 3=3 modes, comparable to or stronger than the m=n ¼ 1=1 component, can be excited during tokamak sawteeth. The stronger the magnetic shear on the q ¼ 1 surface is, the more unstable the higher-m modes are. For smoothly monotonously increased q-profiles, a lower q value on the plasma edge tends to easily excite higher-m harmonics at the same level as the m ¼ 1 mode simultaneously. The spatial characteristics of the eigenmodes in the cases with the typical q-profiles are also discussed. In addition, the basic feature of the magnetic island structures in the nonlinear evolution is numerically obtained, which is consistent qualitatively with the experimentally reconstructed phenomenon. V C 2012 American Institute of Physics. [http://dx.

show abstract

Comparison between resistive and collisionless double tearing modes for nearby resonant surfaces

Cited by 19 publications

References 40 publications

Dynamics of resistive double tearing modes with broad linear spectra

Dynamics of resistive double tearing modes with broad linear spectra

Dynamics of multiple flux tubes in sawtoothing KSTAR plasmas heated by electron cyclotron waves: II. Theoretical and numerical analysis

The q-profile effect on high-order harmonic q = 1 tearing mode generation during sawtooth crashes

Contact Info

Product

Resources

About