Kuang-Ting Chen

Particle confinement and the anomalous Doppler instability during combined inductive and lower‐hybrid current drive

Increases in average density have been observed during lower‐hybrid current‐drive experiments (LHCD) on the Versator II tokamak [Phys. Rev. Lett. 48, 152 (1982)], and on other LHCD experiments where inductive‐Ohmic and lower‐hybrid current drive are combined. In the present experiment it is found that this density increase is the result of an improvement in global particle confinement time τp in comparison to purely Ohmic discharges with similar plasma parameters. Furthermore, it is found that the improved confinement deteriorates when the anomalous Doppler relaxation instability of the anisotropic high‐energy electron tail becomes unstable during LHCD, and the loss rate of tail electrons increases. However, energetic electron losses alone are at least an order of magnitude too small to explain this deterioration in particle confinement.

Unified formalism for calculating polarization, magnetization, and more in a periodic insulator

In this paper, we propose a unified formalism, using Greens functions, to integrate out the electrons in an insulator under uniform electromagnetic fields. We derive a perturbative formula for the Greens function in the presence of uniform magnetic or electric fields. Applying the formula, we derive the formula for the polarization, the orbital magnetization, and the orbital magneto-polarizability, without assuming time reversal symmetry. Specifically, we realize that the terms linear in the electric field can only be expressed in terms of the Greens functions in one extra dimension. This observation directly leads to the result that the coefficient of the

Violation of the Onsager relation for quantum oscillations in superconductors

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Experimental measurements of lower-hybrid wave propagation in the versator II tokamak using microwave scattering

term in any dimensions is given by a Wess-Zumino-Witten-type term, integrated in the extended space, interpolating between the original physical Brillouin zone and a trivial system, with the group element replaced by the Greens function. This generalizes an earlier result for the case of time reversal invariance [see Z. Wang, X.-L. Qi, and S.-C. Zhang, Phys. Rev. Lett. {\bf 105}, 256803 (2010)].

Topological insulator and theθvacuum in a system without boundaries

We studied the quantum oscillations in superconducting vortex mixed states with d-wave pairing. We showed that the Onsager relation does not always apply. Furthermore, at mean field level the quantum oscillations from electron pockets are suppressed by the pairing. We conclude that an interpretation of the experimental results asccoming from the four hole pockets created by a (π, π) folding cannot be ruled out.

LOWER HYBRID HEATING EXPERIMENTS ON THE ALCATOR-C AND THE VERSATOR-II TOKAMAKS

A series of 139 GHz microwave scattering experiments has been performed on the Versator II tokamak (B. Richards, Ph.D. thesis, Massachusetts Institute of Technology, 1981) to study the propagation of externally launched 0.8 GHz lower‐hybrid waves. During lower‐hybrid current drive, the launched waves are found to follow a highly directional resonance cone in the outer portion of the plasma. Wave power is also detected near the center of the plasma, and evidence of wave absorption is seen. Scattering of lower‐hybrid waves in k space by density fluctuations appears to be a weak effect, although measurable frequency broadening by density fluctuations is found, Δω/ω=3×10−4. In the detectable range (2.5<N∥<5.5) the N∥ spectra inferred from the scattering measurements are quite similar above and below the current drive density limit. Numerical modeling of these experiments using ray tracing is also presented.

Lower-hybrid RF current drive and electron-cyclotron heating on the Versator II tokamak

In this paper we address two questions concerning the effective action of a topological insulator in one and three dimensional space without boundaries, such as a torus. The first is whether a uniform

Static electric field in one-dimensional insulators without boundaries

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Detection of lower‐hybrid waves on Versator II using microwave scattering

-term with

Particle confinement improvement during 2.45 GHz lower‐hybrid current‐drive experiments

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