Results 1 - 10 of 3185
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[en] It is identified that barely passing electrons are the drive of the e-fishbones, rather than the barely trapped electrons at low frequency. The frequency jump in e-fishbone experiments is reproduced and analyzed. It is found that the e-fishbone frequency increases with the hot electron energy, which is consistent with the experiments. The growth rate of the mode (m = 2, n = 2) is greater than that of the mode (m = 1, n = 1). (paper)
[en] The two dimensional eigenvalue equation describing the dissipative trapped electron mode is solved exactly in the limit of the mode overlapping many rational surfaces using the Pogutse model for the magnetic field and the pitch angle collision operator. The trapped electron contribution to the growth rate decreases, with respect to the standard theory, by a factor of order Δ/chi sub(T) << 1 where chi sub(T) is the position of the turning point and Δ the distance between rational surfaces
[en] We report a significant increase in the electro-optic (EO) effect of KTaxNb1-xO3 (KTN) crystals that we achieved by injecting carriers into them. The dielectric constant of KTN was increased approximately twofold by carrier injection. The EO beam scanning performance was effectively improved by the increase in the EO effect resulting from the increased dielectric constant. The estimated densities of the trapped electrons were as small as 5.8 × 1020m-3. The very small quantity of injected electrons greatly affected the dielectric constant and EO effect of the KTN crystals
[en] Off-axis rf-driven current can play a critical role in sustaining high Beta spherical torus (ST) plasmas without a central solenoid. Numerical modeling of electron Bernstein wave current drive (EBWCD) for a Β ∼ 40% ST plasma predicts efficient, off-axis, Ohkawa EBWCD. Current can be efficiently driven at r/a greater than 0.5 where the large trapped electron fraction precludes conventional Fisch-Boozer current drive and provides near-ideal conditions for Ohkawa EBWCD. Also, Ohkawa EBWCD efficiency increases with r/a. Enhancement over Fisch-Boozer current drive is a factor of two at r/a ∼ 0.2 rising to over an order of magnitude at r/a ∼ 0.5
[en] Second-harmonic electron cyclotron current drive (ECCD) experiments have been performed in the stellarator/heliotron (S/H) device, Heliotron J. A focused Gaussian beam is injected with the parallel refractive index, N||, ranging from -0.05 to 0.6. The EC driven current is estimated by excluding the bootstrap current from the total current. The experimental results show that the EC driven current is determined by the local magnetic field structure where the EC power is deposited. The maximum EC driven current is attained around N|| = 0.5 when the EC power is deposited at nearly the top of the magnetic ripple. A large increase in electron cyclotron emission (ECE) signals is observed when the EC current is driven, indicating an important role for high-energy electrons in the ECCD. The experimental results for N|| and B dependence agree with a ray-tracing simulation using a parallel momentum conservation model in which the trapped particle effect is included.
[en] Entanglement of isolated elementary particles other than photons has not yet been achieved. We show how building blocks demonstrated with one trapped electron might be used to make a model system and method for entangling two electrons. Applications are then considered, including two-qubit gates and more precise quantum metrology protocols.
[en] Obvious enhancement of blue mechanoluminescence (ML) has been observed for SrnMgSi2O5+n:Eu (1 ≤ n ≤ 2) (SMSE) fabricated via systematically controlling the defective phases. The existence of defective phases affects not only the concentration of trap centers but also the structure of SMSE. The dependence between ML intensity and thermoluminescence integrated intensity showed that the trap centers created by defective phase play an important role in producing the ML of SMSE. Furthermore, when the effect of trap centers on ML eliminated to the smallest, the sample with the easiest deformation structure possessed the highest ML intensity. The strong piezoelectric ability induced by the existence of defective phase is responsible for this phenomenon. These results indicate that the origin of ML is piezoelectricity-induced electroluminescence, that is, piezoelectricity impelled the trapped electrons to escape from the traps and produce ML.
[en] Positron irradiation effects on positronium formation in low-density polyethylene (LDPE), gamma-irradiated LDPE and unplasticized PVC (UPVC) are studied. At least in one of the three different measurements, i.e., prolonged positron annihilation measurement at room temperature, low temperature in darkness and subsequent measurement under light, changes in o-Ps intensity are observed in non-irradiated LDPE and gamma-irradiated LDPE. While in UPVC, change in o-Ps intensity is hardly observable in all the above-mentioned three measurements. Reduction of o-Ps intensity by light indicates that positronium formation via the recombination of a positron and a trapped electron exists in LDPE and gamma-irradiated LDPE. The absence of light bleaching effect, together with the fact that the value of o-Ps intensity in heating and cooling process of a thermal circle is nearly the same, indicates that in UPVC, positronium can not be formed through trapped electron mechanism. This study highlights the speciality of positronium formation in UPVC, positronium is formed exclusively by the recombination of electron-positron pairs with short separations. - Highlights: • Positron irradiation effects at RT and 10 K, in LDPE and in UPVC are studied. • Different factors lead to absence of changes in I3 at RT in irradiated LDPE and UPVC. • Light bleaching effect appears in gamma irradiated LDPE. • Absence of light-bleaching effect in UPVC shows the speciality of Ps formation. • Positronium formation of a positron and a trapped electron doesn’t exist in UPVC.
[en] The impact of impurities on the generation of zonal flow (ZF) driven by collisonless trapped electron mode turbulence in deuterium (D)–tritium (T) plasmas is investigated. An expression for ZF growth rate with impurities is derived by balancing the ZF potential shielded by polarization effects and the ZF modulated radial turbulent current. Then, it is shown that the maximum normalized ZF growth rate is reduced by the presence of fully ionized non-trace light impurities with relatively flat density profile, and slightly reduced by highly ionized trace tungsten, while the maximum normalized ZF growth rate can be enhanced by fully ionized non-trace light impurities with relatively steep density profile. In particular, the effects of high temperature helium from D–T reaction on ZF depend on the temperature ratio between electrons and high temperature helium. The possible relevance of our findings to recent experimental results and future burning plasmas is also discussed. (paper)
[en] A local equilibrium model for an up-down symmetric configuration in the vicinity of a specified magnetic surface is improved. The equilibrium accounts for all the essential features, like the elongation, the triangularity, and the Shafranov shift etc, of a shaped cross section. All needed parameters are self-consistently determined. The model can be used for the research of the radially localized phenomenon in tokamaks. As an application, we apply this model to the numerical calculation of the precession frequency of trapped electrons. (paper)