Effects of trapped electrons on off-axis lower hybrid current drive in tokamaks

The effects of trapped electrons on off-axis lower hybrid current drive （LHCD） in tokamaks are studied, A computer code for solving the Fokker-Planck equation in a toroidal geometry is developed and employed. The code is suitable for various auxiliary heating and current drive schemes in tokamak plasmas. The influence of the resonance regime on the current drive efficiency as well as the influence of trapped particle fraction on the current drive efficiency are emphasized. It is shown that, as an electrostatic force, the lower hybrid wave causes some of the trapped electrons to be untrapped and lose their energy, which can cut the LHCD efficiency by about 30%. The ITER scaling law is also used to estimate the trapped electron effects.[第一段]     

Reliable teleportation in trapped ions

We study a method for the implementation of a reliable teleportation protocol (theoretically, 100% of success) of internal states in trapped ions. The generation of the quantum channel (any of four Bell states) may be done respecting technical limitations on individual addressing and without claiming the Lamb-Dicke regime. An adequate Bell analyzer, that transforms unitarily the Bell basis into a completely disentangled one, is considered. Probable sources of error and fidelity estimations of the teleportation process are studied. Finally, we discuss experimental issues, proposing a scenario in which the present scheme could be implemented. Received 1st June 2000 and Received in final form 17 August 2000     

Dust-acoustic waves in a self-gravitating complex plasma with trapped electrons and nonisothermal ions

It is shown that the nonlinear equations governing the dynamics of the large amplitude waves in a self-gravitating unmagnetized collisionless dust-electron-ion plasma admit stationary dust-acoustic shock solutions. Owing to the adiabaticity of dust-charge variation, inclusion of self-gravitation, and to the departure from the so-called Botzmannian electrons and ions to the trapped electrons and nonthermal ions, the dynamics of the nonlinear wave is found to be governed by a new energy-like integral equation.     

Effect of trapped ions on shielding of a charged spherical object in a plasma

Collisions have traditionally been neglected in calculating the shielding around a small spherical collector in a plasma, and the plasma flow to the collector. We show analytically that, in dusty plasmas under typical discharge conditions, ion charge-exchange collisions lead to the buildup of negative-energy trapped ions which dominate the shielding cloud in the nonlinear region near a dust grain and substantially increase the ion current to the grain, even when the mean-free path is much greater than the Debye length.     

Background-free detection of trapped ions

We demonstrate a Doppler cooling and detection scheme for ions with low-lying D levels which almost entirely suppresses scattered laser light background, while retaining a high fluorescence signal and efficient cooling. We cool a single ion with a laser on the $^{2}\mathrm{S}_{\mbox{\tiny$1/2$}}\leftrightarrow {^{2}\mathrm{P}}_{\mbox{\tiny$1/2$}}$ transition as usual, but repump via the $^{2}\mathrm{P}_{\mbox{\tiny$3/2$}}$ level. By filtering out light on the cooling transition and detecting only the fluorescence from the $^{2}\mathrm{P}_{\mbox{\tiny$3/2$}}\rightarrow {^{2}\mathrm{S}}_{\mbox{\tiny$1/2$}}$ decays, we suppress the scattered laser light background count rate to 1 s^?1 while maintaining a signal of 29000 s^?1 with moderate saturation of the cooling transition. This scheme will be particularly useful for experiments where ions are trapped in close proximity to surfaces, such as the trap electrodes in microfabricated ion traps, which leads to high background scatter from the cooling beam.     

Quantum Zeno effect in trapped ions

A “continuous measurement” quantum Zeno effect (QZE) in the context of trapped ions is predicted. We describe the physical system and study its exact time evolution showing the appearance of Zeno phenomena. New indicators for the occurrence of QZE in oscillatory systems are proposed and carefully discussed.     

Nonlinear localized dust acoustic waves in a charge varying dusty plasma with trapped ions

The problem of nonlinear variable charge dust acoustic waves in a dusty plasma with trapped ions is revisited. The correct non-isothermal ion charging current is presented for the first time based on the orbit motion limited (OML) approach. The variable dust charge is then expressed in terms of the Lambert function and we take advantage of this new transcendental function to investigate nonlinear localized dust acoustic waves in a charge varying dusty plasma with trapped ions more rigorously.     

Accurate mass spectrometry of trapped ions

The Penning trap Ion Cyclotron Resonance (ICR) method we use to weigh atomic masses is reviewed, and our plans for future measurements, new methods, and apparatus improvements are discussed. Our ultimate goal is to develop a new technique for measuring atomic masses with an accuracy of a few parts in 10¹². We will do this by comparing the cyclotron frequencies of two simultaneously trapped ions. In order to successfully implement this new method we are developing a quieter, more sensitive DC SQUID-based detector and a new more harmonic trap, and we plan to use our classical squeezing techniques to reduce the effects of thermal noise. With our improved apparatus we will weigh Cs and Rb to help determine the fine structure constant α, weigh ²⁹Si and ³⁰Si as part of the current effort to replace the artifact kilogram standard with a Si crystal containing a known number of atoms, and measure the ³H-³He mass difference to help set a limit on the mass of the electron neutrino. Our higher accuracy will also enable us to ``weigh' the neutron capture gamma rays of <sup>28</sup>Si, <sup>32</sup>S, and <sup>48</sup>Ti to help determine the molar Planck constant N<sub>A</sub>h and the fine structure constant α. Finally, with a mass measurement accuracy \sim 10<sup>-12</sup> we will be able to ``weigh' chemical bonds. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-frequency coherent edge fluctuations in a high-pedestal-pressure quiescent H-mode plasma

A set of high frequency coherent (HFC) modes (f=80-250 kHz) is observed with beam emission spectroscopy measurements of density fluctuations in the pedestal of a strongly shaped quiescent H-mode plasma on DIII-D, with characteristics predicted for kinetic ballooning modes (KBM): propagation in the ion-diamagnetic drift direction; a frequency near 0.2-0.3 times the ion-diamagnetic frequency; inferred toroidal mode numbers of n～10-25; poloidal wave numbers of k(θ)～0.17-0.4 cm(-1); and high measured decorrelation rates (τ(c)(-1)～ω(s)～0.5×10(6) s(-1)). Their appearance correlates with saturation of the pedestal pressure.     

Strong ExB shear flows in the transport-barrier region in H-mode plasma

We report the first experimental observation of stationary zonal flow in the transport-barrier region of the H-mode plasma. Strong peaks in Er shear mark the width of this region. A strong m = n = 0 low-frequency (f < 0.6 kHz) zonal flow is observed in regions of increased Er, suggesting a substantial contribution of zonal flow to the spatial modulation of Er radial profiles. Radial localization of the zonal flow is correlated with a region of zero magnetic shear and low-order (7/5) rational surfaces.     

Thermodynamic properties of rotating trapped ideal Bose gases

Ultracold atomic gases can be spined up either by confining them in rotating frame, or by introducing “synthetic” magnetic field. In this paper, thermodynamics of rotating ideal Bose gases are investigated within truncated-summation approach which keeps to take into account the discrete nature of energy levels, rather than to approximate the summation over single-particle energy levels by an integral as it does in semi-classical approximation. Our results show that Bose gases in rotating frame exhibit much stronger dependence on rotation frequency than those in “synthetic” magnetic field. Consequently, BEC can be more easily suppressed in rotating frame than in “synthetic” magnetic field.     

Light-pressure cooling of trapped ions in three dimensions

We formulate a Fokker-Planck theory for the three-dimensional cooling of a trapped ion by means of a single laser beam. Both the steady state and the dynamics of the cooling are discussed, and the correlations between the vibrational modes due to the light pressure are elucidated. A few comments on the actual experiments are presented.     

Employing trapped cold ions to verify the quantum Jarzynski equality

We propose a scheme to investigate the nonequilibrium work distribution of a quantum particle under well controlled transformations of the external potential, exploiting the versatility of a single ion in a segmented linear Paul trap. We describe in detail how the motional quantum state of a single ion can be prepared, manipulated, and finally readout to fully determine the free energy difference in both harmonic and anharmonic potentials. Uniquely to our system, we show how an ion may be immersed in an engineered laser-field reservoir. Trapped ions therefore represent an ideal tool for investigating the Jarzynski equality in open and closed quantum systems.     

制备囚禁离子的簇态

提出一个方案用于制备囚禁离子的簇态,制备过程中振动模仅仅是被虚激发。方案用双能级离子制备簇态,只要一束激光照射两个相互作用的离子。方案简单易行,成功几率可达到100.