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"Trapped particles"
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Physics with trapped charged particles : lectures from the Les Houches Winter School
Articles on Physics with Trapped Charged Particles by speakers at the Winter School on Physics with Trapped Charged Particles hosted by the École de Physicque des Houches in January 2012. The articles cover all types of physics with charged particles, and are aimed at introducing the basic issues at hand, as well as the latest developments in the field. It is appropriate for PhD students and early career researchers, or interested parties new to the area.
Book
Electron hole instability as a primordial step towards sustained intermittent turbulence in linearly subcritical plasmas
Electron and ion holes are highly stable nonlinear structures met omnipresently in driven collisionless hot plasmas. A mechanism destabilizing small perturbations into holes is essential for an often witnessed but less understood subcritically driven intermittent plasma turbulence. In this paper we show how a tiny, eddy-like, non-topological electron seed fluctuation can trigger an unstable evolution deep in the linearly damped region, a process being controlled by the trapping nonlinearity and hence being beyond the realm of the Landau scenario. After a (transient) transition phase modes of the privileged spectrum of cnoidal electron and ion holes are excited which in the present case consist of a solitary electron hole (SEH), two counter-propagating 'Langmuir' modes (plasma oscillation), and an ion acoustic mode. A quantitative explanation involves a nonlinear dispersion relation with a forbidden regime and the negative energy character of the SEH, properties being inherent in Schamel's model of undamped Vlasov-Poisson structures identified here as lowest order trapped particle equilibria. An important role in the final adaption of nonlinear plasma eigenmodes is played by a deterministic response of trapped electrons which facilitates transfer of energy from electron thermal energy to an ion acoustic nonuniformity, accelerating the SEH and positioning it into the right place assigned by the theory.
Journal Article
Scientific Objectives of Electron Losses and Fields INvestigation Onboard Lomonosov Satellite
The objective of the Electron Losses and Fields INvestigation on board the Lomonosov satellite (ELFIN-L) project is to determine the energy spectrum of precipitating energetic electrons and ions and, together with other polar-orbiting and equatorial missions, to better understand the mechanisms responsible for scattering these particles into the atmosphere. This mission will provide detailed measurements of the radiation environment at low altitudes. The 400–500 km sun-synchronous orbit of Lomonosov is ideal for observing electrons and ions precipitating into the atmosphere. This mission provides a unique opportunity to test the instruments. Similar suite of instruments will be flown in the future NSF- and NASA-supported spinning CubeSat ELFIN satellites which will augment current measurements by providing detailed information on pitch-angle distributions of precipitating and trapped particles.
Journal Article
Geomagnetic secular variation consequences on the trajectories of radiation belt trapped particles
The trajectories of energetic particles trapped by the geomagnetic field, as those composing the Earth’s Van Allen radiation belts, are usually defined by three cyclic motions: gyration, bounce along field lines and drift around the Earth, which are all controlled by this field. The geomagnetic dipole, in turn, has been declining at a rate of ∼5% every hundred years since at least ∼1840. Even with the possibility of a recovery without an extreme event, the global field intensity will very probably continue to decrease in the near future with a consequent weakening of our planet’s magnetic shield capacity. The expected variations in trapped particle trajectories are analyzed in the present work through an analytical approach considering the observed axial dipolar geomagnetic field component and its secular variation. The variations expected on the mirror point altitude and on the boundary of Störmer forbidden zone are assessed along the period 1900-2020. The structures here analyzed could approximate plausible radiation belt changes for a continuously weakening geomagnetic dipole which might have numerous consequences for technologies that operate in space.
Journal Article
Deduction of the rates of radial diffusion of protons from the structure of the Earth's radiation belts
From the data on the fluxes and energy spectra of protons with an equatorial pitch angle of α0 ≈ 90° during quiet and slightly disturbed (Kp ≤ 2) periods, I directly calculated the value DLL, which is a measure of the rate of radial transport (diffusion) of trapped particles. This is done by successively solving the systems (chains) of integrodifferential equations which describe the balance of radial transport/acceleration and ionization losses of low-energy protons of the stationary belt. This was done for the first time. For these calculations, I used data of International Sun–Earth Explorer 1 (ISEE-1) for protons with an energy of 24 to 2081 keV at L = 2–10 and data of Explorer-45 for protons with an energy of 78.6 to 872 keV at L = 2–5. Ionization losses of protons (Coulomb losses and charge exchange) were calculated on the basis of modern models of the plasmasphere and the exosphere. It is shown that for protons with μ from ∼ 0.7 to ∼ 7 keV nT−1 at L ≈ 4.5–10, the functions of DLL can be approximated by the following equivalent expressions: DLL ≈ 4.9 × 10−14μ−4.1L8.2 or DLL ≈ 1.3 × 105(EL)−4.1 or DLL ≈ 1.2 × 10−9fd−4.1, where fd is the drift frequency of the protons (in mHz), DLL is measured in s−1, E is measured in kiloelectronvolt and μ is measured in kiloelectronvolt per nanotesla. These results are consistent with the radial diffusion of particles under the action of the electric field fluctuations (pulsations) in the range of Pc6 and contradict the mechanism of the radial diffusion of particles under the action of sudden impulses (SIs) of the magnetic field and also under the action of substorm impulses of the electric field. During magnetic storms DLL increases, and the expressions for DLL obtained here can change completely.
Journal Article
Systematic investigation of factors influencing trap stiffness in an optical tweezers setup
Single-beam gradient traps are produced by focusing light using high numerical aperture (NA) microscope objectives, usually with values between 1.2 and 1.4. Optical tweezers have long been used as photonic force microscopes, which probe the mechanics of biological systems that operate in the regime of picoNewtons. This study aims to address and showcase optical tweezers generated with low NA air objectives and compare them directly to traditional high NA objectives. The variation in the force in the presence of spherical aberration and defocus is also investigated along with the refractive index (RI) difference between the sample and the trapped particle, which will also influence the trap stiffness. All of these effects are shown to play a significant role in the lateral stiffness.
Journal Article
Cavity cooling of an optically levitated submicron particle
The coupling of a levitated submicron particle and an optical cavity field promises access to a unique parameter regime both for macroscopic quantum experiments and for high-precision force sensing. We report a demonstration of such controlled interactions by cavity cooling the center-of-mass motion of an optically trapped submicron particle. This paves the way for a light–matter interface that can enable room-temperature quantum experiments with mesoscopic mechanical systems.
Journal Article
A hierarchical Bayesian spatio-temporal model to forecast trapped particle fluxes over the SAA region
The particles trapped in the Earth's inner radiation belts could harm low Earth orbit (LEO) satellites. Although the inner radiation belts are usually stable, their response to extremely large solar geomagnetic events can produce satellite anomalies. The risk is higher because of frequent LEO satellite passes through the South Atlantic Anomaly (SAA). A model for forecasting the trapped particle flux distribution in equatorial LEO based on the hierarchical Bayesian spatio-temporal (HBST) statistical model was developed to address the risk to satellites. This model is applicable to low- and mediumenergy electrons and protons under all solar activity conditions. Dynamic rather than static data were also used. A simple HBST model named the Gaussian process (GP) was developed using NOAA 15 - 17 data, which categorized particle energies as ＞ 30 keV (mep0e1) and ＞ 300 keV (mep0e3) for electrons and 80 - 240 keV (mep0p2) and 800 - 2500 keV (mep0p4) for protons in the SAA region. The goal of this study is to examine the applicability of this model during a quiet period (15 - 19 May 2009) and a period of high solar activity (26 - 30 October 2003). The forecast was then interpolated using a Kriging technique to estimate the particle distribution. Statistical and visual validations showed good indicators, with average mean relative error (MRE) values of 20 - 30% for both periods and a similar pattern as that of the National Oceanic and Atmospheric Administration (NOAA) map. This work contributes a method for predicting the trapped particle flux distribution at low latitude LEOs.
Journal Article
Controlled transfer of transverse orbital angular momentum to optically trapped birefringent microparticles
The interaction between structured light beams possessing optical angular momentum and small particles promises new opportunities for optical manipulation, such as the generation of light-induced torque and rotation of objects. However, so far, studies have largely centred on nanoscale particles. Here we report the observation and measurement of the transfer of transverse angular momentum to birefringent spherical vaterite particles several wavelengths in size. We outline the physics behind the beam used to control the particles, perform quantitative measurements of the transverse spin angular momentum transfer and demonstrate the generation of fluid flow around multiple rotation axes. The findings show that light can impart controllable rotational degrees of freedom to microparticles. In the future, the approach may prove useful for investigating the dynamics of complex fluids in three dimensions, studying the shear force on cell monolayers or cooling an optically trapped particle to the quantum ground state.The angular momentum of light is shown to be able to impart light-induced transverse torque and rotation to microscale birefingent particles.
Journal Article
Simultaneous cavity cooling of all six degrees of freedom of a levitated nanoparticle
Controlling the motional degrees of isolated, single nanoparticles trapped within optical fields in a high vacuum are seen as ideal candidates for exploring the limits of quantum mechanics in a new mass regime. These systems are also massive enough to be considered for future laboratory tests of the quantum nature of gravity. Recently, the translational motion of trapped particles has been cooled to microkelvin temperatures, but controlling all the observable degrees of freedom, including their orientational motion, remains an important goal. Here we report the control and cooling of all the translational and rotational degrees of freedom of a nanoparticle trapped in an optical tweezer, accomplished by cavity cooling via coherent elliptic scattering. We reached temperatures in the range of hundreds of microkelvins for the translational modes and temperatures as low as 5 mK for the librational degrees of freedom. This work brings within reach applications in quantum science and the study of single isolated nanoparticles via imaging and diffractive methods, free of interference from a substrate.Optically trapped and levitated nanoparticles can be used to study macroscopic quantum effects, but fully controlling their motion is difficult. Now, all six roto-translational degrees of freedom have been cooled, although not to the quantum ground state.
Journal Article