Catalin M. Ticos

Dust crystal interaction with plasma flows

A novel experiment is proposed to study the interaction between a dust crystal formed in a low ionized rf plasma (ne ≈ 1015 m−3) with room temperature ions (≈ 0.025 eV) [1, 2] and an incident plasma flow with a few orders of magnitude higher density (ne ≈1017–1018 m−3), ions with temperature ≈ 1 eV and drift velocity of the order of ≈ 10 km/s. The higher density plasma flow is produced inside a miniature coaxial plasma gun powered by a capacitor bank [3]. Of major interest here is the dynamics of the plasma crystal as the density of the charged particles increases. The Debye length is reduced and therefore the electrostatic coupling between the dust particles is expected to be weaker. At the same time the electrical charge on the micron-size dust particles varies rapidly [4]. Real-time monitoring with a high-speed camera of particle trajectories can provide direct information on dust charging, dust-dust and dust-plasma flow interactions. Additionally, the generated plasma flow can create dust wakes in the direction of the flow. A vertical wake structure already exists in the steady crystal residing in the rf plasma sheath and it affects mostly the lower layers of the dust crystal, as ions stream through the sheath to the electrode. For a plasma flow parallel with the horizontal dust layers, wakes could be formed in the horizontal direction of the crystal as well. This can allow the creation of a plasma crystal with a double structure of vertical and horizontal wake potential wells, which can lead to the observation of new interesting phenomena.

M:N phase synchronization of LFF in an chaotic ECSL system

The chaotic behavior of on external-cavity semiconductor laser (ECSL) working in a regime of low-frequency fluctuations (LFFs) can be controlled by external electro-optical phase or intensity current modulation. It is shown by numerical simulation that, for specific values of the modulating frequency and amplitude, the phase difference between the laser power drop-out and the modulator remains constant in time leading to phase-synchronized states, steady LFFs, so called m:n phase synchronization. The degree of stabilization is determined by calculating Shannons entropy and by the analyzing the stability of the phase locking. The synchronization regions are mapped and zones of low and high amplitude chaos are identified. The light emission can be stabilized from a regime of large amplitude chaotic oscillations corresponding to LFFs to one of low-amplitude chaotic or even periodic oscillations. The dynamics of the laser can be controlled when the period of the modulating signal is comparable with the laser itinerancy time between consecutive external-cavity modes.

Micro-Particles as Probes for Laboratory Plasmas

Summary form only given. To diagnose plasmas with least perturbation, while still achieving good spatial resolution, one of the most common and simple approaches is to use small physical probes, which still have a long dimension out to the wall for data transmission. An alternative, which is truly miniature in all three dimensions, is to use microparticles (~10-6 m). The concept of injecting microparticles for plasma diagnostics was first introduced to measure internal magnetic field topology in 500-eV-temperature plasmas [Wang and Wurden, Rev. Sci. Instrum. 74, 1887 (2003)]. Here we suggest that, combined with laser sheet-beam and fast cameras, use of microparticles can be extended to measure plasma flow and turbulence structures by carefully choosing geometry, size, materials, and physical properties of microparticles. Because the surface-to-volume ratio of a microparticle scales like ~1/r, where r is the characteristic dimension, surface conditions will play important role in data interpretation. In the mean time, microparticle charging, electron and ion fluxes, electric and magnetic fields can induce other effects, such as rocket effects. Furthermore, experimental data about microparticles in plasmas may be used as inputs for cosmic dust modeling. It is also interesting to study the effects of the plasma Debye length relative to the dust size. In summary, this talk will discuss the complexity of microparticle-plasma interactions, including both challenges and opportunities for microparticle applications to plasmas.