A combination of time-resolved optical emission spectroscopy measurements and collisionalradiative modeling is used to investigate the phenomena occurring over multiple time scales in the frequency domain of a low-pressure, axially asymmetric, capacitively coupled radiofrequency (RF) argon plasma with pulsed injection of hexamethyldisiloxane (HMDSO, Si 2 O(CH 3) 6). The collisional-radiative model developed here considers the population of argon 1s and all ten 2p levels (in Paschen's notation). The presence of HMDSO in the plasma is accounted for in the model by quenching of the argon 1s states by species generated by plasma processing of HMDSO, including HMDSO-15 (Si 2 O(CH 3) 5), acetylene (C 2 H 2) and methane (CH 4). Detailed analysis of the relative populations of Ar 2p states reveals cyclic evolutions of the electron temperature, electron density and quenching frequency that are shown to be linked to the kinetics of dust formation in Ar/HMDSO plasmas. Penning ionization of HMDSO and its fragments is found to be an important source of electrons for the plasma maintenance. It is at the origin of the cyclic formation/disappearance of the dust cloud, without attenuation of the phenomenon, as long as the pulsed injection of HMDSO is sustained. The multi-scale approach used in this study further reveals the straightforward relation of the frequency of HMDSO pulsed injection, in particular the HMDSO duty cycle, with the frequency of dust formation/ disappearance cycle.

Evolutionary radiations are fascinating phenomena corresponding to a dramatic diversification of taxa and a burst of cladogenesis over short periods of time. Most evolutionary radiations have long been regarded as adaptive but this has seldom been demonstrated with large-scale comparative datasets including fossil data. Originating in the Early Jurassic, irregular echinoids are emblematic of the spectacular diversification of mobile marine faunas during the Mesozoic Marine Revolution. They diversified as they colonized various habitats, and now constitute the main component of echinoid fauna in modern seas. The evolutionary radiation of irregular echinoids has long been considered as adaptive but this hypothesis has never been tested. In the present work we analyze the evolution of echinoid species richness and morphological disparity over 37 million years based on an extensive fossil dataset. Our results demonstrate that morphological and functional diversifications in certain clades of irregular echinoids were exceptionally high compared to other clades and that they were associated with the evolution of new modes of life and so can be defined as adaptive radiations. The role played by ecological opportunities in the diversification of these clades was critical, with the evolution of the infaunal mode of life promoting the adaptive radiation of irregular echinoids.

In microwave plasmas with the presence of a magnetic field, fast electrons could result from collisionless energy absorption under electron cyclotron resonance (ECR) conditions. In this case, electrons are trapped between the two poles of the magnetic field and rotate at the cyclotron frequency ωce. When crossing a zone where the cyclotron frequency equals the microwave frequency (ωce=ω), electrons see a steady electric field in their reference frame and are constantly accelerated by the right handed polarized (RHP) wave. When the plasma density reaches the so-called critical density nc at which ωpe2=ω2±ωωce, where ωpe is the plasma electron frequency, the left handed polarized (LHP) electromagnetic wave can excite electrostatic waves that can produce collisionless electron heating and fast electron generation by Landau damping. In this study, a combination of the Langmuir probe and trace rare gas optical emission spectroscopy (TRG-OES) is used to analyze the electron energy probability function (EEPF) in microwave (2.45 GHz) low-pressure argon plasmas excited at ECR in a dipolar magnetic field. While both TRG-OES and Langmuir probe measurements agree on the effective electron temperature (TeAll) from 1.6 to 50 mTorr, TRG-OES, which is more sensitive to high energy electrons, shows that the EEPF is the sum of two Maxwellian populations: one described by TeAll and a high energy tail characterized by a temperature TeTail. Spatially resolved-TRG-OES measurements show that the high-energy tail (TeTail) in the EEPF is spatially localized near the magnet, while the effective electron temperature (TeAll) stays constant. The ratio between the high energy tail and the effective temperatures is found to increase with the absorbed microwave power and decrease with increasing pressure. The former phenomenon is ascribed to a rise in ECR heating due to a stronger RHP wave electric field and to an enhanced absorption of the LHP waves. On the other hand, the decrease in the ratio is attributed to a smaller magnetic confinement of the electrons (increase in the collision frequency), which lessens ECR heating and to a decrease in the LHP field intensity at the resonant position, which impedes the conversion into electrostatic waves.

In surface-wave plasmas, the energy can be transferred to the plasma electrons through both ohmic (collisional) and collisionless heating mechanisms. At very low pressure, when the electron-neutral collision frequency is much lower than the wave frequency (collisionless regime), a resonance is excited close to the tube walls where the electron plasma frequency in the radially-inhomogeneous plasma column reaches the wave frequency. In such conditions, the sharp rise of the component of the surface-wave electric field perpendicular to the tube axis can induce transit-time heating. At the resonant point, the long-wavelength electromagnetic surface wave can also be converted into short-wavelength electrostatic Langmuir waves that propagate down the density gradient. In this work, spatially-resolved trace-rare-gases optical emission spectroscopy combined with collisional-radiative modeling is used to analyze the electron energy distribution function (EEDF) and wave-particle interactions in low-pressure argon plasma columns sustained by an electromagnetic surface wave at 600 MHz (over-dense plasma). The EEDF is found to depart from a Maxwellian with the presence of a high-energy tail. The relative population of high-energy electrons increases with the axial distance towards the end of the plasma column where the electron density decreases and the resonance point becomes closer to the discharge axis. Over the range of experimental conditions examined, the high-energy tail increases with the characteristic length of the plasma density gradient at the resonance point; a feature that can be linked to collisionless electron heating by Landau damping of Langmuir waves.

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