arXiv subjects

Declan Diver

Publications and source records attributed to Declan Diver.

4 recordsLinked to original sources

arXiv2025

Negative charge acquisition by isolated single microdroplets from plasma exposure at atmospheric pressure

Charged liquid microdroplets have generated significant interest recently due to the observation of chemical reaction rate enhancement by orders of magnitude. Droplet charging by plasma irradiation has been observed along with significantly enhanced reaction rates in liquid. In this paper we measure the charge on fixed size (47 $\mu$m) individual droplets, exposed for approximately 4 ms to a low temperature RF-driven plasma operated at atmospheric pressure. The measured charge values (0.8 - 2.0 $\times 10^{7}$ electrons) approached the Rayleigh limit for the given droplet diameter. Results were compared with finite element simulations of plasma charging which provided estimates of surface electric fields and charge fluxes to the droplet surface and helps advance the development of a theoretical framework for plasma-charged microreactors.

physics.plasm-ph↗

arXiv2025

Free electron charging of microdroplets in a plasma at atmospheric pressure

Gas-phase microdroplets have recently demonstrated exceptional chemical properties via suspected mechanisms such as contact electrification and surface charge pinning, producing high surface electric fields. Here, microdroplets are injected into a low-temperature atmospheric-pressure plasma and exposed to an excess free-electron flux. We report the first measurements of droplet charge in a fully collisional plasma, with averages up to 2.5 $\times 10^{5}$ electrons for 15 $\mu$m droplets, dependent on absorbed power. Simulations indicate solid particles under similar conditions acquire $\sim$40\% less charge, likely due to low-mobility water cluster ion formation around evaporating droplets, and predict surface electric fields up to $10^{7}$ V m$^{-1}$ for the smallest droplets (3 $\mu$m). Plasma exposure also produces H$_{2}$O$_{2}$ in the liquid, with concentrations up to 33 mM, corresponding to remarkable generation rates exceeding 275 M s$^{-1}$. The system involves complex, not yet fully elucidated mechanisms. A controlled plasma environment enables defined charge levels and exposure times, allowing systematic study and enhancing droplet properties.

physics.plasm-ph↗

arXiv2012

Dust cloud lightning in extraterrestrial atmospheres

Lightning is present in all solar system planets which form clouds in their atmospheres. Cloud formation outside our solar system is possible in objects with much higher temperatures than on Earth or on Jupiter: Brown dwarfs and giant extrasolar gas planets form clouds made of mixed materials and a large spectrum of grain sizes. These clouds are globally neutral obeying dust-gas charge equilibrium which is, on short timescales, inconsistent with the observation of stochastic ionization events of the solar system planets. We argue that a significant volume of the clouds in brown dwarfs and extrasolar planets is susceptible to local discharge events and that the upper cloud layers are most suitable for powerful lightning-like discharge events. We discuss various sources of atmospheric ionisation, including thermal ionisation and a first estimate of ionisation by cosmic rays, and argue that we should expect thunderstorms also in the atmospheres of brown dwarfs and giant gas planets which contain mineral clouds.

astro-ph.EP↗

arXiv2010

The optical depth of white-light flare continuum

The white-light continuum emission of a solar flare remains a puzzle as regards its height of formation and its emission mechanism(s). This continuum, and its extension into the near UV, contain the bulk of the energy radiated by a flare, and so its explanation is a high priority. We describe a method to determine the optical depth of the emitting layer and apply it to the well-studied flare of 2002 July~15, making use of MDI pseudo-continuum intensity images. We find the optical depth of the visible continuum in all flare images, including an impulsive ribbon structure to be small, consistent with the observation of Balmer and Paschen edges in other events.

astro-ph.SR↗