High-energy pulsed electron-beam-induced phase transitions in a plasma-levitated crystalline dust cluster

Dust clusters with crystalline structure, formed by charged microparticles in complex plasmas, can undergo phase transitions under external influences. While many studies have focused on the effects of temperature and pressure on crystallization, it is worthwhile to investigate a different factor such as the influence of an electron beam on the structural properties of the cluster. This study investigates the melting of a dust cluster with crystalline symmetry composed of micrometer-size plastic spheres, suspended in a radio-frequency argon plasma, induced by a high-energy pulsed electron beam with a tunable energy range of 9-14 keV. Imaging at 60 frames per second provided high-resolution particle trajectories, enabling structural and dynamical analyses via Voronoi diagrams, pair-correlation functions g(r), and particle tracking velocimetry. The results show that the electron-beam energy governs the melting process. At 9-10 keV, gradual disordering and hexaticlike behavior suggest a continuous transition, with g(r) peaks broadening continuously and particle velocities increasing incrementally. At 11-14 keV, rapid destabilization, chaotic trajectories, and abrupt g(r) collapse indicate a sharp transition, with melting times dropping from 0.6 s to 0.1 s. The process is characterized by the induced rotation of the entire crystal irradiated with 9-10 keV electrons, exhibiting minimal structural deformation, followed by a shear-induced destabilization of the rotating layers and eventual melting of the cluster. Velocity and kinetic-energy distributions further confirm distinct transition regimes. These findings highlight the electron beam's role in controlling phase behavior, offering insights into the dynamics of the crystalline structure with potential applications in astrophysics, semiconductor processing, and fusion research.