DPEx-II: a new dusty plasma device capable of producing large sized DC coulomb crystals

Abstract

The creation of a spatially extended stable DC complex plasma crystal is a big experimental challenge and a topical area of research in the field of dusty plasmas. In this paper we describe a newly built and commissioned dusty plasma experimental (DPEx-II) device at the Institute for Plasma Research. The device can support the formation of large sized Coulomb crystals in a DC glow discharge plasma. The plasma in this L-shaped table-top glass chamber is produced between a circular anode and a long tray shaped cathode. It is characterized with the help of various electrostatic probes over a range of discharge conditions. The dust particles are introduced by a dust dispenser to form a strongly coupled Coulomb crystal in the cathode sheath region. The unique asymmetric electrode configuration minimizes the heating of dust particles and facilitates the formation of crystalline structures with a maximum achievable dimension of 40 cm × 15 cm using this device. A larger crystal has numerous advantages over smaller ones, such as higher structural homogeneity, fewer defects, lower statistical errors due to finite size effects etc. A host of diagnostics tools are provided to characterize the Coulomb crystal. Results of a few initial experiments aimed at demonstrating the technical capabilities of the device and its potential for future dusty plasma research, are reported.

Square lattice formation in a monodisperse complex plasma

“…The ∆z distribution essentially implies that the particles indeed form a bilayer system at V = 400 V with the two distinct peaks in Fig. 3 The unique electrode configuration [26] used in our DC discharge has the effect of moderating the dust-wake interaction. This configuration allows the ions to move towards the cathode with a higher Mach number (M) and leads to a weaker wake potential as compared to those commonly found in RF discharges [32][33][34].…”

“…In this condition, the resistance of the potentiometer is set at 3 kΩ. The plasma parameters such as plasma density and electron temperature, obtained from single and a double Langmuir probe measurements, are in the range of 1 − 2 x 10 15 /m 3 and 2 − 3 eV, respectively, for our discharge conditions [26]. The confinement strength is altered by adjusting the discharge voltage (V) and keeping the gas pressure (P) constant.…”

“…The experiments are conducted in a newly built Lshaped DC dusty plasma experimental (DPEx-II) device as shown in Fig. 1(a) [26]. A SS ring of diameter 6 cm is placed on the cathode to trap the dust particles horizontally.…”

“…As discussed in [21], one needs to suppress the MCI through proper control of the wake field interactions as well as neutral damping to successfully attain the desired structural phase transition. In our experimental device the asymetric electrode configuration has a direct influence on the course of the streaming ions that helps in the stability and ease of formation of the crystalline state [26]. By preventing the ion wake interactions to achieve high values and through a judicious control of the background pressure as well as the confining potential we are able to transition from an extended hexagonal monolayer crystal to a state with a number of small domains of square lattices.…”

Self-sustained non-equilibrium co-existence of fluid and solid states in a strongly coupled complex plasma system

“…Experimental set-up. All the experiments presented in this work have been performed in the Dusty Plasma Experimental-II (DPEx-II) device 42 , which has an L-shaped vacuum vessel made of pyrex-glass consisting of two chambers as shown in Fig. 1a.…”