arXiv subjects

Jie Kong

Publications and source records attributed to Jie Kong.

28 records · Page 2Linked to original sources

arXiv2014

Mode coupling and resonance instabilities in quasi-two-dimensional dust clusters in complex plasmas

Small quasi-two-dimensional (2D) dust clusters consisting of three to eleven particles are formed in an argon plasma under varying rf power. Their normal modes are investigated through their mode spectra obtained from tracking thermal motion of the particles. Detailed coupling patterns between their horizontal and vertical modes are detected for particle numbers up to seven and discrete instabilities are found for dust clusters with particle number greater than nine, as predicted in previous theory on ion-flow induced mode coupling in small clusters. The instabilities are proven to be induced by resonance between coupled horizontal and vertical normal modes.

physics.plasm-ph↗

arXiv2014

Interaction force in a vertical dust chain inside a glass box

Small number dust particle clusters can be used as probes for plasma diagnostics. The number of dust particles as well as cluster size and shape can be easily controlled employing a glass box placed within a GEC rf reference chamber to provide confinement of the dust. The plasma parameters inside this box and within the larger plasma chamber have not yet been adequately defined. Adjusting the rf power alters the plasma conditions causing structural changes of the cluster. This effect can be used to probe the relationship between the rf power and other plasma parameters. This experiment employs the sloshing and breathing modes of small cluster oscillations to examine the relationship between system rf power and the particle charge and plasma screening length inside the glass box. The experimental results provided indicate that both the screening length and dust charge decrease as rf power inside the box increases. The decrease in dust charge as power increases may indicate that ion trapping plays a significant role in the sheath.

physics.plasm-ph↗

arXiv2013

Helical Structures in Vertically Aligned Dust Particle Chains in a Complex Plasma

Self-assembly of structures from vertically aligned, charged dust particle bundles within a glass box placed on the lower, powered electrode of a RF GEC cell were produced and examined experimentally. Self-organized formation of one-dimensional vertical chains, two-dimensional zigzag structures and three-dimensional helical structures of triangular, quadrangular, pentagonal, hexagonal, and heptagonal symmetries are shown to occur. System evolution is shown to progress from a one-dimensional chain structure, through a zigzag transition to a two-dimensional, spindle-like structure and then to various three-dimensional, helical structures exhibiting multiple symmetries. Stable configurations are found to be dependent upon the system confinement, (where are the horizontal and vertical dust resonance frequencies), the total number of particles within a bundle and the RF power. For clusters having fixed numbers of particles, the RF power at which structural transitions occur is repeatable and exhibits no observable hysteresis. The critical conditions for these structural transitions as well as the basic symmetry exhibited by the one-, two- and three-dimensional structures that subsequently develop are in good agreement with the theoretically predicted configurations of minimum energy determined employing molecular dynamics simulations for charged dust particles confined in a prolate, spheroidal potential as presented theoretically by Kamimura and Ishihara [10].

physics.plasm-ph↗

arXiv2011

One-dimensional vertical dust strings in a glass box

The oscillation spectrum of a one-dimensional vertical dust string formed inside a glass box on top of the lower electrode in a GEC reference cell was studied. A mechanism for creating a single vertical dust string is described. It is shown that the oscillation amplitudes, resonance frequencies, damping coefficients, and oscillation phases of the dust particles separate into two distinct groups. One group exhibits low damping coefficients, increasing amplitudes and decreasing resonance frequencies for dust particles closer to the lower electrode. The other group shows high damping coefficients but anomalous resonance frequencies and amplitudes. At low oscillation frequencies, the two groups are also separated by a π-phase difference. One possible cause for the difference in behavior between the two groups is discussed.

physics.plasm-ph↗

arXiv2011

Development of front-end readout electronics for silicon strip detectors

A front-end readout electronics system has been developed for silicon strip detectors. The system uses an application specific integrated circuit (ASIC) ATHED to realize multi-channel E&T measurement. The slow control of ASIC chips is achieved by parallel port and the timing control signals of ASIC chips are provided by the CPLD. The data acquisition is implemented with a PXI-DAQ card. The system software has a user-friendly GUI which uses LabWindows/CVI in Windows XP operating system. Test results showed that the energy resolution is about 1.22 % for alphas at 5.48 MeV and the maximum channel crosstalk of system is 4.6%. The performance of the system is very reliable and suitable for nuclear physics experiments.

physics.ins-det↗

arXiv2010

A Simple Method to Measure the Interaction Potential of Dielectric Grains in a Dusty Plasma

A simple minimally perturbative method is introduced which provides the ability to experimentally measure both the radial confining potential and the interaction potential between two individual dust particles, levitated in the sheath of a radio-frequency (RF) argon discharge. In this technique, a single dust particle is dropped into the plasma sheath to interact with a second individual dust particle already situated at the system's equilibrium point, without introducing any external perturbation. The resulting data is analyzed using a method employing a polynomial fit to the particle displacement(s), X(t), to reduce uncertainty in calculation. Employing this technique, the horizontal confinement is shown to be parabolic over a wide range of pressures and displacements from the equilibrium point. The interaction potential is also measured and shown to be well-described by a screened Coulomb potential and to decrease with increasing pressure. Finally, the charge on the particle and the effective dust screening distance are calculated. It is shown for the first time experimentally that the charge on a particle in the sheath of an RF plasma decreases with increasing pressure, in agreement with theoretical predictions. The screening distance also decreases with increasing pressure as expected. This technique can be used for rapid determination of particle parameters in dusty plasma.

physics.plasm-ph↗

arXiv2009

Measurement of the vertical non-uniformity of the plasma sheath in a complex plasma

Employing an attenuated oscillation method, the anisotropic interaction force between two vertically aligned dust particles located in the sheath of a complex plasma was measured experimentally based on a linear approximation to the interaction force. Experimental data shows that although both particles experience a repulsive interaction force, the upper particle experiences a stronger magnitude force than does the lower. This result can be explained by the ion wakefield since the lower particle resides within the ion wakefield generated by the streaming ions passing through the sheath and around the upper particle.

physics.plasm-ph↗

arXiv2007

Using dust particle vertical chains for wakefield investigation

Dust particles often form vertical chains due to the influence of the wakefield produced by the streaming ions in the plasma sheath. These particle chains are proving useful as a unique diagnostic tool for investigating the physics behind the basic properties of the ion wakefield within the plasma sheath. In this paper, an experimental method is presented for investigating the ion wakefield which employs a new oscillation technique designed to perturb a two-particle vertical chain. Using this technique, damped free fall oscillations are generated via an external DC bias to the lower electrode. A fast Fourier transformation is then used to produce a spectrum from the collected oscillation data and a center of mass oscillation is identified.

physics.plasm-ph↗

arXiv2007

Vertical Dust Particle Chains-Mass and Charge Measurements

Dusty plasmas have generated a large amount of interest since the discovery of ordered structure (crystal) formation in experimentally generated complex plasmas in 1994. Dust particles within the plasma sheath generated in these complex plasmas can form vertical chains due to the streaming ion wakefield. For the simplest of these configurations (a two particle chain), the particle closest to the lower electrode will generally remain in the shadow of the particle farthest from the lower electrode. These results in the two particles feeling differing ion drag forces: the top particle is acted on by the ion drag force directed from the plasma to the lower electrode, while the bottom particle is acted upon by the resulting wakefield produced by the interaction of the upper particle with the ion drag force. This dynamic situation currently provides the best known experimental environment for examining the physics behind the ion drag force and its interaction with the plasma sheath. An experimental method for investigating the interaction between pair-particle chains based on modulating the bias on the lower electrode employing a DC bias modulation technique will be presented.

astro-ph↗

arXiv2007

Relationship between the DC Bias and Debye Length in a Complex Plasma

The levitation height of a dust particle layer within a RF discharge plasma sheath is known to be related to the DC bias, the background pressure, and the Debye length. In this paper, a new experimental technique for measurement of the Debye length is introduced. This technique is based on the relationship between an externally applied DC bias and the particle levitation height and shows that under appropriate conditions, the addition of an externally applied DC bias provides a mechanism for evaluation of the Debye length. When compared with existing techniques, this new method appears to be simpler to implement in some cases.

astro-ph↗