Papers by Keyword: Langmuir Probe

Abstract: The Langmuir probe plasma parameters diagnostics method was studied based on the ICP plasma chemical processing system. Single Langmuir probe with high-frequency compensation system and the special electrical circuit was designed and constructed. CV dependences in various working pressures were registered.

Abstract: There are several techniques to deposit the metal oxide thin film such as electron beam evaporator, pulse laser deposition and reactive magnetron sputtering deposition. In this experiment, magnetron sputtering deposition techniques will be used to produce a copper oxide thin film due to its simplicity and repeatability performance. Recently, copper oxide thin film has been studied because of its low cost material, sensitivity to ambient condition and easiness to produce oxide thin film. It is one of the p-type semiconductor oxides materials that are suitable to be used as a gas sensing material. In order to increase the sensitivity and to optimize the properties of copper oxide thin film, it is essential to study on the plasma properties during the deposition of copper oxide. In current studies, Langmuir probe was used to investigate the effect of substrate bias towards the fabrication of copper oxide thin film at rf dissipation power of 400 W. The oxygen flow rate was fixed at 8sccm. The Langmuir probe tip was focus at roughly 2 cm above the substrate holder. The ion and electron current were collected from the plasma environment. Then the electron temperature, electron density, ion density, ion flux, Debye length and plasma potential at various substrate biases were evaluated from the current-voltage curve. The electron temperature at various oxygen flow rates was almost unchanged. The effect of substrate bias toward the electron temperature was also almost unseen, except that the electron temperature at-40 V bias voltage was slightly lower than others. In addition, the ion flux at the same plasma condition shows that the ion flux was higher at-40 V substrate bias voltage. The results suggest that the ion bombardment effect toward the deposited copper oxide thin film would be higher at low oxygen flow rate. Thus it will create a rough surface morphology or nanostructured copper oxide thin film. This is a potential ways to improve the sensitivity of copper oxide gas sensor.

Abstract: We report on the characteristics of argon inductively coupled plasma (ICP) for the ITER neutral beam injection system. In argon ICP, it was found by using Langmuir probe that the radial distribution of electronic density (N_e) was uniform while the radial distributions of both electron temperature (kT_e ) and electric potential (V_P) were non-uniform. The former depend on two factors: the variation of N_e was small, and the value of N_e was very large. The latter is owing to the generation and disappearance of the negative ions in the ICP, where the additional dynamic processes produce the instability. In addition, both kT_e and V_P profiles were very similar at the cylinder height H=14 cm, which proves the plasma sheath theory to some extent. Finally, both kT_e and V_P began flatter with the reduction of the cylinder height, which is owing to the decrease of the negative ions in the ICP.

Abstract: A current-model Triple Langmuir probe was developed and used to measure electron temperature and density of the Pulsed Plasma Thruster plume. To decreasing the errors in measurement, Probe, collection circuit and glow cleaning devices were elaborately designed. A FIR digital Filter based on Matlab was designed and the software for date processing was developed by Labview. Measurements were taken at various position in the plume of a Pulsed Plasma Thruster operating at discharge energy of 6-24J. The results show the thruster plume has electron temperatures in the range between 0.6and 5.4eV, electron densities between 0.9×10¹⁹ and 4.1x10²¹m^-3 for all discharge energy levels considered. Electron temperature and density decrease with increasing angle away from the centerline and with decreasing discharge energy.

Abstract: In this paper, temperature field and stress field have been simulated on a Langmuir Probe and its dissipation system in certain diagnostic equipment under intense radiation in use of Abaqus. The results show that there are strongest thermal stresses on the ceramic barrels inside the system, which would be extremely easy to get broken. The reasons to have such dreadful stresses are discussed in the paper. And improving suggestions to avoid extra stresses are put forward for the structure design of Langmuir Probe and its heat dissipation system due to the simulation results.

Abstract: In order to study the influence of electrode flare angle on the performance of Ablation Pulsed Plasma Thruster. Discharge character, plasma velocity and performance over different electrode flare angles of the Pulsed Plasma Thruster at 13.5J initial energy are measured experimentally, the effect of electrode flare angle on the electrode inductance gradient, equivalent circuit parameters and energy transfer efficiency are analyzed. It can be seen that the circuit parameters and inductance distribution are changed with electrode flare angle, the impulse bit, specific impulse, thruster efficiency and mean exhaust velocity increase non-linearly with flare angle increasing from 0 degree to 27 degree and the Pulsed Plasma Thruster gets the maximum thruster performance at 27 degree flare angle. It shows that with the increase of electrode flare angle the fraction of ablated mass accelerated magnetically and the impulse bit created by Lorentz force decrease are the reasons inducing the change in thruster performance.

Abstract: The quality laser cutting of thick sheet metals is demanding due to requirements of high precision, lost cost, and short processing time. However, the surface plasma is formed during the cutting process to influence the end product quality. The surface plasma is transiently hot and lowers the resulting cutting quality via increasing thermal erosions from the cut edge edges. In the present study, the surface plasma characteristics are examined using the Langmuir probe. Electron temperature and electron number density are determined in the surface plasma. The cutting quality is, then, related to the plasma characteristics. Scanning Electron Microscopy (SEM) is carried out to examine the microstructural changes at the cut edges. It is found that cutting quality improves at a particular assisting gas pressure; in which case, the influence of surface plasma on the cutting process becomes the minimum.

Abstract: A single rf-compensated cylindrical Langmuir probe has been developed in order to characterise a plasma RF discharge. A circuit using radiofrequency filtering and the passive compensation method was employed to minimize the probe curve distortions. The effect of the rfcompensation on the probe measurements was discussed. The latter were performed at power and pressure of 50 W and 510-2–1.2 mbar, respectively. Compensated measurements of the electron energy distribution function (EEDF) and plasma parameters were conducted at powers ranging from 5 to 120 W and pressure of 0.3 mbar. They exhibit a transition between the stochastic electron heating mode operating at low powers and the secondary-electron emission heating mode (γ) operating at high powers. The electronic density increases from 1.5×109 to 3.2×1010 cm-3 while the effective electron temperature decreases from 3.7 to 2.3 eV. The EEDFs were found to be Druyvesteyn-like in the range of 5–80W and then evolve to the Maxwellian beyond 90W.

Abstract: Based on deposition rate of coatings and ion flux measured by Langmuir probe in sputtering environment, bombardment energy Ec1 of sputtered neutral atoms and bombardment energy Ec2 of bombardment ions accepted by substrate surface micro-area per unit time were calculated. The magnitude of Ec1 and Ec2 was approximately the same, surface diffusing processes of the top layer atoms in the coating were accelerated by the simultaneity action of Ec1 and Ec2, bulk diffusion processes of the atoms under the top layer in the coating were promoted by energy accumulation and temperature rise effect caused by the continuance action of Ec1 and Ec2.

Abstract: The characteristics, such as electron temperature and the electron density, of CF4/Ar discharge in 2.45GHz microwave has been investigated by using a Langmuir probe with the microwave power and position. The results showed that the electron temperature and the electron density decrease with increasing distance from the plasma source. Increasing power enhances the dissociation and ionization of gas, and increases the electron densities. The electron temperature was decreased by reducing the mean free path of electrons with increasing microwave power. The electron temperature is 7.63 ~ 2.49 eV, and the electron density is 0.85×1011 ~ 4.3×1011 cm-3. From obtained electron energy distribution function, we known that high energy electron decreased with increasing microwave power and distance from the plasma source. The generated plasma by developed our system has good quality as results of Debye length λD = 35.8 ~ 67.3 μm, and Ln(ND) = 33.4 ~ 35.2.