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On the Effect of Base Pressure Upon Plasma Containment
Published in B. Raneesh, Nandakumar Kalarikkal, Jemy James, Anju K. Nair, Plasma and Fusion Science, 2018
G. Sahoo, R. Paikaray, S. Samantaray, P. Das, J. Ghosh, A. Sanyasi
Electric probes (Langmuir probes) [20] are used for plasma diagnostics. The ion saturation current of plasma is measured with Langmuir probe for different base pressure and is shown in Figure 7.2. It is observed that plasma stays for longer time at higher base pressure (> 1 mb). This is an indication of better containment of plasma at higher base pressure. Since, the pulse duration of PFN that energies plasma gun is 140 ps at higher base pressure the long-lived plasma structure is a matter of interest for investigators. The spatial variation of density shows that the plasma density remains almost constant up to 8 cm from plasma gun at higher base pressure (~ 1 mb or more). The trend is shown in Figure 7.3.
Experiments
Published in Dikshitulu K. Kalluri, Electromagnetics of Time Varying Complex Media, 2018
To obtain the rise time for the plasma frequency, two sets of measurements were made. First, the peak plasma density was measured by a Langmuir probe technique. Second, the time resolved discharge current was measured using a fast current transformer in the discharge current feed. This second measurement yields the plasma time rate of formation, assuming that the time integral of the absolute value of the discharge current is proportional to the plasma density. (A correction to the original thesis material is made at this point.) The current as a function of time is shown in Figure 13.11.
Plasma Surface Modification and Etching of Polyimides
Published in Malay K. Ghosh, K. L. Mittal, Polyimides Fundamentals and Applications, 2018
Frank D. Egitto, Luis J. Matienzo
Measurements of average sheath potentials can be made using electrostatic probes. Langmuir probes measure current-voltage (I-V) characteristics in the plasma. Current to the probe (a sum of electron and ion currents) is measured as a function of the DC potential applied to the probe. Although a considerable amount of care is required to obtain accurate data, Langmuir probe characteristics can yield a quick check on several important plasma parameters. One can determine the plasma potential (referenced to ground potential) and floating potential (Fig. 4). In addition, the I-V characteristics can be used to calculate the number densities and energies of electrons and ions in the plasma. Vp,Vf, and ion saturation current, Ii, can be obtained from this I-V characteristic curve as indicated in Figure 4. The I-V characteristic curve is obtained by incrementally or continuously changing the DC voltage applied to the probe tip. The means of determining Ii shown in the diagram is as proposed by Friedmann et al. [34]. A useful approximation states that the ion saturation current is proportional to (1/2)A(n+)(kTe/M)1/2, where A is the area of the probe tip, n+ is the volume density of positive ions, Te is the electron temperature, and M is the mass of the ion [35]. Te is inversely proportional to the slope of a plot of probe voltage vs. ln(Ie) in the region bounded by Vp and Vf, where Ie is the electron current. The relative energy delivered by ions to a unit area of a floating polymer surface per unit time, refered to here as the ion fluence, Fi, is proportional to (ϕf × n+). For electrically grounded substrates, Fi is proportional to (Vp × n+). In RF configurations, the potential difference between the plasma and the RF-driven electrode, Vc, is given by (Vp + Vdc), where Vdc is a self-induced DC bias. Vdc develops at a capacitively coupled cathode that is smaller than the anode (electrical asymmetry), since electrons in the plasma have a higher mobility than ions.
Obtaining plasma parameters by Langmuir probes and optical emission spectroscopy in low-pressure DC plasma
Published in Radiation Effects and Defects in Solids, 2023
Kenan Senturk, Tuba Sen, Turgay Coruhlu, Aamir Shahzad, Necdet Aslan
A DC voltage of 250–550 V is applied between the anode (holding surface to be coated) and cathode (holding the sputtering target) to partially ionize Ar atoms introduced into the chamber. When this potential reaches the gas breakdown voltage, the ionized Ar plasma initiates sputtering on the Cu target surface. The process leads to the ejection of target atoms from the target surface because of circulating Ar ion bombardment (circular force) to create the growth of the Cu thin film on the substrate surfaces. The atoms sputtered from the target material move in a volume from the cathode to the anode, performing thin coating on the surface attached to the anode. The MS vacuum system used in this study and coated glass, metal, and textile surfaces are shown in Figure 1. During such a coating process, the Langmuir probes that are placed in this volume are activated and the measurements were performed to obtain plasma properties such as electron and ion temperatures, plasma ion density, and plasma potential distribution.
Spatially Resolved Ion Density Measurements in an Oxyfuel Cutting Flame
Published in Combustion Science and Technology, 2022
Langmuir probes are merely metal surfaces with an electrical bias inserted into a plasma. The probes need to be no more sophisticated than a wire, sphere, or wall, and if the identity of the ion is already known, the local ion densities can be inferred from the measured current. Early measurements using Langmuir probes in flames were performed at low pressures (Calcote and King. 1955), which permitted the use of the sparse plasma theory available at the time (Langmuir 1924). However, the low-density plasma model must be modified in dense “collision-dominated” systems (Fialkov 1997, 406), and a satisfactory extension of Langmuir probe theory to dense flowing plasmas was not available until 1970’s. Despite their advantages, contemporary use of Langmuir probes in flames is limited, primarily appearing in works extending the probe theory (Dawe, Syed, Rizvi 1993; MacLatchy 1979; MacLatchy and Smith 1991). In this work, we consider two candidate models for estimating ion density from probe measurements offered by Clements and Smy (1969, 1970a).
Characterization of Arc Plasma by Movable Single and Double Langmuir Probes
Published in Fusion Science and Technology, 2019
Ghanshyam Thakur, Raju Khanal, Bijoyendra Narayan
Langmuir probes have been widely used to measure plasma parameters (electron temperature, plasma density, and plasma potential as well as space and floating potential) for characterization of the edge plasma of fusion devices and for many other widely ranging applications over the last several decades.1–4 A Langmuir probe consists of a bare wire or metal disk that is inserted into a plasma and electrically biased with positive ion current.5 The Langmuir probe has been primarily used as a diagnostic tool for measuring plasma parameters. But, it has also received considerable attention in the study of direct-current (dc), radio-frequency (rf), and arc plasma.5–7 A Langmuir probe has the benefit of measuring local values of plasma parameters when it is fixed in rf, dc, arc, and other different types of plasma.