Microplasma sources typically take advantage of pd (pressure × size) scaling by increasing pressure to operate at dimensions as small as tens of microns. In many applications, low pressure operation is desirable, which makes miniaturization difficult. In this paper, the characteristics of low pressure microplasma sources excited by microwave power are discussed based on results from experimental and computational studies. The intended application is production of VUV radiation for chemical analysis, and so emphasis in this study is on the production of resonant excited states of rare gases and radiation transport. The systems of interest operate at a few to 10 Torr in Ar and He/Ar mixtures with cavity dimensions of hundreds of microns to 1 mm. Power deposition is a few watts which produces fractional ionization of about 0.1%. We found that production of VUV radiation from argon microplasmas at 104.8 nm and 106.7 nm saturates as a function of power deposition due to a quasi-equilibrium that is established between the electron temperature (that is not terribly sensitive to power deposition) and the population of the Ar(4s) manifold.
In this paper we investigate the feasibility of creating a high-density ~ 10 12-10 14 cm-3 , large volume seed plasma in air constituents by laser (300 mJ, 20(±2) ns) preionization of an organic gas seeded in high-pressure gas mixtures and then sustained by efficient absorption of rf power (1-25 kW pulsed) through inductive coupling of the wave fields. A multi-turn helical antenna is used to couple radio-frequency power through a capacitive matching network. A 105 GHz interferometer is employed to obtain the plasma density in the presence of high collisionality utilizing phase shift and amplitude attenuation data. TMAE Plasma decay mechanisms with and without the background gas are examined.
Even if ion pumps are widely and mostly used in ultra-high vacuum (UHV) conditions, virtually every existing ion pump has its maximum pumping speed around 1E-6 mbar (1E-4 Pa). Discharge intensity in the ion pump Penning cell is defined as the current divided by pressure . This quantity reflects the rate of cathode bombardment by ions, which underlies all of the various pumping mechanisms that occur in ion pumps (chemisorption on sputtered material, ion burial, etc.), and therefore is an indication of pumping speed. A study has been performed to evaluate the influence of magnetic fields and cell dimensions on the ion pump discharge intensity and consequently on the pumping speed at different pressures. As a result, a combination of parameters has been developed in order to design and build an ion pump with the pumping speed peak shifted towards lower pressures. Experimental results with several different test set-ups are presented and a prototype of a new 200 l/s ion pump with the maximum pumping speed in the 1E-8 mbar (1E-6 Pa) is described. A model of the system has also been developed to provide a framework for understanding the experimental observations.
The Universiry of Texas a t Austin It is well known that electromagnetic waves propagating along the magnetic field direction in the plasma are strongly absorbed when the wave frequency matches the electron cyclotron frequency. This absorption can be eliminated by adding a weak magnetic undulator that leads to the Undulator-Induced Transparency (UIT) of the plasma. Moreover, the group velocity of the waves in the plasma is strongly reduced, resulting in the extreme compression of the wave energy in the plasma. Compressed waves are polarized primarily in the longitudinal direction, and can be used for synchronous electron or ion acceleration. Numerical simulations reveal yet another interesting property of the EM waves in UIT plasma: strong coupling and conversion between two wave polarizations. Depending on how important mode conversion is, several propagation regimes have been identified. We demonstrate that plasma with undulator induced transparency is perfect testing ground for verifying the theory of mode conversion in plasma.This paper presents results of a curious observation of changes in helicon plasma source Ar I1 optical emission characteristics related to wave character at higher densities when the coupled power or magnetic field is increased. Experiments on both the WOMBAT' experiment at Canberra and the University of Wisconsin2 helicon sources measured similar excited Ar I1 optical emission characteristics, yet the magnetic fields, coupled rfpowers and plasma densities are quite different. The wave and peak optical emission characteristics measured during the 70 ns rfperiod change from a spatially traveling wave character at lower powers and magnetic fields in the "transition mode" to an apparent spatially constant phase at higher coupled powers and magnetic fields where the plasma is in the "blue mode". The "blue mode" is achieved on the WOMBAT experiment by increasing the coupled power from 2.3 kW to 3.4 kW at a magnetic field of 100 G with a rise in density from 1.2 to l.8x10'21cc. The "blue mode" regime is achieved in the UW experiment by increasing the magnetic field from 200 G to 1000 G at a constant coupled power of 800 W with the plasma density rising from 0.4 to 2 . 5~ I0"Icc. Contour plots of the space-time emission modulation characteristics and the wave magnetic field plots illustrate the transition from a traveling wave to an increased standing wave character at higher densities where the optical peak emission phase is constant relative to the driving rfphase as the optical probe is moved. The emission characteristics are shown to correspond to the dominant m=+l mode in both the experiments although the probe was centered on the axis in the WOMBAT experiment and located just outside the Pyrex vacuum chamber for the UW experiment. The optical emission and wave characteristics and plasma deviation from a Maxwellian are discussed for the different regimes. Possible reasons for the emission observations including an increased standing wave character of the wave at higher densities and a thre...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.