Microwave-induced Plasma Discharge Research Articles

Microwave induced plasma discharge in multi-cell superconducting radio-frequency cavity.

A R&D effort for in situ cleaning of 1.5 GHz Superconducting Radio Frequency (SRF) cavities at room temperature using the plasma processing technique has been initiated at Jefferson Lab. This is a step toward the cleaning of cryomodules installed in the Continuous Electron Beam Accelerator Facility (CEBAF). For this purpose, we have developed an understanding of plasma discharge in a 5-cell CEBAF-type SRF cavity having configurations similar to those in the main accelerator. The focus of this study involves the detailed investigations of developing a plasma discharge inside the cavity volume and avoids the breakdown condition in the vicinity of the ceramic RF window. A plasma discharge of the gas mixture Ar-O2 (90%:10%) can be established inside the cavity volume by the excitation of a resonant 4π/5 TM010-mode driven by a klystron. The absence of any external magnetic field for generating the plasma is suitable for cleaning cavities installed in a complex cryomodule assembly. The procedures developed in these experimental investigations can be applied to any complex cavity structure. Details of these experimental measurements and the observations are discussed in the paper.

Optical emission spectroscopy for simultaneous measurement of plasma electron density and temperature in a low-pressure microwave induced plasma

The simple optical emission spectroscopy technique for diagnostics of low pressure microwave induced plasma (MIP) in hydrogen or in MIP seeded with hydrogen is described and tested. This technique uses the Boltzmann plot of relative line intensities along Balmer spectral series in conjunction with the criterion for partial local thermodynamic equilibrium for low electron density (Ne) plasma diagnostics. The proposed technique is tested in a low pressure MIP discharge for simultaneous determination of electron density Ne (1017–1018 m−3) and temperature Te.

Uniform Long-Slit Microwave Plasma Generation From a Longitudinal-Section Electric Mode Coupling

A stable uniform long-slit atmospheric argon plasma is produced by coupling a longitudinal-section electric (LSE) mode in a dielectric-loaded rectangular waveguide. The microwave-induced plasma discharge system consists of a 2.45-GHz microwave source, a circulator, a three-stub tuner, a transformer, and a tapered rectangular waveguide loaded with two dielectric slabs. A uniform 98-mm-long atmospheric argon plasma is observed at a relatively low microwave power level of 350 W and a gas flow rate of 10-15 L/min

Generation of Microwave-Induced Plasmas in Automotive Exhaust Gas Mixtures Using Pulsed Microwave Energy

Microwave energy at 2.45 GHz was applied to a mixture of exhaust gases from a petrol engine at atmospheric pressure. It was found that by pulsing the microwave energy with a 50% duty cycle, the average power required to sustain a microwave-induced plasma discharge was decreased by about 40%. The ratio of absorbed to incident power was unaffected. These findings were confirmed for pulse frequencies from 10 to 300 Hz.

Enthalpy-probe diagnostics of an atmospheric-pressure unleaded petrol exhaust-gas microwave-induced plasma

An unleaded petrol exhaust-gas microwave-induced plasma (MIP) at atmospheric pressure was generated in a TE/sub 101/ resonant-mode cavity. The microwave discharges were generated at three incident microwave power levels: 500 W, 700 W, and 1500 W. An enthalpy probe was used to characterize the exhaust-gas MIP discharge, yielding values of enthalpy, velocity, and heavy-particle temperature along the microwave-discharge axis. The heavy-particle temperature was found to be 710 K, 940 K, and 1065 K, with velocities of 140 m s/sup -1/, 148 m s/sup -1/, and 155 m s/sup -1/, at the exit plane of the discharge tube for an exhaust-gas flow rate of 3.5 l min/sup -1/ at 500 W, 700 W, and 1500 W respectively. The assumption of local thermodynamic equilibrium is required in the calculation of temperature and velocity in the microwave discharge from the enthalpy-probe data. In microwave-induced plasmas, the electron temperature is significantly higher than the heavy-particle temperature. We present arguments that indicate that the calculated heavy-particle temperature and velocity values are nevertheless accurate.

Enthalpy probe diagnostics of an atmospheric pressure argon microwaveinduced plasma

An argon microwave-induced plasma (MIP) at atmospheric pressure wasgenerated in a TE10 mode waveguide. The discharge was sustained bya relatively low absorbed power of around 215 W. An enthalpy probe was used tocharacterize the argon MIP discharge, yielding values of enthalpy, velocityand heavy particle temperature along the jet axis. The theory of the enthalpyprobe operation and calibration is reviewed and the system for itsimplementation is described. The heavy particle temperature is found to beabout 1600 K and the velocity to be about 150 m s-1 at theexit plane of the discharge tube for an argon flow rate of 1.6 l min -1. Although the assumption of local thermodynamic equilibrium isrequired to determine the temperature and velocity in the jet from the enthalpyprobe measurements, it is argued that the values obtained should be reasonableeven if, as expected in MIPs, the electron temperature issignificantly higher than the heavy particle temperature.

Spectroscopic study of argon MIP discharge used for analysis of solutions

Microwave-induced plasma (MIP) is an attractive excitation source which seems to be competitive to ICP-AES discharge. Reduced requirements in power and amounts of carrier gas and solution are considerable in comparison with ICP-AES. However, some disadvantages (such as a partial atomization and instability of discharge) can arise from the reduced power. Fundamental studies of MIP could be a help for control and proper selection of operating parameters of this discharge type. The behavior of solutions sprayed into an argon plasma was studied in a commercial MIP under different experimental conditions (argon and aerosol flow rates, discharge power). Rotational and vibrational energy distributions on the basis of the OH A 2Σ − X 2π molecular spectra and electronic energy distributions on the basis of atomic spectra have been measured under operative conditions and discussed from the point of view of analytical applications of MIP.

Modified microwave-induced plasma discharge chamber

Modified microwave-induced plasma discharge chamber