Roy B. Tumlos

Characterization of a Microwave-Induced Atmospheric-Pressure Ar–N 2 Plasma Pencil

A microwave-induced atmospheric-pressure plasma pencil was developed with an Ar–N2 gas mixture supplied to a coaxial transmission line. High-frequency simulation showed sufficient high electric field at the tip of the inner conductor, which resulted to automatic plasma ignition and a stable operation. The dependence of the characteristics of the plasma pencil from Ar and N2 gas flow rates was extensively studied. At moderate Ar gas flow rates, the plasma pencil can be operated at several tens of watts to achieve a near room-temperature and centimeter-long Ar–N2 plasma plume with OH and NO radicals as active species. Optical emission spectroscopy was also used to determine the vibrational and rotational temperatures of the plasma pencil. The vibrational temperature of N2 from the second positive system (2PS) can be obtained at moderate gas flow rates, since there was a good linear fitting with the Boltzmann distribution. At these gas flow rates, the vibrational and rotational temperatures of N2 from 2PS were found to be 0.42 and 0.29 eV, respectively.

A 2.45-GHz Microwave Air Plasma Under a Double-Hexapole Magnetic Field

Presented here is an image of a microwave air plasma produced from a 2.45-GHz source. To assist in the plasma ignition and confinement, a set of samarium-cobalt (Sm-Co) permanent magnets arranged in a double-hexapole configuration is used. In the image presented, air in the vacuum chamber is ignited into the plasma at a pressure of 3 × 10-3 torr. The plasma exhibits a distinct pattern where brighter areas appear at alternate regions of magnetic cusps. Based on particle-in-cell simulations, the bright areas coincide with regions where the electron energies and electron densities are relatively high.

High Dynamic Range Imaging of Magnetized Sheet Plasma

High dynamic range (HDR) imaging was used to obtain a wide intensity map of a magnetized sheet plasma. A set of 12 low dynamic range (LDR) photographs with various shutter speeds (1/200-1/2 s) was captured with an Olympus FE-19 digital camera. The LDR images were processed to recover color channel response functions of the camera needed to produce RGB radiance maps. The HDR image was finally generated from the combined radiance maps via linear tone mapping. By comparison of histograms, the HDR image uses the whole range of intensity values compared with the underexposed and overexposed LDR images.

Development of a simple 2.45 GHz microwave plasma with a repulsive double hexapole configuration

A simple and inexpensive 2.45 GHz microwave plasma source with a repulsive double hexapole configuration is described and characterized. In this work, the operation of the source is shown to be flexible in terms of electron density, electron temperature, and plasma uniformity even at low-pressures (approximately millitorr). It allows for easy control of the electron temperature (2-3.8 eV) and density ( approximately 10(9)-10(10) cm(-3)) by removing either of the two hexapoles or by varying the separation distance between the two hexapoles. Characterization was done via information gathered from the usual Langmuir probe measurements for electron temperature and density. The source makes a resonant surface with its repulsive double hexapole magnetic configuration providing an additional longitudinal confinement near the walls midway between the two hexapoles. Magnetic field maps are presented for varying double hexapole distances. Power delivery for various settings is also presented.

Intensity Modulated Radiotherapy (IMRT) Phantom Fabrication Using Fused Deposition Modeling (FDM) 3D Printing Technique

Design and fabrication of patient-specific radiotherapy phantom is now more accessible and cost-effective using 3D printing technology. This study fabricates a 3D printed radiotherapy phantom for quality assurance of Intensity Modulated Radiotherapy (IMRT). Using an IMRT Thorax anthropomorphic phantom (CIRS) as a substitute for an actual patient, a 3D printed radiotherapy phantom was designed based on a patient computed tomography (CT) scan during treatment planning. Before printing the phantom, the tissue equivalence of Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA) polymers used in 3D printing was characterized by quantifying its CT number and relative electron density to water. In the 3D printed phantom fabricated, it was shown that soft tissue and lungs can be simulated using PLA 100% infill \( \left( {\rho_{e,w}^{130kV} = 0.99} \right) \) and 20% infill plastic \( \left( {\rho_{e,w}^{130kV} = 0.20} \right) \).

Investigation of the drying characteristics of microalgae using microwave irradiation

Microalgae is one of the alternative feedstock for biofuel production with the highest yield per land area. However, current method in microalgae drying process requires high energy which accounts to about 60% of the total energy of the biofuel production chain. Moreover, conventional means of drying results to uneven drying of the microalgae with respect to slurry thickness. This study investigated the drying of microalgae (Chlorella vulgaris) using microwave irradiation which offers a faster means of drying while providing even drying patterns across the slurry thickness. In this paper, the experiment used three (3) microwave intensity levels (300W, 600W, and 900W) to 10g, 20g, and 30g of microalgae sample, a total of nine (9) samples. Results showed that 30 W/g is the best microwave intensity level per gram of microalgae to attain the bone dry mass of the microalgae, while intensity level 20W/g is best to meet the requirement of obtaining a maximum 10% moisture content in the sample.