RF Power Supply Research Articles

Study of the relationship between the target tissue necrosis volume and the target tissue size in liver tumours using two-compartment finite element RFA modelling

Purpose: The aim of this study was to investigate the relationship between the target tissue necrosis volume and the target tissue size during the radiofrequency ablation (RFA) procedure.Materials and methods: The target tissues with four different sizes (dxy = 20, 25, 30 and 35 mm) were modelled using a two-compartment radiofrequency ablation model. Different voltages were applied to seek the maximum target tissue necrosis volume for each target tissue size. The first roll-off occurrence or the standard ablation time (12 min) was taken as the sign for the termination of the RFA procedure.Results: Four different maximum voltages without the roll-off occurrence were found for the four different sizes of target tissues (dxy = 20, 25, 30 and 35 mm), and they were 36.6, 35.4, 33.9 and 32.5 V, respectively. The target tissues with diameters of 20, 25 mm can be cleanly ablated at their own maximum voltages applied (MVA) but the same finding was not found for the 35-mm target tissue. For the target tissue with diameter of 30 mm, the 50 °C isothermal contour (IT50) result showed that the target tissue can be cleanly ablated, but the same result did not show in the Arrhenius damage model result. Furthermore, two optimal RFA protocols with a minimal thermal damage to the healthy tissues were found for the target tissues with diameters of 20 and 25 mm, respectively.Conclusions: The study suggests that target tissues of different sizes should be treated with different RFA protocols. The maximum target tissue volume was achieved with the MVA without the roll-off occurrence for each target tissue size when a constant RF power supply was used.

Coincident ion acceleration and electron extraction for space propulsion using the self-bias formed on a set of RF biased grids bounding a plasma source

We propose an alternative method to accelerate ions in classical gridded ion thrusters and ion sources such that co-extracted electrons from the source may provide beam space charge neutralization. In this way there is no need for an additional electron neutralizer. The method consists of applying RF voltage to a two-grid acceleration system via a blocking capacitor. Due to the unequal effective area of the two grids in contact with the plasma, a dc self-bias is formed, rectifying the applied RF voltage. As a result, ions are continuously accelerated within the grid system while electrons are emitted in brief instants within the RF period when the RF space charge sheath collapses. This paper presents the first experimental results and a proof-of-principle. Experiments are carried out using the Neptune thruster prototype which is a gridded Inductively Coupled Plasma (ICP) source operated at 4 MHz, attached to a larger beam propagation chamber. The RF power supply is used both for the ICP discharge (plasma generation) and powering the acceleration grids via a capacitor for ion acceleration and electron extraction without any dc power supplies. The ion and electron energies, particle flux and densities are measured using retarding field energy analyzers (RFEA), Langmuir probes and a large beam target. The system operates in Argon and N2. The dc self-bias is found to be generated within the gridded extraction system in all the range of operating conditions. Broad quasi-neutral ion-electron beams are measured in the downstream chamber with energies up to 400 eV. The beams from the RF acceleration method are compared with classical dc acceleration with an additional external electron neutralizer. It is found that the two acceleration techniques provide similar performance, but the ion energy distribution function from RF acceleration is broader, while the floating potential of the beam is lower than for the dc accelerated beam.

RF sputtering of polycrystalline (100), (002), and (101) oriented AlN on an epitaxial 3C-SiC (100) on Si(100) substrate

In this paper, the RF sputtering of polycrystalline AlN thin film on epitaxial 3C-SiC(100) on Si(100) substrate is presented. The effect of nitrogen concentration, deposition temperature and sputtering pressure are studied. These parameters are optimized to improve the crystal quality and deposition rate. Nitrogen concentration was varied from 40% to 100%, and it was found that the maximum deposition rate was observed at 40%. The RF bias power on substrate was also varied from 100 to 400 W, and it was observed that the deposition rate increases proportionally. The process temperature was varied from 200 to 400 °C to see the effect on the crystal quality and deposition rate; it was found that temperature variation does not yield significant shifts. This paper is able to demonstrate a successful RF sputtering of a polycrystalline AlN (100), (101), and (002) on epitaxial 3C-SiC(100) using RF power supply of 550 W.

The LUE-200 accelerator at the IREN facility: Current status and development

The general scheme and current status of an electron linear accelerator with an S-band travelling wave (f = 2856 MHz) accelerating structure—a driver for a pulsed neutron source (the Intense Resonance Neutron source (IREN)) at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research—are presented. The parameters of the accelerating system and the measured parameters of the electron beam—pulse-beam current, duration of the current pulse, repetition rate, electron-energy spectrum, and loading characteristics of the accelerating structure—are given. The beginning of the implementation of the project of the second stage of the IREN facility, which forms the basis for the development of the accelerator aimed at increasing its beam power, is reported. Technical solutions underlying the modernization of the accelerator’s electrophysical systems are discussed: accelerating system, RF power supplies, and modulators.

Experimental investigation of possible warmth perception from a head exposure system for human provocation studies with TETRA handset-like signals.

An experimental investigation of warming and warmth perception caused by handset EMF exposure was performed in order to examine its possible impact on blinding. Healthy male participants (15) were exposed to three different exposure conditions: sham and Terrestrial Trunked Radio (TETRA) handsets with maximum 10 g averaged SAR values of 1.5 and 6 W/kg each on three days. The study followed a randomized, double-blind design. TETRA signals simulated exposure from a handheld device consisting of a 385 MHz carrier modulated with a pulse length of 14.17 ms and a pulse period of 56.67 ms (i.e., duty cycle 25%; 17.65 Hz pulse modulation). A body worn antenna was used and fixed at the left ear. In addition to subjective ratings, skin temperatures at two locations close to the radiating element of the body-worn antenna were measured. The measurements revealed a temperature rise proportional to the supplied RF power with an average temperature increase measured at the two locations of 0.8 °C following the high exposure level of 6 W/kg. However, subjects were not able to distinguish between exposure conditions based on their subjective perception and thus the double-blinding was ensured.

Ways to improve the efficiency and reliability of radio frequency driven negative ion sources for fusion

Large RF driven negative hydrogen ion sources are being developed at IPP Garching for the future neutral beam injection system of ITER. The overall power efficiency of these sources is low, because for the RF power supply self-excited generators are utilized and the plasma is generated in small cylindrical sources ("drivers") and expands into the source main volume. At IPP experiments to reduce the primary power and the RF power required for the plasma production are performed in two ways: The oscillator generator of the prototype source has been replaced by a transistorized RF transmitter and two alternative driver concepts, a spiral coil, in which the field is concentrated by ferrites, which omits the losses by plasma expansion and a helicon source are being tested.

Temperature Behavior in a Tandem Type of Modulated Induction Thermal Plasma for Materials Processings

A tandem type of modulated induction thermal plasma (Tandem-MITP) system has been developed using two rf power supplies and two coils for one plasma torch. This system was developed to control temperature and reaction fields temporally and spatially in a thermal plasma. The modulation of each coil current can change the thermal plasma temperature in the torch temporally and spatially. Time variation of Ar excitation temperature was estimated by the two-line method using Ar atomic lines. The Tandem-MITP could be established successfully, and the Ar excitation temperature in the thermal plasma could be controlled temporally and spatially by the developed system.

L-band surface-coil resonator with voltage-control impedance-matching for EPR tooth dosimetry

A surface-coil resonator that is capable of voltage-control for impedance-matching is described in the context of its application in electron paramagnetic resonance (EPR)-based tooth dosimetry. Varactor-based coupling of an 1,150 MHz surface-coil resonator was achieved to supply RF power. The developed resonator consists of a single-turn loop, 9 mm in mean diameter; a capacitor made of a polytetrafluoroethylene (PTFE) substrate; a quarter-wavelength parallel transmission line; a half-wave line balun, and varactors. The surface coil and the PTFE substrate capacitor were connected to a quarter-wavelength parallel transmission line. For the newly developed resonator, an RF magnetic field-generation efficiency of 130 μT/W1/2 was achieved, and the sensitivity of the surface-coil resonator was investigated with an irradiated tooth. Measurements consisting of six sets of EPR spectra on a 10 Gy irradiated tooth using this newly developed resonator achieved a standard error of the mean (SEM) of 1.1 Gy. This level of accuracy of dose measurements was comparable to the SEM with a previously developed resonator; however, the previous resonator was not capable of voltage-control for impedance-matching adjustment, which represents a significant advance in facilitating automation. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 43B:32–40, 2013

Effect of Duty Cycle on the Characteristics of Pulse-Modulated Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge

Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.

Detection of atomic oxygen and nitrogen created in a radio-frequency-driven micro-scale atmospheric pressure plasma jet using mass spectrometry

In this paper we show mass spectrometry results for a radio-frequency-driven micro-atmospheric pressure plasma jet (μ-APPJ) discharge obtained using a mass analyzer with triple differential pumping allowing us to sample directly in ambient atmospheric pressure environment (Hiden HPR-60). The flow of the buffer gas (mixture of helium and 1% oxygen) was 2 slm and 3 slm and the excitation frequency was 13.56 MHz. We monitored production of atomic oxygen and nitrogen in the plasma for different flows and powers given by the RF power supply. These measurements were made for energies of electrons emitted from the ionization filament below the threshold for dissociation of O2 and N2. In addition to oxygen and nitrogen atoms, yields for O2, N2, NO and O3 are recorded for different powers and gas flows. It is shown that the μ-APPJ is symmetrical and operates in α-mode. The power transmitted to the discharge was below 5 W in all measurements.

RF power supplies for the RFQ cooler and buncher RFQ1L

In order to match directly the beams from the gas-filled recoil separator, a RFQ cooler and buncher RFQ1L has been designed to have a large radius (r0=60 mm), thus the RF power supply becomes not a trivial problem. We have successfully solved this problem by two different methods, and the RF power supplies specific to the RFQ1L have been developed and tested. Technical descriptions and test results are presented in this paper. It shows that the power supply with series resonance circuits should be used for the operation of the RFQ1L.

Transparent and crystalline Al-doped ZnO film-embedded heterojunction Si solar cell

A heterojunction of Al-doped ZnO (AZO) and Si was applied as a solar cell. Quality AZO films were grown by a co-sputtering technique using a RF power supply for ZnO while a DC one for Al. The Al content significantly modulates the electrical performance and crystalline structure of the AZO films. The lowest resistivity of AZO film was achieved to be 5.4×10−4Ωcm. The crystalline structures of different Al-containing AZO films were systematically investigated by X-ray diffraction.A transparent AZO film was deposited onto an n-Si substrate. This AZO/Si heterojunction diode offers an ideality factor of 1.19. Under illumination, the heterojunction provided a short-circuit current of 15.64mA/cm2 and an open-circuit voltage of 321mV.This research presents the quality growth of AZO films by using a co-sputtering method. It also discusses the working mechanism of the heterojunction n-AZO/n-Si solar cells with unique design schemes.

Design of RF Power System for CPHS

Abstract The Compact Pulsed Hadron Source (CPHS) system has been proposed and designed by the Department of Engineering Physics of Tsinghua University in Beijing, China. It consists of an accelerator front-end—a highintensity ion source, a 3 MeV radiofrequency quadrupole linac (RFQ), and a 13 MeV drift-tube linac (DTL), a neutron target station, and some experimental stations. In design of our RF power supply, both RFQ and DTL share a single klystron which is capable of 2.5 MW peak RF power and a 3.33% duty factor. The 325 MHz klystron contains a modulating anode and has a 100 kW average output power. Portions of the RF power system, such as pulsed high voltage power supply, modulator, crowbar protection and RF power transmission are all presented in details in this paper.

Biocompatible thin films obtained from Heparim-methane plasma process

Heparin is an appropriate molecule to suppress the thrombus formation in the initial stages of blood contact with an artificial material. Therefore the covering of a synthetic material with heparin-like molecules is a great importance issue in biomaterial science and engineering. In order to reach this goal this paper deals with the plasma deposition of thin heparin-like films on microscope slides from RF-excited heparin/methane low pressure plasmas. Plasma were excited by a RF-power supply operating on 13.56 MHz at a fixed power of 50 W. Heparin was diluted in ethanol and fed into the plasma chamber in mixtures of 50% of CH4 (in pressure) at 10 Pa. Films molecular structure was characterized by Fourier transform infrared spectroscopy (FTIR here in). Molecular spectra presented absorption bands due C-H, O-H and C-O stretching and bending modes. Films surface wettability was investigated by contact angle measurements. The experimental results show values varying from 650 to 200. Surfaces optical microscopy showed the occurrence of heparin islands distributed almost uniformly over the _lm. The bloods coagulation time placed in contact with glass substrate covered by plasma deposited heparin/methane films was measured by thrombosis time and activated thromboplastin.

Particle Simulations of Sheath Dynamics in Low-Pressure Capacitively Coupled Argon Plasma Discharges

A numerical study of low-pressure capacitively coupled plasma (CCP) discharges in Ar has been performed including the transport of ions in a sheath onto a substrate. We employ a two-dimensional axisymmetric particle-in-cell with a Monte Carlo collision (PIC-MCC) method for an asymmetric capacitive discharge with an external electrical circuit containing a blocking capacitor and an rf power supply. The PIC-MCC results show that for the gas pressure (5–100 mTorr), rf voltage (50–500 V), and frequency (6.78–40.68 MHz) ranges examined for a single-frequency CCP, the peak plasma density increases linearly with gas pressure, rf voltage, and frequency squared. With a decrease in pressure or increases in plasma density and sheath potential, the sheath becomes less collisional and thus significant peaks at high energies of ion energy distributions appear and narrow ion angular distributions are obtained. The tendency is in a reasonable agreement with experimental results.

Particle Simulations of Sheath Dynamics in Low-Pressure Capacitively Coupled Argon Plasma Discharges

A numerical study of low-pressure capacitively coupled plasma (CCP) discharges in Ar has been performed including the transport of ions in a sheath onto a substrate. We employ a two-dimensional axisymmetric particle-in-cell with a Monte Carlo collision (PIC-MCC) method for an asymmetric capacitive discharge with an external electrical circuit containing a blocking capacitor and an rf power supply. The PIC-MCC results show that for the gas pressure (5–100 mTorr), rf voltage (50–500 V), and frequency (6.78–40.68 MHz) ranges examined for a single-frequency CCP, the peak plasma density increases linearly with gas pressure, rf voltage, and frequency squared. With a decrease in pressure or increases in plasma density and sheath potential, the sheath becomes less collisional and thus significant peaks at high energies of ion energy distributions appear and narrow ion angular distributions are obtained. The tendency is in a reasonable agreement with experimental results.

Properties of hydrogenated amorphous carbon films deposited by PECVD and modified by SF6 plasma

Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125W. After deposition, the films were submitted to SF6-plasma treatment for 5 minutes. SF6 plasmas were generated at a pressure of 13.3Pa by a RF power supply operating at 13.56MHz with the output fixed at 70W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF6 plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF6 plasmas with surface species was responsible for the decrease of the film thickness and surface energy, and for the increase of the film roughness and hydrophobicity.

Hydrogenated amorphous carbon and carbon nitride films deposited at low pressure by plasma enhanced chemical vapor deposition

Hydrogenated amorphous carbon (a-C:H) films were deposited by plasma enhanced chemical vapor deposition from methane, argon diluted methane, and nitrogen diluted methane at 26.7 Pa with a 13.56 MHz RF power supply. In this pressure regime, multiple-scattering of carbon species within the plasma phase is expected during the transport to the substrates placed on both the driven and the earthed electrodes. These films were analyzed using UV–VIS optical transmittance, monochromatic ellipsometry, Raman spectroscopy and current–voltage measurements. From these results, the effect of the plasma conditions and the effective flux of the carbon species controlled by the input power through the negative self bias are found to be important in the deposition process. The growth conditions at the higher pressure regime are important to synthesize a-C:H films from low energetic carbon species, since it reduces the defect density and improves the quality of the films. Furthermore, the effect of nitrogen on the growth conditions of a-C:H:N films is observed.

A novel technique to enhance surface properties of DLC films deposited on the inner wall of cylindrical PET barrel by DC-RF hybrid discharge

A newly proposed technique has been utilized to improve surface properties of gas barriering DLC films deposited on PET bottle. The discharge in the bottle is induced by radio-frequency discharge and an external DC system is coupled to the RF power supply to control the potential of discharge electrode. In contrast to conventional discharge configuration, this leads to the capability to optimize the ion bombardment energy and surface properties of deposited films. The effect of negative DC voltage on the adhesion strength, optical transmittance, surface profile, roughness, and permeability of DLC coated PET samples has been investigated using immersion test, UV-visible spectroscopy, optical profilometry, and gas permeability tester, respectively. The results have demonstrated that the DLC coated PET samples with external bias show slight damage during beer immersion tests. Lower light transmittance is induced for the films deposited at high negative bias due to larger ion bombardment effect. There exists a proper bias to give rise to a small surface roughness. The gas permeability of DLC coated PET samples deposited with external bias has been substantially decreased compared to that of untreated one.

Note: New design of a cryogenic linear radio frequency multipole trap

A new design of a cryogenic linear 22-pole ion trap has been constructed and tested. It is essentially a copper housing to which opposite inner walls two electrode sets are attached via sapphire insulators. These stainless steel electrodes are electroformed in one piece to guarantee good heat conduction. Connected to an external coil, they form an LC-circuit of about 19 MHz resonance frequency. This circuit is excited with a rf power supply made of a commercial digital synthesizer followed by a 10 W amplifier. Buffer gas-cooled H(2)D(+) ions have been stored in this trap at a nominal trap temperature of 14 K. Spectroscopy of the ions confirmed that the kinetic (Doppler) temperature is in reasonable agreement with this value.