Amount Of RF Power Research Articles

Si/SiC heterostructure MITATT oscillator for higher-harmonic THz-power generation: theoretical reliability and experimental feasibility studies of quantum modified non-linear classical model

Modelling/simulation and high-frequency characterization of hetero-junction Avalanche Transit Time (ATT) oscillators, operating in tuned harmonic mode, are reported in the paper. An equivalent circuit, that incorporates self-consistent, non-linear, single-frequency impedance and admittance properties of the device at fundamental, 1st harmonic and 2nd harmonic mode of oscillation frequencies within the THz (0.5–1.5 THz) domain, is simulated. The prospects of Si/4H-SiC versus Si/6H-SiC exotic hetero structures are studied and compared for the generation of considerable amount of RF-power at higher harmonic THz region. For this, a generalised non-linear Mixed Quantum Drift Diffusion (MQDD) model is developed indigenously. The authors have made the simulator realistic by incorporating the temperature dependent carrier ionization rate, saturation drift velocity, mobility and effective mass of the base material-pairs in the analysis. In addition to these, the effects of punch-through phenomena as well as parasitic series resistance related detrimental issues are duly addressed in the present analysis. The authors have made the model realistic by studying the performance of the proposed novel structures under room temperature as well as under elevated temperature conditions. Due to the incorporation of hetero-structure in the active region of the device, considerable amount of power could be generated at 2nd harmonic oscillation frequency (~ 1.7 THz). The study shows that both the Si/4H-SiC and Si/6H-SiC hetero-junction devices are oscillating at 0.5 THz (fundamental frequency). Si/4H-SiC hetero-junction device, due to its less lattice mismatch factor, is more efficient (45%) than its Si/6H-SiC (15%) counterpart under similar structural/electrical/thermal operating conditions. The validity of the MQDD model is established in this paper by comparing the data with corresponding experimental observations at microwave/millimeter-wave region. To the best of authors’ knowledge, this is the first report on harmonic power generation from Si/4H-SiC and Si/6H-SiC hetero-junction ATT devices at higher terahertz region.

Design of RF system for CYCIAE-230 superconducting cyclotron

The CYCIAE230 is a low-current, compact superconducting cyclotron designed for proton therapy. The Radio Frequency system consists of four RF cavities and applies second harmonic to accelerate beams. The driving power for the cavity system is estimated to be approximately 150kW. The LLRF controller is a self-made device developed and tested at low power using a small-scale cavity model. In this paper, the resonator systems of an S.C. cyclotron in history are reviewed. Contrary to those RF systems, the cavities of the CYCIAE230 cyclotron connect two opposite dees. Two high-power RF windows are included in the system. Each window carries approximately 75kW RF power from the driver to the cavities. Thus, the RF system for the CY-CIAE230 cyclotron is operated in driven push–pull mode. The two-way amplifier-coupler-cavity systems are operated with approximately the same amount of RF power but 180° out of phase compared with each other. The design, as well as the technical advantage and limitations of this operating mode, of the CYCIAE230 cyclotron RF system is analyzed.

Fabrication of microstructure array directly on β-phase poly(vinylidene fluoride) thin film by O2 reactive ion etching

The ability to pattern a thin film of poly(vinylidene fluoride) (PVDF), a piezoelectric, pyroelectric and ferroelectric polymer, has potential applications in the fields of microelectromechanical systems (MEMS), nonlinear optics and nonvolatile ferroelectric random access memory technology. Low pressure O2 reactive ion etching (RIE) was employed to realize fine pitch microstructures on a β-phase PVDF (β-PVDF) film for the first time; a line and space (70/130 μm) microstructure array with a height of over 30 μm was fabricated. Different to the traditional method of PDMS molding, the proposed technology did not result in significant loss of piezoelectricity. Furthermore, unlike the x-ray photo-etching method, there was no etching saturation limit with the proposed method. Here, we introduce the fabrication process technology in detail and report on the etching properties of the β-PVDF film under different process conditions. The effect of process variables, such as supplied gas flow, applied RF power and etch time, on the PVDF etching characteristics were investigated in detail. The RF power and etch time showed a more predominant influence on PVDF etching progress than the gas flow. The etched depth was linearly increased with the etch time and the amount of RF power. Etching rates over 10 μm h−1 were achieved and increased linearly with the applied RF power. By means of a responding photomask design and control of process conditions, much finer and higher microstructure arrays are also possible.

Properties of ITO Films Deposited on Plastic Substrate by RF Superimposed DC Magnetron Sputtering Method

Tin doped indium oxide (ITO) films were deposited on plastic films by RF superimposed DC magnetron sputtering method using an In2O3 – 10 wt.% SnO2 target without intentionally heating substrates. We have investigated the effects of an RF superimposed DC power system on the electrical, optical, and mechanical properties of the ITO films by using Four-Point Probe, Hall Effect Measurement, UV-Vis-NIR Spectrophotometer, XRD, and Residual Stress Measurement. With increasing the amount of RF power superimposed on DC power, the sputtering discharge voltages of DC power supply were decreased from –290 V to –100 V, i.e., plasma impedance decreased with an increase of the amount of RF power. The resistivity of the samples drastically decreases with increasing RF power, and shows the lowest value of 3.8×10-4 8·cm. Hall effect measurements explain that the increase of carrier mobility is strongly related with the enhancement of the resistivity of ITO films even though there is no difference on its concentration. The RF power superimposed on DC power also reduces the residual stress of the samples up to the stress level of ~ 200 MPa at optimum values of RF power.

Method to reduce microphonics in superconducting resonators

The control of superconducting resonators requires a large amount of rf power due to their narrow bandwidth and the presence of microphonics in the ambience, although only a small part is dissipated inside the resonator to generate the accelerating field. A simple and innovative method has been devised to reduce the effect of microphonics on the quarter-wave resonators. Experiments have been conducted successfully at room temperature and at 4.2 K to demonstrate the effect of the new damping mechanism. A detailed report of the experiments with the superconducting resonators in a test cryostat and an on-line linac cryostat is presented in this paper.

Selective averaging for high-resolution solid-state NMR spectroscopy of aligned samples

Solid-state NMR experiments benefit from being performed at high fields, and this is essential in order to obtain spectra with the resolution and sensitivity required for applications to protein structure determination in aligned samples. Since the amount of rf power that can be applied is limited, especially for aqueous protein samples, the most important pulse sequences suffer from bandwidth limitations resulting from the same spread in chemical shift frequencies that aids resolution. SAMPI4 is a pulse sequence that addresses these limitations. It yields separated local field spectra with narrower and more uniform linewidths over the entire spectrum than the currently used PISEMA and SAMMY experiments. In addition, it is much easier to set up on commercial spectrometers and can be incorporated as a building block into other multidimensional pulse sequences. This is illustrated with a two-dimensional HETCOR experiment, where it is crucial to transfer polarization from the amide protons to their directly bonded nitrogens over a wide range of chemical shift frequencies. A quantum-mechanical treatment of the spin Hamiltonians under high-power rf pulses is presented which gives the scaling factor for SAMPI4 as well as the durations of the rf pulses to achieve optimal decoupling.

Techniques for maintaining design efficiency when operating klystron amplifiers at levels below the maximum output power

Some accelerator designs require that the amount of RF power supplied to the accelerating cavities be varied along the accelerator length. In order to minimize operating expense for a high-power, CW system, it is also desirable to maximize RF-generator efficiency. Klystrons are the traditional source used for RF-accelerator applications, but a high-efficiency klystron design is optimized to provide high efficiency at only one operating point, usually at saturation. Different klystron designs could be used for different power levels to maintain high efficiency; however, this approach would increase the capital costs of the accelerator. We discuss several methods of varying the output power of a klystron and show semi-empirically a way to preserve klystron efficiency. We derive two semi-empirical methods to predict the variations in power and efficiency under nonoptimum operating conditions. Experimental data from a 1.25 MW klystron are also shown. These data support our hypothesis and our models. >

Treatment of menorrhagia by radiofrequency heating

A new technique is described for the treatment of menorrhagia by heating the whole of the endometrial cavity of the uterus. A capacitively coupled probe at 27.12 MHz is inserted into the uterine cavity, which causes the basilis layer to be raised to approximately 50-55 degrees C whilst the rest of the pelvic contents remain at approximately normal (body) temperature. A major advantage of the method is that no special hysteroscopic skills are required, unlike the two other techniques currently used for endometrial ablation: the Nd-Yag laser or the hysteroresectoscopic loop. Also no toxic flushing/distension fluids are necessary, as are required for all hysteroscopic surgery. The method, however, does require the application of a large amount of RF power to the probe and so care must be taken to position the probe correctly in order to prevent any serious complications. Of 32 patients given a single treatment at a power level of 550 W for 20 min, the 'success rate' was 84% with 31% becoming amenhorrhoiec and 53% showing significant reduction in menstrual bleeding. However, retreatment is possible and by this means, combined with improved treatment techniques, an even higher success rate could be achieved. In two of the earlier patients treated at 550 W a fistula was produced at the anterior vaginal wall which had to be surgically repaired. The probe was subsequently modified, since when this problem has not recurred. This new treatment approach offers an alternative to hysterectomy in the treatment of menorrhagia and may offer a number of significant advantages over methods currently used for endometrial ablation.

Energy balance simulation of RF heated tokamak plasma in a hybrid reactor regime

The state, close to the stationary one, for RF heated tokamak with hybrid reactor-like parameters is discussed. The plasma is heated by the absorption of lower hybrid waves; for the absorption mechanism, a simple model is used. The dependences of the near-stationary state characteristics on density, temperature and thermal conductivity are discussed and the required amount of RF power is established, together with the amount of the driven current.

Superconducting Accelerators

In this paper the application of superconductivity to several devices which conventionally require large amounts of rf power is considered. Design characteristics are given for superconducting electron linacs, cavities for electron synchrotrons, rf separators and microtrons.