To improve borehole siting for rural water supply, an advanced resistivity method was adapted for developing country use and demonstrated in Malawi. The method was designed to be low cost, developing-country accessible, efficient. It allows single or multiple operators to acquire the multiple vertical electrical soundings (VESs) required that are inverted together in 2-D, to give a true cross-section of subsurface resistivity. Application at four sites generated true cross-sections of subsurface resistivity to around 100 m depth relevant to groundwater-resource investigation. A wide range of (hydro)geological features was identified, including fractured/weathered basement, gneiss domes, well-developed fault zones and several types of deltaic deposits. Imaging performance appears comparable to that of 2-D surface ERT (electrical resistivity tomography) that uses more expensive equipment, often unaffordable in developing countries. Based on the subsurface configurations determined and hydrogeological conceptualisation subsequently undertaken, the local aquifer potential could be evaluated, thereby providing a decision-making basis for future borehole siting at the sites surveyed. The technology is far superior to conventional 1-D VES, electromagnetic profiling or magnetic profiling currently used for borehole siting in Malawi. Technology adoption currently under consideration nationally would make use of existing VES capacity and permit much improved targeting of aquifer resource, more sustainable siting of boreholes and greater future resilience of Malawi’s rural water-supply infrastructure.
The ever increasing demand for higher and higher powered millimeter-wave devices has created the need for devices other than the traditional helix type traveling-wave tubes (TWT's). Helix derived circuits such as the ring-bar circuit offer several advantages over traditional helix circuits including higher power levels, higher efficiencies, and improved thermal capabilities while maintaining equivalent costs. This development program is directed toward a 800 watt tube operating at 35 GHz, at duties up to 30 per cent.A detailed description of the ring-bar design along with the RF performance data on one of the development tubes ispresented. Performance tests have demonstrated in excess of 700 watts at 31 GHz. The tube features PPM focusing, conduction cooling, and a non-intercepting gridded gun design.
has developed an experimental PPM focused, coupledcavity traveling-wave tube which produces between 235 and 250 watts of CW RF output power over an 85 MHz frequency band centered at 12.080 GHz. A photograph of the TWT is shown in Figure 1. The basic efficiency of this tube is greater than 30%, reaching 33% at midband. An overall efficiency in excess of 50% is obtained with a ten stage (nine depressed elements) collector in conjunction with a spent beam refocusing section designed at NASA, Lewis Research Center. The collector is cooled by radiation.The tube utilizes a two-section, coupled-cavity RF interaction structure to provide 36 dB of gain at saturation. The high basic efficiency is obtained with a two-step velocity taper at the RF circuit output. This taper was designed and optimized using a large signal interaction computer program which accurately predicted the TWT performance. The electron gun and PPM focusing structure designs were also optimized using computer programs which included thermal velocity effects.The TWT was developed under sponsorship of the National Aeronautics and Space Administration, Lewis Research Center. Electrical CharacteristicsThe operating parameters are summarized in Table I for a saturated RF output power of 250W at midband. Figure 2 shows the output power versus frequency with constant input power over a 100 MHz band centered at 12.080 GHz. For an optimum RF drive level of 16 dBm (40 mW) the output power varies between 233 and 250 watts across the 85 MHz design band. The constant drive performance over an extended frequency range is displayed in Figure 3. With a drive level of 18 dB the tube delivers 2OOW nominal output power over 150 MHz with less than 0.3 dB amplitude variation.The saturated efficiency is plotted in Figure 4 . The basic efficiency across the design bandwidth is between 31 and 33 percent, and the depressed efficiency is close to 53 percent. With the heater and refocusing solenoid power included, the overall efficiency is 51 percent.Also shown in Figure 4 are the basic efficiencies at four frequencies across the band calculated with a large signal interaction couputer program. The calculation used circuit cold test data and assumed a cathode voltage and current of -8.0 kV and 84.1 mA respectively. The agreement between calculated and measured efficiencies is good, noting that the higher operating voltage and current improve the low frequency performance and overall bandwidth and efficiency.The ohmic loss of the RF circuit strongly influences the efficiency and thermal performance of the tube. With an output power level of 250W a total ohmic loss of 78 watts was computed. The intrinsic depressed collector efficiency was estimated to be 75 percent at a baseplate temperature of 6OoC. Mechanical and Thermal CharacteristicsA cross-section view of the radiation coaled, ten stage collector is shown in Figure 5. The electrode voltages (given in Table I) provide a smooth decelerating force on the electrons. The spike on the last element provides an additional radial for...
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.
hi@scite.ai
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.