Gyrotron performance is sensitive to cavity structure parameters, and the cavity shape is temperature dependent due to thermal deformation induced by temperature rise from ohmic loss power on finite-conductivity cavity wall. Accordingly, this paper studies a frequency-tuning scheme for terahertz gyrotron by properly controlling the cavity thermal deformation. By combining gyrotron nonlinear theory and finite-element method software, controllable thermal-frequency-tuning capability of a continuous-wave 263-GHz gyrotron is systematically investigated, toward maintaining gyrotron operating under gyromonotron condition in frequency-tuning band, and achieving high efficiency in broadband frequency-tuning range. After studying cavity thermal distribution, structure deformation, and electron beam-wave interaction, an optimized cavity structure with transition sections on both ends is proposed. Simulation predicts that with the two-transition-section cavity, via additional thermal tuning, the continuous-frequency-tuning band is capable of reaching 1.75 GHz, which is 5 times of the initial bandwidth. Furthermore, using the thermal-frequency-tuning technology, impressive high efficiency above 17% is obtainable in the whole frequency-tuning range.
As the largest energy infrastructure in China, the power sector consumed approximately half of China's coal over the past decade and threatened air quality and greenhouse gas (GHG) abatement targets. In this work, we assessed the evolution of coal-fired power plants and associated emissions in China during 2010-2030 by using a unit-based emission projection model, which integrated the historical power plant information, turnover of the future power plant fleet, and evolution of end-of-pipe control technologies. We found that, driven by stringent environmental legislation, SO2, NOx, and PM2.5 (particulate matter less than 2.5 mu m in diameter) emissions from coal-fired power plants decreased by 49%, 45%, and 24%, respectively, during 2010-2015, compared to 15% increase in CO2 emissions. In contrast to ever-increasing CO2 emissions until 2030 under current energy development plan- ning, we found that aggressive energy development planning could curb CO2 emissions from the peak before 2030. Owing to the implementation of a "near zero" emission control policy, we projected emissions of air pollutants will significantly decrease during 2016-2030. Early retirement of small and low-efficiency power plants would further reduce air pollutants and CO2 emissions. Our study explored various mitigation pathways for China's coal-fired power plants, which could reduce coal consumption, air pollutants, and CO2 emissions and improve energy efficiency.
This paper presents two D-band frequency quadruplers (FQs) employing different circuit techniques. First FQ is a 129–171-GHz stacked Gilbert-cell multiplier using a bootstrapping technique, which improves the bandwidth and the conversion gain with respect to the conventional topology. Stacked architecture enables current reuse for the second frequency doubler resulting in a compact and energy-efficient design. The circuit reaches 3-dB bandwidth of 42 GHz, which is the highest among similar reported quadruplers. It achieves 2.2-dBm saturated output power, 5-dB peak conversion gain, and 1.7% peak DC-to-RF efficiency. The stacked FQ occupies 0.08 mm2 and consumes 22.7 mA from 4.4-V supply. Second presented circuit is a transformer-based injection-locked FQ (T-ILFQ) employing an E-band push–push voltage-controlled oscillator (PP-VCO). The VCO is a self-buffered common-collector Colpitts oscillator with a transformer formed on emitter inductors. Proposed configuration does not reduce the tuning range of the VCO, thus providing wide locking range and high sensitivity with respect to the injected signal. The T-ILFQ achieves 21.1% locking range, which is the highest among other reported injection-locked frequency multipliers. The peak output power is −4 dBm and the input sensitivity reaches −22 dBm. The circuit occupies 0.09 mm2 and consumes 14.8 mA from 3.3-V supply.
