RESUMEN
A series of nearly single-phase Ca- and Pb-codoped BiCuSeO bulks are fabricated via 4 min of microwave heating and 5 min of spark plasma sintering (SPS). The phase composition, microstructure, and valence state of the samples are investigated systematically, and the effects of Ca and Pb dopants being added into the samples to the alternative Bi sites on the cooperative optimization of the electrical and thermal transport properties are discussed. After codoping, the electrical conductivity and power factor of the samples are significantly improved by synchronously optimizing the carrier concentration and carrier mobility. The codoping of Ca and Pb reduces the lattice thermal conductivity, which is attributed to the introduction of high-density stacking faults and nanoprecipitates formed in the process of microwave synthesis and SPS, as well as the fluctuation of volume and mass. As a result, a maximum ZT value of 1.04 in Bi0.88Ca0.06Pb0.06CuSeO is achieved at 873 K, which is â¼2 times larger than that of the undoped BiCuSeO. The remarkable enhancement of the thermoelectric properties combined with the simplicity and high efficiency of the synthesis method emphasizes that the preparation process will have a wide range of application prospects in the future thermoelectric field.
RESUMEN
BiCuSeO oxyselenide, one of the best oxygen-containing thermoelectric materials, is promising with great potential applications. In this work, we present a high ZT of >1.3 in Bi0.90Pb0.10Cu0.96Fe0.04SeO fabricated via microwave synthesis and subsequent spark plasma sintering (SPS). We added 3-4 atom % Fe to the Pb-doped BiCuSeO to regulate the hole carrier concentration and mobility to 0.8-1.0 × 1020 cm-3 and â¼40 cm2 V-1 S-1, respectively, achieving moderate electrical conductivity, high Seebeck coefficient, and low carrier thermal conductivity simultaneously in a dual-doped sample. Under the synergistic enhancement by stress field, dislocation, and nanophase, the lattice thermal conductivity of Bi0.90Pb0.10Cu0.96Fe0.04SeO is limited to 0.24-0.49 W m-1 K-1 at 300-873 K. The development of efficient preparation methods for high-performance thermoelectric materials is significant to promote the application of thermoelectric conversion technology.
RESUMEN
In order to achieve steady state operation in experimental advanced superconducting tokamak (EAST), a 6 MW/4.6 GHz lower hybrid current drive system with twenty-four 250 kW/4.6 GHz high power klystron amplifiers (model VKC7849A) has been developed. A 4.6 GHz lower hybrid wave (LHW) power control system (4.6 GHz LPCS) with continuous wave mode has been set up, which was used to control the LHW power as needed. This paper introduces the architecture and software design of LPCS system, including microwave preamplifier subsystem, power measurement subsystem, power control computers, and so on. Proportional integral differential (PID) closed-loop control time is less than 100 µs due to the use of high-speed acquisition cards and user-programmable Field Programmable Gate Arrays. So far, high power CW operation and power control experiments with PID feedback mode by plasma parameters (beta, loop voltage, and so on) were performed in detail. Results show that 4.6 GHz LPCS is stable and reliable, suggesting that it meets the needs of EAST.
RESUMEN
The lower hybrid current drive (LHCD) is an effective approach for auxiliary heating and non-inductive current drive in the experimental advanced superconducting tokamak. The 6 MW/4.6 GHz LHCD system is being designed and installed with twenty-four 250 KW/4.6 GHz high power klystron amplifiers. The test bench operating at 250 KW/4.6 GHz in continuous wave mode has been set up, which can test and train microwave components for the 6 MW/4.6 GHz LHCD system. In this paper, the system architecture and software of the microwave test bench are presented. Moreover, the test results of these klystrons and microwave units are described here in detail. The long term operation of the test bench and improved performance of all microwave component samples indicated that the related technologies on test bench can be applied in the large scale LHCD systems.