Development of a Compact Measurement System of Transport Characteristics in HTS Conductors by Using an HTS Current
In order to realize HTS power machines and devices with high performance, it is important to evaluate the characteristics of HTS conductors quantitatively. We developed a compact system to measure the transport characteristics of HTS conductors under various experimental conditions. This system enables us to measure the transport characteristics of straight HTS conductors up to a current capacity of 1 kA class at 77 K, 66 K, and 4.2 K. The measurement of transport current losses is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both potential leads and pickup coils. An HTS current transformer (HTS-CT) is used to feed current to the sample conductor for the measurement. A secondary current of about 1 kA at 77 K can be induced when the primary current is 40 A. The sample conductor is connected to the secondary coil of this transformer. As a sample conductor, we used a conductor consisting of 16 parallel Ag-sheathed Bi-2223 multifilamentary tapes. The joint method between the HTS-CT and sample conductors is also examined. Based on these results, the usefulness of this measurement system is discussed.
Measurement of Transport Characteristics in HTS Conductors With Large Current Capacity by Using an HTS Current Transformer
In order to quantitatively elucidate the transport characteristics of HTS conductors with large current capacities, we minutely investigated the relation between the current distributions in the sample conductor and the circuit parameters such as joint resistance and sample inductance. A high temperature superconducting current transformer (HTS-CT) was used to energize a large current in the sample conductor. No change in the joint resistance was observed with an increase of the sample current. On the other hand, the current ratio of the HTS-CT decreased with an increase in the sample current. This is considered to be equivalent to the inductance becoming large with an increase in the sample current. From the measured current distributions, we see that the current in the central area of the conductor is increased with increasing sample current. Based on these experimental results, the relation between the change of the current distributions and the increase of the sample inductance is discussed.
Microwave source with enhanced radiation power based on orbitron MASERs
We have proposed the design of high power microwave source in a vacuum tube based on the theory of negative mass instability. The proposed source does not operate based on a slow-wave structure but instead makes use of accelerated charged particles. In our structure, an electron emitter injects the charged particles into to the cavity. Emitted particles move around the anode, which leads to electron acceleration and emission of electromagnetic waves with a specific frequency. In this paper, we have enhanced the output power and frequency of microwave source by variation of particles initial energy and the number of anodes incorporating their specific arrangement and applied voltages. Working at room temperature, compactness, wide bandwidth, and tunability of output frequency are among the advantages of the proposed source.