Search

Direct observation of lightning current is a fundamental approach to evaluating lightning parameters, which are among the most basic factors for the lightning protection design of various grounded objects. However, for a tall grounded structure, upward lightning flashes initiated from the top of the structure have usually been observed, and the direct observation results of downward flashes have been limited. We developed and installed a pair of Rogowski coils at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower in Japan (35.71°N, 139.81°E), and have conducted direct observation of lightning flashes striking the tower. As of November 2018, 70 lightning flashes striking the tower, 26 downward and 44 upward, have been observed since the end of February 2012. In this paper, we focus on the downward negative flashes that occurred at the tower for seven years from 2012 to 2018 and report on the observed results of typical waveform parameters of lightning stroke currents in comparison with other observed results on downward negative flashes. [ABSTRACT FROM AUTHOR]

An unusual negative lightning flash was recorded at the Säntis Tower on June 15, 2012. The flash did not contain an initial continuous current typical of upward negative lightning, which is the most common type of event at the Säntis Tower. The flash contained four strokes, the last three of which were normal while the current associated with the first stroke resembled a Gaussian pulse with an unusually high peak value of 102.3 kA, a long risetime of 28.4 μs, and a pulsewidth of 53.8 μs, which was followed by an opposite polarity overshoot with a peak value of 8.5 kA. Our current records suggest the involvement of a long upward connecting positive leader in response to the approaching downward negative leader in the formation of this flash. Lightning location system (LLS) data indicate that a positive cloud-to-ground stroke occurred 1 ms prior to the first stroke of the flash. In this paper, we present a detailed description of the data associated with this event. Moreover, both a return stroke model and an M-component model are used to reproduce the far-field waveform of this bipolar stroke. The simulations result in a radiated electric field waveform that is similar to those of large bipolar events (LBEs) observed in winter thunderstorms in Japan. A sensitivity analysis of the used simulation models reveals that, by proper selection of the input parameters, all field waveform characteristics, except for the positive half-cycle width, can be made to fall in the range of LBE field characteristics reported in Japan. [ABSTRACT FROM AUTHOR]

The betatron tune, which is defined as the number of transverse oscillations in one turn of a ring accelerator, is one of the most important parameters. An undesired betatron tune increases the amplitude of the transverse oscillation so that many particles are lost from the ring sooner than designed. Since a betatron tune is controlled by the magnetic fields in the ring, the ripple of the magnet current directly displaces the betatron tune from its designated value. We have developed a system that corrects the betatron tune displacement using the measured magnet current at the Japan Proton Accelerator Research Complex main ring. We adopted field programmable gate arrays to convert from the measured magnet current to the betatron tune in real time. Using the system, we have decreased the fluctuation of the betatron tune $\sigma _{\nu }$ from $5.2\times 10^{-4}$ to $3.3\times 10^{-4}$ at the frequencies less than 250 Hz. [ABSTRACT FROM AUTHOR]

Japan Proton Accelerator Research Complex aims at a megawatts-class proton accelerator facility. One of the promising solutions for increasing the beam power of the main ring is the converters of the main magnets with new ones for this upgrade. We have a plan to replace and develop the power converters of main magnets for this upgrade. According to develop the new power converter. We have developed a new control system for the new power converters. This control system consists of four parts: the current measuring device, the feedback control system, the gate pulse generator, and the slow control system. Considering a reproducibility in the mass production and the facilitation of the control algorithm, the digital control system is adopted. We will report the design of this control system and some test result with a new power converter for small quadrupole magnets. [ABSTRACT FROM AUTHOR]