Improved Design of Beam Tunnel for 42 GHz Gyrotron

In gyrotron, there is the chance of generation and excitation of unwanted RF modes (parasite oscillations). These modes may interact with electron beam and consequently degrade the beam quality. This paper presents the improved design of the beam tunnel to reduce the parasite oscillations and the effect of beam tunnel geometry on the electron beam parameters. The design optimization of the beam tunnel has been done with the help of 3-D simulation software CST-Microwave Studio and the effect of beam tunnel geometry on the electron beam parameters has been analyzed by EGUN code.     

Design of Electron Gun for 1.5 MW, 140 GHz Gyrotron

This paper presents the design of the triode type electron gun for a 140 GHz, 1.5 MW gyrotron with the transverse to the axial velocity ratio of the beam 1.4 and the transverse velocity spread 1.28%. The operating mode of the gyrotron is TE_24,8 and it is operated in the fundamental harmonic. The analytic trade-off equations for the electron gun design have been used to estimate the initial gun parameters. The electron trajectory tracing program has been used to optimize the electron gun design. The parametric dependences of modulating anode voltage, beam voltage and cathode magnetic field on the beam quality has also been studied.     

Design of 84 GHz 500 kW Gyrotron for Technological Millimeter Wave Applications

In this paper, the design and the numerical simulation of the 84 GHz, 500 kW gyrotron at first harmonic operation for technological applications is described. The operating mode of the gyrotron is TE_{10, 4}. Various in-house developed and commercially available computer codes are used for the design purpose. The triode-type magnetron injection gun with the accelerating voltage 70-kV, the beam current 10-A and the maximum transverse velocity spread less than 5% is designed. The preliminary design is obtained by using some trade-off equations. The mode selection, the cold cavity and the beam-wave interaction analysis are discussed for the design of weakly tapered open resonator type of the interaction cavity. The parametric analysis of the interaction cavity and the electron gun is also presented.     

Numerical Analysis of Interaction Cavity for 1.5 MW/127.5 GHz Gyrotron

This paper presents the design of 127.5 GHz ITER start-up gyrotron interaction cavity. Particle-in-Cell electromagnetic simulation approach has been used for the cold cavity and beam-wave interaction analysis. In-house developed code GCOMS has been used for the mode selection. TE_24,8 mode has been chosen as the operating mode. The simulation results show the output power more than 1.5 MW at the operating frequency of 127.8 GHz and the cavity centre magnetic field of 5.1 T. The study of the parametric dependency of the output power and the efficiency on the electron beam and the cavity geometry parameters has also been carried out.     

Design and Misalignment Analysis of 140 GHz, 1.5 MW Gyrotron Interaction Cavity for Plasma Heating Applications

In this paper the design of 140 GHz, 1.5 MW gyrotron interaction cavity is described in detail. The interaction cavity is designed and simulated by using Particle-in-Cell code for TE_24,8 operating mode. The obtained simulation results show more than 1.5 MW of output power at 139.83 GHz of frequency. A thorough parametric and misalignment study is also presented to support the actual fabrication and assembling of the device.     

Numerical Design of Megawatt Gyrotron with 120 GHz Frequency and 50% Efficiency for Plasma Fusion Application

The design of 120 GHz, 1 MW gyrotron for plasma fusion application is presented in this paper. The mode selection is carried out considering the aim of minimum mode competition, minimum cavity wall heating, etc. On the basis of the selected operating mode, the interaction cavity design and beam-wave interaction computation are carried out by using the PIC code. The design of triode type Magnetron Injection Gun (MIG) is also presented. Trajectory code EGUN, synthesis code MIGSYN and data analysis code MIGANS are used in the MIG designing. Further, the design of MIG is also validated by using the another trajectory code TRAK. The design results of beam dumping system (collector) and RF window are also presented. Depressed collector is designed to enhance the overall tube efficiency. The design study confirms >1 MW output power with tube efficiency around 50% (with collector efficiency).     

Effect of Li on Safety of Cu Components for EAST

Cu–Li–Cu multilayers were deposited on Si substrate by alternately using magnetron sputtering and resistance evaporation. Scanning Electron Microscope (SEM) and Rutherford Backscattering Spectrometry (RBS) were utilized to study the interaction and diffusion between Cu and Li after 8 h heat treatments at 100, 280, and 480 °C. The RBS results reveal that Li can diffuse into Cu when the temperature rises to 480 °C. As a supplementary experiment on Cu corrosion by Li at lower temperature, bulk Li and Cu were annealed at 240, 320 and 400 °C for 8 h separately in a high-temperature furnace after sealing in quartz ampoules. Morphology images show that Li corrodes grain boundaries of Cu preferentially when the temperature is higher than the melting point of Li, and the corrosion rates are 0.7875, 0.925 and 3.3275 mg/h, respectively. The results are helpful for understanding the Cu corrosion and protecting the Cu components in EAST.     

Polarization and Mode Control of EAST 140 GHz ECRH&CD System

The 140 GHz electron cyclotron heating and current drive (ECRH&CD) project was launched in 2011 on EAST tokamak facility, which is designed to launch 4 MW of total power for the duration up to 1,000 s into the plasma. The heating and current drive efficiencies depend on the wave coupling mode in plasma and the coupling performance relies on polarization characteristics of injected beam, so polarization control is necessary for efficient plasma heating and current drive. Two polarizer miter bends will be used to control the wave polarization for each transmission line on EAST ECRH&CD system, any required wave polarization can be produced by adjusting the mirror rotation angle of each polarizer miter bend. This work mainly shows the calculated polarizer mirror settings as a function of the injection angles for pure second extraordinary harmonic mode coupling.     

Experimental study on breakup and fragmentation behavior of molten material jet in complicated structure of BWR lower plenum

To estimate the state of reactor pressure vessel of Fukushima Daiichi nuclear power plant, it is important to clarify the breakup and fragmentation of molten material jet in the lower plenum of boiling water reactor (BWR) by a numerical simulation. To clarify the effects of complicated structures on the jet behavior experimentally and validate the simulation code, we conduct the visualized experiments simulating the severe accident in the BWR lower plenum. In this study, jet breakup, fragmentation and surrounding velocity profiles of the jet were observed by the backlight method and the particle image velocimetry (PIV) method. From experimental results using the backlight method, it was clarified that jet tip velocity depends on the conditions whether complicated structures exist or not and also clarified that the structures prevent the core of the jet from expanding. From measurements by the PIV method, the surrounding velocity profiles of the jet in the complicated structures were relatively larger than the condition without structure. Finally, fragment diameters measured in the present study well agree with the theory suggested by Kataoka and Ishii by changing the coefficient term. Thus, it was suggested that the fragmentation mechanism was mainly controlled by shearing stress.     

Study on a Plasma-Jet Triggered Trigatron Switch in a 1.0 MJ-Flashlamp Driven Power System

In the Pre-ionization lamp-check module of the inertial confinement fusion (ICF) power system, the trigatron switch was widely used for its compact structure and high reliability. A plasma-jet triggered trigatron switch (PTTS) for the PILC module of a 1.0 MJ-flashlamp driven ICF power system was developed and evaluated in this paper. The performance of the PTTS and the erosion characteristics were measured after about 4000 discharge cycles of the lifetime tests. The results showed that the ablation of the polymers tube between trigger pin and graphite electrode had a significant influence on the performance degradation of the PTTS. The delay time increased from 9 to 20 µs and the jitter was less than 1.0 µs under operating voltage of 23.5 kV, the erosion of the graphite electrodes was not serious and a stable self-breakdown voltage was obtained, the degradation of the PTTS was mainly attributed to the ablation of the polymers tube, good performance of the PTTS could be obtained when the polymers tube was renewed.     

Monte Carlo Simulations of 17.9–22.3 MeV Energetic Proton Irradiation Effects on bcc-Zirconium Fusionic Materials

Advanced fusion structural materials (FSMs) have impact role in terms of efficiency of nuclear energy production. Besides engineering and design of fusion reactors, radiation durability of FSMs is another valuable issue that cannot be ignored. 17.9–22.3 MeV proton irradiation of bcc-Zirconium Fusion Structural Material was evaluated by using Monte Carlo based simulation tools. Total binary reaction cross sections were respectively calculated as 1167.6 and 1273.92 mb for 17.3- and 22.3 MeV proton energies via TALYS-1.6 version. Additionally, residual production cross sections and total particle production cross sections were obtained and analyzed by the TALYS code. Radiation damage parameters as Displacement Per Atom (DPA) and Stopping Power (SP) were studied by SRIM-2013 version. FLUKA 2011.1 used for only DPA calculations and making a complete comparison with the other calculation results. SP and Number of Secondaries were found by using GEANT4.10.p.04 version simulations. Natural Zr(p,x) reactions were studied in the given energy values in the plane of reaction probability and radiation damage calculations.     

Effects of water chemistry and potential distribution on electrochemical corrosion potential measurements in 553 K pure water

The effects of water chemistry distribution on the potential of a reference electrode and of the potential distribution on the measured potential should be known qualitatively to obtain accurate electrochemical corrosion potential (ECP) data in BWRs. First, the effects of oxygen on a platinum reference electrode were studied in 553 K pure water containing dissolved hydrogen (DH) concentration of 26–105 μg kg^?1 (ppb). The platinum electrode worked in the same way as the theoretical hydrogen electrode under the condition that the molar ratio of DH to dissolved oxygen (DO) was more than 10 and that DO was less than 100 ppb. Second, the effects of potential distribution on the measured potential were studied by using the ECP measurement part without platinum deposition on the surfaces connected to another ECP measurement part with platinum deposition on the surfaces in 553 K pure water containing 100–130 ppb of DH or 100–130 ppb of DH plus 400 ppb of hydrogen peroxide. Measured potentials for each ECP measurement part were in good agreement with literature data for each surface condition. The lead wire connecting point did not affect the measured potential. Potential should be measured at the nearest point from the reference electrode in which case it will be not affected by either the potential distribution or the connection point of the lead wire in pure water.     

Safety assessment of nuclear power plant under volcanic phenomena part2 – revision of JEAG4625 on the safety assessment of severe accident measures equipment and maintenance programme

Japan is one of the countries with abundant active volcanoes. In the field of Nuclear Energy, it is necessary to assess safety against volcanic hazards, and voluntary guidelines were published in JEAG4625 in 2009 to set up the requirements of site assessments and the basic designs of nuclear power plants (NPPs). Revised guidelines were published in 2014, which stated the need to examine volcanic phenomena and concrete countermeasures in the detailed designs of NPPs. A further revision included the requirement of the safety assessment of equipment used for measures in a severe accident. This paper focuses on the background and technical basis of the revision of the voluntary guidelines and shows the basic policy on the concept of defence in depth for protecting NPPs against volcanic phenomena and the requirements of equipment to perform measures in the case of a severe accident to prevent nuclear hazards due to volcanic phenomena and the maintenance programme after a volcanic eruption.