On the detection of RF breakdowns in ICRH Resonant Double Loop antennas

A voltage breakdown in an ion cyclotron resonance heating (ICRH) system is usually detected as an abrupt change in the module of the reflection coefficient |Γ_in| at the power source output. The same effect can be due to a large load variation. This paper presents the study of some new concept for detecting voltage breakdowns in ICRH Resonant Double Loop (RDL) systems, to be used in conjunction with the one identifying an arc by the detection of an excessive standing wave ratio (SWR), either at the operating frequency or within the band below the operating frequency. The method should be able to help discriminating fast load variations from voltage breakdowns in any of the in-vessel components under the torus vacuum, and therefore selecting the proper corrective action.     

A Ray-Tracing Analysis of ICRH in Tokamaks

Power deposition profiles generated by Ion Cyclotron Resonance Heating （ICRH） in non-circular tokamaks are studied using a ray-tracing technique. The simulation results for the Experimental Advanced Superconductor Tokamak （EAST） D-shaped plasma are presented. It is indicated that the spatial distributions of plasma parameters （plasma density, species temperature, minority ion concentration, etc.） have an significant influence on the power deposition profiles. The findings may be highly useful to the planned plasma heating and experiments in EAST.     

Development of Embedded RF Coil for Optical Pump Magnetometer

<正>Alkali metal optical pump magnetometer is widely concerned because of its high sensitivity,wide dynamic magnetic measurement range and other advantages.It is the key equipment of high sensitivity magnetic measurement technology.At present,some alkali metal optical pump magnetometers have entered the application stage,     

Thermal limitation of the mean power rating of coaxial transmission lines for ICRH

A limitation of the mean power rating of a coaxial transmission line arises from the coupling elements, which connect adjacent sections of the inner conductor by means of contact springs that are subjected to thermal degradation. This paper is focused on the design applied in a commercially available transmission-line coupling element. The main scope is to demonstrate the possibility to extend the working range of its spring contacts up to 200 °C. Presently this component is extensively used in several transmission lines of fusion experiments working with short pulses and operating with a maximum temperature of 150 °C at the inner conductor.Test components are successively exposed to a well controlled temperature of 200 °C over certain time periods and are characterized afterwards with regard to the resilient forces of the contact lamellae with an accurate experimental setup. The weakening of the spring force in dependence of the cumulative annealing time is studied and the remaining spring force is compared to the minimum required force to ensure proper electrical contact, which is also determined experimentally within this work.     

Determination of the fatigue crack growth threshold in cold-worked Zr-2.5 wt% Nb in the acoustic frequency range

Using infrared analysis, we found that the reaction rate of gaseous uranium hexafluoride and tritium is determined solely by the rate at which energy from the radioactive decay of tritium is absorbed in the reaction mixture. Because uranium hexafluoride and tritium absorb β-energy with different efficiencies, the reaction rate is somewhat dependent on the initial reactant concentrations. Reaction products include uranium subfluorides and tritium fluoride. A radiochemistry model has been developed that includes β-energy production and absorption in the gas phase to allow calculation of the reaction yield per ion pair formed. With this model it was found that the reaction mechanism does not include lengthy chain propagation steps-only about 10 uranium hexafluoride molecules are consumed for each ion-pair formed in the gas phase. Many possible reaction steps are suggested that could contribute to the observed overall mechanism.     

Parametric study of one triplet of the ITER ICRH antenna by numerical modeling

Each of the two ITER ICRF antennas consists of a close-packed array of 24 straps arranged in a 6 poloidal by 4 toroidal array. Three poloidally adjacent straps (a “triplet” of straps) are fed together through a 4-port junction from one 20 Ohm feeding line. The complete array has to radiate 20 MW of RF power over a frequency range of 40 MHz to 55 MHz and for different toroidal phasings. The RF optimization of the antenna has been performed numerically on one triplet of straps (1/8th of the antenna) [1], [2]. In parallel a number of reduced-scale mock-ups of one triplet of the ITER ICRH antenna were constructed in order to validate the results of the numerical optimization [1], [3].The aim of this work is primarily to benchmark the CST MWS^® [4] numerical modeling against numerous measurements done on the mock-up of the 2007 design. Moreover MWS calculates the 3D distribution of the currents and of the fields of the triplet. Hence it gives the possibility to check the fields and current distributions resulting from the optimisation study of the ITER ICRH antenna triplet done by changing geometrical parameters of the straps and antenna box of the mock-up of 2007 design [1], [2], [3]. The considered parameters are: strap width, antenna box depth and vertical septum recess with respect to the front of the current strap. The impact of the presence of the Faraday screen is also evaluated.Excellent agreement between modeled and measured S parameters is obtained. Analysis of the fields and currents distributions on the straps is reported. Excellent current balance is confirmed.     

Summary and results of the study of the hybrid matching option implementation of the ITER ICRH system

The hybrid option has been chosen for the load-resilient matching of the ITER ICRH system. The corresponding 3 dB hybrid matching circuit has been developed and fully implemented on a low-powered scaled mock-up at the LPP-ERM/KMS. The circuit features 23 simultaneously active feedback loops to minimize reflections on the 8 triplet lines, reduce the mutual coupling between the triplets and control the antenna array strap current distribution. The article discusses the employed methods for the implementation on a test-bench of the matching system including the derivation of closed-form analytical matching solutions for the tuners, the development of real-time control algorithms and the feedback systems. Furthermore, the achieved results are compared to numerical simulations of the ideal transmission line model of the matching system and the significance of these results for the extrapolation to the ITER case is discussed.     

Electron-impact excitation of argon: Optical emission cross sections in the range of 300-2500 nm

We present measurements of optical emission cross sections for excitation from the ground state of the Ar atom into over 185 excited atomic and ionic levels. Measurements were made at electron energies of 25, 50, and 100 eV, at a gas pressure of 5 mTorr. Due to radiation trapping of resonance levels, many of the cross sections depend on the target pressure. Detailed pressure dependence for over 50 levels is also provided. The energy dependence of the excitation cross sections for over 175 levels in the energy range of 0-250 eV are provided as fitted parameters for a standard analytical function.     

兰州重离子加速器冷却储存环射频堆积过程模拟

考虑了重离子冷却储存环中粒子纵向相振荡的运动特性及电子冷却的作用,模拟兰州重离子加速器冷却储存环（HIRFL－CSR）主环中的射频堆积过程,给出了高频参数在射频堆积过程中随时间的变化曲线,为高频腔的设计及机器运行时的参数预置了理论依据。     

Characterization and dielectric properties of GeOx thin films prepared by radio frequency (RF) reactive sputtering

Dielectric properties of germanium oxide have not been investigated in detail. But, it has been investigated from an optical viewpoint as light waveguide materials. Its electrical properties have rarely been studied for electronic device applications.We have examined the previous investigations on Ge-O films deposited by radio frequency (RF) reactive sputtering. The dissipation factor tan δ, the capacitance per area, the breakdown field of GeO_x films were studied as well as its composition by RBS analysis. Aiming at obtaining the higher value of the dielectric constant or capacitance per area, we have attempted to fabricate Ge-Pb-O films by the same deposition method. An optimization of the dielectric properties of these materials has been done, using the best conditions of sputtering for each oxide, the alternated pile layers as dielectric multilayer capacitors and thermal treatments.These dielectric properties have been improved by thermal treatments, and the dielectric multilayer made with alternated GeO₂ and Ge-Pb-O films capacitors has a breakdown field superior to that of each simple layer.     

RF modeling of the ITER-relevant lower hybrid antenna

In the frame of the EFDA task HCD-08-03-01, a 5 GHz Lower Hybrid system which should be able to deliver 20 MW CW on ITER and sustain the expected high heat fluxes has been reviewed. The design and overall dimensions of the key RF elements of the launcher and its subsystem has been updated from the 2001 design in collaboration with ITER organization. Modeling of the LH wave propagation and absorption into the plasma shows that the optimal parallel index must be chosen between 1.9 and 2.0 for the ITER steady-state scenario. The present study has been made with n_|| = 2.0 but can be adapted for n_|| = 1.9. Individual components have been studied separately giving confidence on the global RF design of the whole antenna.     

Estimation of manufacturing defects in the creep range

Various concepts are available for the estimation of crack-like manufacturing defects of components operated in the creep regime. All these methods raise questions as to their practicable application respectively transferability to the component. Discussing these problems resulted in the demand for the development of a “Two-Criteria-Diagram” which can represent practicable load conditions and make statements on the failure modus.     

On the Donnell's equations in the creep range

This paper is concerned with assessing the accuracy of Donnell's approximation when employed in the creep analysis of a class of circular cylindrical shells. Basic formulation of a general method describing the creep behaviour of two-dimensional cylindrical shells is first presented. The terms affected by Donnell's approximation are then pointed out. The solution of governing equations is obtained through coupling the ‘extended Newton's method’ and finite difference technique in an iterative procedure. A number of examples having geometries falling within the shallow shell definition, around the limit, and beyond the range of applicability, are solved using both theories. It has been noted that the parameter α, representing the shell geometry, has a pronounced effect on the accuracy of Donnell's simplification. As α increases the deviation between the two theories decreases. It is concluded that for the class of circular cylindrical shells considered herein Donnell's approximations yield accurate results for creep analysis, particularly for higher values of creep exponent n. Of course, employing Donnell's approximations results in simpler formulation and a reduction in computational time.     

光电倍增管射频电磁辐射敏感性研究

分析了典型光电倍增管的电子束聚焦过程和射频电磁场对其干扰的机理,在此基础上利用脉冲光源和TEM小室设计了一套实验装置,开展了光电倍增管电磁辐射敏感性研究。在实验中通过观察光电倍增管计数率的变化,确定了其存在一个最敏感的干扰角度,找出了在此敏感角度下的干扰阈值和最易受干扰的频率点。最后对光电倍增管的两种电磁屏蔽措施进行了对比,给出了一种较为满意的设计方案,并应用于某型β射线探测器。     

The Improvement of Confinement by the Use of RF Waves

It is suggested that the ponderomotive force induced by radio frequency (rf) waves in the range of the Alfven frequency can create a transport barrier in a tokamak. The linear and nonlinear behaviour of the drift-like perturbation with a parallel velocity shear is studied in the presence of rf waves. It is shown if the radial profile of the rf field energy is properly chosen the linear mode is stabilised and turbulent momentum transport reduces. The rf power required for this stabilisation is found to be rather modest and hence should be easily obtained in actual experiments.     

用于DC-SC光阴极微波电子枪中的Cs2Te光阴极研制

文章介绍DC-SC光阴极微波电子枪中的关键部件——Cs2Te光阴极的研制。采用两种方法制得了高量子效率要求的Cs2Te光阴极，并实验比较了两种制备方法的效果。针对制备中的超高真空、精确控制Cs原子流量和阴极温度等关键问题，设计了用于DC-SC光阴极微波电子枪中的光阴极制备室。