Development and application of a new method to shim first harmonic in compact cyclotron

In order to adequately eliminate 1st harmonic in the magnetic field of the compact cyclotron, CIAE has developed a 1st harmonic shimming method that can be applied to the four-sector compact cyclotron. The amplitude of the 1st harmonic can be reduced by adjusting the azimuthal width of the shimming bars at both sides of the sector in this method. Based on the beam dynamics requirement on the amplitude of 1st harmonic, the principle of 1st harmonic shimming method is illustrated through numerical analysis, and meanwhile, the shimming has been implemented on the magnet of CYCIAE-CRM by processing the azimuthal width using NC milling machining. The shimming result shows that it satisfies the requirement of beam dynamics. The shimming effect using this method is also analyzed and expounded in detail. The extension of this method is conducted so that it can be used to shim β_θ at the median plane induced by the installation error of the upper and lower sector poles.     

用飞行时间法测定回旋加速器束流能量

我所改建后的等时性回旋加速器,质子能量从10—30MeV连续可变。如何测定这些束流的能量,方法很多,如弹性、非弹性散射,核反应等。本工作用飞行时间法测定了该所等时性回旋加速器的束流能量。其优点是方法简单、可靠,测量结果准确度较高,在较宽的能量范围内都可以适用。     

Numerical study on the loss of fast ions produced by minority ion cyclotron resonance heating in EAST

The classical prompt loss of fast ions produced by minority ion cyclotron resonance heating(ICRH)is studied by a guiding center orbit following code in the Experimental Advanced Superconducting Tokamak(EAST).It is found that the loss of fast ions produced by ICRH mainly appears in both ends of the resonance layer,while the loss of fast ions in the middle resonance layer is very small.The dominant fast loss comes from trapped ions,rather than from passing ions.Controlling the location of resonance layer at the plasma core may be more beneficial to the EAST tokamak ICRH.In addition,the loss distribution of fast ions is studied.The results show that the fast ions are mainly lost near the midplane in the poloidal direction,but almost uniformly in the toroidal direction.Moreover,we investigate the dependence of fast ion loss on the ICRH power.The simulation results show that the loss fraction of fast ions in both ends of the resonance region increases with the ion cyclotron range of frequencies(ICRF)power,but barely affects the loss of fast ions in the middle region.     

一种加偏压减小磁场对样品电流信号影响的方法

在用样品电流法测量X射线磁性圆二色谱中,外磁场的存在严重降低了样品电流信号.针对合肥NSRL软X射线磁性圆二色实验站内置式可旋转磁铁设计并安装一个紧靠磁极的高压金网,来增强磁场下的样品电流信号.发现不同磁场下随偏压升高,样品电流信号迅速增强并趋于饱和;磁场越强,达到饱和需要的偏压越高;比较相同磁场和偏压下均匀氧化的Al箔和CoFe薄膜正反磁场下的吸收谱,发现加磁场和偏压引入的系统误差仅相当于Co的圆二色值的2.17%;表明用这种方法进行X射线磁性圆二色谱的测量是可行的.     

Enhancement of hydrogen isotope retention capacity for the impurity deposited tungsten by long-term plasma exposure in LHD

The stress relieved tungsten samples were placed at three positions, PI (sputtering erosion dominated area), DP (deposition dominated area) and HL (Higher heat load area) during 15th plasma experiment campaign in Large Helical Device (LHD) at National Institute for Fusion Science (NIFS), Japan and were exposed to ～ 6700 shots of hydrogen plasma in a 15th long-term experiment campaign in LHD. Thereafter, the additional deuterium ion implantation to these tungsten samples was performed to evaluate the change of hydrogen isotope retention capacity in the samples by long-term plasma exposure. It was found that the carbon-dominant mixed-material layer with more than 100 nm thickness was formed on a wide area of the tungsten surface. The thicker mixed-material layer was formed on the DP sample, where the deuterium retention was about 21 times as high as that for pure W. The major desorption temperature of deuterium was shifted toward higher temperature side, which was comparable to the trapping characteristic of carbon or irradiation damages.     

Investigation of the packing structure of pebble beds by DEM for CFETR WCCB

Li₂TiO₃/Be₁₂Ti mixed pebble beds with multi-sized particles are one of the potential candidates for the WCCB (water-cooled ceramic breeder blanket) of the CFETR (China Fusion Engineering Test Reactor). To meet the neutronics requirements of a WCCB, a study of the packing structure of the concerned pebble bed is necessary. In this paper, the discrete element method (DEM) is applied to produce a prototypical blanket pebble bed by directly simulating the contact state of each individual particle using basic interaction laws. According to the current simulation, the packing factor of a mono-sized pebble bed is 0.62–0.64, while the value will become more than 0.75 for Li₂TiO₃/Be₁₂Ti mixed breeding pebble bed with a diameter ratio of not less than 5 as well as an appropriate mixed volume ratio, and thus can meet the neutronics requirements.