Design and field measurement of a dipole magnet for a newly developed superconducting proton cyclotron beamline

The design, field quality optimization, multipole field analysis, and field measurement of a dipole for a newly developed superconducting proton cyclotron(SC200) beamline are presented in this paper. The maximum magnetic field of the dipole is 1.35 T; the bending radius is 1.6 m with a proton beam energy in the range of70–200 Me V. The magnetic field was calculated with 2 D and 3 D simulations, and measured with a Hall mapping system. The pole shim and end chamfer were optimized to improve the field quality. Based on the simulated results,the multipole field components in the good-field region were studied to evaluate the field quality. The results showed that the field quality is better than ± 5 × 10~(-4) at1.35 T with shimming and chamfering. For the transverse field homogeneity, the third-order(B3) and fifth-order(B5)components should be controlled with symmetrical shims.The second-order(B2) component was the main disturbance for the integral field homogeneity; it could be improved with an end chamfer. The magnet manufacturing and field measurement were performed in this project. The measurement results demonstrated that the magnetic design and field quality optimization of the 45° dipole magnet can achieve the desired high field quality and satisfy the physical requirements.     

Study of Plume Characteristics of a Stationary Plasma Thruster

Electron density and temperature of the plume are measured by a double Langmuir probe in an experimental chamber. A numerical model based on both particle-in-cell scheme and direct simulation Monte Carlo hybrid method is developed to simulate the flow field of plume. The equation for plasma potential is solved by alternative direction implicit technique. The simulation is verified by comparing the computational results with the measured data. The study indicates that the electron temperature of flow field is about 2 eV and the electron density is about 2.5 ×10^16 - 5×10^15 m^-3 at the central line with a distance of 0.3 - 1.0 m downstream of the thruster exit. The model can well predict the flow field parameters of the steady plume. The efforts of this paper are referable for further investigation.     

Temperature detection circuit on the low-temperature superconducting coils

Experimental Advanced Superconducting Tokamak(EAST) is the fully superconducting Tokamak.The EAST magnet system comprises 16 D-shaped toroidal field coils and 14 poloidal field coils which are cooled by supercritical helium at 4.2 K and 3.8 K.The temperature of superconducting coils is measured by Cernox as a new type low-temperature sensor,and monitored during the cooling and operation.The helium temperature can offer reference for quench signal.In this paper,a technique for the weak temperature signal measurement of superconducting coils is introduced,and its weak voltage is extracted from the intrinsic noise of the amplifier by the low-noise instrumentation amplifier,filter circuit,and high-linearity analog optocoupler.The temperature detection circuit works accurately and safely whether in cooling or operating process.This technique is an effective for the temperature detection on the low-temperature superconducting coils.     

Experimental Investigation on Airfoil Shock Control by Plasma Aerodynamic Actuation

An experimental investigation on airfoil （NACA64-215） shock control is performed by plasma aerodynamic actuation in a supersonic tunnel （Ma -= 2）. The results of schlieren and pressure measurement show that when plasma aerodynamic actuation is applied, the position moves forward and the intensity of shock at the head of the airfoil weakens. With the increase in actuating voltage, the total pressure measured at the head of the airfoil increases, which means that the shock intensity decreases and the control effect increases. The best actuation effect is caused by upwind-direction actuation with a magnetic field, and then downwind-direction actuation with a magnetic field, while the control effect of aerodynamic actuation without a magnetic field is the most inconspicuous. The mean intensity of the normal shock at the head of the airfoil is relatively decreased by 16.33%, and the normal shock intensity is relatively reduced by 27.5% when 1000 V actuating voltage and upwind-direction actuation are applied with a magnetic field. This paper theoretically analyzes the Joule heating effect generated by DC discharge and the Lorentz force effect caused by the magnetic field. The discharge characteristics are compared for all kinds of actuation conditions to reveal the mechanism of shock control by plasma aerodynamic actuation.     

Measurement system for SSRF pulsed magnets

This paper describes the magnetic field measurement system for pulsed magnets in SSRF.The system consists of magnetic probes,analog active integrator,oscilloscope,stepper motor and a controller.An application pro- gram based on LabVIEW has been developed as main control unit.After the magnetic field mapping of a septum magnet prototype,it is verified that the test results accord with the results of theoretical calculation and computer simulation.     

The Enhanced Effect of Optical Emission from Laser Induced Breakdown Spectroscopy of an Al-Li Alloy in the Presence of Magnetic Field Confinement

In this paper,the influence of magnetic field strength on laser-induced breakdown spectroscopy(LIBS) has been investigated for various pressures.The plasma plume was produced by employing Q-switch Nd:YAG laser ablation of an Al-Li alloy operating at a 1064 nm wavelength.The results indicated that the LIBS intensity of the Al and Li emission lines is boosted with an increase of magnetic strength.Typically,the intensity of the Al Ⅰ and Li Ⅰ spectral emissions can be magnified by 1.5-3 times in a steady magnetic field of 1.1 T compared with the field-free case.Also,in this investigation we recorded time-resolved images of the laser-produced plume by employing a fast ICCD camera.The results show that the luminance of the plasma is enhanced and the time of persistence is increased significantly,and the plasma plume splits into two lobes in the presence of a magnetic field.The probable reason for the enhancement is the magnetic confinement effect which increases the number density of excited atoms and the population of species in a high energy state.In addition,the electron temperature and density are also augmented by the magnetic field compared to the field-free case.     

Remote open-path laser-induced breakdown spectroscopy for the analysis of manganese in steel samples at high temperature

A remote open-path laser-induced breakdown spectroscopy(LIBS) system was designed and studied in the present work for the purpose of combining the LIBS technique with the steel production line. In this system, the relatively simple configuration and optics were employed to measure the steel samples at a remote distance and a hot sample temperature. The system has obtained a robustness for the deviation of the sample position because of the open-path and alloptical structure. The measurement was carried out at different sample temperatures by placing the samples in a muffle furnace with a window in the front door. The results show that the intensity of the spectral lines increased as the sample temperature increased. The influence of the sample temperature on the quantitative analysis of manganese in the steel samples was investigated by measuring ten standard steel samples at different temperatures. Three samples were selected as the test sample for the simulation measurement. The results show that, at the sample temperature of 500 ℃, the average relative error of prediction is 3.1% and the average relative standard deviation is 7.7%, respectively.     

Multi-channel retarding field analyzer for EAST

A multi-channel retarding field analyzer (MC-RFA) including two RFA modules and two Langmuir probes to measure the ion and electron temperature profiles within the scrape-off layer was developed for investigations of the interplay between magnetic topology and plasma transport at the plasma boundary. The MC-RFA probe for the stellarator W7-X and first measurements at the tokamak EAST was designed. The probe head allows simultaneous multichannel ion temperature as well as for electron temperature measurements. The usability for radial correlation measurements of the measured ion currents is also given.     

Investigation of the self-induced magnetic field characteristics in a pulsed plasma thruster with flared electrodes

The self-induced magnetic field in a pulsed plasma thruster(PPT)with flared electrodes is investigated for a better understanding of the working process and the structural design of the thruster.A two-dimensional model of the magnetic field is built and is validated by comparing the simulated results with the experimental results in literature.The magnetic flux density in the discharge channel during the working process is presented and analyzed regarding the electrode structures.The calculated magnetic field flux density decreases from 0.8 T at the upstream to 0.1 T and below at the downstream in the discharge channel(68 J).The peak of the magnetic flux density over time lags behind the current peak,which provides evidence for the existence of a moving plasma sheet in the discharge process.The magnetic field induced by the current in the extra bending part of the anode enhances the Lorentz force,which acts on the charged particles near the propellant.Finally,the geometric study indicates that the electromagnetic impulse bit does not monotonically increase with the flared angle of the electrodes.Instead,it reaches a maximum at a certain flared angle,which could provide significant suggestions for structural optimization.     

Experiment on low-frequency electromagnetic waves propagating in shock-tube-generated magnetized cylindrical enveloping plasma

We propose a method of applying a static magnetic field to reduce the attenuation of the magnetic field component(S_H) of low-frequency electromagnetic(LF EM) waves in dense plasma. The principle of this method is to apply a static magnetic field to limit electron movement, thereby increasing the equivalent resistance and thus reducing the induced current and S_H. We consider the static magnetic field acting on the plasma of the entire induced current loop rather than on the local plasma, where the induced current is excited by the magnetic field component of LF EM waves. Analytical expressions of S_H suitable for magnetized cylindrical enveloping plasma are derived by adopting an equivalent circuit approach, by which S_His calculated with respect to various plasma parameter settings. The results show that S_H can be reduced under a static magnetic field and the maximum magnetic field strength that mitigates blackout is less than 0.1 T. Experiments in which LF EM waves propagate in a shock-tubegenerated magnetized cylindrical enveloping plasma are also conducted. S_H measured under the magnetic field(the magnetic field strength B0 acting on the magnetic field probe was about0.06 T) reduces at f=10 MHz and f=30 MHz when n_e≈1.9×10~(13) cm~(-3), which is consistent with theoretical results. The verification of the theory thus suggests that applying a static magnetic field with a weak magnetic field has the potential to improve the transmission capacity of LF EM waves in dense plasma.     

应变电测技术新发展及在反应堆结构等工程中的应用

文章首先介绍了实验力学应变电测技术的新发展:各种新型特殊高低温、防水、抗磁性、大应变电阻应变计,各种结构用压力、位移、荷载、加速度等新型应变式传感器以及新型高速静态数据采集仪,小型多通道动态应变及温度记录仪,超动态应变仪及相应测试技术.其次,列举了在电厂高温管道三通热态工况下的应力测试,核电厂结构构件高温高压下的应力测试,核电厂安全壳结构整体性试验,新核反应堆运行中压力壳和管道首期应力测试方案等的应用实例.     

Thermal anchoring of wires in large scale superconducting coil test experiment

Effective and precise thermal anchoring of wires in cryogenic experiment is mandatory to measure temperature in milikelvin accuracy and to avoid unnecessary cooling power due to additional heat conduction from room temperature (RT) to operating temperature (OT) through potential, field, displacement and stress measurement instrumentation wires. Instrumentation wires used in large scale superconducting coil test experiments are different compare to cryogenic apparatus in terms of unique construction and overall diameter/area due to errorless measurement in large time-varying magnetic field compare to small cryogenic apparatus, often shielded wires are used. Hence, along with other variables, anchoring techniques and required thermal anchoring length are entirely different in this experiment compare to cryogenic apparatus. In present paper, estimation of thermal anchoring length of five different types of instrumentation wires used in coils test campaign at Institute for Plasma Research (IPR), India has been discussed and some temperature measurement results of coils test campaign have been presented.     

Alignment and Cryogenic Deformation Analysis of Cold Mass-in Superfluid Helium Cryomodule

To meet the alignment requirement of superconducting radio frequency (SRF) cavity and superconducting magnet at cryogenic temperature in the accelerator system, the design of adjustment and alignment of the cold mass in superfluid helium cryomodule should be analyzed. The cryogenic deformation of the cold mass at the 2 K superfluid helium temperature level was simulated and obtained by the finite element method, meanwhile the simulation analysis method was checked by the cryogenic deformation data of the cold mass online measured by the wire of position monitor (WPM). The results show that the simulation result and measurement result have a good consistency, and it provides an important data foundation for the alignment design in the type of bottom supported cryomodule.     

超流氦低温恒温器冷质量准直调节及低温变形分析

为满足超导射频腔及超导磁体低温下的加速器准直精度要求，对超流氦低温恒温器冷质量的准直调节方案进行分析。通过对冷质量的低温位移进行有限元模拟计算，获得其在2 K超流氦温区的位移变形量，利用拉伸丝型位移监测仪（WPM）在线测量数据来验证模拟分析方法。结果表明，模拟值与测量值具有较好的一致性，为底部支撑型式低温恒温器的准直调节方案设计提供了重要的数据基础。     

Magnetic ordering in superconducting YBa2(Cu1−xFex)3Oy oxide

Magnetic susceptibility measurement and the zero-field muon-spin-relaxation experiment have been made for the YBa₂(Cu_1−xFe_x)₃O_y system. The susceptibility has been measured in the field strong enough for the magnetic flux to penetrate the superconductor and the resultant temperature dependence has demonstrated the field cooled effect and a cusp at low temperatures below T_c. The cusp has been observed when the high field has been applied. The dynamical depolarization rate of the muon obtained by the muon-spin-relaxation experiment has shown the maximum at the same temperature as the cusp. The results suggest that the spin glass freezing of localized magnetic moment takes place at the temperature of the cusp, which is consistent with the previous Mössbauer effect experiments. The magnetic phase diagram for the system has been obtained.     

Manufacture and test of the non-planar coils for WENDELSTEIN 7-X

The stellarator WENDELSTEIN 7-X, a superconducting fusion experiment, is presently under construction at the Greifswald branch of the Max-Planck-Institut für Plasmaphysik (IPP). The standard magnetic configuration of WENDELSTEIN 7-X (W7-X) is formed by 50 non-planar superconducting coils. Twenty additional planar superconducting coils can modify the magnetic configuration.This paper describes the production of the non-planar coils including the production of the winding packs, the cases and the assembly procedure of the coils. Five coils are already finished and tested at room temperature at the manufacturer's site.All coils will also be tested under cryogenic conditions. The main tests are at nominal current, a quench test by increasing the temperature of the helium, a high voltage test, a pressure and a helium leak test, the measurement of the shrinkage during cool down and the deformations due to electromagnetic forces. The test procedure and the results of the first tests of the coils are also presented.     

The magnetic field configuration measurement on EAST tokamak

The magnetic field configurations of poloidal field (PF) and toloidal field (TF) are the base of tokamak plasma operation. They are determined by the parameters such as positions and structures of PF and TF coils. Parameters of TF and PF coils of a new fully superconducting tokamak with non-circular cross-section EAST will change when the coils are cooled down from the ambient temperature to 4 K. Because of the cryogenic and refrigerator system, these parameters cannot be measured directly. Using magnetic probes signals, we measured and reconstructed magnetic field configuration of TF and PF coils. Parameters such as the positions of PF coils, the profile of the toloidal field in radial direction, the ripple and error field of toloidal field are obtained from the measurements.     

TMP结构、材料对冷冻靶温度场的影响

氘氚冰靶的均匀性和表面光滑程度对靶的表现非常重要，高质量的冷冻靶要求靶丸表面最大温差不高于0.1 mK，而影响冷冻靶温度场的因素众多。本文采用计算流体力学软件FLUENT研究了套筒壁厚（0.2、05、0.75、1、1.25、1.5、1.75、2 mm）、材料（AL5052、SS304和高纯铜）以及黑腔结构（单凸环和双凸环）对冷冻靶温度场的影响。计算结果表明:黑腔采用双凸环结构，靶丸表面温差较小；随套筒壁厚的增加，黑腔内气体自然对流强度降低，靶丸表面温度场均匀度提高，靶丸表面温差减小；由于铜具有高的导热系数及比热，选用铜作为套筒材料使得靶丸表面温度更低，温度场更加均匀。将套筒壁厚、材料、黑腔结构综合考虑，发现套筒壁厚为1 mm、材料选用高纯铜、采用黑腔结构双凸环设计时靶丸表面温度场均匀性最好。     

Present status and one upgrading method with a cold compressor of the EAST sub-cooling helium cryogenic system

Since 2006,the superconducting toroidal field (TF) coils of the Experimental Advanced Superconducting Tokomak (EAST) have been successfully cooled by supercritical helium at a temperature of 4.5 K and a pressure of 4 bara in eleven experiments.To obtain higher operating currents and magnetic fields it is necessary to lower the operating temperature of the TF coils.The EAST sub-cooling helium cryogenic system,with a warm oil ring pump (ORP),was tested twice in cool-down experiments,which made the TF coils operate at 3.8 K.However,the long term operational stability of the sub-cooling system cannot be guaranteed because of the ORP's poor mechanical and control performance.In this paper,the present status of the EAST subcooling helium cryogenic system is described,and then several cooling methods below 4.2 K and their merits are presented and analyzed.Finally,an upgrading method with a cold compressor for an EAST sub-cooling helium cryogenic system is proposed.The new process flow and thermodynamic calculation of the sub-cooling helium system,and the main parameters of the cold compressor,are also presented in detail.This work will provide a reference for the future upgrading of the sub-cooling helium system for higher operation parameters of the EAST device.     

Effects of TMP Structure and Material on Cryogenic Target Temperature Field

The ice layers in the deuterium-tritium capsule must be uniform and smooth enough, and the maximum temperature difference of the target surface is not higher than 0.1 mK for high quality cryogenic target. However, there are many factors affecting the cryogenic target temperature field. In this paper, the effects of sleeve wall thicknesses (0.2, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2 mm), materials (AL5052, SS304 and high-purity copper) and hohlraum structures (single convex and double convex) on the cryogenic target temperature field were studied with FLUENT software. The results show that the temperature difference of target surface is small when hohlraum structure is double convex ring. With the increase of sleeve wall thickness, the natural convection intensity of the hohlraum and the temperature difference on the surface of the target decrease. There is a lower temperature and more uniform temperature field around target surface when copper is used as sleeve material, because of its high heat conduction and specific heat. Considering the wall thicknesses, materials and hohlraum structures, the surface temperature field of the target is best when the sleeve adopts high-purity copper with thickness of 1 mm, and the hohlraum structure is double convex ring.