Anbin Chen

Magnetic and Cryogenic Design of MICE Coupling Solenoid Magnet System

The Muon Ionization Cooling Experiment (MICE) will demonstrate ionization cooling in a short section of a realistic cooling channel using a muon beam at Rutherford Appleton Laboratory in the UK. The coupling magnet is a superconducting solenoid mounted around four 201 MHz RF cavities, which produces magnetic field up to 2.6 T on the magnet centerline to keep muons within the iris of RF cavities windows. The coupling coil with inner radius of 750 mm, length of 285 mm and thickness of 102.5 mm will be cooled by a pair of 1.5 W at 4.2 K small coolers. This paper will introduce the updated engineering design of the coupling magnet made by ICST in China. The detailed analyses on magnetic fields, stresses induced during the processes of winding, cool down and charging, and cold mass support assembly are presented as well.

Design of the HTS Permanent Magnet Motor With Superconducting Armature Winding

The superconducting motor generally adopts superconducting magnets to supply high flux density in the air-gap around the rotor. This structure can decrease the volume as a result of the high magnetic load, but it also creates cooling difficulty problems due to the cooling mediums spin sealing. Therefore, the superconducting magnets need frequent maintenance, and this structure cannot be applied in the industry field. So a novel high temperature superconducting motor with a superconducting armature coils is researched. This motors stator uses ferromagnetic material and the superconducting windings are located in the slots. The ferromagnetic material can decrease the magnetic field in the superconducting coils, so the current carrying ability of the superconducting coils can be increased. The rotor adopts the permanent magnets as the excitation. Such design details of the motor can ensure the superconducting coils can undertake larger current and reduce AC loss. In this paper the electromagnetic field distribution of the HTS motor stator coils is analysed. Finally, the detailed HTS motor parameters are presented to analyse the output torque characteristic. From the characteristics, it can be seen that the novel HTS motor has the same power density as the traditional HTS motor.

Design of the Cryogenic System for a 400 kW Experimental HTS Synchronous Motor

A 400 kW radial-axial flux type experimental HTS synchronous motor is designed. There are twelve armature coils used HTS wires in the motor. They are accommodated in the cooling vessels made of FRP material, and twelve cooling vessels are enclosed in the vacuum vessel. In order to cool the HTS coils of the motor, a sub-cooled liquid nitrogen cryogenic system is presented. The operation temperature is below 70 K. This system consists of HTS coils cryostats, liquid nitrogen transfer-line, liquid nitrogen dewar and a cold box with liquid nitrogen pump, G-M cryorefrigerators and some control valves inside. In this paper, different kinds of the heat loads of the system including the AC loss, current lead, supporters and radiation are presented. Basis on the heat load and operating temperature, the main parameters and equipments of the system are determined.

Design and Construction of Test Coils for MICE Coupling Solenoid Magnet

The superconducting coupling solenoid to be applied in the Muon Ionization Cooling Experiment (MICE) is made from copper matrix Nb-Ti conductors with inner radius of 750 mm, length of 285 mm and thickness of 102.5 mm at room temperature. The magnetic field up to 2.6 T at the magnet centerline is to keep the muons within the MICE RF cavities. Its self inductance is around 592 H and its magnet stored energy is about 13 MJ at a full current of 210 A for the worst operation case of the MICE channel. The stress induced inside the coil during cool down and charging is relatively high. Two test coils are to build and test in order to validate the design method and develop the fabrication technique required for the coupling coil winding, one is 350 mm inner diameter and full length same as the coupling coil, and the other is one-quarter length and 1.5 m diameter. The 1.5 m diameter coil will be charged to strain conditions that are greater than would be encountered in the coupling coil. This paper presents detailed design of the test coils as well as developed winding skills. The analyses on stress in coil assemblies, AC loss, and quench process are carried out.

Sub-Cooled Liquid Nitrogen Test System for Cooling HTS Synchronous Motor

A 400 kW radial-axial flux type experimental HTS synchronous motor is designed. There are twelve armature coils using HTS wires in the motor. They are accommodated in the cooling vessels made of FRP material, and twelve cooling vessels are enclosed in the vacuum vessel. In order to cool the HTS coils of the motor, a sub-cooled liquid nitrogen cryogenic system is presented. The operation temperature is below 70 K. This system consists of vacuum system, liquid nitrogen dewar, data acquisition system and a cold box with liquid nitrogen pump, G-M cryorefrigerator, cryogenic valve and a heater inside. The heater can present the heat of the HTS coils. In this paper, the design and the composition of this test cooling system are presented. When liquid nitrogen is injected into the vessel and the cryorefrigerator is operating, the cool down curve of the test system is obtained. After adding heat to the system, the capacity curve of the system is presented in this paper. The results proved that this sub-cooled liquid nitrogen system can be used for cooling the actual armature windings in the HTS motor.

AC Loss Prediction in BSCCO-Tape Armature Winding Design of a Synchronous Motor

A permanent-magnet synchronous motor with high-Tc superconducting (HTS) armature operated at sub-cooled liquid nitrogen temperature has been designed. The prototype model has a ten-pole rotor and twelve sets of armature windings which are fabricated with BSCCO tapes, and its output power is 400 kW at the rated speed of 250 rpm. In order to decrease the AC loss of HTS coils to an appropriate level, the conventional stator iron cores are adopted. The coil design, behaviors of HTS conductors, even cooling system design will be proved in the armature case. And the prediction of AC loss in stacked tape conductor exposed to external magnetic fields with various directions have been carried out using FEA method. Based on the 3D magnetic field finite element analyses, this paper presents an AC loss analysis method for the armature winding and provides upper the limit of operating temperature for the cooling system.

AC Current Carrying Property of High-

Current carrying capabilities of HTS tapes and coils can be defined by critical current when carrying DC current. While there is no standard criterion to judge their AC current carrying capability. In actual industrial applications, HTS tapes and coils often need to work in AC conditions. Accurately calculating the current carrying ability of tapes and coils is a precondition of designing a HTS machine. DC and AC V - I properties are measured using four-probe method under different background magnetic field. The method of measuring and obtaining the AC maximum working current is given. The applicability of the method and phenomenon of experiment is discussed based on the Anderson-Kim flux creep model. The content of this paper moderately contributes to the completion of superconducting technology. And the paper can be referenced when designing HTS machine with HTS tapes or coils carrying AC current.

T_{c}

A superconducting coupling magnet made from copper matrix NbTi conductors operating at 4 K will be used in the Muon Ionization Cooling Experiment (MICE) to produce up to 2.6 T on the magnet centerline to keep the muon beam within the thin RF cavity windows. The coupling magnet is to be cooled by two cryocoolers with a total cooling capacity of 3 W at 4.2 K. In order to keep a certain operating temperature margin, the most important is to reduce the heat leakage imposed on cold surfaces of coil cold mass assembly. An intermediate temperature shield system placed between the coupling coil and warm vacuum chamber is adopted. The shield system consists of upper neck shield, main shields, flexible connections and eight supports, which is to be cooled by the first stage cold heads of two cryocoolers with cooling capacity of 55 W at 60 K each. The maximum temperature difference on the shields should be less than 20 K, so the thermal analyses for the shields with different thicknesses, materials, flexible connect...

Superconducting Tapes and Its Magnetic Field Dependence

The technique of subdivision protection is extensively applied to protect large superconducting solenoid magnets such as accelerator magnets and MRI magnets. The number of subdivision and the parameters of protection circuit are usually decided by the quench simulation results. The accurate current data during quench process is important to verify the quench simulation code and estimate the magnet performance. But not like voltage signal, the acquisition of which just needs to attach a pair of voltage taps on both side of each protection resistor, current signal is very difficult to be obtained from cryogenic environment. This paper presents an algorithm to calculate the quench current from the quench voltage measurement result. By this algorithm the temperature rise history of protection resistor is obtained simultaneously.

Structural Design and Thermal Analysis for Thermal Shields of the MICE Coupling Magnets

Peking University Superconducting Accelerator Facility (PKU‐SCAF) will be constructed as a multi‐disciplinary integrated base for fundamental and application researches at Peking University in China since 2004. The main SC accelerator shall produce an electron beam of 20MeV for different kinds of experiments. Electrons from the source are being accelerated by two superconducting resonators, which are TESLA‐type 1.3GHz 9‐cell superconducting RF cavities operating at 2K and integrated in one cryostat. A superconducting 2.5‐cell resonator also working at 2K will serve as capture cavity. Consequently, a cryogenic system with the capacity of about 100W at 2K has to be designed, fabricated, tested and operated for the PKU‐SCAF. This paper presents the cryogenic design for PKU‐SCAF using computational process analysis software. The cryogenic characteristics of cryomodule, design concept and layout of overall system are discussed. The critical thermal parameters for major components in the superfluid system are given.