New Development of VPI Process for Large Superconducting Coils

High vacuum is required for Vacuum Pressure Impregnation (VPI) process of large coils used in cryogenic. The defects such as dry spots and over rich resins should be minimized in large superconducting coils used. Both sealing problems associated with the mold and over rich resin problems are eliminated by using vacuum bag mold method with which we can simplify the design of vacuum mold.

Transient multi-physics behavior of an insert high temperature superconducting no-insulation coil in hybrid superconducting magnets with inductive coupling

A transient multi-physics model incorporated with an electromagneto-thermomechanical coupling is developed to capture the multi-field behavior of a single-pancake(SP)insert no-insulation(NI)coil in a hybrid magnet during the charging and discharging processes.The coupled problem is resolved by means of the finite element method(FEM)for the magneto-thermo-elastic behaviors and the Runge-Kutta method for the transient responses of the electrical circuits of the hybrid superconducting magnet system.The results reveal that the transient multi-physics responses of the insert NI coil primarily depend on the charging/discharging procedure of the hybrid magnet.Moreover,a reverse azimuthal current and a compressive hoop stress are induced in the insert NI coil during the charging process,while a forward azimuthal current and a tensile hoop stress are observed during the discharging process.The induced voltages in the insert NI coil can drive the currents flowing across the radial turns where the contact resistance exists.Therefore,it brings forth significant Joule heat,causing a temperature rise and a uniform distribution of this heat in the coil turns.Accordingly,a thermally/mechanically unstable or quenching event may be encountered when a high operating current is flowing in the insert NI coil.It is numerically predicted that a quick charging will induce a compressive hoop stress which may bring a risk of buckling instability in the coil,while a discharging will not.The simulations provide an insight of hybrid superconducting magnets under transient start-up or shutdown phases which are inevitably encountered in practical applications.

Calculation of AC Losses of CICC for Superconducting Outsert Coils in a Hybrid Magnet

This paper is devoted to predict AC loss of cable in conduit conductor （CICC） which is of importance in the design of conductors. The consideration for the conductor＇s design and main parameters for the magnets are introduced. In order to attain a good accuracy in the calculation of AC losses, the field distribution within superconducting outsert should be considered. Calculation of the AC losses, including hysteresis losses and coupling losses, is conducted. An emphasis is put on the hysteresis loss during the ramp up of the current to the operational current （15.3 kA） and the coupling loss of the conductor in a power-down condition for insert. The results are obtained to be 74.9 kJ and 950 J for 40 T hybrid magnets, respectively. Based on the calculation, a brief analysis of losses effect on the conductor design and the operation of magnet is given for the purpose that the capacity of the cryogenertor can be evaluated and the stability regime can be improved in our future work on the hybrid magnets.

Strain Measurement on the Toroidal Field (TF) Coil Cases

The stress-strain state of the structure is a matter of interest to designer. The strain measurement of superconducting magnets at cryogenic temperature is a specific technique. Based on strain measurement of TF coil case for EAST, this paper presents a measuring technique at cryogenic temperature and on intense magnetic field. The compensation methods for both temperature and magnetic field effects of the gauges, together with the measured results are involved, and the discussions of the measured results are given in the paper.

Three-dimensional simulation of the coupled electromagnetic-mechanical responses in a no-insulation racetrack coil

This study investigates the coupled behavior of the mechanical and electromagnetic responses of a high-temperature superconducting(HTS)no-insulation(NI)racetrack coil.A three-dimensional(3D)equivalent circuit network model and mechanical model with nonlinear contact are incorporated into the coupled model.The stress and separation of adjacent turns under a high magnetic field are analyzed by considering the electromagnetic force and cooling process.The numerical results demonstrate that the straight and curved parts of the racetrack coil exhibit distinct mechanical behaviors.Under a strong external magnetic field,the separation between adjacent turns reduces the charging delay of the coil.The maximum stress occurs in the transition regions between the curved and straight parts.The straight part exhibits a larger rotation angle,while the separation regions between adjacent turns are relatively fewer in those parts.The curved part shows a higher proportion of separation regions in the steady stage.The different separation areas in the straight and curved parts also result in distinct turn-to-turn losses during the charging process.Subsequently,a comparative study is conducted on the influence of residual currents induced by discharging.Finally,the effects of overband and inner diameter on the separation behavior are investigated.

Proton linac-based therapy facility for ultra-high dose rate (FLASH) treatment

As an advanced treatment method in the past five years,ultra-high dose rate(FLASH)radiotherapy as a breakthrough and milestone in radiotherapy development has been verified to be much less harmful to healthy tissues in different experiments.FLASH treatments require an instantaneous dose rate as high as hundreds of grays per second to complete the treatment in less than 100 ms.Current proton therapy facilities with the spread-out of the Bragg peak formed by different energy layers,to our knowledge,cannot easily achieve an adequate dose rate for FLASH treatments because the energy layer switch or gantry rotation of current facilities requires a few seconds,which is relatively long.A new design for a therapy facility based on a proton linear accelerator(linac)for FLASH treatment is proposed herein.It is designed under two criteria:no mechanical motion and no magnetic field variation.The new therapy facility can achieve an ultrahigh dose rate of up to 300 Gy/s;however,it delivers an instantaneous dose of 30 Gy within 100 ms to complete a typical FLASH treatment.The design includes a compact proton linac with permanent magnets,a fast beam kicker in both azimuth and elevation angles,a fixed gantry with a static superconducting coil to steer proton bunches with all energy,a fast beam scanner using radio-frequency(RF)deflectors,and a fast low-level RF system.All relevant principles and conceptual proposals are presented herein.

Ramping loss and mechanical response in a no-insulation high-temperature superconducting layer-wound coil and intra-layers no-insulation coil

The layer-wound coil has a great potential in nuclear magnetic resonance and magnetic resonance imaging owing to the better spatial homogeneity of the magnetic field.However,high-temperature superconducting(HTS)coil wound by no-insulation(NI)layer-wound technique has been verified with a long field delay time.A new method named the intra-layer no-insulation(LNI)winding technique has been proposed to reduce the charging delay time of the coil.This paper is mainly to study and compare the ramping loss and mechanical characteristics of the layer-wound coil and LNI coil.The results indicate that the total ramping loss can be significantly reduced by using the LNI winding method.The effects of the ramping rate of power supply current and the contact resistivity on the ramping loss are also discussed in the paper.Furthermore,the stress distributions in the layer-wound coil and LNI coil are compared,where the cooling process and Lorentz force are both considered.It can be found that the copper sheet of the LNI coil experiences relatively higher stress than its(RE)Ba;Cu;O;(REBCO)conductor layer.Meanwhile,the magnitude of stress generated in the REBCO conductor of the LNI coil is slightly different from that of the layer-wound coil.