Wen Kang

20-T Dipole Magnet With Common-Coil Configuration: Main Characteristics and Challenges

The Institute of High Energy Physics (Beijing, China) is pursuing R&D of high-field accelerator magnet technology for the recently proposed CEPC-SPPC project, which will need thousands of 20-T level accelerator magnets in 20 years. A long-term plan has been made aiming to realize the 20-T magnets in 15 years. The conceptual design study has been ongoing from 2014 based on the current Jc level of superconductors. As both Nb3Sn and high-temperature superconductor superconducting materials are strain sensitive, the common-coil configuration has been chosen as the first option for the design study of the 20-T dipoles, to simplify the coil structure, raise the bending radius, and lower the strain level in superconducting coils. The magnetic analysis, mechanical analysis, and preliminary design study of the straight section and the coil ends have been completed for a 20-T common-coil dipole magnet. The main characteristics and challenges of this design concept will be presented in this paper.

Magnetic Design Study of the High-Field Common-Coil Dipole Magnet for High-Energy Accelerators

The Institute of High Energy Physics (IHEP, Beijing, China) is proposing a two-stage particle collider: CEPC-SppC. The first stage is a circular electron-positron collider (CEPC), expected to carry out high-precision studies on Higgs bosons. Upon completion of the CEPC experiment, it will be upgraded to a super proton-proton collider (SppC), aiming at the discovery of physics beyond the standard model. The circumference of the accelerator for CEPC and SppC will be 50 ~ 70 km. The required dipole held strength is 20 T for SppC. As the start of a long-term R&D plan for high-held accelerator magnet technology at IHEP, a 15-T short sample held Nb3Sn dipole is planned to be developed within the next five years. The common-coil configuration is adopted to provide space for two apertures with a maximum diameter of 60 mm. The 10-4 level held uniformity will be reached at a reference radius of 15 mm. Magnetic analytical modeling and FEM cross section study of this high-held common-coil dipole has been done and will be presented here. A preliminary cross section study of the 20-T common-coil dipole will also be introduced; the design is based on the current Jc level of Nb3Sn and HTS superconductors.

Status of CSNS Project

The China Spallation Neutron Source (CSNS) accelerator is designed to accelerate proton beam pulses to 1.6 GeV at 25 Hz repetition rate, striking a solid metal target to produce spallation neutrons. The accelerator provides a beam power of 100 kW on the target in the first phase and then 500 kW in the second phase by increasing the average beam intensity 5 times while raising the linac output energy. The project construction has been formally launched in 2011 and it is planned to complete the project in March 2018. It is one of the high intensity proton accelerator projects in the world and it imposes a great challenge to Chinese accelerator community. This presentation will cover the status and challenges of the CSNS project.

Research and Development of the AC Magnets for CSNS/RCS

Chinese Spallation Neutron Source (CSNS) is a facility planned to be built in China in the coming years. It is composed of 80 MeV Linac, 1.6 GeV Rapid Cycling Synchrotron (RCS) and target station. To accelerate the proton beam from 80 MeV to 1.6 GeV, the RCS requires the field of dipole and quadrupole magnets to change with sine waveform of 25 Hz plus a biased DC. For large amplitude AC magnets with large aperture, there are critical issues to be addressed, such as eddy current induced in the magnet yoke, coils and endplates, vibration of the yoke and coil, field tracking between dipoles and quadrupoles, and so on. To study these issues, one prototype dipole magnet and one prototype quadrupole magnet have been developed and tested. In this paper, the design, fabrication and tests of the two magnets will be described.

Design and Prototype Test of CSNS/RCS Injection and Extraction Magnets

The China Spallation Neutron Source (CSNS) accelerator consists of a linear accelerator (Linac), a rapid cycle synchrotron (RCS) and two beam transport lines. The injection and extraction systems of the RCS play an important role in connecting these four parts of accelerator. The injection system consists of three sets of bump magnets and two septum magnets, and the extraction system is composed of ten fast kicker magnets and a Lambertson magnet. The design of all these magnets is carefully considered. To prove the design concepts, a prototype bump magnet and a prototype kicker magnet have been successfully developed and tested.

Magnetic Field Simulation of Serpentine Quadrupole Coil

Based on the line current approximation, a semi-analytical method for 3D magnetic field computation of the serpentine quadrupole coil is presented. Using the Biot-Savart law, the integral field of a line current with finite length located at an arbitrary position is derived. By dividing the coil into many line current segments, and summing up the integral field of each segment, the total integral field strength and field quality are obtained. The traditional line current theory is extended to 3D. This method is applied to an example of BEPCII serpentine quadrupole coil, and the magnetic field calculation results are in good agreement with the results of OPERA-3D. Harmonic correction is introduced by changing the coil geometry to compensate the unwanted multipole field. In addition, the influence of the increased reference radius on the computation accuracy of higher order multipole field is presented.

Fringe Field Interference Research on Quadrupole-Sextupole Assembly in BEPC-II

Many compact accelerators are increasingly popular nowadays. The studies on fringe field interference effect between adjacent magnets are becoming more important. Based on the 3-D multipole expansion technique, the integrated gradient deviation in a quadrupole magnet due to the appearance of neighboring sextupole is investigated. The quad-sext interference effect had been evaluated for BEPC-II. The relative impacts on accelerator tune shift will be obtained further and confirmed by experiments finally.

Magnetic Field Measurements of RCS Dipole for CSNS

The China Spallation Neutron Source (CSNS) is an accelerator-based multidisciplinary user facility. The CSNS facility consists of an 80 MeV H- linear accelerator (1inac), a 1.6 GeV rapid cycling synchrotron (RCS), beam transport lines, a target station, and three sets of instruments with auxiliary equipments. The RCS consists of 24 dipole magnets, 48 quadrupole magnets, 16 sextupole magnets and some corrector magnets. The magnets of the RCS are excited with a repetition frequency of 25 Hz AC bias DC. The magnetic field measurements of the dipole prototype under DC and 25 Hz AC bias DC were carried out at the Institute of High Energy Physics (IHEP). The integral field distribution, harmonic components, transfer function were measured. The measurement results are presented in this paper.

Bioaccumulation and photosynthetic activity response of sweet sorghum seedling ( Sorghum bicolor L. Moench) to cadmium stress

A hydroponic experiment was conducted to investigate bioaccumulation and photosynthetic activity response to Cd in sweet sorghum seedlings. The seedlings were treated with 0, 50, and 100 μM Cd for 15 d. Our results showed that morphological characteristics of sweet sorghum were significantly affected by Cd treatments. The Cd concentrations in roots and shoots increased with increasing Cd concentrations in the nutrition solution; higher Cd accumulation was observed in the roots. Meanwhile, the photosynthetic activity decreased significantly and a shape of chlorophyll (Chl) a fluorescence transient in leaves was altered by Cd treatments. The Chl contents in the leaves decreased significantly, which was demonstrated by a change of spectral reflectance. Our data indicated that the higher Cd concentration reduced Chl contents and inhibited electron transport in the leaves, leading to the decrease of photosynthetic activity.

Application of Transient Electromagnetic Simulation to the DC-Biased AC Dipole Magnet for CSNS/RCS

In this paper, we investigate the magnetic field properties and temperature rise in the China Spallation Neutron Source (CSNS)/Rapid Cycling Synchrotron (RCS) dipole magnets powered by dc-biased alternating currents. To understand the properties of these magnets, we perform transient electromagnetic simulation and thermal analysis. Eddy current losses from the transient electromagnetic results are applied in the thermal analysis. The eddy current losses from the transient electromagnetic simulations are discussed. The results of the thermal analysis are in good agreement with the test results of the prototype dipole magnet. Finally, the method has been applied to the optimization of the slit arrangements for the standard dipole magnets in CSNS/RCS.