Lu Xiang-Yang

The 5000-year environmental change and associated human activities at Sokho-nor Lake, Inner Mongolia, P.R. China

Abstract Sokho-nor Lake is situated in the western part of Inner Mongolia, Northwest China. Human beings have been living in this area since the New Lithic Age. Throughout history, this area has undergone repeated desert-oasis periods, associated with changing river inputs through time. The varying population in the area has been strongly influenced by the water resources available. Inhabitants included members of the Han race and people from northern nomadic tribes. Their activities in the past were affected by changing lake levels. Today, the lake is completely dry, and the environmental impact on the region is a serious problem.

Study on the steady operating state of a micro-pulse electron gun

Micro-pulse electron gun (MPG) employs the basic concept of multipacting to produce high-current and short-pulse electron beams from a radio-frequency (RF) cavity. The concept of MPG has been proposed for more than two decades. However, the unstable operating state of MPG vastly obstructs its practical applications. This paper presents a study on the steady operating state of a micro-pulse electron gun with theory and experiments. The requirements for the steady operating state are proposed through the analysis of the interaction between the RF cavity and the beam load. Accordingly, a MPG cavity with the frequency of 2856 MHz has been designed, constructed, and tested. Some primary experiments have been finished. Both the unstable and stable operating states of the MPG have been observed. The stable output beam current has been detected at about 3.8 mA. Further experimental study is under way now.

A preliminary quadrupole asymmetry study of a β=0.12 superconducting single spoke cavity *

An Accelerator Driven System (ADS) has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully evaluated for cavities. Single spoke cavities are the main accelerating structures in the low energy front-end. The single spoke cavity has small transverse electromagnetic field asymmetry, which may lead to transverse RF defocusing asymmetry and beam envelope asymmetry. A superconducting single spoke resonator (PKU-2 Spoke) of β=0.12 and f=325 MHz with a racetrack-shaped inner conductor has been designed at Peking university. The study of its RF field quadrupole asymmetry and its effect on transverse momentum change has been performed. The quadrupole asymmetry study has also been performed on a β=0.12 and f=325 MHz ring-shaped single spoke cavity. Our results show that the quadrupole asymmetry is very small for both the racetrack-shaped and the ring-shaped single spoke cavity.

The First Nine-Cell TESLA Cavity Made in China

A totally home-made 9-cell TESLA type superconducting cavity is made at Peking University. The cavity fabrication is according to DESY specification. The cavity is made of high purity niobium from OTIC, Ningxia. The electron beam welding is carried out at Harbin Institute of Technology, Harbin. By the cooperation, the cavity is tested at Thomas Jefferson National Accelerator Facility, USA. The preliminary result shows the acceleration gradient Eacc is 23MV/m without quench and has potential for improvement.

Applications of AMS radiocarbon dating in Chinese archaeological studies

Over the past three years we have applied the AMS 14C technology to a variety of areas in Chinese archaeology. This paper outlines cases of dating archaeological sites and ancient human bones. We also describe some evidence of the beginning of pottery. Some dating results of Miaoyan and Yuchanyan sites are presented. The data show that the ages of potsherds are about 15.6 Ka and 14.4 Ka BP, respectively, and these potsherds might be the earliest pottery products discovered in the world.Over the past three years we have applied the AMS 14C technology to a variety of areas in Chinese archaeology. This paper outlines cases of dating archaeological sites and ancient human bones. We also describe some evidence of the beginning of pottery. Some dating results of Miaoyan and Yuchanyan sites are presented. The data show that the ages of potsherds are about 15.6 Ka and 14.4 Ka BP, respectively, and these potsherds might be the earliest pottery products discovered in the world.

Electromagnetic design and beam dynamics simulation of a new superconducting accelerating structure for extremely low β protons

For the application of high intensity continuous wave (CW) proton beam acceleration, a new superconducting accelerating structure for extremely low β protons working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The cavitys longitudinal length is 368.5 mm, and its transverse dimension is 416 mm. The RF frequency is 162.5 MHz, and the designed proton input energy is 200 keV. A peak field optimization has been performed for the lower surface field. The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. The first four gaps are operated at negative synchronous RF phase to provide longitudinal focusing. The subsequent gaps are 0° sections which can minimize the transverse defocusing effect. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10 mA CW proton beam is simulated by the TraceWin code. The simulation results show that the beams transverse size is under effective control, while the increase in the longitudinal direction is slightly large. Both the TraceWin simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6 MV/m. On the whole, our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range.

MAGNETIC PROPERTY IMPROVEMENT OF NIOBIUM DOPED WITH RARE EARTH ELEMENTS

A new idea is proposed by the PKU group to improve the magnetic properties of the Type-II superconductor niobium. Rare earth elements like scandium and yttrium are doped into ingot niobium during the smelting processes. A series of experiments have been done since 2010. The preliminary testing results show that the magnetic properties of niobium materials have changed with different doping elements and proportions while the superconductive transition temperature does not change very much. This method may increase the superheating magnetic field of niobium so as to improve the performance of the niobium cavity, which is a key component of SRF accelerators. A Tesla-type single-cell cavity made of scandium-doped niobium is being fabricated.

Electromagnetic design and optimization of a superconducting quarter wave resonator

Superconducting (SC) cavities currently used for the acceleration of protons at a low velocity range are based on half wave resonators. Due to the rising demand on high current, the issue of beam loading and space charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using an SC quarter wave resonator (QWR). We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The electromagnetic design and optimization of the prototype have been finished at Peking University. An analytical model derived by the transmission line theory is used to predict an optimal combination of the geometrical parameters, with which the calculation by Microwave Studio shows a good agreement. The thermal analysis to identify the temperature rise of the demountable bottom plate under various levels of thermal contact also has been done, and the maximum increment is less than 0.5 K even though the contact state is poor.

Geometry dependent multipacting of a superconducting quarter-wave resonator at PKU

A superconducting quarter-wave resonator (QWR) of frequency=162.5 MHz and β=0.085 (β=v/c) has been designed at Peking University. The multipacting (MP) simulation and analysis for the QWR with CST Particle Studio has been performed. The simulation results reveal that there is no sign of MP with its normal operating accelerating gradients in the range of 6–8 MV/m. The accelerating gradient range that may incur MP is from about 1.4 to 3.2 MV/m, and the places where MP may be encountered are mainly located at the top part of the QWR. So the effect of different top geometries on MP has also been studied in depth. Our results show that an inward convex round roof is better than other round roofs, and plane roofs have an advantage over round roofs on the suppression of MP in general. While considering the optimization of its electromagnetic (EM) design, our initial designed model is also acceptable.

A preliminary study of the feasibility of using superconducting quarter-wave resonators for accelerating high intensity proton beams

The superconducting (SC) cavities currently used for the acceleration of protons at a low velocity range are based on half-wave resonators. Due to the rising demand on high current, the issue of beam loading and space-charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using SC quarter-wave resonators (QWR). We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The main factor limiting SC QWRs being applied to high current proton beams is vertical beam steering, which is dominantly caused by the magnetic field on axis. In this paper, we intend to analyze steering and eliminate it to verify the qualification of using QWRs to accelerate high intensity proton beams.