Guo Zhi-Yu

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.

Continuous operation of 2.45-GHz microwave proton source for 306 hours with more than 50 mA DC beam*

This paper describes a long-term operation of the 2.45-GHz microwave proton source at Peking University. The DC proton beam of 50–55 mA with energy of 35 keV has been run for 306 hours continuously. Total beam availability, defined as 35-keV beam-on time divided by elapsed time, is higher than 99%. Water cooling machine failures cause all the downtime, and no plasma generator failure or high voltage breakdown is observed. The longest uninterrupted run time is 122 hours.

Mono-Energetic Proton Beam Acceleration in Laser Foil-Plasma Interactions

Acceleration of ions from ultrathin foils irradiated by intense circularly polarized laser pulses is investigated using a one-dimensional particle-in-cell code. As a circularly polarized laser wave heats the electrons much less efficiently than the wave of linear polarization, the ion can be synchronously accelerated and bunched by the electrostatic field, thus a monoenergetic and high intensity proton beam can be generated.

Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility and its application prospects

Radioactive-ion beam (RIB) experiments open up new exciting fields and frontiers in nuclear physics and nuclear astrophysics. The experiments can provide unprecedented opportunities to explore new phenomena such as new magic numbers and probe the isospin mechanisms occurring in shell evolution. Other experiments probe the limits of nuclear stability on the neutron-rich side, provide insights into the synthesis of superheavy elements and nuclear giant halo structures, and offer the possibility to investigate new nuclear decay modes as well as the nucleosynthesis of nuclides beyond Iron. To achieve this goal, many nuclear physics laboratories all over the world are building large-scale powerful new RIB facilities. The “Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility (BISOL)” is a joint project proposed by the China Institute of Atomic Energy (CIAE) and Peking University. This facility will combine two techniques: Projectile fragmentation (PF) and isotope separation on line (ISOL). The BISOL facility will operate based on a dual driver system, including reactor driving and intense deuteron-beam driving modes. The existing high flux research reactor, the China Advanced Research Reactor at CIAE provides reactor driving. At the BISOL facility ISOL separation of fission fragments, post acceleration, and fragmentation of neutron-rich fission fragment beams will be available. By combining ISOL and PF techniques in one facility the technical advantages of both can be merged. The BISOL will deliver intensive rare ion beams of very neutron-rich isotopes; the intensity of these beams will be of the order of at least 1-2 magnitudes higher than currently available ones. Intense deuteron-beam driving is an established technology, which provides an intense neutron beam source and can be operated independently in the facility. Characterizing material performance and performing lifetime experiments are the challenges facing researchers working on the current and next-generation nuclear energy systems. Intense radiation sources, especially neutron sources, are indispensable for these experiments. The intense deuteron accelerator proposed in this project will be able to generate intense neutron beam. These beams will be able to probe nuclear materials and will provide vital results to push forward the boundaries of nuclear physics.

Preliminary Study on Neutron Radiography with Several Hundred keV Fast Neutrons

Several hundred keV fast neutron radiography (HKFNR) can be a complementary technique to common thermal neutron radiography (TNR) and several MeV fast neutron radiography (MFNR). We tested HKFNR on a 4.5 MV Van de Graaff accelerator, and the experimental results show that the spatial resolution of this technique is better than MFNR and close to TNR. Several hundred keV fast neutrons can penetrate some thermal neutron absorbers such as Cd, and it is feasible to investigate its use on some materials which are transparent to cold/thermal neutrons, such as aluminum, using this technique.

Radio-Frequency Power Test of a Four-Rod RFQ Accelerator for PKUNIFTY

A four-rod radio frequency quadruple (RFQ) accelerator is designed, manufactured, installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY). This 2699.6-mm-long RFQ accelerator with the mean aperture radius of 3.88mm is operating at 201.5 MHz in pulse mode. An inter-electrode voltage of 70 kV is needed to accelerate the injected 50 keV 40 mA D+ ions up to 2 MeV. We present the rf system, high rf power feeder design, lower rf measurements and higher rf power test. Especially, the rf commissioning was carried out with rf power up to ~280 kW and duty factor of 4%. The measured x-ray spectrum shows that the rf inter-electrode voltage reaches 70.7 kV. It is found that the specific shunt impedance of the RFQ cavity reaches 52.7 kΩm.

Simulation and experiments of rf tuning of a 201.5 MHz four-rod RFQ cavity

A four-rod radio frequency quadruple (RFQ) cavity has been built for the Peking University Neutron Imaging Facility (PKUNIFTY). The rf tuning of such a cavity is important to make the field distribution flat and to tune the cavitys resonant frequency to its operating value. Plate tuners are used to tune the RFQ, which have an effect on both the cavity frequency and field distribution. The rf performance of the RFQ and the effect of plate tuners are simulated. Based on the simulation, a code RFQTUNING is designed, which gives a fast way to tune the cavity. With the aid of the code the cavity frequency is tuned to 201.5 MHz and the flatness deviation of the field distribution is reduced to less than 5%.

Theoretical Design of a 104 MHz Ladder Type IH-RFQ Accelerator

Beam dynamics and rf designs of a 104 MHz ladder type IH-RFQ (L-IH-RFQ) accelerator are finished at Peking University for the acceleration of 14C+ from 40keV to 500keV. As a specific feature, the output beam energy spread is as low as 0.6% achieved with the internal discrete bunching method, which makes potential applications of RFQ feasible, such as accelerator mass spectrometry and ion implantation. Tolerances of the beam dynamics design are studied by means of changing the input beam parameters, and the results are quite satisfying. On the other hand, the L-IH-RFQ structure is employed, taking advantage of its mechanical stability and the absence of inter-electrode voltage asymmetry. Radio-frequency properties are studied and optimized for reducing power loss with Microwave Studio (MWS). Tuning of the field flatness and frequency is investigated in principle.

Study of separated function radio frequency quadrupoles accelerator

SFRFQ (Separated Function Radio Frequency Quadrupoles) accelerator is a new post accelerator of RFQ (Radio Frequency Quadrupoles) type, which has been developed since the beginning of the 1990s at Peking University. In order to demonstrate the possibility of the SFRFQ, a prototype cavity has been designed. A special dynamics design method has been proposed to avoid the sparking problem and decrease the energy spread at the exit of SFRFQ. It consists of two aspects: the asymmetry structure design for transverse focusing and the inner buncher design for longitudinal bunching. This allows the improvement of the beam properties without increasing the cavity length. The simulation results show that the energy spread can be substantially reduced by using the inner buncher in the SFRFQ structure.

Preliminary design of a laser accelerator beam line

A Compact laser plasma accelerator (CLAPA) is being built in Peking University, which is based on RPA-PSA mechanism or other acceleration mechanisms. According to the beam parameters from preparatory experiments and theoretical simulations, the beam line is preliminarily designed. The beam line is mainly constituted by common transport elements to deliver proton beam with the energy of 1~50MeV, energy spread of 0~1% and current of 0~108 proton per pulse to satisfy the requirement of different experiments. The simulation result of 15MeV proton beam with an energy spread of 1%, current of 1x108 proton per pulse and final spot radius of 9mm is presented in this paper.