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The vacuum system of Heavy Ion Research Facility in Lanzhou (HIRFL) is a large and complex system. HIRFL consists of two ECR ion sources, a sector focus cyclotron (SFC), a separate sector cyclotron (SSC) and a multi-purpose cooling storage ring system which has a main ring (CSRm) and an experiment ring (CSRe). Several beam lines connect these accelerators together and transfer various heavy ion beams to more than 10 experiment terminals. According to the requirements of the ion acceleration and ion lifetime, the working pressure in each accelerator is different. SFC is nearly 50 years old. After upgrade, the working pressure in SFC is improved from 10-6mbar to 10-8mbar. The pressure in SSC which was built in the 1980s reaches the same level. The cooling storage ring system with a length of 500m came into operation in 2007. The average pressures in CSRm and CSRe are 5×10-12mbar and 8×10-12mbar respectively. Different designs were adopt for vacuum system of a dozen beam lines to meet specific requirement of each experiment terminal. Along with the extensive development of the heavy ion researches and applications, new accelerators of HIRFL are under construction. The vacuum system of the new machines will be designed and constructed followed the overall schedule.

A new method of ultrasonic vibration electrical discharge machining (UEDM) in gas is proposed in this paper. It is shown that electrical discharge machining (EDM) with ultrasonic aid can be achieved well in a gas medium. The tool electrode is formed into a thin-walled pipe, and a high pressure gas medium is supplied through it. During machining, ultrasonic vibration of the workpiece can improve the machining process. Molten workpiece material can be ejected from the base body of the workpiece with the aid of ultrasonic vibration and be removed/flushed out of the working gap without becoming reattached to the electrode. Selecting #45 steel and copper as the workpiece material and electrode material, respectively, experiments have been carried out, the results showing that UEDM is a method with a high material removal rate (MRR). The greatest advantages of this technique are lower pollution and a low electrode wear ratio.

A new machining method, named "Ultrasonic vibration assisted electrical discharge machining" (UEDM) in a gas environment is proposed in this paper. It is shown that ultrasonic assisted electrical discharge machining can be achieved well in a gas medium. The tool electrode is made of a thin-walled pipe, and the high pressure gas medium is supplied from inside. During machining, ultrasonic vibration of the workpiece can improve the machining process. A theoretical model to estimate the roughness of the finished surface has been developed. AISI 1045 steel and copper are selected as the workpiece material and electrode material respectively. Experiments have been carried out, and the results show that the roughness of finished surface increases with an increase in the discharge voltage (Ue), the discharge current (Ie) and the pulse duration (tS ).