Transcript Document
Visits to Chinese accelerator companies Peter Pearce (April 2004) • Two companies were visited. • Beijing Medical Equipment Institute at Chongping and Beijing • Cowell MV Electronics Company Shanghai Applications of Linacs in China • • • • • • • Low energy linear accelerator technology has been developed in China for about 40 years, and has advanced greatly in recent times. Various RF structures have been researched to accelerate ions and electrons. These include disk-loaded drift tube linacs (DTL), side-coupled, on-axis-coupled, annular coupled, disk and washer (DAW), RFQ’s and helix waveguide structures. Electron medical linacs are the most common type of accelerator. There are about 680 of these installed, and about half are made domestically. About 310 of these SW linacs are used for treating cancer. There are 4 manufacturers of these systems in China. In recent years about 2 million patients per year are diagnosed as suffering from cancer in China. About 60 to 70% of these patients require radiotherapy with accelerators. This need has motivated the huge development in medical linac systems since the early 1960’s. Electron linacs are also being used as radiation sources for container inspection systems at ports. About 40 have these have been made with 30 installed in China and the rest in Asia and the Middle East. Electron linacs are used for radiography in the heavy industries (metal casting etc) and 12 systems are installed. Very many electron linacs are used in industry and university research for irradiation of semi-conductors, particularly thyristors, to improve high frequency performance. BMEI 6MeV medical accelerator system BMEI 6 MeV SW accelerating tube designed by Tsinghua University, Beijing 6 MeV accelerating tube basic specification • The 6 MeV tube is an on-axis magnetic coupling standing wave structure with a DC diode electron gun, titanium vacuum window or xray target, microwave power coupler with ceramic window and a small ion pump to maintain vacuum pressure. • Power source is Magnetron MG5193 (E2V, UK) • Working frequency is 2998 MHz +- 0.5 MHz • Input RF power is ~ 2.2 MW • Electron gun high voltage is ~ 10 kV • Vacuum pressure is ~ 5. 10-5 Pa • Electron output energy is 6 MeV • Electron pulse current is ~ 80 mA • For x-rays, dose rate is ~ 800cGy/min at 1 metre from target • Pulse duration is ~ 4us • Repetition rate 250 Hz 4 MW PFN-Line type modulator Designed by Cowell-MV, Shanghai Accelerating tube driven by Magnetron Modulator Accelerating tube driven by a Klystron Modulator