Vol.2 No.3 2009
Research paper : Development of battery-operated portable high-energy X-ray sources (R. Suzuki)−224−Synthesiology - English edition Vol.2 No.3 (2009) 2. Energy is used only during the time when it is needed.3. Energy is used only at the place where it is needed.4. Latest technology with high energy efficiency is used.To determine the specifications of the devices that would be renovated or newly acquired based on the above principles, it was necessary to see when, where, and how much energy (electrical power) was consumed. Therefore, the power consumed in each section was surveyed, and measures were taken within the budget allotted for renovations.The main measures were decentralization of the water cooling/heating and air conditioning systems and the renewal of the high-power microwave generator of the electron linac. By estimating and considering the consumed power under various experimental conditions for the water cooling/heating and air conditioning systems, it was found that drastic reduction in power consumption could be achieved in a decentralized system rather than a centralized one. Therefore, a decentralized system was introduced that allowed ON/OFF of the water cooling/heating and air conditioning of different parts according to the type of experiment.The S-band electron linac used eight 22 MW klystron devices, which were state-of-the-art at the time of construction, to generate high-power microwaves for electron acceleration. Currently, 80 MW klystron with about four times the output has been developed, and three to four old devices were replaced with one newest device. Since the power consumption of the conventional klystron did not stabilize at low pulse rate, pulse rate of 50 pps or over had to be used even when it was for injecting electrons to the storage ring, and therefore, the power consumption became high at about 30 kW per device or about 100 kW for three devices. The newly installed 80 MW klystron could be operated at 2 pps that was more optimal for electron injection to the storage ring, and the average power consumption was reduced to 10 kW or less. In this section alone, the renovation brought about the decrease of energy consumption to 1/10. This allowed reduction in the capacity of water cooling/heating and air conditioning systems, and large-scale energy savings became possible.Various other measures were taken based on the above principles, and, as shown in Fig. 5, 60 % reduction in the amount of power used was achieved for the total facility compared to before renovations. Through these measures, the operation time of the electron linac increased and the researches could be conducted more efficiently.The energy-saving know-hows obtained by being directly involved in these measures led to the development of a low-power driven circuit for an ultra-small electron accelerator and a new X-ray source.3.2 Development of C-band small electron acceleratorsThe research using high-intensity slow positron beam was conducted using the aforementioned S-band electron linac. However, since this was a time-shared accelerator, the positron experiment had to be interrupted when the storage ring injection was done, and the time for experiments was limited. Also, since the accelerator was not built for the purpose of positron generation, the generation efficiency of positrons was poor. To solve these issues, an exclusive electron linac was needed, and it was necessary to install a small electron linac with good positron generation efficiency within the limited shielded space.Moreover, in experiments using the positron beam, high pulse rate of the accelerator was desirable to prevent the detector from becoming saturated. Therefore, we selected the C-band electron accelerator which has a short microwave filling time in the accelerating tube and with which the pulse rate could be set high, and developed the components for this system (Fig. 6). This C-band electron accelerator, because it had a smaller resonator, had the advantage over the conventional S-band electron linac since the sizes of accelerating tube and waveguide could be downsized.Fig. 5 Annual amount of power used at the electron linac building (Tsukuba Central 2-4 Bldg., AIST) (bar graph) and annual operation time of the electron linac (line graph).Fiscal YearAnnual amount ofpower consumed (kWh)Annual operation time (h)2003200820072006200520041×1063×1062×10600100020003000400030 cmFig. 6 First part of C-band electron accelerator.