View from the encoder side, Xianjing Sun puts a coil on the harmonic coil system.

Wan Chen checks the harmonic coil system.

Electrons and positrons travel several tens of kilometres nearly at the speed of light, needing to stay on course as they zoom through various components of the machine. How, you ask? Electrons have a negative charge and positrons have a positive charge, and moving charges receive forces in the magnets when they travel in magnetic fields. In the International Linear Collider, there will be about 17,000 magnets – and knowing precisely all of their field properties is the key to success for beam control. A challenge arises, however, because some of the ILC magnets are extremely hard to measure – 1 metre long magnets with an aperture of only 12 milimetres.

In China, a research group at the Institute of High Energy Physics Chinese Academy of Sciences (IHEP, China) has been working on magnetic field measurements. As upgrade construction to the BEPC-II of the accelerator BEPC enters its final stage at IHEP, this group is finding new research opportunities in other projects. IHEP sent Jie Gao from the Asian group into a Damping Ring designing group, and they considered the resistive magnets and cost estimates. Fostering the next generation is another important agenda for IHEP. For these reasons, IHEP sent two engineers, Xianjing Sun and Wan Chen, to KEK for the first time to see how they handle magnet quality assurance and quality control work.

In magnetic field measurement work at IHEP, each member is responsible for his own distinct post, such as magnet installation and alignment, power source, data acquisition system hardware, software, manufacturing of magnetic field instrument, magnetic field measurement work, and data analysis. While this makes it smooth for each member to deepen his own expertise, challenges reside in having these members grasp the "big picture". On the other hand at KEK, one researcher is in charge of almost all of them, so he must pay attention to whole system of magnetic field measurement.

During their visit, Sun and Chen had their first opportunities to experience posts other than their own at IHEP. Chen has been working on magnetic field measurement of dipole magnet and data acquisition system for more than ten years. "For me, this is a very good experience at KEK," she said. "I learned the importance of details when we measure magnetic fields." Sun, who is working on engineering design of magnets and magnetic field measurement, said, "I was very impressed by the hard-working people at KEK. I learned many things, such as room temperature and coolant temperature have a serious influence on magnetic field measurements."

Ryuhei Sugahara, the former group leader of KEKB magnet division and member of ILC-GDE Reference Design Magnet group, and Mika Masuzawa, the present group leader of KEKB magnet division expert of magnetic field measurement, hosted the two IHEP engineers during their stay at KEK. After spending some time with Sun and Chen, Masuzawa said, "At IHEP, they have very splendid technology." Sugahara added, "They work in highly efficient ways. Their measurement techniques are good. I hope that they bring home something that further improves their skills at their institute."

-- Nobuko Kobayashi