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Accelerator Laboratory of KEK accepts graduate students majoring in accelerator science at the Graduate University for Advanced Studies (SOKENDAI) and provides them with research guidance toward their degrees. An outstanding achievement conducted by one of such students is presented in this article.<\/p>\n
In a variety of accelerators at KEK, we conduct machine studies to improve their performance and to study the properties and behavior of the beams running in accelerators. Some of these machine studies are allocated to the research conducted by graduate students. Machine studies using real beams can lead to the discovery of new phenomena that no one has ever seen before. Therefore, machine studies provide an opportunity of exciting scientific adventure. When we find a new phenomenon, we analyze and study it in detail, and then, submit a paper to a scientific journal.<\/p>\n
Takaaki Yamaguchi was one of the graduate students who entered SOKENDAI in 2018. He decided to major in a field related to accelerating beams and began studying accelerator science and radio frequency acceleration. In addition to reading textbooks and papers, he deepened his knowledge through active discussions among his research group. During these studies, Yamaguchi interested in a phenomenon known as the static Robinson instability. When the beam intensity is increased in circular accelerators, the beam cannot be accelerated stably. This phenomenon was predicted by K.W. Robinson 60 years ago and is now considered to be established theoretically. However, Yamaguchi was very curious to know whether this phenomenon occurs in an actual accelerator just as formulated in published papers.<\/p>\n
Then, Yamaguchi and his advisors suggested to conduct their machine study at the Photon Factory (PF) electron storage ring at KEK. The PF ring is usually operated for users of synchrotron radiation. Fortunately, Yamaguchi was granted his time for machine study among valuable operation periods.<\/p>\n
Figure 1 shows a picture of Yamaguchi conducting his machine study at the PF ring. We can see that he was seriously working on the experiment surrounding by many electronics. In this machine study, Yamaguchi confirmed that the static Robinson instability actually occurred when the beam intensity is increased. By setting up a unique equipment, Yamaguchi also succeeded in observing the process of beam instability (Fig. 2).<\/p>\n
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\nFigure 1: Machine study being conducted by Takaaki Yamaguchi at the Photon Factory storage ring.
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\nFigure 2: Waveforms that indicate the beam becoming unstable (reproduced from [Ref.])
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\nIn another machine study conducted on a different day, Yamaguchi measured the frequency at which the beam oscillates in the direction of beam motion (in a technical term, the coherent synchrotron frequency) at various beam intensities and accelerating voltages. He then compared these data with what was predicted by the theory. As a result, Yamaguchi discovered beam oscillations that were not predicted by the theory. The unpredicted beam oscillations were observed just before the beam became unstable. Figure 3 shows such unpredicted oscillations where the sharp peaks indicated by an arrow corresponds to the unexpected beam oscillations.<\/p>\n