Experimental studies of a low emittance electron beam in the KEK-ATF damping ring with a laserwire beam profile monitor

Production of a low-emittance beam is one of the key technologies in realizing the future linear colliders. The Accelerator Test Facility at KEK has been built to establish technologies to generate the required low-emittance beam, and to experimentally study the effects which might limit emittance reduction. A beam monitor called the laserwire beam profile monitor was developed to measure the emittance of a stored beam in the ATF damping ring. This monitor has been upgraded to enable faster measurements of both transverse beam sizes with a better spatial resolution. The signal detection scheme was also modified to separately measure the beam profiles of each bunch in a multi-bunch beam. Continuous efforts have been made to reduce emittances further, and intensive studies have been done with the upgraded laserwire monitor. Four-dimensional beam sizes and their intensity dependence were measured in various bunch volume conditions. In particular, it was found that the vertical emittance of a single-bunch mode was reduced to 4 pm·rad in the zero current limit, the smallest emittance ever achieved in the world, and it grow by about factor of 1.5 at the intensity of 10 electrons per bunch. The overall nature of two transverse emittances, bunch length, and momentum spread seemed to have no serious disagreement with the expectation of the model calculation involving the intra-beam scattering. The emittance was also measured in the multi-bunch operational mode. It was found that the generation of a similar small emittance was possible to those realized in a singlebunch mode. No large bunch-to-bunch difference was seen in the beam intensity studied so far. All the results above, obtained with the laserwire monitor, have proved to be an important milestone for realizing future linear colliders. Acknowledgments This thesis could not have been written without the help and support of many people. Firstly, I would like to express my gratitude to my supervisor Prof. N. Sasao of Kyoto University and Prof. J. Urakawa of High Energy Accelerator Research Organization (KEK). I am particularly grateful to the members of the laserwire development group: Prof. Y. Higashi, T. Taniguchi, T. Okugi, S. Araki, M. Takano, M. Nomura, K. Hirano, Y. Yamazaki, H. Sakai and K. Takezawa, for their generous help and suggestions through all the work. I would like to express my gratitude to all the members of KEK-ATF: Prof. H. Hayano, K. Kubo, N. Terunuma, S. Kuroda, M. Kuriki, T. Naito, Prof. N. Toge, Prof. S. Kamada, Prof. Higo, Prof. T. Suzuki, Prof. K. Nakajima, Prof. T. Tauchi, T. Omori, Y. Kurihara, N. Kudo, T. Saeki, V. Vogel, N. Delerue, H. Sasaki, people from E-cube co. and KantoJoho co. Witout their hard work to develop and operate the ATF, this study never be accomplished. I would like to acknowledge to all the students worked together at ATF: K. Dobashi, T. Imai, I. Sakai, T. Muto, M. Fukuda, R. Kuroda, P. Karataev, A. Higurashi, K. Hasegawa, A. Aoki, T. Oshima, T. Iimura, K. Iida, T. Hirose, Y. Inoue, A. Ohashi, I. Yamazaki, M. Matsuda, K. Watanabe, T. Suehara, H. Fujimoto and others. I am grateful to collabolators from other facilities: M. Ross, J. Frisch, D. McCormick, M. Woodley, J. Nelson, J. Turner, T. Raubenheimer, A. Wolski, F. Zimmermann, G. Blair, T. Kamps and others. Fruitful discussions with them helped us a lot. Last but not least, I would like thank to the members of High Energy Physics group of Kyoto university: Prof. K. Nishikawa, Prof. H. Sakamoto, Prof. T. Nakaya, R. Kikuchi, T. Nomura, M. Yokoyama, M. Suehiro, Y. Takeuchi, K. Murakami, Y. Ushiroda, T. Inagaki, T. Fujiwara, T. Nakamura, N. Nakamura, T. Shima, S. Nishida, H. Yokoyama, H. Yumura, S. Mukai, I. Kato, A. Shima, E. Shinya, H. Maesaka, K. Mizouchi, K. Uchida, M. Hasegawa, S. Yamamoto, T. Sumida, S. Tsuji, T. Sasaki, H. Morii, S. Ueda, K. Hayashi, T. Morita, J. Kubota, T. Shirai, N. Taniguchi, K. Hiraide, and others. I am thankful to the secretary of our group T. Ishino and A. Nakao and the secretariat members of the physics department, K. Nakagawa, A. Saito and A. Nishino. I have been staying in KEK, but always been supported by all of them. Kyoto, Japan August 15, 2004. Yosuke HONDA