Takuya Kamitani*^), Mitsuo Akemoto ^), Dai Arakawa ^), Yoshio Arakida ^), Naoko Iida ^), Mitsuo Ikeda ^), Hiroshi Iwase ^) , Atsushi Enomoto ^) , Yoshinori Enomoto ^) , Satoshi Ohsawa ^) , Yukiyoshi Ohnishi ^) , Naoki Okada ^), Yujiro Ogawa ^), Kazuhisa Kakihara ^), Shingo Kazama ^), Hiroshi Kaji ^), Hiroaki Katagiri ^), Eiichi Kadokura ^), Mitsuo Kikuchi ^ , Feng Qiu ^ , Miho Kurashina ^ , Haruyo Koiso ^ , Masanori Satoh ^ , Lei Zang ^ , Tetsuo Shidara ^ , Xiangyu Zhou ^), Akihiro Shirakawa ^), Masaaki Suetake ^), Hiroshi Sugimoto ^), Tsuyoshi Suwada ^), Toshikazu Takatomi ^), Tateru Takenaka ^), Madoka Tanaka ^), Masafumi Tawada ^), Rui Zhang ^), Katsumi Nakao ^), Hiromitsu Nakajima ^), Takuya Natsui ^), Toshiyasu Higo ^), Shigeki Fukuda ^), Yoshihiro Funakoshi ^), Kazuro Furukawa ^), Hiroyuki Honma ^), Hideki Matsushita ^), Shuji Matsumoto ^), Toshihiro Matsumoto ^), Takako Miura ^ , Katsuhiko Mikawa ^ , Shinichiro Michizono ^ , Toshihiro Mimashi ^ , Fusashi Miyahara ^ , Takashi Mori ^) , Akio Morita ^) , Yoshiharu Yano ^) , Kazue Yokoyama ^) , Mitsuhiro Yoshida ^) , Daisuke Satoh β , ^)KEK/SOKENDAI, B)TITECH
Abstract
This paper reports on the three topics recently achieved in the KEK positron source upgrade for SuperKEKB. (1) We have constructed a double-deck layout of the two pre-injectors for a low-emittance electron beam and a high-intensity primary beam for a positron generation.  While the low-emittance beam is generated by a photo-cathode RF gun and injected to the linac straightly, the primary beam is generated by a thermionic gun followed by an RF bunching section and transported into the linac through a 24-degree merger line. (2) In order to avoid high-voltage accidents in a power transmission line of the flux concentrator, we have upgraded coaxial cables, reconstructed a parallel plate line into a tri- plate layout and increased a capacitance in a pulse power supply. A test operation with a spare flux concentrator, the pulse power supply and the renewed transmission line has been performed at a test stand. No breakdowns and excessive heating have been observed at t e design current (12 kA) in 200 hours continuous operation.  (3) We have been constructing a radiation shield structure above the positron production target. The shield is essential for a beam operation with a radiation level under a regulation even at t he highest beam intensity. A radiation level observed at a ground level above the positron production target were below the regulation. 1 . KEK SuperKEKB [1] 1.4 FC KEKB RF 12 kA 200 SuperKEKB RF 2 . KEKB 3.1 GeV 2015 RF SuperKEKB (γε y ≤ 20 μm) (5 nC/bunch) [2] RF (10 nC/bunch) [3][4] RF RF Fig.1 750 mm Fig.l SHB1: 114 MHz   SHB2: 571 MHz 2856 MHz RF 3 . 2m 45 MeV 24 Fig.2 KEKB SuperKEKB FC FC Figure 1: 24 24 dispersion achromatic hard-edge 20 % FC 2015 1.3
24 180 2014 6 kA FC [1] 6 kA 2014 12 kA 2014 12 kA FC 12 kA FC 6 kA FC FC Figure 4: FC 12 kA FC ( 12 kA) ( 6 kA) 12.6/6.0 KEKB FC RH2.5M-NH- NH-20D-2E-S Fig.3 60 mm 250 mm 2000 mm 2.3 mm 7.4 mm Fig.5 35 mm 40 kV μH 0.70 μH 1.11 μH  FC 1.00 μH 3.60 μH 11.26 18 m 10 DC 19 kV 3.26 μH 1.4 FC 19 kV 18 m 10 0.23 μH 0.45 μH 10 FC 1.2 (4) (5) Fig.6 FC FC (12 kA) 88 12 kA 200 FC FC (1) CT 10 CT 10 10 1 (2) CT (1) FC 4 . (3) nA 1250 6 m Fig.7 [5] 15 Hz 5 . SuperKEKB (1) RF RF (2) 12 kA 200 (3) [1] , MOOM07 ""SuperKEKB ", 11 2014 [2] , WEP006 “  SuperKEKB RF gun ." 12 2015 [3] , THP007 ~  SuperKEKB
(II)~ l 2 , FSP022 “  KEK 2015 [4] 12 [5] 2015 ".
2015