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O iceYamakawa, Koichiro; Shimizu, Genki*; Suzuki, Natsumi*; Nasu, Hirokazu*; Tsuboi, Rei*; Kurahashi, Hiroyuki*; Arakawa, Ichiro*
no journal, ,
no abstracts in English
Kamiya, Junichiro; Yamamoto, Kazami; Takano, Kazuhiro; Kotoku, Hirofumi; Wada, Kaoru*; Yanagibashi, Toru*; Kurosawa, Shunta*
no journal, ,
The vacuum system in the rapid cycling synchrotron of Japan Proton Accelerator Research Complex was constructed based on the design concept considering the effect of a dynamic pressure caused by a high-power proton beam operation. However, the high-power beam operation clearly has more effects than expected at the time of the design. The dynamic pressure with the beamline pressure runaway characterized by an extreme pressure rise of more than orders of magnitude occurred during beam operation. A systematic data observation showed that the pressure rise mechanism is a result of the gas desorption from the wall triggered by the hitting of the residual gas molecules ionized by the proton beam. The numerical calculation based on that model well reproduced the measured dynamic pressure behaviors in the beam operation. The calculation also showed that a large pumping speed and a small surface density of the adsorbed molecules are required to suppress the pressure runaway.
ortho-para conversion on a stepped Pd surfaceUeta, Hirokazu; Sasakawa, Yuya*; Ivanov, D.*; Ono, Satoshi*; Ogura, Shohei*; Fukutani, Katsuyuki
no journal, ,
We present a direct measurement of fast Ortho-Para conversion of molecularly chemisorbed H on Pd(210) at a surface temperature of 50 K. The determined conversion time was about 2 sec, which is in reasonably agreement with a previous theoretical calculation. This agreement supports that ortho-para conversion mechanism of the molecularly chemisorbed H on Pd(210) is the two-step process based on the hyperfine-Coulomb excitation.
Baba, Yuji*; Shimoyama, Iwao
no journal, ,
no abstracts in English