IHEP 2008 - 7 (In Russian)
	A.V.Larionov, E.N.Lomakin, V.S.Seleznev, A.N.Sytin, Y.S.Hodyrev
	Numerical Simulation of the Hydrogen Diffusing Processes at the Outgassing of the Secondary Emission Monitor
	Protvino, 2008. – p. 19, figs. 14, tables 3, refs.: 12.

The beam loss monitoring system for LHC in CERN includes the group of the special secondary emission monitors (SEM) for measurements of the background radiation with the very high levels. For an operational reliability of such monitors, one of the basic requirements to the SEM design is the vacuum keeping better than 10^-7 atm during the period of 20 years without external pumping. With this goal, in particular, an outgassing of SEM is carried out on the vacuum stands in CERN and IHEP. The results of numerical simulation of the diffusion of H₂ into the SEM vacuum chamber walls for the different technological stages of the outgassing and operating conditions are presented in this paper. The time dependences of all diffusion parameters and degassing flux from the chamber surface are obtained in accordance with vacuum-temperature regimes of the bakeout, pinch off and operation. Activation of the st707 getter inserted in the SEM during of bakeout on the IHEP stand and the getter pumping efficiency after pinch off are analyzed. These calculations allow to determine 1 the optimum temperature and pressure for the SEM pinch off. These parameters equal of 473±20^o and (2-4) · 10^-13 atm, accordingly. It is shown also that the getter can guarantee the main vacuum requirement to the H₂ content in the chamber for the 20 years operation.

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