Page 225 - Fundamentals of Magnetic Thermonuclear Reactor Design

Vacuum and Tritium System Chapter | 6 207

TABLE 6.7 Parameters of Interaction Between a Molecule and a Sorbing
Surface

Factors
determining
the elemental
Active
Gas Elemental centre interaction
absorption interaction physical Coefficients parameter
mechanism parameter analogue η ϑ
Sorption by Number of χ Deposited χ −1 Getter layer
a constantly deposited getter thickness
renewable getter atoms atoms
getter film per one gas
molecule
Condensation Condensa- β Set of β 1.0 Condensate
tion points on a layer thickness
coefficient cryosurface
Adsorption Sticking β Adsorption 1.0 Relative Adsorbate
coefficient centres concentration surface
of adsorption concentration
centres
Chemisorption Chemical β Sorption 1.0 Relative Adsorbate
bond centres concentration volume
formation of sorption concentration
probability centres
Implantation Implantation µ The same µ 1.0 Density of
coefficient implanted
particles

geometrically more complex device that has adsorbing surfaces, any part of
which is able to maintain a minimum flow of active centres necessary for the
pumped-out gas absorption, is believed to be an optimum design solution.
Thus, the optimisation design methods must be based on a quantitative esti-
mate of the degree to which the designed structure approaches its optimum the-
oretical model. The independent or controlled external factors can in this case
be the 3D flow distribution of the removed gas, the geometrical structure of the
surface-action pump and the vacuum duct as a whole, as well as characteristics
of the sorbing surfaces (Table 6.8).
The term ‘useful work’ in Table 6.8 refers to any physical parameter char-
acterising the high-vacuum system’s purpose and operation requirements.
Optimisation of a vacuum pumping duct implies, among other things, the use of
a differential pumping, localisation of elevated molecular concentration regions,
and creation of a network of channels for high-density gas flows.