LIGO Document E1800358-v2

BT pressure code Mathematica

Document #:
Document type:
E - Engineering documents
Other Versions:
07 Mar 2019, 14:10
This code solves the free molecular diffusion model Rai W. used in btwaterleak. There are two versions, version 1,(kernal bt7, see version 1 of this document) has the surface outgassing simplified so the user can input the familiar rate/unit surface area/second. Version 1 is handy to check steady-state solutions, and runs very quickly.

The beamtube can be broken up into sections, with user defined leaks, pump arraignments, etc. The code solves the coupled differential equations for each section. Result is steady-state pressure distribution for the given set of pumping and outgas (and leak) conditions.

You can also calculate conductance if you set one end of the tube as a source and the other as a sink.

The second version (bt7_LMA_4.8) uses the Dubinin-Raduskevich (DR or D-R) isotherm and calculates the outgassing rates of each beamtube section depending on the activation energies, pressure, injected water, temperature etc. This code has to loop through many iterations so runs slowly, but uses detailed surface physics that the simpler code omits.

Notes and Changes:
Version 4.8 uses probev module to calculate the outgassing coefficients of each section. Uses DR isotherm.

Included is Rai's Fortran listing, also some background information on how he developed the model. See page 13 forward for a discussion of the way the model works.

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