LIGO Document E1800358-v4

BT pressure code Mathematica

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Document type:
E - Engineering documents
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12 Mar 2019, 09:04
08 Mar 2019, 07:39
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.

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Notes and Changes:
Updated kernalbt7 to kernalbt7.1

This version also uses fixed ajj outgassing rates, which is useful to quickly calculate the steady state pressure in the BT. Can also plot the pressure distribution if a leak is found, for example during valve modulation experiments.

Update includes an example of the code calculating conductance. I also updated the section on how to pick out pieces of the data, including how to plot various pieces of the data.

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