Transient response of a beam tube during leak checking

Document #:

LIGO-T1200375-v2

Document type:

T - Technical notes

Abstract:

Suppose we need to localize a vacuum leak somewhere in the LIGO beam tube using a helium mass spectrometer. This is not a textbook leak hunting application, since the volume is large (4.5 million liters) while the effective tube conductance is quite modest (177 liters/second for He at 2 km). The resulting long time constants and diminished flux, combined with an uncontrolled environment around the tube, suggest many false background paths. These may include foreline backstreaming, or transport of spilled He to distant areas far from the intended test zone. To help veto false positives, it s useful to predict the transient signature expected from an actual leak.

Files in Document:

• helium_transient.pdf (2.6 MB)

Other Files:

• helium_transient.docx (2.2 MB)
• matlab mfile to generate 2d plots (pressure_transient.m, 1.7 kB)
• matlab mfile to generate surface plot (pressure_symbolic.m, 2.3 kB)

Topics:

• System Test
• Vacuum

Authors:

• Michael Zucker
• Rainer Weiss

Keywords:

vacuum beamtube helium leak pressure transient

Notes and Changes:

Added heuristic model due to Weiss.

Referenced by:

• LIGO-T1300553-v1: Effect of leak-test port separation; measurement of He transient at z = 250m
• LIGO-T1300087-v1: Beamtube recovery technical document repository
• LIGO-E1600037: Beamtube Leakage