LIGO Document T1800507-v1

Email thread on potential geomagnetic artifacts and audio-band electric field attenuation

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T - Technical notes
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I attach these two threads because I think there is a valuable discussion of the potential for artifacts in the gravitational wave channel from naturally generated EM fields that our PEM sensors would not detect. It is mainly our responses to questions raised about the first detection by Gary Godfrey, SLAC. I suggest that the audio-band electric field reflection by the combination of our grounded steel-sheathed buildings and our vacuum enclosures would, in the most naive estimate, make the proposed mechanism too small by more than twelve orders of magnitude. This is one reason that magnetometers are the best monitors of intersite audio-band electric fields. I think, in the end, Gary agreed that the effect was too small to produce our signal. Also discussed are numerous other good questions and checks supporting our first and subsequent detections, and some good proposals and discussion between Gary and Rai. We all agreed that electric field sensors in the chambers would be good, if only for local, self-inflicted fields. These are full downloads from Gmail, so look for the email headers to avoid repeated emails.

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