John,
I'll come to the first part of today's telecon in Walt's office, but I can
only stay a short time today (less than an hour).
There should be a feedback range that eliminates glitches for any individual pixel (i.e.
stays in only one flux state), but there may be too much variability in zero-level
environmental flux offset from pixel to pixel to make this realizable for all pixels. But
it may be worth investigating. Off-state bias is an interesting question. It wouldn't
hurt to extend the analysis in the memo to include non-zero bias.
It would be great to talk about the deglitcher algorithm to understand what it takes out.
I'd be happy to work with Sarah on conducting a more thorough analysis of the impact
of this on BICEP-2 Keck, but haven't talked to Sarah about it since the last
meeting.
Kent
----- Original Message -----
From: "John Kovac" <jmkovac(a)cfa.harvard.edu>
To: "Kent David Irwin" <irwin(a)stanford.edu>
Cc: "bicep2-list" <bicep2-list(a)lists.fas.harvard.edu>
Sent: Tuesday, August 27, 2013 8:18:39 AM
Subject: Re: [Bicep2-list] Analysis of hysteretic crosstalk in BICEP-2 / Keck
Hi Kent,
Thank you very much for this writeup! In it you say:
"What are the conditions for this hysteresis? .... In the two-junction
squid, this happens most readily when the feedback flux is zero. If the
equation is single-valued for zero feedback flux, it is single-valued
for all fluxes."
For Keck (which must continue to operate with these SQUIDs), can we
conclude that there is no set of revised MUX operating parameters (e.g.
a feedback range we might restrict ourselves to, off state bias, etc.)
that we might choose a priori to avoid the hysteretic effect?
Can we also conclude that we expect the hysteretic steps to occur
occasionally in our B2 and Keck CMB data, at FBU amplitudes comparable
to what we observe in beam maps? What fraction of these do we expect to
be eliminated by our deglitcher?
Sarah: you volunteered last week to look at this in more detail. Can
you be prepared to say something about it on today's telecon?
How do we proceed to convince ourselves whether this crosstalk mechanism
could be significant for our CMB results?
John
On 8/20/13 1:28 PM, Kent David Irwin wrote:
All,
Attached, please find a memo describing and analyzing crosstalk from flux hysteresis in
'off' SQUID channels in BICEP-2 and Keck.
Kent
_______________________________________________
Bicep2-list mailing list
Bicep2-list(a)lists.fas.harvard.edu
https://lists.fas.harvard.edu/mailman/listinfo/bicep2-list
--
___________________________________________________________________
John Kovac jmkovac(a)cfa.harvard.edu
Associate Professor, Harvard University Astronomy Department
160 Concord Ave rm 310, Cambridge MA 02138, 617-496-0611