Detector Watch

Mike Hewson
Mike Hewson
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Topic 191925

I've taken a mind to browsing the detector logs regularly. I thought I'd try to kick off a 'regular' thread, which I'll sticky ( if you ever want any thread stickied let me know ). Would it be of interest if I report on anything I find of interest? We won't find any 'detections' there, but I quite like the technical side of these magnificent machines and I'm hoping others may wish to discuss and help clear up a few questions I may have...

They are publicly viewable via the Username: 'reader' and Password: 'readonly' at either Hanford or Livingstone

I hope to keep images and sizes to a minimum, for the sake of non-broadbanders. Please anyone jump in and post if it is of interest, otherwise .... oh well :-)

Anyhows I'll fire up by showing the effect of a nearby earthquake on Hanford:

as you can see the Seismic blip at about -4hrs and simultaneous loss of the NS/NS Inspiral Range estimate, the State Vector ( I think this is a sort of 'Defcon' counter ) and Cal Lines ( I think meaning 'calibration' ).

This is listed in the log as '....due to an earthquake in SW Washington: Mag 4.5 ...'

Cheers, Mike.

(edit) Please feel free to throw in your own observations on the detectors ... :-)

(edit) To be polite, I've copied and resized etc, then uploaded/posted to an image-hoster ( File Lodge ) to avert banging the server for the e-logs every time someone loads this page.

(edit) Trying ImageShack instead..... ahh, that's better!

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

AnRM
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Detector Watch

Thanks for the 'heads up' about these sites, Mike. I for one would be very interested in any observations you have....Cheers, Rog.

Chipper Q
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Good thread, thanks Mike. It

Good thread, thanks Mike. It looks like the 4.5 shaker also knocked Livingston out of science mode briefly, but not until half an hour after the event, and then operation was intermittent for several hours (while Hanford remained down). The seismic event looks fairly brief, and it looks like Hanford partially recovered after about half an hour (going by the State Vector plot); does it normally take hours to get back into science mode, or were things still vibrating too much?

@Mike: Probably no one here more keenly aware than myself of how thoughtful you were with this thread; many bases to cover that aren't mentioned with the bbcode instructions, that's for sure :) So hats off to you for the great idea of the sticky thread and the first-rate presentation of the content!

Mike Hewson
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RE: Good thread, thanks

Message 47928 in response to message 47927

Quote:

Good thread, thanks Mike. It looks like the 4.5 shaker also knocked Livingston out of science mode briefly, but not until half an hour after the event, and then operation was intermittent for several hours (while Hanford remained down). The seismic event looks fairly brief, and it looks like Hanford partially recovered after about half an hour (going by the State Vector plot); does it normally take hours to get back into science mode, or were things still vibrating too much?

@Mike: Probably no one here more keenly aware than myself of how thoughtful you were with this thread; many bases to cover that aren't mentioned with the bbcode instructions, that's for sure :) So hats off to you for the great idea of the sticky thread and the first-rate presentation of the content!


Thanks for the encouragement! :-)
Yes it certainly looks like hours to recover. I don't think it's the persistent shaking of the ground, but the nature of the gadget. I guess it takes a while for the energy of the induced wobbling to subside. There are lots of possible disturbances, say this stuff at Livingstone ( 'AS' is a seismic sensor, 'Yend' is the end of the 'Y' arm of the interferometer - the other is the 'X', 'UTC' is Co-ordinated Universal Time - a high precision standard for time worldwide ):

Quote:

Operations Log
D Sellers 10/7/06
All times UTC

03:27 AS trigger trip due to train
03:41 Reset AS trigger, locked in science mode (segment 3308)
04:15 Lost lock
04:39 Reboot l1awg
05:02 Locked in science mode (segment 3309)
05:45 AS trigger trip
05:50 AS trigger trip was caused by two or more ATVs driving around on the Yend road. Alan Weinstein and I proceeded to ride to the end station but once our presence was noticed the trespasser's took off "I guess they were scared off by Alan and I massive size". The point of entrance was the last gate before the Yend station, the gate is intact but the fence will need to be repaired.
06:58 AS trigger trip due to train
07:04 Lost lock due to train
07:21 Locked in science mode (segment 3311)
07:41 Lost lock
07:55 Locked in science mode (segment 3312)

Speaking of disturbances, the North Korean nuke test may have upset the LIGO's:

Quote:

I note that the USGS confirms that the North Korean nuke test
was at 01:35:37 on 2006 October 9 and registered 4.2 on the Richter

In perusing the i-logs at LHO and LLO I found that both had problems
at 1:58

LHO See this ilog
entry by Lisa Goggin

01:58 knocked out of lock, initially looked like a train, but a series of spikes in Y_end 1-3Hz followed. Joe
drove down to check it out, but couldnt see of hear anything. Danny says it looks like what they saw last
night.

LLO See this entry
by Joe Hanson

0158 AS trigger activated, Train?
There is a lot of noise in the 1-3&3-10,I drove down
there but saw nothing, could hear a little somthing but?

-- That is a 23 minute delay, but might be consistent with travel times.


This will behave like an earthquake, the delay refers to the time taken for the quake wave to travel across the Pacific ( under it actually ). The USGS refers to the United States Geological Survey which tracks seismic events, you can actually hook up to an RSS feed if you like!
Cheers, Mike.

( edit ) 'Earthquake' depth at 0.0km is the give-away for a nuke test BTW. Standard causes are at kilometre depths.

( edit ) Correction AS is 'anti-symmetric' ie. the science signal output of the interferometer.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Ernesto Solis
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Mike, Thanks for the info,

Mike,

Thanks for the info, way to go hombre.

Ernie

Mike Hewson
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OK, detector fiends, I

OK, detector fiends, I thought I'd give an explanation of what I've derived from my study of some of the screens available on the logs. Forgive me if it seems too simple or over-explained.

( Bear in mind I have no official status here, this is a private reverse engineering effort, based upon the following:

Quote:

For guests:

* Read-only access is available to anyone by entering "reader" as the username and "readonly" as the password when entering any of the logs.
You will want the Detector Log if you are looking for interferometer information.

)

So let's start with an easier one - the 'State Vector' plot. I don't think it's actually a vector in the usual sense, but like 'DEFCON' ( defense condition ) used to indicate the status of the project at a glance. It's not science data, and they are replicated at both Hanford:

and Livingstone:

In both, the bottom left indicates T0=date time. T0 pronounced 'time zero' is when the screenshot was taken. Date is in DD/MM/YYYY ( D = day, M = Month, Y = year ) format and time in HH:MM:SS ( H = hour, M = minute, S = second ) format. A 24 hour clock format ie. 00:00:01 ( 1 second past midnite ) to 23:59:59 ( 1 second prior to midnite ). It is in UTC or 'Universal Co-ordinated Time', pretty well the replacement for the old 'Greenwich Meridian Time' for those that recall that.... :-) Thus the data is logged in this time reference and not with regard to any particular local time.

As it's name suggests it treats the entire world as a single time zone. That way events in different places can be compared easily if brought back to that clock. ( Recall that light can travel about seven times around the world in a second. That's fast, but not instantaneous - so strictly speaking events aren't exactly simultaneous in the usual sense - but we'll leave that be for now ).

Anyhows that sets the time that the plot is marked at '0' on the right hand edge of the lower axis. This axis is then marked along to the left in hours before the time in question ( smaller divisions 1/4 or 1/2 hour, larger divisions 1 or 2 hours ). So it is marked in Time(h). I belabour this explanation as many of the other plots have this setup.

Now the vertical axis on the left is the State (*) where the asterisk '*' indicates no physical units apply. So it is simply a number. Values clearly go from 0 thru to 4. I haven't yet seen used the '-1' that appears on the Hanford plot. The LIGO has three interferometers ( IFO's ) in the continental US. ( Though I believe GEO in Germany is contributing I can't find any publicly access route to that operational data ). H1 ( in red ) at Hanford has 4km long arms, H2 ( in blue ) also at Hanford has 2km long arms, with both contained in the same building - indeed the same vacuum space. L1 ( in green ) at Livingstone has the same design as H1. Their substantial physical separation is important for a host of good reasons. Note the plots from both sites have the same features but are offset horizontally simply because they were snapped at different times ( ie. different T0's ).

The horizontal bars used to plot each detector are slightly offset vertically and of slightly different widths, so that you can see them distinctly when overlaid. But the values are exactly integral.

So what does the scale mean? Well here's my shot/guess:
0 - not working
1 - mode cleaner ( MC ) operating
2 - case 1 plus arms powered up
3 - case 2 plus control system powered up
4 - case 3 plus IFO 'locked'

I envision it like the flow of photons from the laser through 'gates' into the machine proper.

The mode cleaner, as it's name suggests, 'purifies' the light by removing unwanted photon types ( my guess is wavelength, polarisation, maybe unwanted resonances/sidebands ).

The 'Both arms locked 12h Export' refers to the optimal ( ie. science ) operation of the IFO's. This produces the good data for us crunchers to churn and burn! :-)

So with the recent plots shown above, clearly it was a fiddly time for H2 and L1, but rather well locked for H1.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Chipper Q
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Interesting that seismic is

Interesting that seismic is measured in units of micrometers per square-root of Hertz; are these rms values for a spectrum of amplitudes (I saw 'Amplitude Spectral Density' (ASD) in some of the papers*)? I think 'PEM' stands for Physical Environment Monitor (going by this list of LIGO acronyms and abbreviations). The various seismic plots pertain to low frequency ranges ... why a total of 8 plots? One's for the LVEA (Laser and Vacuum Equipment Area) monitoring frequencies between 3-10 Hz, and the others look like they pertain to both arms. And as long as the vibrations are within +- ~100 micrmeters per sqrt(Hz) then the interferometer can function at design sensitivity – which I just noticed peaks at ~15 Mpc in H1 (Hanford's 4 km arm?). It was around 12-13 Mpc a little over a year ago (last time I was poking around the logs, I think before S5 started). So 15 Mpc includes everything in our local cluster of galaxies? That's a lot of stars!

*Just to give a small idea how difficult seismic isolation is, note how relativity's equivalence principle comes into play: no sensor, by itself, can tell the difference between sensing an acceleration of the framework, and sensing a tilt in the framework (see Fig. 1 in this 12-page pdf document, "Low Frequency Vibration Isolation for Advanced LIGO").

Mike Hewson
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RE: Interesting that

Message 47932 in response to message 47931

Quote:
Interesting that seismic is measured in units of micrometers per square-root of Hertz; are these rms values for a spectrum of amplitudes (I saw 'Amplitude Spectral Density' (ASD) in some of the papers*)?

Yes, I've been mulling over that one too... there are a few quantities/signals expressed in that general form. I think I understand 'per Hertz', but I'll get back to you when I've conquered 'per root Hertz'..... :-)

Quote:
I think 'PEM' stands for Physical Environment Monitor (going by this list of LIGO acronyms and abbreviations).

Yep, I read that too. Have you found the LIGO document server here? It helps to have the key to their coding/naming as well. I've been steadily trawling the ( thousands of... ) papers there and downloading some of the more interesting/pertinent pdf's. I'm currently in the 'T' or technical group..... :-)

Quote:
The various seismic plots pertain to low frequency ranges ... why a total of 8 plots? One's for the LVEA (Laser and Vacuum Equipment Area) monitoring frequencies between 3-10 Hz, and the others look like they pertain to both arms.

I suppose you're referring to one like this at Livingstone :

If I am correctly reading the upper left legend, then it includes the end stations ( ETM ) the corner apparatus ( LVEA ) for both arms ( X and Y ) in the frequency ranges 0.1 to 0.2 Hz and 0.2 to 0.35 Hz ( where 'p' represents the decimal point ). Thus covering that 0.1 to 0.35 Hz seismic range on that plot at least. Anyhow, all those plots presumably cover the gamut of seismic disturbances - to aid understanding of loss of interferometer lock from shaking, and perhaps any overlap in that range with our desired astronomical detections.

Quote:
And as long as the vibrations are within +- ~100 micrmeters per sqrt(Hz) then the interferometer can function at design sensitivity – which I just noticed peaks at ~15 Mpc in H1 (Hanford's 4 km arm?). It was around 12-13 Mpc a little over a year ago (last time I was poking around the logs, I think before S5 started). So 15 Mpc includes everything in our local cluster of galaxies? That's a lot of stars!


Yes it's a terrific instrument isn't it?
H1 - Hanford 4km arms
H2 - Hanford 2km arms
L1 - Livingstone 4km arms
The difference this year is that the interferometers are 'up' at science mode more of the time - they are simultaneously locked for the best data. Each increment in range ( of detection ) increases the volume enclosed somewhat proportionally more - as a sphere's volume goes by it's radius cubed - thus potentially snagging more targets.

Quote:
*Just to give a small idea how difficult seismic isolation is, note how relativity's equivalence principle comes into play: no sensor, by itself, can tell the difference between sensing an acceleration of the framework, and sensing a tilt in the framework (see Fig. 1 in this 12-page pdf document, "Low Frequency Vibration Isolation for Advanced LIGO").


Thanks for that link, downloaded in a jiffy :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
Mike Hewson
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If you want to get a feel for

If you want to get a feel for the difficulties encountered by the operators of the LIGO's then check out the Hanford log for 12/10. It describes the rigamarole around the 'H2 all inclusive bootfest',


which would seem to be a pernickety day all around for the technical teams there! Don't worry if you miss the gist of the tech-talk ( I did! ). What alot of busy bees ...... :-)

Cheers, Mike.

( edit ) H2 is the blue trace going up and down like a yo-yo, and it never got to full science mode ( level 4 ).

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
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So let's next look at the

So let's next look at the NS/NS Inspiral Range.

This has the horizontal axis showing time as defined before. The vertical axis represents distance, but in a standard astronomical unit. A parsec is short for 'a parallax of one arc second', a fairly bizarre name for everyday use. It's a lot further away than the shops... :-)

Historically parallax was/is a way of measuring distances to relatively nearby stars or other objects. If you make two measurements of the direction of an object, when the Earth is on opposite sides of the Sun in it's orbit ( ie. taken six months apart ) then you can form a triangle. The 'base' is the diameter of the Earth's orbit, and the angles between that line and each of the two directions of observation, to the same object of interest, give the other sides.

The angle between the long sides ( or strictly speaking half of it ) is referred to as the parallax angle. It is very similiar to standard surveying 'triangulation'. It only works if the said object is not too far distant, as the angle gets smaller and is harder to measure the further out the object is. For things outside the range of parallax deduction then you use some other measure(s) which overlap in some range - so one can calibrate one type of yardstick to the other. Hence you can still speak of the parsec measure for really long distances even if no parallax measurement actually applies. Now in a full circle you have 360 degrees, each of which can be finely divided into 60 parts - called arc minutes - which in turn can be divided in to another 60 parts - called arc seconds. Hence 1 arc second = 1/(60 * 60 * 360) = 1/1296000 of a complete circle...... pretty small huh?

For the Earth's orbit ( average about 150 million kilometres in radius ) then an object would have to be placed at a distance of 3.26 light years to have an evident parallax of one arc second. Thus 'one parsec' is a shorthand way of saying that.

[ Mind you this gives a linear scale, not an inverse one, so that 'two parsecs' is twice the distance of one parsec and NOT a parallax of two arc seconds, which would in fact give a distance of half a parsec .... ]

So now I'm talking 'light years'! A light year is the distance that light, at 300,000 kilometres per second, would travel in one year. This is 300,000 ( km ) * 60 ( seconds per minute ) * 60 ( minutes per hour ) * 24 ( hours per day ) * 365.25 ( days per year ) = 9,460,730,472,580,800 metres. I have used the International Astronomical Union's ( IAU ) definition of year length, see here.

The second nearest star ( our Sun being closest ) is one of the Alpha Centauri group, Proxima Centauri, and is around 4 and 1/3 light years away or about 1.4 parsecs. The 'thickness' of our Galaxy is approx. 1000 light years and say 100,000 light years in diameter. Andromeda ( next nearest ) Galaxy is 2 and a bit million light years away.

So back to the vertical scale is marked in Mpc - Mega-parsecs ie. millions of parsecs. Altogether the 'design' range of the LIGO's is roughly 15 Mpc = 45 million light years!

Phew! Nearly there! :-)

Now because big things make big waves, and smaller things make smaller waves then the 'detection range' refers to a standard type of event. This is a bit arbitrary in a sense, but has been chosen to be representative of expected detections. The exact definition needn't worry us too much, but see here and here if you are curious. So if the NS/NS Inspiral Range is at 15 Mpc then we expect to at least detect an event ( as defined ) out to that distance.

I do hope that is clear..... :-)

Also if the images are to large ( I am trying to keep well under 100Kb ) for dial-up users, let me know. I'm using mostly gif's which compress pretty well for diagrams and aren't overly lossy.

Cheers, Mike.

( edit ) Again, red is H1 ( Hanford 4km ), blue is H2 ( Hanford 2km ) and green is L1 ( Livingstone 4km ).

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
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More on seismic frequency

More on seismic frequency ranges ( from Livingstone log ):

Quote:

Templates for Seismic Sources of Lock Loss
I have modified templates created by Kent Blackburn (at LHO) for investigating seismic sources of lock loss for use at LLO. Each of the three templates look at different bands:

* 0.02 - 0.1 Hz used for looking at seismic activity caused by distant earthquakes
* 0.3 - 2 Hz for nearby seismic disturbances
* 3 - 10 Hz for trains

H2 not above state 1 ( from Hanford log ):

Quote:
If it was a horse, well, lets just not go there.

H1 pretty good, except for H2 work ( from Hanford log ):

Quote:
H1 has been Powered Up for most of the shift (lock broken earlier due to EY reboots), and was out of science mode due to H2 boots and traffic related to H2 investigations/work.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

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