Let's go hump hunting!

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mrgumby
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Re: Let's go hump hunting!

Post by mrgumby » Sun Apr 25, 2010 9:22 am

A totally different idea...

From this site http://www.oicinc.com/history_sonars.html

Marine geologists use bottom penetrating sonar

Quote
"most research boats these days are equipped with 3.5Khz sub-bottom profilers"

The LHC passes under Lake Geneva.......????? :think:

I wonder if a research program started in November 09?

oxodoes
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Re: Let's go hump hunting!

Post by oxodoes » Sun Apr 25, 2010 11:08 am

mrgumby wrote:The LHC passes under Lake Geneva.......????? :think:
The LHC has a minimum distance of 3km to Lake Geneva (see Google Earth).

Yesterdays log suggested that the hump might be related to betatron cleaning.

Kasuha
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Re: Let's go hump hunting!

Post by Kasuha » Mon May 10, 2010 8:02 am

Looks like quite successful (physics-wise) weekend has passed - and I can't find any signs of hump appearing. Have they cured it already?

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chriwi
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Re: Let's go hump hunting!

Post by chriwi » Tue May 11, 2010 7:01 am

May 10 9:30PM (e-log) "Hump clearly visible on B2 (beneath and beside the tune)" :(

But it was only in a 450GeV setuprun at least not in a physicsrun.
bye

chriwi

zaim
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Re: Let's go hump hunting!

Post by zaim » Wed May 19, 2010 5:08 pm

Hump still there. From tuesday:

13:28: B1 and B2 10^11 injected OK
13:44: We lost half of B2 doing a Q' measurement;
Probably we hit the hump during the measurement

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PhilG
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Re: Let's go hump hunting!

Post by PhilG » Mon May 24, 2010 5:36 pm

The attached image shows some info from this report of 21st may
http://indico.cern.ch/conferenceDisplay.py?confId=95508
Attachments
hump.jpg
hump.jpg (96.2 KiB) Viewed 3610 times

tomey36
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Re: Let's go hump hunting!

Post by tomey36 » Wed May 26, 2010 11:26 pm

it is hard to belive that with some of the smartest people in the world working at cern they still havent found what is causing the hump!

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PhilG
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Re: Let's go hump hunting!

Post by PhilG » Sun May 30, 2010 7:44 am

As the bunch intensity increases, finding the source of The Hump becomes more cirtical. We have seen from various reports that it causes a vertical spreading of the bunch that steadily reduces luminosity. When it hits the tune frequency it can lead to beam losses and can even trigger a dump. Its varying frequency and unpredictability make it very hard to work around. The information we see in the reports is limited so it is hard to gauge what is being done but they may not consider it safe to proceed to higher intensity beams until The Hump is resolved.

Here is some info from a report on beam stability at the beginning of May (http://cdsweb.cern.ch/record/1267395/fi ... 10-008.pdf)

The source of the broad-band excitation signal around
the nominal vertical tune working point (0.31) visible in
Figure 1 remains elusive. Similar to the 8 kHz lines, once
this perturbation is in the vicinity of the tune, the beam
gets resonantly excited, subsequently decreasing beam lifetime.
While the effect has been observed on both beams, it
is more dominant in the vertical plane of B2. A higher
temporal analysis revealed that the broad-frequency distribution
is actually caused by a narrow-band single frequency
with the same shifting mean frequency for both
beams, as shown in Figure 10. The central frequency of
the hump shifted typically between 0.15 and 0.45 frev over
a duration of a few minutes to hours. The B1 to B2 hump
frequency correlation factor is about 0.896. Nevertheless,
the ’hump’ is visible independent of whether there are one
or two beams circulating in the machine. The magnitude
spectrum of the hump frequency shift as a function of time
revealed a 1/f dependence. As visible in Figure 1, the
amplitude of the ’hump’ corresponding to a few hundred
nano-metre is extremely small and – provided it is caused
by a single dipolar-type kick – corresponds to a deflection
angle in the order of a few nano-rads. Due to the huge
number of elements in the machine that a priori could potentially
create these minuscule deflections, the identification
and location of the true perturbation source proved to
be extremely difficult. Based on switching ’off’ given accelerator
elements, the orbit correctors, transverse damper
exciter, injection septa, transfer lines, pre-injector accelerators,
experimental magnets and higher-ordermagnets could
be ruled out as the cause for the ’hump’. Despite a series
of investigations, the true source of the ’hump’ remains unknown,
and its investigation and mitigation is a priority of
the ongoing LHC commissioning.

CONCLUSIONS
[...] While the initial performance is
sufficient for present operation, some effects such as the
residual un-explained tune oscillations, the large tune jitter
during injection and the ’hump’ will need to be addressed
in view of nominal LHC operation.


It is indeed worrying that they have not been able to identify the source after so much time. Yes the LHC is complicated with many components, but there are engineers who know it very well. Why can they not identify the cause given its peculiar frequency characteristics?

They have not said if they have considered using sensors around the tunnel to detect vibrations or EM interference. As time goes on and more components are eliminated, the likelihood that the source comes from outside the LHC is increasing. Switching bits off and on may not be enough to find it.

Harbles
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Re: Let's go hump hunting!

Post by Harbles » Sun May 30, 2010 11:16 pm

PhilG wrote:The attached image shows some info from this report of 21st may
http://indico.cern.ch/conferenceDisplay.py?confId=95508

And here is that LHC status update talk.
http://cdsweb.cern.ch/record/1268170

It's still a mystery.

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PhilG
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Re: Let's go hump hunting!

Post by PhilG » Wed Jun 02, 2010 8:36 am

Schedule for Friday shows "Hump investigation (cryo - vacuum …)"

robbartz
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Re: Let's go hump hunting!

Post by robbartz » Sat Jun 05, 2010 9:40 am

Don't know much about the strength of the electo/magnetic fields that faulty devices can generate or how far there range can be. I know the LHC is a very sensitive machine.

There are homes above the LHC Tunnel, could the hump be cause by a faulty/noisy domestic appliance that is switched on 24/7 such as a freezer/Computer,CRC Monitor/TV etc?

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Bornerdogge
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Re: Let's go hump hunting!

Post by Bornerdogge » Sat Jun 05, 2010 10:21 am

Well the fact is the LHC is roughly 100m under the ground... You'd need a hell of a big TV to be able to cause any disturbance... :mrgreen:

Plus, the frequency of the hump varies, which would not be if it came simply from some regular apparatus above the ground.

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PhilG
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Re: Let's go hump hunting!

Post by PhilG » Sat Jun 05, 2010 12:11 pm

The depth is as little as 50m in some places and something penetrating from ground level is quite possible and not unprecedented, but the plausibility of some common electrical appliance causing it is not really on.

The way in which the frequency varies over a period of several minutes is very peculiar so it is surprising that nobody seems able to identify it from that alone, especially if it is some part of the LHC machinery. Actually the way it sweeps slowly over the range of frequencies available for the beam tune is so odd and inconvenient that it seems almost suspicious.

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Bornerdogge
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Re: Let's go hump hunting!

Post by Bornerdogge » Sat Jun 05, 2010 7:53 pm

Hmm maybe that's why we don't hear from our friend ivan anymore ^^

He's there, in Switzerland, trying to slow down the LHC operations!


...

I'm out XD :text-blondmoment:

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PhilG
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Re: Let's go hump hunting!

Post by PhilG » Wed Jun 09, 2010 11:37 am

Hump studies yesterday could not find any connection between the cryo systems and the hump. "When you have eliminated the impossible, whatever remains, however improbable, must be the truth", Ivan?, jealous Fermilab physicists?, a camel from the future? who knows?

They are commissioning some systems that improve stability of the beams. Perhaps The Hump will not be a problem after that even if they can't locate its source. I hope so because they will not be able to safely increase intensity levels much further without good control.

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