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The official song for hump hunters is of course "Changing Opinion" by Philip Glass. (Thanks for the tip, Photino!)
Lyrics: http://www.lyricstime.com/philip-glass- ... yrics.html

If the actual source were a higher frequency, then a smaller relative frequency shift would, after subtracting multiples of the 11.2 kHz sampling frequency, produce the fairly large frequency instabilities that are noted. Since the frequency is observed at 0.28±0.05 times 11.2 kHz, it could really be any of:

• 11.2 kHz × 0.28±0.05 (2.6–3.7 kHz)
• 11.2 kHz × 0.72±0.05 (7.5–8.6 kHz)
• 11.2 kHz × 1.28±0.05 (13.8–14.9 kHz)
• 11.2 kHz × 1.72±0.05 (18.7–19.8 kHz)

etc. The absolute range stays the same, but the relative frequency ranges are ±17.86%, ±6.94%, ±3.91%, ±2.91%, ±2.19%, ±1.84%, etc. I have an easier time believing a ±3% fluctuation than a ±18%.

Normally, when sampling a signal, it is first fed through a low-pass "antialiasing filter" to remove the higher frequencies, so you know that you're only measuring the baseline. Is there some equivalent built into the LHC, so higher frequencies have decreasing effects on the beam?

OMG I knew that they have mobile phone coverage in the tunnel. But I didnt know they wouldnt switch of the transmitters during operation (No one is in the tunnel, so why would they need mobile phone coverage??). There are going to be hump studies at 450 GeV today with the GSM being switched off and on. So lets see if this is going to have any effect.

oxodoes wrote:OMG I knew that they have mobile phone coverage in the tunnel. But I didnt know they wouldnt switch of the transmitters during operation (No one is in the tunnel, so why would they need mobile phone coverage??). There are going to be hump studies at 450 GeV today with the GSM being switched off and on. So lets see if this is going to have any effect.

Josch mentioned the possibility of GSM interference on April 3.

The results of the GSM Hump test was negative. Just another possibility ruled out.

Tau wrote:The official song for hump hunters is of course "Changing Opinion" by Philip Glass. (Thanks for the tip, Photino!)
Lyrics: http://www.lyricstime.com/philip-glass- ... yrics.html

LOVE IT!!!

Following recent announcements in the press one might be led to believe it's Fermilab trying to stall physics at Cern. Or have I been reading too many conspiracy theories.

Some thoughts:

Did they really believe GSM could affect the beam directly?
If so, any switch-mode power converter with insufficient or defective input- or
output filter has the potential to do the same. Provided it is installed in or somewhere
near the tunnel or the wiring leads to somewhere near the beam.

If they thought there is an influence on the equipment (EMI disturbing some
control loop and modulating some current in a non-superconductive magnet for
example), again, the same applies with the exception that GSM is more likely to
disturb electronic equipment. The pulsed RF can be very hard to shield.

The question arises if it would be possible to see any modulation of the current
on a magnet, is there enough bandwith?

But maybe it would be the best to try to measure possible hump-generating magnetic
fields nearby the beam pipes instead of trying to switch off and on one component
after the other. If it is a component that is needed to get a beam there is no chance
to find it this way.
Why don't they prepare some carts with SQUIDs and a DAQ-system and simply take measurements and try to correlate with the hump. At every access they move them
around in the tunnel. If they find some signal they might be able to do some
coarse direction finding and can place the carts at a better position.
In the end they may able to locate the source, regardless if it is at CERN or at a
location outside.

Another idea about a possible source:
As far as i know the kicker magnets -at least for injection- consists of some coils
and some matching capacitors. If the kicker magnets for dumping have a similar
construction there may be an excitation of "ringing" in these LC-circuits through the
bunches itself, or from an outer source: The yoke looks pretty "open".

According to the Wednesday morning meeting slides they will be putting in magnetic probes for hump related studies. I guess this means they will use sensitive instruments that could pick up magnetic field oscillations around the collider. If they can detect something that matches the hump signall they should be able to track down where it is coming from by moving the probes around.

Although Meyers was joking about it and claimed that the transverse dampers cure the hump problem during his ICHEP talk, I think it must be still a serious problem that is affecting beam lifetimes.

hump hunting is more on thrill. Be careful and enjoy your mission.