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What do the displays mean ?

Posted: Sun Nov 22, 2009 5:43 am
by Xymox
The short answer is im not sure. The LHC team has not explained them. I have asked, but they are busy guys.

My best guesses are below.

We need more discussion on this. I am working on a web page that describes these pages.

"Page 1"

Page 1 changes. It has a bunch of modes. It can display all sorts of things. Its currently displaying a sort of setup screen. The 4 windows are alignment screen. Normally they show a dot, which is the beam, in the tube. Up and down is up and down in the tube, L/R is L/R. Color is intensity.. They can choose any 4 locations from anywhere along the beam. This allows them to see the beam and align it to be centered in the tube. However im not sure what is going on with the ones they are showing now. There is no dot !?! Normally those screen are all blue/green with a bright red dot close to center..

The numeric stuff close to the top like "BCT TI8" is the luminosity or power of the beam. 8 refers to the position along the ring. They can choose these to display. Blue is beam 1 and red is beam 2.

the E: at the top of the screen is the power its set to. Not the measured power.

I dont know exactly what the SMP flags are in the lower right corner. What they say seems to be what they are.

"Cryo status" or "LHC2"

Its easy

Green means that section of magnets is supercooled and ready to go.
Red means its gotten to hot to use.

ANY red on this page stops the machine until it gets cold again.

"Status - Operation"

As far as the Status Op page goes. yea... tuff one..

Luminosity is the measured power of the beam.

I dont understand background, BKGD

Re: What do the displays mean ?

Posted: Sun Nov 22, 2009 10:59 am
by chriwi
In my oppinion this subpage of the field page gives a much better visualisation of the cryo-status:

By theway what do theese messages about external and internal clock mean and what is this "TDI .. gaps / mm" stuff?

Re: What do the displays mean ?

Posted: Sun Nov 22, 2009 12:21 pm
by morgad
The 'beam status' flags had me confused yesterday. They were running beam 1, but the beam 2 'beam presence' flag kept coming on, while the beam 1 one stayed off.

stuff being tested, or wires crossed over? ;)


Re: What do the displays mean ?

Posted: Sun Nov 22, 2009 1:12 pm
by chriwi
There was a message (in the lower left) yesterday that teh beam statusflags might become green also if it is not true at this time, due to some testing.

Re: What do the displays mean ?

Posted: Sun Nov 22, 2009 1:58 pm
by Xymox
They also run testing/simulation programs. These will cause the entire system including the status displays to simulate real conditions. I have seen that many times.

Yeap, the comments, if you can decipher them, provide the answers..

Re: What do the displays mean ?

Posted: Mon Nov 23, 2009 5:13 pm
by Danny252
Having looked at "Page 1", some googling reveals that:

TI2 and TI8 are transfers from the SPS to the LHC. The SPS is the final acceleration stage for whatever Cern are throwing in that day. TI2 points clockwise and feeds Beam 1, TI8 anticlockwise feeding Beam 2. These seem to join the LHC at positions 2 and 8.

The TDIs are Collimators - which are, from what I understand, devices used to control the intensity of the beam. I'm guessing these need to be aligned correctly so that they are able to control what must be a very thin beam.

Luminosity is a measure of how much stuff is passing through an area - number of particles per unit area per time. I seem to remember from one of the pages here cm-2 s-1 being Cern's unit.

Intensity is the number of protons/particles per bunch (so I read). I assume the LHC isn't a continuous stream, but lots of individual bunches flying around?

Re: What do the displays mean ?

Posted: Mon Nov 23, 2009 5:34 pm
by MarkyB
Hi all. I just joined. Portal is just great.

Looking through the CERN site I found a page for Web Based Monitoring...

Two "useful" pages are LHC Monitor and Page Zero... ... LhcMonitor ... t/PageZero

Sometimes the links work, sometimes not, so keep trying them.


Re: What do the displays mean ?

Posted: Mon Nov 23, 2009 11:06 pm
by Xymox
You do need a CERN external account for that link.

Once there it does have some interesting stuff indeed.

Good job MarkyB

I have asked CERN if these are ok links to use...
The answer so far every time I have asked is "yes" so we should be good.

My stance on putting up links is that I clear them with CERN first. Mostly so they can be sure that the link we post can handle the traffic from the public. Sometimes its just a small computer in a rack. We dont want to cause issues with our links to them. So I always ask first. CERN is VERY kind to leave all these links open for us to use. That could change any minute. So we need to be nice.

So if you find something. Best to PM me with it first so I can check it.

Re: What do the displays mean ?

Posted: Tue Nov 24, 2009 4:26 am
by rhowe
The information displays (vistars?) seem to display information about multiple experiments at CERN.

CPS_EAST seems to relate to an experimental testbed area in CERN:

More information about what the CPS_EAST vistar displays can be found at ... ontrol.pdf

page 21

Also, page 22 seems to cover the CPS display (maybe an older version?)

LIN I assume is LINAC2, the linear accelerator which is the first link in the chain leading to the LHC

Re: What do the displays mean ?

Posted: Tue Nov 24, 2009 5:39 am
by Xymox
The Vistar system is new. There is a older system that was kinda spread out across a number of places. The Vistar system has brought them all together.

The general info from the links is still good tho :)

The LHC actually requires output from Linac to PS to SPS and then into the LHC. So when the LHC is in use, all of those are used.

There are a number of accelerator "page 1" status' available from the Vistar


Re: What do the displays mean ?

Posted: Tue Nov 24, 2009 5:55 am
by Xymox
This layout shows the points along the LHC we see referenced in the Vistars and in comments.


Re: What do the displays mean ?

Posted: Tue Nov 24, 2009 3:44 pm
by Xymox
From another thread on the forum comes a awesome description of what is going on..

From chtephan
During "regular physics running" (which is still weeks-months away), the LHC mode of operations will be done in "cycles".

Each cycle consists of several steps. First, the magnets are brought to currents needed for injection energy beam (450 GeV per beam, which is what the maixum SPS energy is). Then the beam is actually injected from the SPS until the LHC ring is full. The next step is then the "ramp", i.e. the beams are accelerated. Once the energy is reached (2.2 TeV around christmas, then 3.5 TeV next year, eventually 5 TeV and 7 TeV in a few years after some major improvements), the beams are kept at that energy (flat top) for a few hours and squeezed (i.e. compressed to be as thin as possible) so that the collisions at the experiments lead to a best-possible collision rate (luminosity). Once the beams are depleted, the remains are dumped and the current in the magnet ramped down (snapback). Then the whole story restarts from the beginning.

The LHC state that is shown on page 1 is the mode that the LHC is currently in, i.e. which "master program" is controlling the components. There are a few of them, some having a lot of automatism (which is for the future when the LHC will mostly run autonomously), but also some needed for testing, where manual adjustments are allowed by the operators.

The "pre-cycling" stage would be a stage where basically the LHC system is ready, but none of the magnets are operating, i.e. the state before the start of a new cycle (sort of "standby"). The next strage would then be "injection" or "fill".

Re: What do the displays mean ?

Posted: Wed Nov 25, 2009 10:27 pm
by photino
This site explains the codes above the four images on LHC Page1. They denote the beam TV camera the image is coming from. ... ies.BTVLHC

It would be nice to understand better the actual image itself ;)

Re: What do the displays mean ?

Posted: Wed Nov 25, 2009 10:57 pm
by Danny252
I think the colour of the image shows the [atom?] density over a cross-section of the LHC - blue being empty, red being "stuff here". Hence why you get red dots appear when a beam is supposedly running - I think the red bars that appear are actually part of the machinery being picked up for some reason.

Looking at the Status Op page, why is it that ATLAS has such high background readings, whilst the other 3 detectors are virtually zero? On Background 2, Atlas is sat at 3000+. Are the other background detectors just not plugged in?

Re: What do the displays mean ?

Posted: Wed Nov 25, 2009 11:19 pm
by photino
Or maybe the red bar (like for instance at the moment on the right at BTVST.A4R8.B2) is a beam that is not very collimated? Then the red bar on the left display (BTVST.A4L2.B1) would also be the presently circulating second beam? Ah well, maybe someone from CERN will enlighten us at some point...