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What does ... mean?

Posted: Wed Nov 25, 2009 7:31 pm
by Danny252
Obviously, CERN has plenty of terms and acronyms that the majority of us don't understand. So, we may as well have somewhere to ask about what certain things mean.

First off, what does "quiet beam" mean? Simply running a beam without doing anything to it (collisions, adjusting stuff, etc.)?

Re: What does ... mean?

Posted: Thu Nov 26, 2009 9:21 pm
by Xymox
Yes your right we need a dictionary of terms.. Whew.. Thats quite a project..

The big problem is I just dont know most of it either...

So lets do this. You have the perfect thread title. Everybody if you know what something means post it here... I will then take what we figure out and make a "What does ... mean?" page with everything we figure out definitions for.

Good idea...

Re: What does ... mean?

Posted: Thu Nov 26, 2009 11:02 pm
by Danny252
May as well list what I do know, to help start it off. Not alphabetical, it came out of my head like this!

Beam: What's being circulated in the LHC or attached accelerators at high speeds (nearly the speed of light) and (relatively) high energy. This can be protons, ions or possibly something more exotic.

Beam 1/B1: Clockwise beam, usually shown in blue. Joins the LHC from the SPS at Point 2 (TI2).

Beam 2/B2: Anticlockwise beam, usually shown in red. Joins the LHC from the SPS at Point 8 (TI8).

Point/Octant [x]: The LHC has 8 "points" around it. They are as such:
Point 1: ATLAS
Point 2: ALICE, Beam 1 Entry
Point 3: Beam Cleaning (Momentum)
Point 4: RF (Radio Frequency, meaning..?)
Point 5: CMS
Point 6: Dump
Point 7: Beam Cleaning (Betatron)
Point 8: LHCb, Beam 2 Entry

Sector [xy]: The area between 2 Points. Sector 12 is between ATLAS and ALICE, Sector 23 between ALICE and Beam Cleaning, etc.

Dump: Disposing of the beams after use. Because of their high energy nature, they must be dealt with carefully to prevent irradiation of staff and damage to equipment. Don't think they're weak because they're small - the beams can punch a hole through solid metal! See the Collimator link below/on Outreach for pictures of this.
See: ... m-dump.htm

Magnets: These are used to steer, contain and focus the beam. This is due to the fact that a charged particle within a magentic field is deflected. The LHC has over 1200 of these. See: ... agnets.htm

Collimator: A Device used to catch stray particles from the beam, stopping them from damaging equipment or irradiating staff. See: Dump, ... uction.htm

Cryo/Cryogenics: The LHC must be kept at a very cold temperature in order to operate - a few degrees above absolute zero. Most notably, the superconductors used to power the magnets require very cold temperatures. See: ... genics.htm

LIN/LINAC: Linear Accelerator. First stage used to accelerate protons and ions. See:

PS or Pre-Injector: Proton Synchrotron. Second stage used to accelerate protons, third for ions. A former CERN accelerator like the LHC in its own right, now 50 years old, and part of the LHC complex.

SPS or Injector: Super Proton Synchrotron. Final stage of acceleration for protons and ions before the LHC. A former CERN accelerator like the LHC in its own right, now part of the LHC complex.

LEP: Large Electron-Positon collider. A former CERN accelerator for Leptons (a Lepton accelerator called LEP, fancy that!) such as electrons and positrons, quite obviously. This was taken out of use in 2000, and the tunnels of the LEP were re-used for the LHC.

LEIR: Low Energy Ion Ring. Secondary Ion Acceleration.

Injection/Injecting: Putting various types of particles into the LHC - creating a beam.

Luminosity: A measure of how many particles are going through an area per second. Used to measure how many particles are in a beam (?), units are cm-2 s-1 (Particles per centimeter squared per second).

Intensity: A measure of the power of the beam (?)

Electron Volt/eV/MeV/GeV/TeV: Used to measure how much energy the particles in the accelerator. A very small amount of energy (lifting an apple 1 metre would require 6.25 billion billion eV!)

To indicate many eV, SI prefixes may be used. The LHC commonly uses:
MeV - Mega Electron Volt - 1,000,000 eV - 1e6 eV
GeV - Giga Electron Volt - 1,000,000,000 eV - 1e9 eV - 1,000 MeV
TeV - Tera Electron Volt - 1,000,000,000,000 eV - 1e12 eV - 1,000 GeV

Re: What does ... mean?

Posted: Fri Nov 27, 2009 5:26 am
by Xymox
Wow !


COOL !!!

Jeeze I think you got everything !


Re: What does ... mean?

Posted: Fri Nov 27, 2009 3:24 pm
by Danny252
Haha, the basics, yeah. What on earth Intensity actually means, what the RF section does, why it's related to clocks, how collimators work... I still don't know those!

Re: What does ... mean?

Posted: Fri Nov 27, 2009 4:04 pm
by Xymox
Yes we need MORE INFO.... I know CERN professionals are hanging around our forum.

P L E A S E let us know these things :)

Of course the LHC guys are rather BUSY right now ! hehehe.... so its ok we can wait.. maybe.. Sorta..

Re: What does ... mean?

Posted: Fri Nov 27, 2009 6:11 pm
by Danny252
Page 1 mentioned QPS, so I googled it :)

Quench - The overheating of one or more magnets. At very low temperatures (7K and down), the LHC's cables and busbars are superconducting, and have no electrical resistance. Above this, they conduct normally - but therefore have resistance. A quench is when the superconducters overheat and enter the normally conducting state - causing multiple problems due to the huge amount of energy they contain and their newfound resistance. A large-scale quench caused the shutdown of the LHC for over a year from September 2008.

QPS - Quench Protection System. In order to prevent a large scale quench in future, multiple detectors are positioned in the LHC to monitor the temperatures and electrical resistances of the superconductors.

Re: What does ... mean?

Posted: Fri Nov 27, 2009 9:10 pm
by Danny252
Page 5 and onwards of this has a large glossary and set of definitions:

Under LHC > Web Site > Beam Parameters if Adobe is acting up - it only worked when I saved the file locally


EDIT: I went deeper into CERNLand and found:

Technical specifications for the LHC!

Available via LHC > Web Site > Baseline Documentation


RF - The RF system is used for acceleration, it seems. Radio Frequency electric fields are used to accelerate whatever ions you have in the LHC (same process used in some other accelerators too). I assume this means hi-frequency AC, which apparently has to be running at multiples of 200MHz for the LHC.


Kicker - Powerful magnets used to "kick" the beam into a certain position - for example, into the beam dump system. These can be switched on and off quickly, have a very short startup time so that the beams are not dragged across, but instantly switched. Breaks are provided in the beam to aid the instant switch.


I really have too much time on my hands...

Useful CERN acronyms: ... ronyms.htm

Re: What does ... mean?

Posted: Fri Nov 27, 2009 10:26 pm
by Danny252
CERN has kindly allowed us to link to their EDMS system - a massive collection of technical documents relating to the LHC (and possibly other CERN projects?) ... top=&open=

The "LHC Hardware Baseline" is probably the most interesting to us.

(I need to organise all the info I've thrown in here!)

Re: What does ... mean?

Posted: Sat Nov 28, 2009 12:35 am
by photino
This contains a nice explanation of luminosity and intensity... there's lots and lots of detail there.

roughly speaking,
intensity = number of particles in a bunch
luminosity = number of particles going through a cm^2 per second

Re: What does ... mean?

Posted: Sat Nov 28, 2009 11:17 pm
by LHC_Insider
Danny252 wrote:What does "quiet beam" mean?
It means that the operators are not playing with it, the profile is understood (i.e. the spread in 3 dimensions), and it can be considered stable. This means that experiments can choose to turn on sensitive inner detectors that could be damaged by bad beam conditions. Note that collisions generally imply that both beams are quiet.

Re: What does ... mean?

Posted: Sun Nov 29, 2009 1:11 am
by MarkyB
Danny252, a minor update for a component you missed the PSB - Proton Synchrotron Booster...

The Booster (and ISOLDE) section is responsible for the operation of the PS Booster and the On-Line Isotope Mass Separator ISOLDE. The PS Booster is a synchrotron composed of four superimposed rings. It delivers a variety of beams for the downstream PS, SPS and LHC machines as well as high intensity beams for ISOLDE. The section is also responsible for the specification and programming of controls software. ISOLDE delivers stable and radioactive beams for changing user groups in the fields of nuclear and atomic physics, solid-state physics, life sciences and material science. Responsibilities of the section include target changes, setting up and delivery of stable and radioactive beam on ISOLDE's two mass separators as well as maintenance and upgrade of hardware and controls software.

Here is a really useful link to the PSB layout and operation (though it might be fairly old)...

Points on the graphic are clickable. Of particular interest are the Spectrometer, Injection, and Ejection links.

Re: What does ... mean?

Posted: Sun Nov 29, 2009 1:21 am
by MarkyB
Also an update on the 2 types of beam life cycle (and an alternative graphic)...


The accelerator complex at CERN is a succession of machines with increasingly higher energies. Each machine injects the beam into the next one, which takes over to bring the beam to an even higher energy, and so on. In the LHC—the last element of this chain—each particle beam is accelerated up to the record energy of 7 TeV [eventually!]. In addition, most of the other accelerators in the chain have their own experimental halls, where the beams are used for experiments at lower energies.

1. The brief story of a proton accelerated through the accelerator complex at CERN is as follows:
- Hydrogen atoms are taken from a bottle containing hydrogen. We get protons by stripping orbiting electrons from hydrogen atoms.
- Protons are injected into the PS Booster (PSB) at an energy of 50 MeV from Linac2.
The booster accelerates them to 1.4 GeV.
- The beam is then fed to the Proton Synchrotron (PS) where it is accelerated to 25 GeV.
- Protons are then sent to the Super Proton Synchrotron (SPS) where they are accelerated to 450 GeV.
- They are finally transferred to the LHC (both in a clockwise and an anticlockwise direction, the filling time is 4’20’’ per LHC ring) where they are accelerated for 20 minutes to their nominal energy of 7 TeV. Beams will circulate for many hours inside the LHC beam pipes under normal operating conditions.
- Protons arrive at the LHC in bunches, which are prepared in the smaller machines.

2. In addition to accelerating protons, the accelerator complex also accelerates lead ions.
- Lead ions are produced from a highly purified lead sample heated to a temperature of about 500°C. The lead vapour is ionized by an electron current. Many different charge states are produced with a maximum around Pb29+.
- These ions are selected and accelerated to 4.2 MeV/u (energy per nucleon) before passing through a carbon foil, which strips most of them to Pb54+.
- The Pb54+ beam is accumulated, then accelerated to 72 MeV/u in the Low Energy Ion Ring (LEIR), which transfers them to the PS.
- The PS accelerates the beam to 5.9 GeV/u and sends it to the SPS after first passing it through a second foil where it is fully stripped to Pb82+.
- The SPS accelerates it to 177 GeV/u then sends it to the LHC, which accelerates it to 2.76 TeV/u.

Re: What does ... mean?

Posted: Sun Nov 29, 2009 2:03 am
by Xymox
LHC Insider,,, good explanation of Quiet Beam.

MarkyB,,, good graphic and explanation. While perfect in detail I gotta make it simpler for a lay person to understand. That aint easy. But I am reasonable good at that. So I will work on it. I also missed the PSB..

Re: What does ... mean?

Posted: Sun Nov 29, 2009 2:42 am
by MarkyB
Simpler summary of above, but without the numbers...