What exactly is pre-cycling?

[neutralino]

What exactly means pre-cycling?

[chtephan]

I gues you'd have to ask a machine expert to know what exactly it means. However, I can roughly estimate what it means:

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".

[Xymox]

W O W !!!

THAT was a great description of how things work !

That explained a lot...

[Xymox]

I quoted your explanation and placed it in the "what do these displays mean" thread because your description covers a tremendous amount of ground in describing what we are watching.

viewtopic.php?f=3&t=46&start=10

Thank you !

[LHC_Insider]

The pre-cycle is indeed the step before injection of a new beam, however it's not just a stable state. Following a ramp-down of the magnets from the previous fill, there are various residual effects in the magnets (for those who know physics lingo, this are hysteresis effects). These need to be essentially reset such that the state of the machine is know before starting the next fill and ramp. The pre-cycle is the step by which this occurs. For more details, you can read (e.g.) here:

http://cdsweb.cern.ch/record/1199585/fi ... 09-007.pdf

[Xymox]

Interesting.....

Im never going to get my work done in making a info page for the LHC with interesting posts like this..

"The main
origin of this was found to be the generation of long range
coupling currents in the strands of the superconducting
cables in the magnets, which interacted with the persistent
currents in the superconducting filaments."

wow... I never considered superconductors had such interesting complex interactions.

Sort of off topic,, the LHC must generate some interesting RFI / EMI ?? Not powerful I would not think but the spectrum and temporal qualities must be rather unique ? I wonder if you could pick it up on some shortwave band ? It would be cool if you could listen to the LHC run by listening to the RFI it produces on a cheap SW radio...

[pcatom]

A pre-cycle is a standard magnetic cycle that the whole machine is put through without beam in order to (re-)establish the magnetic history. It is used to increase the reproducibility of the machine settings.