What is an LHC Fill? According to the information I gathered from CERN wiki pages, an LHC fill is a collection of several good runs. Am I right? Also, is an LHC run defined as a discontinuous period of data collection which contains several million events? Please clarify.
 A: A "fill" is surprisingly difficult to define. The best definition I've found is that it's just a number that the LHC operators can increment by 1. You can think of it as a bookmark to refer to a period of activity.
The term is most commonly used to refer to a discrete interval of time containing a period where the beam is "full" (i.e. the beams have successfully been injected according to the desired filling scheme).
A typical "physics fill", in terms of machine modes, goes "injection" → "ramp" → "flat top" → "squeeze" → "adjust" → "stable beams" → "dump" → "ramp down". The fill number is then changed before the next injection.
However, there are lots of exceptions to this. A fill need not contain a ramp: it can remain at injection energy. There may be any number of beam dumps during a fill, particularly at injection and during "inject and dump" fills. There are even fills without any beam at all!
The word "run" is used very differently for the LHC and the experiments. For the LHC, a "run" is a period between "long shutdowns". Run 1 was 2010 to early 2013, Run 2 is 2015 to 2018, etc. There are thousands of LHC fills in a LHC run.
For the experiments, a "run" is a discrete interval of data-taking. Usually run changes occur when something about the detector itself changes, such as trigger configuration or a subdetector is enabled/disabled. There may even be a timer that changes run after a prescribed period (certainly this is the case at LHCb). There can be many runs per fill, or runs can occur independently of fills, particularly if there's no beam or the LHC is in "machine development".
A: A single LHC fill has roughly the following steps:


*

*A dose of protons enters the accelerator complex

*Protons are accelerated through the chain (Linac, PSB, PS, SPS, LHC)
to the maximum energy

*Protons are kept in the LHC ring to collide at the interaction points

*After some time (1-35 hours) the proton beam is dumped: it exits the
ring


The duration of a fill can vary wildly. Some fills can end prematurely due to technical issues. Information about various fills can be found here. When the machine is ready for the next fill, the process is repeated. Sometimes there are other activities happening in LHC between the fills (short technical breaks). You can check the actual status in real time here.
A fill consists typically of $10^{14}$ protons, grouped into bunches which form the proton beam. During a fill there is roughly 600 million collisions per second, that is $10^{12}$ collisions per hour. Below you can see a time graph of a typical fill: the injection happened around 2 am, beam was dumped shortly after 3 pm. Energy per proton was 6.5 GeV, the beam intensity was gradually dropping due to losses in collisions.

LHC Run consists of many fills. A Run is either a single year span of LHC work, or sometimes it is understood as a period of several years or operation without major stops: right now we are in the middle of Run 2 which started in 2015.
