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Waiting for the vacuum activity on fill 1960 to fall... 4 hours later and still waiting...

So what is vacuum activity that's been holding up the current fill?

Vacuum activity means in certain parts of the ring they don't have as good vacuum as they would like. If they leave it as is, the beam collisions with particles in the pipe may induce losses and beam dump (actually too high pressure may cause beam dump on its own) that's why they are waiting for the condition to improve before further beam manipulation.

Well, there are various definitions on what a vaccum activity exactly is. But the most suitable answer for your question has been answered here by Kasuha for it is something that occurs as a result of the lack of proper vaccum in some areas of the ring. This therefore creates a series of collisions with the particles in the pipe which further creates reductions and beam dumps. This obviously explains the delay of beam manipulation.