what is meant by the term "beam spill"?

Doofy

in the context of a beam of particles from an accelerator?

mfb

Some accelerated particles can hit the walls of the pipe (-> beam spill). If too many particles do that, it is bad for the accelerator.

Doofy

hmm are you sure? I'm seeing it being quoted in units of time.

jtbell

Consider a synchrotron which is being used in "fixed target" mode, not in "collider" mode. You have a circular accelerating ring that gets the particles up to the desired energy. Extending tangentially from the ring is a linear beamline which then branches off to form various subsidiary beamlines for different experiments.

This setup doesn't produce a continuous beam. You inject (usually) protons at low energy into the ring, the ring accelerates them to the desired energy (which takes a few seconds as the magnetic field ramps up to keep the beam contained in the beampipe), and finally a deflecting magnet turns on and "spllls" the contents of the ring into the linear beamline(s). Then you inject a fresh batch of protons into the ring and the cycle repeats.

IIRC "beam spill" refers to the time period during which the accelerated particles are actually being "spilled" out of the ring.

mfb

As this is proportional to the number of particles, I would expect this unit. Beam loss in the LHC is usually reported like this - a beam lifetime of 100h means ~1% loss per hour.

Bill_K

As jtbell says, beam spill is defined as "the removal of a controllable quantity of the particle beam current at a controllable rate onto an adjacent target." See here for the detailed description of a beam spiller.

the Wikipedia article on the OPERA experiment mentions that the proton beam spill used to generate the neutrinos is 10.5 microseconds.