Fermilab Background Issues

Can divide concerns up:


First observation is that machine's main concern is beam loss rather than background per se.

Abort Gap

This systematically fills every shot. Why is still not clear: RF noise is a possible candidate (although it is noted with the use of Tetrodes rather than klystrons things might be expected to be quieter).

Cleaning the abort gap is possible. It is monitored using sync. light by the accelerator. The loss rate from the abort gap is also monitored by CDF. Beam in the abort gap makes the experiments very nervous because they get hit by some of the contents on an abort. Note that it is the small amplitude kick on the rising edge that pushes beam into experiments.

Some debate between machine and CDF about measuring losses from abort gap rather than contents.


Halo character

Not totally clear what is populating halo. Beam is breathing: magnet vibrations, quad movements, insertion quad movements with temperature variations "breathing the beam against the collimators".

Anything slow, such as beam-beam, can be mopped up with collimators.

Spikes look common. Fast diagnostics (60 Hz fast time plots) are crucial.


Definite orbit control short comings. Clear that properly optimized orbit (position and angle) though the detector is important. Things like:

Beam loss

Worry about radiation field in tracking volume, in collision hall - concerns include radiation damage to silicon, and effect of radiation field on electronics. Note that the experiments didn't properly vet for radiation hardness. Typical SEU effects: lock-up necessitating power cycles.

Worries include:


Defintely an issue. Locally bad vacuum clearly can cause problems. E.g. F sector graphite and halo induced heating.




Clear that experiments have done well to

  1. Protect themselves
  2. Provide additional diagnostics

Other measures include appropriate interlocks (if roman pots not where they should be - switch off silicon)

Feed machine with a lot of data including transverse beam position. RT calulation of shape of luminous region - including hour glass.


Very important to build up relationship with IPs. Cross-domain problem solving. (Note existence of fixed target culture at Fermilab before the Tevatron.)


CDF pulls in a lot of stuff. BLMs, RF (klystrons, modulators, abort gap, vacuum, separators). Active participation in accelerator monitoring. Try to avoid knock-on in sudden MP events.

Seismometers. Quads - traffic vibrations.




c/o Jim Patrick...

Some talks by Rick Tesarek on losses and monitoring at CDF are:
Latest version: http://ncdf67.fnal.gov/~tesarek/halo/BeamMonitors.pdf
Earlier versions given at various LHC radiation monitoring workshops:
http://indico.cern.ch/conferenceDisplay.py?confId=a044378 (near bottom)
http://indico.cern.ch/conferenceDisplay.py?confId=a044378 (towards bottom)


Links from Rick Tesarek




Notes - Mike Lamont December 2007. Thanks to Jerry Annala, Dean Still, Jim Patrick, Rick Tesarek.