Discussion of e+/e- tertiary beams in Hall D
From GlueXWiki
- Running conditions of 2-photon experiment in Hall B, based on numbers in this talk by Robert Bennett
- primary beam energy: 5.5 GeV
- max beam current: 120 nA
- radiator thickness: 0.009 radiation lengths
- max power in photon beam: 5.9 W
- For comparison, here are the maximum design numbers for polarized running with GlueX. Note that these rates are a bit higher than the standard high-luminosity running conditions, but these are the upper limits that we simulated when we designed the collimator cave shielding and beam line instrumentation.
- primary beam energy: 12 GeV
- max beam current: 3 μA
- radiator thickness: 0.00014 radiation lengths (20 micron diamond)
- max power in photon beam: 5.1 W
- Imagine just taking the running conditions from the TPE experiment in Hall B and replicate them in Hall D, sticking as close as possible to the GlueX photon beam configuration.
- primary beam energy: 12 GeV
- max beam current: 3 μA
- radiator thickness: 0.00036 radiation lengths (50 micron diamond)
- max power in photon beam: 13 W
- The radiator thickness was increased just enough to get the same photon beam intensity as the Hall B experiment. Notice that the total photon beam is only a factor 2.5 higher absorbed dose in the collimator cave than expected for high-luminosity running in GlueX. A more conservative configuration with the same photon beam power might be the following, with the same photon beam intensity.
- primary beam energy: 12 GeV
- max beam current: 300 nA
- radiator thickness: 0.0036 radiation lengths (500 micron diamond)
- max power in photon beam: 13 W
- Another idea to think about: O(m/E) precollimation of photon beam at exit from tagger hall would give factor 2.7 reduction in beam power, also harden the spectrum. A 1m/E collimator @ 30m (radiator - tagger hall exit) has diameter 2.6mm which is feasible in terms of alignment and beam focal spot size. Under these conditions, the following would apply.
- primary beam energy: 12 GeV
- max beam current: 300 nA
- radiator thickness: 0.0025 radiation lengths (500 micron diamond)
- max power in photon beam: 4.8 W
Now one is fully within the limits of the beamline design for GlueX, in terms of photon beam power being incident at the collimator cave. One might even get comparable reduction by simply taking the primary collimator out of the collimator cave and installing it at the exit from the tagger hall. In that case, the active collimator could also be used for active stabilization of the photon beam.
