Discussion of e+/e- tertiary beams in Hall D

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: 0.0001 radiation lengths

  max power in photon beam: 4.8 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: 0.00025 radiation lengths (50 micron diamond)

  max power in photon beam: 12 W

This 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 would be the following.

• primary beam energy: 12 GeV

  max beam current: 300 nA

  radiator thickness: 0.0025 radiation lengths (500 micron diamond)

  max power in photon beam: 12 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.

  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: 4.5 W