We have developed new beamline optics for the PiBeta experiment. In order to reduce positron contamination in the pion beam, a 4mm thick carbon degrader is inserted remotely in the middle of the ASY51 dipole magnet directly in front of the FSH52 horizontal collimater which is used to define the momentum acceptance. The tradition beam optics used for the piE1 beamline has a tight horizontal focus (x' rms ~ 25 mrad) with a high divergence (~ 3 cm/%) at the FSH52 horizontal collimator located in the middle of the ASY51 dipole magnet in order to definite the momentum acceptance (see the 1997 Setup above). The beam is also essentially parallel in the vertical direction at FSH52 (i.e. it has a rms virtical divergence of less then a few mrad) with the traditional beam optics. At a momentum of 116 MeV/c, the 4mm carbon degrader causes an 24 mrad rms addition to the beam phasespace. This causes a moderate but acceptable increase in the horazontal beamsize; however, it causes a very significant increase in the vertal beamsize. The new optics takes advantage of a focus in both the horizontal and vertical planes at FSH52 which reduces the phasespace broadening effects of the carbon degrader. A significantly higher luminosity at the PiBeta target can thus be achieved which allows the pions to be stoped in a smaller region.
Below is the momentum spectrum of the pions before stopping in the target.
p = (113.5 +- 0.5) MeV/c
The PiBeta TRANSPORT and PiBeta TURTLE files I have set up for the PiBeta Experiment are available for use.
I have a Beamline Settings Excel Worksheet available to calculate DAC settings from the magnetic fields and magnetic fields from DAC settings. This also contains all the magnet parameters and formulas necessary to make these calculations and has enough notes that it should one should need no further explanation. NEW: I just added a TURTLE simulation of the FSH52 Momentum Slit Callibration to the spreadsheet.
If you want information on how to get (and a short discription on how to use) TRANSPORT, TURTLE, OPTIMA, SETPOINT, COMBI-CONTROL, and other programs see About the Available Programs