E907 Beam MC 5 and 6
The beamline enclosure MC5 is upstream of the Meson Hall building, MC6 is within the building. The basic idea of the beam is to allow both 120 GeV/c running with the Main Injector primary beam and to be able to target the primary beam and produce a momentum selected secondary beam. To accomplish this task the proposed beamline bends the primary beam through a "dog leg" using 4 dipole magnets. The first two dipoles bend the beam onto the primary target in MC5. Two additional dipoles bend the beam back onto the beam center line for Meson Center. When running in 120 GeV/c mode, the target is out and the beam is steered through the "dog leg". Between the two dipoles downstream of the primary target, four quadrupoles focus the beam onto a jaw collimator whose vertical aperture can be varied. The strength of the downstream dipoles determines the central momentum value of the beam. The "momentum bite" of the beam, the dp/p, is set by the jaw aperture size. After this jaw collimator, the beam is refocused onto the E907 experimental target by three additional quadrupoles.
The quad focussing scheme utilizes existing quadrupoles in the beam line. The quads are doubled up to provide the necessary focussing gradiants given the length. The beamline is modeled in Transport, a beamline design tool. The input "deck" provides the beamline configuration, the strength of the magnets, etc. A copy of the deck used to model the MC 5 and 6 beamline elements is provided here, the output here. The output of Transport was used to tune the beam at 115 GeV/c. The focussing tune is shown below.
The beam spot size can also be calculated. The spot fits through the various apertures of the magnets for the beamline as shown below in plot also produced by Transport output. The apertures of the magnets is shown as dotted lines. The two rectangular apertures indicate two different types of dipoles available for the beamline.
The latest transport deck (from D.Carey) may be found here and the output here.
EPH, 06/11/01