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Figure 4

magnet geometry

Cross section (XY) at the end of the second dipole overlaid with tracks from the last 50cm of the magnet

Here we show the cross section of the downstream end of the dipole magnet superimposed with the projection of the particle tracks near the dipole end. Of the few tracks shown here which overlap the superconductor, some are actually produced as backscatter from the collimator rather than as direct scattering from within the dipole itself. A reentrant collimator design would help to reduce such coil energy deposition due to the collimator. This same effect can be seen with Figure 9. Figure 9 also shows an end cross section but with an added shield that is used to stop synchrotron radiation photons generated from the decay electrons.

Contact Info

Brookhaven National Laboratory
Superconducting Magnet Division
Bldg. 902 - P.O. Box 5000
Upton, NY 11973-5000

Ph.: (631) 344-3231
Fax: (631) 344-2190
email: parker@bnl.gov

MARS13 Tracking: Some Screen Snapshots

  1. Plan view (XZ) of toy model geometry showing half cell with back-to-back 5 m dipoles, collimator and quadrupole magnet. The design orbit starts with 300 mrad inclination and ends up parallel to the Z-axis at X=0, Z=1000 cm. This coordinate system convention simplifies viewing tracks near the end of the second dipole. Note 1000 muon decays were generated for this and subsequent plots.
  2. Detail near the end of the second dipole showing decay electrons exiting the second dipole and hitting the collimator and quadrupole magnet.
  3. Close up near the end of the second dipole showing decay electron tracks, synchrotron radiation photons and low energy showers from particles hitting the inner vacuum beam pipe edge. Note very few tracks penetrate beyond the indicated yoke fiducial area. Contrast this plot with Figure 5, which covers the same region but has electron plotting turned off.
  4. Cross section (XY) at the end of the second dipole overlaid with tracks from the last 50 cm of the magnet. Some tracks that appear to cross superconductor are actually backward going albedo particles from the collimator.
  5. Repeat of Figure 3 but with electron plotting turned off. By not plotting the primary particles it is easier to spot tracks from showers initiated in the vacuum beam pipe.
  6. Cross section of the toy model warm quadrupole overlaid by particle tracks along its length. For the toy model the quadrupole coils are not defined but it is clear that there are tracks which could hit an unprotected coil. If these coils are not superconducting such hits may not be too much of a concern. For normal conducting coils the 1 T pole tip field assumed for the toy magnet is probably close to the practical limit.
  7. Extreme close up near the inner vacuum beam pipe edge. With large magnification it is possible to make out individual decay electron tracks. A few of these electrons are in the reversed field region and are starting to be bent back away from the wall. Other low energy electrons hit the wall and start showers that are nearly contained in the yoke fiducial volume. The majority of decay electron tracks are making a short cut across the low field region due to the dipoles saggita.
  8. Same as Figure 1 except that we have added a shield to contain the synchrotron radiation photons generated by the decay electrons.
  9. Same plot as Figure 4 except that we have added a shield to contain the synchrotron radiation photons generated by the decay electrons. Also the tracks are taken from a longer Z-section. Note that the shield shown here is overly thick to completely stop synchrotron radiation. A much thinner shield is expected to work just fine. With the shield the beam pipe can be made smaller horizontally. There would then be space for distributed vacuum pumping outside the shield and yoke mass could then be reduced on the ring outside.