Negative bending   updated Feb. 2, 2010  ©D. Carrigan carrigan@fnal.gov (subject line must be sensible)

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Negative Particle Planar and Axial Channeling and Channeling Collimation is now available as a preprint Fermilab-conf-09-618-AD.

Negative particle deflection for accelerator collimation?

Recently I have been wondering if bent crystal channeling could have any implication for antiproton collimation in colliders. The current installation in the Tevatron will do some interesting work on proton collimation. There is still the other half of the problem. The useful book by Biryukov, Chesnokov, and Kotov (Springer, 1997) contains a section on negative particle bending on p. 124 (3.10.2).

There is some experimental information on negative bending. Bak et al. did studies of negative particle axial deflection at 10 - 12 Gev with pions
[S. Anderson et al., Nucl. Phys. B167, 1 (81), J. Bak, et al., Nucl Phys. A389, 533(82)]. They show that there can be some deflection for axial bending out to on the order of several critical angles. They observe  that there is  little negative planar deflection at their energies. As far as I can tell our Fermilab team never published any information on negative particle deflection.








More recently Greenenko and Shul’ga [NIM B90, 179 (94)] studied negative deflection with a simulation program that had “angular momentum” incorporated in it. At 400 GeV they saw deflection at somewhat the same scale as the Schiott simulation. Figure 1 shows the results for positive particles for L = 1 cm (left) and L= 3 cm. Figure 2 shows the distributions for negative particles. The ticks on the x axis are 0 and 0.3 mrad.
CERN negative deflection
Green 1
From the standpoint of simulation Schiott discussed negative particle deflection in his chapter in Carrigan and Ellison (Relativistic Channeling, NATO 165, Plenum (87)). He used BINCOL and showed that for 10 GeV particles one could get the behavior Bak et al. had seen. Schiott did show some rather interesting rosettes for negative particle behavior in bent lattices. Green fig 2
Rosette
In thinking about the possibility of negative particle deflection in the early eighties I tended to discount it because I thought in terms of discrete angular deflections in the spirit of an external beam. The situation is different for collimation where the important thing is to give the particles a kick, any kick, provided it is somewhat more than the multiple scattering. Multiple pass channeling also helps. High energy may also help.

My question is, could the Biryukov/Mokhov/Drozhdin collimation simulation programs be run for negative particles, namely 1 TeV antiprotons? One could try to find ways to optimize the crystal length and bend.

Clearly, this is not something with relevance to LHC. They have the advantage of protons for both beams.