Real Photon Collaboration Technical Note RPC-3

March 20, 2001

(No) Soft Bend Magnet for Photon Beam

by P. Bosted


It appears that we do not need a soft bend magnet in the A-line, contrary to what was shown in the E159-E161 proposals

Calculation of Power

I assume that the first magnet that deflects the electron beam towards the dump has a gap of 7.5 cm and a central field of about 20 kG. I assume a beam energy of 48.5 GeV, which will give the highest amount of radiation. The distance to the 2 mm diameter collimator is assumed to be about 50 m. Thus we are interested in the total synchrotron radiation emitted as the electrons bends by the first 20 mircrorad (urad). The integrated field needed to bend this amount is Bdl=(2E-5)(33.356)(48.5)=0.03 kG-m. We can approximate this by a 3 kG field over a length of 0.01 m, in the fringe field of the first magnet. This gives an energy of 1.5E-8 * (48.5 GeV)**2 * (3 kG)**2 * 0.01 m = 3E-6 GeV per electron. Since the energy radiated in real photons by a 0.0007 r.l. diamond is 0.04 GeV, there is 10,000 times less power in synchrotron radiation than in real photons, so there should be negligible impact on any of the experiments. I conclude that a soft bend magnet is not needed for the Real Photon experiments.