E-rhic-ir-l mailing list

["Parker, Brett" <parker AT bnl.gov>]

Dear Bob et.al.,

 

Based upon the discussion we had yesterday at our IR working group meeting, I have updated the proton rear side layout and optics. A new summary document, dated 18/Mar/2017 is attached to this email. The essential differences between this and the previous version are described below.

 

1.       The e-ring beamline geometry and optics is unchanged. Although in the schematic figure I did adjust the green dashed path for the electrons going to the e-tagger to indicate that these particles have to pass cleanly through the electron IR magnet apertures before making it out to the tagger. I also indicated rough estimates for the longitudinal positions of the start of the e-tagger and the lumi-monitor foil.

 

2.       For the hadron beam line, as you indicated, we probably don't need (or even want) such a strong dipole immediately after the Q1PR and Q2PR quadrupoles, so I got rid of the dipole at that position and replaced it with a quadrupole, Q3PR, that has the same length to line up with the B1ER dipole on the electron beam line. Note this also means that now the common cryostat for the hadron and electron IR magnets end at the same position rather than having Q3PR extend beyond B1ER as it did in my previous solution.

 

3.       B1PR is then shifted downstream to about where you created a B2PR dipole to bring the beam back and the total bend at that location becomes -22 mrad. For a 22 mrad bend I looked around to re-using RHIC magnets and found that a 6.92 m (D5I) insertion dipole would have plenty of integrated field to make this bend even at 275 GeV/c momentum  (field about 2.9 T). Note if it is not convenient to use a recycled D5I the D5O (8.71 m) or an Arc dipole (9.45 m) would also work. We may however want to consider using a warm magnet here instead; however, it would take 15 m of dipole at 1.333 T to have the same integrated field. For this option I don't believe that there are enough warm HERAp-ring dipoles to do this (have to check) but such warm dipoles would not be that hard to design/fabricate.

 

4.       Under the assumption that we re-use a RHIC superconducting dipole for B1PR, I used another 1.11 m magnetic length for the Q4PR and Q5PR quadrupoles used to provide the beta functions for the crab cavities and then start the match back into the RHIC ring. Again if we want this to be done with warm magnets that should be possible also; in fact the HERA-p straight sections have plenty of warm quadrupoles that probably would be a suitable design option.

 

5.       Note the new proton layout is a little bit more compact so the proton crab cavities now are closer to the IP than the electron crab cavities. I still left the "worst case" longitudinal space for the crab cavities so even if we go with warm dipoles and quads we should be able to make things fit.

 

By separate email I will send along the secondary information you need to incorporate the above into your IR design code but I hope this email gives everyone a good heads up on how we are converging to a complete design for the IR rear side optics for both rings. It seems to me this this geometry meets the experimental requirements without wasting a lot of space so we should have enough freedom to match to the geometry and optics of the RHIC ring as a next step. – Brett

 

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                    Brett Parker, SMD/AM

                     Building 902A

                     Brookhaven National Laboratory

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Attachment: rr_summary_18mar2017.pdf
Description: rr_summary_18mar2017.pdf