SR Background Update for JLEIC M. Sullivan March 1-2, 2018

Outline Introduction New IR magnet design 10 GeV masking Engineering Input New IR magnet design New electron beam lattice 10 GeV masking What the mask stops 12 sigma X and 15 sigma Y 8 sigma X and 10 sigma Y Masking material(s) 3/1/18 SR Update

Outline (2) Central Beam pipe SR on the cold bore magnets Suggested design? SR on the cold bore magnets Upstream side Downstream side With and without an extra mask Further Issues Summary and Conclusions 3/1/18 SR Update

Introduction It has been a while since the SR background was studied There have been changes to the IR magnets to make them more realistic Many thanks go to R. Rajput-Ghoshal, M. Wiseman and others for taking a first look at how these magnets might be constructed (slides) New central beam pipe design from C. Hyde 3/1/18 SR Update

Initial Engineering Work The final focus magnets for the electron beam have been redesigned They are all super-conducting Cold bore vacuum chambers (never been done for a high current electron beam) Super-conducting allows the magnet strengths to increase and the lengths to be shorter First look at cross-talk between magnets appears under control Cryostat sizes and design still under study 3/1/18 SR Update

Engineering (2) L* has been increased in order to get more space between the two beamlines Some of this comes from making the magnets shorter Magnet Grad. (T/m) Length (m) Z Face (m) Q1 up -37.26308052 0.6 2.96 Q2 up 42.51112873 4.16 Q3 up -29.39050179 6.61 Q1 dn -44.78044515 2.20 Q2 dn 43.46563611 3.40 Q3 dn -13.62947239 4.60 3/1/18 SR Update

BSC Envelope Started with a more or less regular Beam-Stay-Clear envelope for tracking SR photons 12 sigma X and 15 sigma Y Found that the mask at 1 m upstream must be very tight to protect the central chamber from direct SR hits for a 10 GeV beam (Not very different from before) Also found that the cold bore beam pipe gets hit by SR (check this) 3/1/18 SR Update

Regular Beam Envelope X view 3/1/18 SR Update

Regular Beam Envelope Y view 3/1/18 SR Update

Electron beam lifetime Vaisily mentioned that the stored beam lifetime will be artificially shortened in order to keep the electron polarization above 80% The easiest way to do this is to collimate the beam at some location far from the IR The beam tails are scrapped off and the lifetime of the beam gets shorter The beam tail distribution used in the SR simulation aims for a 1 hr lifetime at about 15 sigma X 3/1/18 SR Update

Lifetime (2) In order to maintain the polarization of the beam – the lifetime will be reduced to about 4 min for the 10 GeV beam (from Fanglei) 3/1/18 SR Update

Smaller Beam Envelope X view 3/1/18 SR Update

Smaller Beam Envelope Y view 3/1/18 SR Update

Results from the smaller envelope No radiation directly strikes the cold bore We will have to worry about backscatter photons Also upstream forward scattering to the cold bores The central chamber now has no direct hits from SR Need to check tip scattering Also backscattering (see below) 3/1/18 SR Update

Suggestion for a Central Beam Pipe 3/1/18 SR Update

Closer view 3/1/18 SR Update

Detector angles 3/1/18 SR Update

Downstream cold bore The downstream magnets start to intercept SR from the upstream FF at about 4 m from the IP If we introduce a downstream mask we can shadow the downstream cold bore to about 6-7 m Also have to look at tip scattering from the new mask 3/1/18 SR Update

Added mask downstream 3/1/18 SR Update

Summary and Conclusions Many new issues have cropped up now that we have some engineering help This is a great step forward More things to study Now the fun begins! 3/1/18 SR Update