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

2. 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

3. 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

4. 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

5. 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

6. 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
0.6
2.96
Q2 up
4.16
Q3 up
6.61
Q1 dn
2.20
Q2 dn
3.40
Q3 dn
4.60
3/1/18
SR Update

7. 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

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

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

10. 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

11. 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

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

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

14. 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

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

16. Closer view
3/1/18
SR Update

17. Detector angles
3/1/18
SR Update

18. 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

19. Added mask downstream
3/1/18
SR Update

20. 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