1. Some of the Points Raised During my JLAB Visit
M. Sullivan
June 5, 2015

2. Compton Polarimeter for e- Beam
Polarimeter x-ray backgrounds
Suggest putting a soft bend magnet inside each of the bend magnets on either side of the Compton IR
Vasiliy or Fanglei will check
The needed bend angle is about 10mm/4m =~2.5 mrad. If the B field can be 1/3 of the main bend (2.224 kG for a 5 GeV beam) then L needs to be 0.56 m. This should lower the critical energy by 1/3 and reduce the power incident on the window of the beam pipe.
Extend the chicane about 3m overall

3. Injection Issues Injection background issues
The size of the beam pipe in the detector needs to be carefully studied with injection orbits
Ideally one wants the BSC in the detector area to be the largest in the entire ring (15 radius for X and 15 fully coupled s for Y)
This may not be possible with the given crossing angle at all electron beam energies
Hopefully this is true for up to ~7 GeV beam energy
For higher beam energies (larger ring emittance) one may have to go to larger * values or possibly more flat beams to keep the beam size in the FF magnets OK

4. Another Injection topic
Coast and fill vs Continuous top up
Coast and fill is a good starting point but trickle charge (continuous top up) is preferred for improved accelerator performance
Tune is constant
Luminosity can be more easily tuned
PEP-II saw a 40% increase in integrated luminosity
Detector backgrounds may be lower
Integrated detector radiation dose should be lower

5. Detector field
Some concern about the fringe field of the detector and how it affects the beam orbit
The ion beam will be most affected
Also concerns about the final focus elements of the electron beam which are in the end cap region of the detector
How to make these FF elements work with either a close to saturated iron endcap or a double solenoid end field
Non-uniform compensation
Fringe field introducing octupole term in Fe face of inner quad

6. Central detector beam pipe
HOM power from e- beam traveling up ion beam pipe from shared central chamber
How much? (Sullivan will try to get an estimate)
Where will it go?
Inner radius between 2-3 cm (prefer 2.5 cm)
Flat beam pipe?
Possibly smaller radius in Y
2 cm in Y by 3 cm in X radius
Make sure SR from e- does not go into ion beam pipe

7. Other IR beam pipes
Need to get a first cut at the design of the beam pipes that attach to the central beam pipe
There are 4 other pipes
What does the detector group need?
Hyde has started on this
Especially WRT very low angle detectors
Inside the vacuum or outside the vacuum?
Where can pumps be placed?
What is the vacuum profile? (Sullivan)
PEP-II had a relatively high vacuum at the IP (10 nTorr) due to an inability to get a local pump close enough

8. Beam-gas interactions
Probably eventually more important for the ion beam
However, e- beam has x6 more current
Also has much more outgassing from SR
This is called dynamic pressure and can increase pressure x3 even after scrubbing
May dominate backgrounds during first year of running
Study should be done assuming x10 base pressure
Collimators will be needed
Very minimum 4-6
More likely twice that
Initially, the electron beam lifetime will most likely be dominated by this effect and will limit the beam current
SuperKEKB factory assumes at least 3 months of running without the detector to “scrub” the beam pipe

9. Detector layout
Need to start laying out a picture of the detector in an interaction region hall
How much Z space is needed
Related to crane motion range
How big is the crane (tons)
On beam line detector access
One needs to be able to open the endcaps
How might this be done
Gets tricky when FF quads are inside the endcap
KEK puts nearby machine elements on rails
ILC design has long “boat” with FF quad at the end (vibration issues)
Minimize the number of detector roll-on and roll-off events
Perhaps to just once or twice?
Reproducibility

10. Summary Lots of interesting things to worry about
Need ideas and plans that can be explained in a CD1 report
If possible, and when it makes sense, suggest a writeup for how a particular problem is solved or how a procedure will solve something
Are we having fun yet?
We are certainly not there yet!