SR and Detector Backgrounds

1. SR and Detector Backgrounds M. Sullivan Mini-workshop on the MEIC design Nov 2, 2012

2. Outline • Introduction • Accelerator Parameters • Previous Synchrotron Radiation estimates • Other SR issues • Other detector backgrounds • Points of Interest • Summary

3. Introduction • Motherhood statements first • IR is one of the most important regions of a collider • Detector requirements and accelerator requirements must coexist • Usually the detector and accelerator constraints conflict • Compromises must be made on both sides without jeopardizing either side’s design goals • (I hope the following machine parameters are still accurate)

4. Table of Parameters (electrons) • Electron beam • Energy range 3-11 GeV • Beam-stay-clear 12 beam sigmas • Emittance (x/y) (5 GeV) (5.5/1.1) nm-rad • Betas • x* = 10 cm x max = 435 m • y* = 2 cm y max = 640 m • Final focus magnets • Name Z of face L (m) k G (11 GeV) • QFF1 3.5 0.5 -1.7106 -62.765 • QFF2 4.2 0.5 1.7930 65.789 • QFFL 6.7 0.5 -0.6981 -25.615

5. Table of Parameters (proton/ion) • Proton/ion beam • Energy range 20-100GeV • Beam-stay-clear 12 beam sigmas • Emittance (x/y) (60 GeV) (5.5/1.1) nm-rad • Betas • x* = 10 cm x max = 2195 m • y* = 2 cm y max = 2580 m • Final focus magnets • Name Z of face L (m) k G (60 GeV) • QFF1 7.0 1.0 -0.3576 -71.570 • QFF2 9.0 1.0 0.3192 63.884 • QFFL 11.0 1.0 -0.2000 -40.02

6. Ultra forward hadron detection Small angle hadron detection Central detector with endcaps Low-Q2 electron detection ion quads dipole Large aperture electron quads IP dipole dipole Small diameter electron quads ~50 mrad crossing Solenoid yoke + Muon Detector Solenoid yoke + Hadronic Calorimeter RICH Tracking RICH Muon Detector EM Calorimeter EM Calorimeter Hadron Calorimeter HTCC IR Design Copied from an old talk Courtesy PawelNadel-Tournski and Alex Bogacz 5 m solenoid

7. Most recent picture of the IR Q3P 100 P+ Q2P 75 Q1P cm D1P 50 25 Q3e e- 0 Q1e Q2e Q5e Q4e 0 5 10 15 Meters M. Sullivan JLAB_EP_3M_4R July 30, 2012

8. Initial SR background calculations Synchrotron radiation photons incident on various surfaces from the last 4 electron quads 38 P+ 8.5x105 2.5W 4.6x104 240 2 e- 3080 Rate per bunch incident on the surface > 10 keV Beam current = 2.32 A 2.9x1010 particles/bunch X Rate per bunch incident on the detector beam pipe assuming 1% reflection coefficient and solid angle acceptance of 4.4 % Z Electron energy = 11 GeV x/y = 1.0/0.2 nm-rad M. Sullivan July 20, 2010 F$JLAB_E_3_5M_1A

9. Other SR Issues • Local forward and back scattering rates from nearby beam pipe surfaces • The electron beam current is comparable to the B-factories and to the super B-factories • This may still NOT be very important for the MEIC • The central beam pipe is large which helps a lot • Still it needs to be checked – especially for various running conditions • The large set of running conditions for the MEIC means that several IR lattice designs need to be checked for SR backgrounds

10. More SR Issues • The MEIC detector design with a suite of very forward detectors means that we will have to trace SR fans from bend magnets to see where the power goes and how this interacts with the beam pipe design in front of these detectors • The proton/ion beam does not have this issue but it has another issue that is also a concern for the electron beam that the super B-factory designs are struggling with right now

11. Another background (neutrons) • The high current super B-factories (Superb and superKEKB) are working quite hard to identify and shield sources of neutrons • In general, these sources occur after the beam has been bent going through a dipole and this is essentially what the MEIC detector wants to do to study the very low Q2 physics region • The low angle detectors for these events will become neutron source points from the shower development in these detectors as well as other regions of the beam line on either side of the detector • The super B-factories are simulating the beam line (full GEANT4) out to at least 20 m from the IP This topic is mentioned in the most recent MEIC report

12. Other backgrounds (Beam-beam) • Beam-beam interactions do affect the accelerator performance and preliminary studies have been made in this regard • But beam-beam effects also produce non-gaussian tails in the transverse beam dimensions and these tails can create backgrounds • Tails are not studied much in accelerators except for lifetime estimate calculations

13. Possible points of interest • Machine flexibility (mentioned in the MEIC report) • First is the energy range of each beam together with possible extreme combinations • Are there any lattice changes just outside of the detector region? • What are the machine parameters of these different cases? • How does the machine change? • What are the performance requirements for the physics These have already been thought about at some level

14. Points of interest (2) • More on machine flexibility • What possible upgrades are being envisioned • From the accelerator • From the detector • From the physics • Initial startup scenerios • Machine commissioning time without the detector • Vacuum scrubbing for the electron beam

15. POI (3) HERA • HERA experience • (I believe this has been mentioned before) • Is there anything we can learn from HERA? • Physics range • Backgrounds uncovered and fixed • Accelerator experience • Energy range is very much higher than MEIC • 28 GeV e- on 920 GeV P+

16. POI (4) Crab Cavities • The crab cavities as a possible upgrade seem to be located fairly close to the IP • These cavities are sensitive to SR fans of radiation and a careful study for these cavities is called for • Special masking may be needed • PEP-II experience is that SR from the last bend magnet affected the first RF cavity in the RF straights • The cavities may be in or near the low angle detector areas • Need to keep in touch with accelerator folks

17. POI (5) Detector Solenoid • The effect of the solenoid on the beams will need to be studied in detail • Solutions to accelerator problems created by the detector field may affect the detector design and/or solid angle acceptance • Skew quads, compensating solenoids, etc. are some examples • Close integration with both teams will be needed

18. Suggestions • Perhaps we can make a list of things that need further study • Then set some priorities (there are never enough people to do everything you would like to do) • Also identify which areas need close cooperation with accelerator and detector people

19. Summary • The MEIC design is a good starting point • The design looks solid and further study should reinforce this • Effort now is to look for weak points or overlooked issues • Many times these studies can uncover something that forces a design change – the sooner these are found the better

20. Conclusion We want to get to the point where we actually think this thing can be builtand it has a good chance of working!