M. Sullivan Mini-workshop on the MEIC design Nov 2, 2012

 Introduction  Accelerator Parameters  Previous Synchrotron Radiation estimates  Other SR issues  Other detector backgrounds  Points of Interest  Summary

 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)

 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 ◦ NameZ of face L (m) k G (11 GeV) ◦ QFF ◦ QFF ◦ QFFL

 Proton/ion beam ◦ Energy range GeV ◦ 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 ◦ NameZ of face L (m) k G (60 GeV) ◦ QFF ◦ QFF ◦ QFFL

EM Calorimeter Hadron Calorimeter Muon Detector EM Calorimeter Solenoid yoke + Hadronic Calorimeter Solenoid yoke + Muon Detector HTCC RICH Tracking 5 m solenoid IP Ultra forward hadron detection dipole Low-Q 2 electron detection Large aperture electron quads Small diameter electron quads ion quads Small angle hadron detection dipole Central detector with endcaps ~50 mrad crossing Copied from an old talk Courtesy Pawel Nadel-Tournski and Alex Bogacz

cm Meters M. Sullivan JLAB_EP_3M_4R July 30, 2012 Q1P D1P Q1e Q2e Q3e Q4e Q5e e- P+ Q2P Q3P

x x W 38 2 Synchrotron radiation photons incident on various surfaces from the last 4 electron quads Rate per bunch incident on the surface > 10 keV Rate per bunch incident on the detector beam pipe assuming 1% reflection coefficient and solid angle acceptance of 4.4 % M. Sullivan July 20, 2010 F$JLAB_E_3_5M_1A Beam current = 2.32 A 2.9x10 10 particles/bunch X P+P+ e-e- Z Electron energy = 11 GeV  x /  y = 1.0/0.2 nm-rad

 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

 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

 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 Q 2 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

 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

 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

 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

 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+

 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

 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

 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

 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

We want to get to the point where we actually think this thing can be built and it has a good chance of working!