Interaction Region The Interaction Region M Sullivan 5

Interaction Region The Interaction Region M. Sullivan 5 th Super. B Workshop Paris May 9 -11, 2007 1 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Outline • Design Issues • IR Design • Toward an improved design • Summary 2 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Detector Considerations • Reasonable angular acceptance – ± 300 mrad • Small radius beam pipe – 10 mm radius • Thin beam pipe • SR backgrounds – Rates comparable to PEP-II • Few hits per crossing on Be beam pipe • Little or no hits on nearby beam pipes 3 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Detector Considerations (2) • BGB backgrounds – Keep nearby upstream bending to a minimum – Suggest upstream bending further away from the detector (>10 m) to minimize the BGB integral – Low vacuum pressure upstream of the detector 4 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Detector Considerations (3) • Luminosity backgrounds – Beam lifetimes – Radiative bhabhas – Beam-beam • Local HOM power – Small diameter beam pipes trap higher frequencies – Always get modes when two pipes merge to one 5 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Accelerator parameters Energy (Ge. V) Current (A) No. bunches Bunch spacing (m) Beat x* (mm) Beta y* (mm) Emittance x (nm-rad) Emittance y (pm-rad) Full crossing angle (mrad) LER 4. 0 3. 95 HER 7. 0 2. 17 3466 0. 63 20 0. 2 1. 6 4 34 These parameters constrain or define the IR design 6 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Summary of Present Design • Crossing angle of ± 17 mrad • Beam pipe diameter of 20 mm at the end of QD 0 for both beams (same size as IP pipe) • This leaves enough room (~10 mm) to place a permanent magnet quadrupole and get the required strength (Using Br = 14 k. G) • We have placed small bending magnets between QD 0 and QF 1 on the incoming beam lines to redirect the QF 1 SR • The septum QF 1 magnets for the outgoing beams are tilted in order to let the strong SR fans escape • The outgoing beams B 0 magnets are a C shape design in order to allow the strong SR fans to escape 7 5 th Super. B Workshop May 9 -11, 2007

Interaction Region IR design parameters 8 L* QD 0 H B 00 L B 00 H QF 1 L QF 1 H B 0 L B 0 H Length 0. 30 m 0. 46 m 0. 29 m 0. 40 m 2. 0 m QD 0 offset 6. 00 mm 7. 50 mm Starts at 0. 0 0. 30 m 0. 76 m -1. 05 m ± 1. 45 m ± 2. 05 m Strength -820. 6 k. G/m -2. 2 k. G 1. 5 k. G 293. 2 k. G/m 589. 1 k. G/m 0. 3 k. G 0. 526 k. G Comments Drift Both HER and LER HER only Incoming LER only Incoming HER only LER only (sign? ) HER only (sign? ) Incoming HER Incoming LER 5 th Super. B Workshop May 9 -11, 2007

Interaction Region SR Power Numbers The design (G 3) has a total SR power comparable to PEP-II SR power in QD 0 (k. W) for beam currents of 1. 44 A HER and 2. 5 A LER No QD 0 offsets Ver. F 1 Ver. G 3 PEP-II 3 A on 1. 8 A Incoming HER 41 9 4 49 Incoming LER 28 1 1 16 Outgoing HER 41 152 93 49 Outgoing LER 28 67 55 16 138 230 153 130 Total 9 5 th Super. B Workshop May 9 -11, 2007

Interaction Region 10 5 th Super. B Workshop May 9 -11, 2007

Interaction Region LER SR fans 11 5 th Super. B Workshop May 9 -11, 2007

Interaction Region HER SR fans 12 5 th Super. B Workshop May 9 -11, 2007

Interaction Region ± 1 meter 13 5 th Super. B Workshop May 9 -11, 2007

Interaction Region SR fans 14 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Some SR background details • We are using a gaussian beam distribution with a second wider and lower gaussian simulating the “beam tails” • The beam distribution parameters are the same as the ones used for PEP-II • We allow particles out to 10 in x and 35 in y to generate SR • Unlike in PEP-II the SR backgrounds in the Super. B are dominated by the particle distribution at large beam sigma, so we are more sensitive to the exact particle distribution out there 15 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Radiative Bhabhas • The outgoing beams are still significantly bent as they go through QD 0 • Therefore the off-energy beam particles from radiative bhabhas will get swept out • Knowing this, we will have to build in shielding for the detector 16 5 th Super. B Workshop May 9 -11, 2007

Interaction Region HER radiative bhabhas 17 5 th Super. B Workshop May 9 -11, 2007

Interaction Region LER radiative bhabhas 18 5 th Super. B Workshop May 9 -11, 2007

Interaction Region How to improve the design • The best improvement would be to reduce the radiative bhabha background – Note that there is only a small gain in beam separation from the strong outgoing bending because one has to allow the outgoing SR to escape (see slide 14) – The only gain comes from the BSC moving away from the septum 19 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Attempts to improve the design • Three possibilities so far looked at – Reduce the strength of the shared element • Difficult to control beta functions (Can’t let the beta functions get too big) – Try a high strength but very short and close to the IP shared element (minimal off-axis trajectories) • Need a VERY high strength field to control beta functions • High field still bends a beam even with a small off-axis traj. – Eliminate the shared element • Wants a maximum crossing angle (± 24 mrads? ) • Can start one focusing magnet for one of the beams first and then follow with the focusing magnet for the other beam as soon as possible • Still need to control beta functions • Just got started on this option: no conclusion yet 20 5 th Super. B Workshop May 9 -11, 2007

Interaction Region More designs • Other possibilities thought about – A longer, weaker shared element • End up with more bending at the outboard end • Wants a minimal crossing angle • Difficult to control beta functions – Asymmetric IR (more like ILC? ) • Well controlled incoming beta functions • Outgoing beta functions allowed to get bigger • OK for ILC—not so good for storage rings 21 5 th Super. B Workshop May 9 -11, 2007

Interaction Region Summary • We have an IR design that has acceptable SR backgrounds with a crossing angle of ± 17 mrad an energy asymmetry of 7 x 4 • The BGB and coulomb scattered beam particles as a background need to be calculated and controlled (been done? ) • Radiative bhabha backgrounds are still high due to the strong bending of the outgoing beams • The total SR power generated by the IR is high for the same reason. This can cause emittance growth. Especially vertical emittance growth since this is in a coupled region. • A through exploration of parameter space is needed to find the best IR design 22 5 th Super. B Workshop May 9 -11, 2007