Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 1 PEP-II Interaction Region Upgrade M. Sullivan for the Super-B Factory Workshop Hawaii January 19-22, 2004

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 2 Outline Present design Upgrade parameters Why upgrade the IR 1 st IR Upgrade Attempt Beta functions Crossing angle Present IR Upgrade Study SR fans and power SR backgrounds Summary

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 3 Machine Parameters that are Important for the IR PEP-IIKEKB LER energy3.13.5GeV HER energy9.08.0GeV LER current A HER current A  y * mm  x * 25 60cm X emittance5020nm-rad Estimated  y * 52.2  m Bunch spacing m Number of bunches Collision anglehead-on  11mrads Beam pipe radius2.51.5cm Luminosity7.2   cm  sec 

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 4

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 5 PEP-II Proposed Upgrade Plans Now Projected Upgrade LER energy GeV HER energy GeV LER current A HER current A  y * mm  x * cm X emittance nm-rad Estimated  y *  m Bunch spacing m Number of bunches Collision anglehead-on head-on head-onmrads Beam pipe radius cm Luminosity6.6    cm  sec 

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 6  Lower the vertical beta function to 6-7 mm  Keep maximum betas low  Lower the beam-beam effect from the parasitic crossings  Possibly get enough separation to allow filling every RF bucket Why Upgrade (Initial motivations)

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 7  Replace the last 20 cm of each B1 magnet with quadrupole field (50% stronger than QD1 field)  Introduce a crossing angle to recover beam trajectories so we don’t have to redesign or move any magnets. We need a certain amount of separation at QF2.  Relatively easy change to make  Moves the focusing closer to the IP Initial upgrade attempt

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 8

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 9 Beta functions Low-energy beam Present design beta x* (cm)beta y*(mm)beta x maxbeta y max With Initial Attempt High-energy beam Present design With Initial Attempt

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 10  Crossing angle Early last year, Ohmi-san from KEK announced that his beam- beam simulation code indicated a rapid luminosity degradation as a function of increasing crossing angle. Last summer, Yunhai Cai at SLAC confirmed Ohmi’s beam-beam result. The effect is most pronounced for very high tune shifts (~0.1).  Parasitic crossings The introduction of a crossing angle increases the beam separation at the parasitic crossings which would lower the effect we presently see from parasitic crossings in by2 bunch patterns. Lowering  y * also increases parasitic crossing effects since the  y at the PC is larger. Crossing angle and parasitic crossings

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 11 Plot of luminosity degradation as a function of increasing crossing angle (courtesy of Yunhai Cai)

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 12 LER PC tune shifts vs  /2 for different  y * normalized to the IP tune shift for  l (bunch length) = 9 and 7 mm HER PC tune shifts vs  /2 for different  y * normalized to the IP tune shift for  l = 9 and 7 mm The tune shift from the first parasitic crossing normalized to the main collision tune shift as a function of crossing angle and plotted for various  y * values for PEP-II (courtesy of Marica Biagini)

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 13  Keep head-on collisions  Increase the beam separation at the 1 st parasitic collision as much as possible  Allow for 6-7 mm  y *  Do not change QF2 septum magnet Present Working Design Constraints

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 14  Stronger B1 magnet to increase separation at 1 st parasitic crossing 20% stronger first 5 slices (first 12.5 cm with the weakest field and the largest lever arm)  Slightly increase the beam energy asymmetry 9.1 x 3.08 GeV  Stronger, closer QD1 magnets 30% stronger slices for 1 st 5 slices Move radial ion pump behind B1 to behind QD1 Put higher strength focusing in present pump place Minimal hardware change Higher strength material has higher temperature coefficient Present Working Design

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 15 Modified Head-on design

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 16 Orbit comparison with upgrade and present design Work in progress 1 st horizontal corrector 1 st vertical corrector +z side LER beam

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 17 +z side HER beam 1 st horizontal corrector 1 st vertical corrector Work in progress

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 18  Need to correct the position and angle in the x and y orbit on the +Z and –Z sides for each beam (8 orbits in total – two constraints for each orbit)  Too many variables for 8 total correctors  Allow adjusting the vertical collision point  Allow adjusting the horizontal collision angle  Allow the new sections of QD1 to have a variable offset (variable bending – but it affects both beams)  Allow (small) beam energy adjustments as long as we are still on the 4S resonance Steps toward a new design

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 19 Beta functions (revisited) Low-energy beam Present design  x* (cm)  y* (mm)  x max (m)  y max (m) With upgrade # With upgrade # High-energy beam Present design With upgrade # With upgrade #

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 20  The proposed high beam currents (4.5A LER and 2A HER) will generate a large amount of SR in the IR  The HER vacuum elements were designed for 2A so the HER parts should be OK. There is some question about the High-Power Downstream Dump that absorbs the HER B1 SR power  There are 2 vacuum chambers that see the LER SR power that need to be looked at more closely  The LER downstream crotch chamber that sees B1 radiation  The upstream LER SR mask for the Be beam pipe. It sees upstream QD1 radiation SR fans and power

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 21

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 22

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 23  The present power levels on the multi-tipped LER SR mask are about 30 W/mm at 2.1A beam current. This goes to 50 W/mm at 3.6A and 65 W/mm for 4.5 A of LER beam. This mask is under study. Presently it looks like this chamber may just work at 3.6 A but that it will need to be rebuilt for a 4.5 A beam  The crotch chamber design allowed for overlapping B1 radiation fans. This can only happen when the detector solenoid is off. We never intend to run high current beams with the solenoid off so we have some margin here. SR fans and power (cont.)

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 24  The present LER SR mask (multi-tipped mask) does? (not completely checked yet) an adequate job of shielding the detector if we upgrade the B1 and QD1 magnets. We are trying to maintain the beam orbits such that the present design will work with minor modifications.  In any case, the extra power from the higher current LER beam means that SR backgrounds have to be studied in more detail  The very high beam current of the LER means that we need to check to make sure that back-scattered photons from the downstream crotch chamber do not strike the detector beam pipe SR backgrounds

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 25  The initial upgrade proposal replaced the last 4 slices of the B1 magnets with quadrupole field. This allows for lower beta y* values with a smaller increase in the maximum beta y.  The replacement of the B1 slices with quad field introduces a ± 3.3 mrad crossing angle at the IP which reduces the beam-beam effect at the 1 st parasitic crossing. However, recent beam-beam simulations indicate a luminosity reduction for beams with a crossing angle.  An alternative proposal currently under study is to strengthen the IP end of QD1 effectively moving the center of the magnet closer to the IP. At the same time, increase the beam separation at the 1 st parasitic crossing by increasing the strength of the initial B1 slices. This maintains the PEP-II head-on collision.  The high beam currents of the upgrade plans generate significant SR power in the IR that must be handled  SR backgrounds look like they can be controlled but have not yet been thoroughly studied Summary