Interaction Region Design Options e+e- Factories Workshop for a Super-B Factory M. Sullivan for the International Committee for Future Accelerators e+e- Factories Workshop October 13-16, 2003 1

Outline General B-factory parameters and constraints Present B-factory IRs Super B-factory IRs Summary 2

Some Issues and Constraints There is always some local synchrotron radiation from bending magnets PEP-II generates a large amount of local SR in order to make head-on collisions. KEKB also generates a lot of SR even though they have a large crossing angle because they designed for on-axis incoming beams. This shifts all of the bending SR to the downstream side and consequently increases the power levels of the fans striking the nearby vacuum chambers. 3

Constraints... The Q1 magnet is always going to be shared At least one beam is always bent in this magnet generating SR bending fans. The Q2 magnet must be a septum magnet If this magnet is shared by both beams then one loses most of the beam separation because it is x-focusing. Making this magnet a septum magnet forces a certain amount of beam separation at the face of the Q2 magnet (about 100 mm between beam center lines). 4

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Detector requirements Maximum solid angle Try to keep all accelerator components far enough away from the IP to maximize the detector acceptance This conflicts with accelerator requirements to minimize the spot size by pushing in the final focus magnets Adequate shielding from local SR The collision beam pipe (usually Be) must be shielded from locally generated SR and lost beam particles at least well enough to avoid swamping the detectors. 7

More detector requirements Minimum amount of material in the detector beampipe This conflicts with having enough SR shielding (usually a thin coating of Au) to keep detector occupancy at acceptable levels Minimum radius for the beam pipe This must be balanced with the requested thinness of the beam pipe. The smaller the beam pipe the more power it must be able to handle (kW). 8

Still more detector requirements Large high-field solenoid This forces the final shared magnet (Q1) to be either permanent magnet or super-conducting (maybe also Q2) Adequate shielding from beam backgrounds Collimators and shield walls are needed to protect the detector from backgrounds generated around the ring Low pressure vacuum system near the IP This minimizes lost beam particles generated near the IP that can not be collimated out 9

Machine Parameters that are Important for the IR PEP-II KEKB LER energy 3.1 3.5 GeV HER energy 9.0 8.0 GeV LER current 1.55 1.38 A HER current 1.18 1.05 A  y* 12.5 6.5 mm x* 25 60 cm X emittance 50 20 nm-rad Estimated sy* 5 2.2 mm Bunch spacing 1.89 2.4 m Number of bunches 1034 1284 Collision angle head-on 11 mrads Beam pipe radius 2.5 2.0 cm Luminosity 6.61033 10.61033 cm-2 sec-1 10

Beam Parameters for a PEP-III 11036 Luminosity Accelerator 11

PEP-III Super B Now Projected Upgrade Super B LER energy 3.1 3.1 3.1? 3.5 GeV HER energy 9.0 9.0 9.0? 8.0 GeV LER current 1.8 3.6 4.5 22.2 A HER current 1.0 1.8 2.0 9.7 A y* 12.5 8.5 6.5 1.5 mm x* 28 28 28 15 cm X emittance 50 40 40 70 nm-rad Estimated sy* 4.9 3.6 2.7 1.7 mm Bunch spacing 1.89 ~1.5 1.26 0.63 m Number of bunches 1034 1500 1700 3400 Collision angle head-on head-on 03.25 12 mrads Beam pipe radius 2.5 2.5 2.5 1.5-2.0? cm Luminosity 6.61033 1.81034 3.31034 11036 cm-2 sec-1 12

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2 cm radius and 1 cm radius beam pipes The 1 cm radius beam pipe intercepts about 5 kW of power from the LER and nearly the same amount of power from the HER 19

Further optimization possibilities Lower the amount of upstream SR at the expense of increasing the downstream SR (more like KEKB) Offset the Q1 magnets as shown in the drawing (B. Parker’s suggestion) ….. 20

KEKB Upgrade Plans Now Upgrades SuperKEKB LER energy 3.5 3.5 3.5 GeV HER energy 8.0 8.0 8.0 GeV LER current 1.38 2.0 9.4 A HER current 1.05 1.1 4.1 A y* 6.0 6.0 3.0 mm x* 58 58 15 cm X emittance 20 20 33 nm-rad Estimated sy* 2.2 2.2 2 mm Bunch spacing 2.4 2.4 0.6 m Number of bunches 1284 1284 5018 Collision angle 11 crab 15 (crab) mrads Beam pipe radius 2.0 1.5 1-2 cm Luminosity 1.061034 2-31034 2-61035 cm-2 sec-1 21

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Summary The Interaction Region of a B-Factory has many conflicting requirements. The very high beam currents challenge the IR design in the areas of backgrounds, HOM power, SR power, … The trick is to achieve a kind of best balance between these requirements that maximizes the luminosity for a given B-factory design. 23