Future Very High Luminosity Options for PEP-II John T. Seeman For the PEP-II Team e+e- Factories Workshop October 13-16, 2003

Thanks Many people helped with the results here: –A few of them: M. Sullivan, U. Wienands, –S. Novokhatski, S. Heifets, S. Ecklund, A. Fisher, –Y. Cai, Y. Nosochkov, D. Hitlin, A. J. S. Smith, –J. Fox, D. Teytelman, Y. Yan, …

Topics Luminosity equations Lessons learned from the two B-Factories PEP-II luminosity keeping the present RF frequency 476 MHz but allowed to change IR and LER vacuum chambers. Luminosity with an RF frequency change (952 MHz) but allow a change to the IR, most ring magnets, and all vacuum systems. Power losses versus luminosity Total site power Conclusions

PEP-II e + e - Collider

PEP-II is a two ring e+e- asymmetric collider

Lessons learned from the present B-Factories Asymmetric beam energies work. Energy transparency conditions are weak. Interaction regions with asymmetry can be operated. IR backgrounds can be handled. High current RF can be operated. (1A x 2 A). Bunch-by-bunch feedbacks work (4 nsec spacing). Beam-beam tune shifts reached 0.08 (v) to 0.10 (h). Injection rates good. Continuous injection feasible! Electron Cloud Instability (ECI) ameliorated for now!

Luminosity Equation  y is the beam-beam parameter (~0.06)  I b is the bunch current (1 ma x 2 ma)  n is the number of bunches (~942)  y * is the IP vertical beta (~11 mm)  E is the beam energy (3.1 and 9 GeV)  Luminosity is about 6.11 x cm -2 s -1

New techniques of the Next Generation B-Factory Beam lifetimes will be low  continuous injection. Very low  y * (6 to 12 mm  1.5 to 3 mm). Higher tune shift (trade beam-beam lifetimes for tune shifts). Higher beam currents (x 10 or so) (Watch total power!). Higher frequency RF (more bunches). Bunch-by-bunch feedbacks at the 1 nsec scale. (Started  Fox) Very short bunch lengths (2-3 mm). High power vacuum chambers with antechambers and improved or no bellows. (Started) Reduce energy asymmetry to save wall power.

PEP-II parameters in about FY2008 with Standard Upgrades E+ = 3.1 GeV E- = 9.0 GeV I+ = 4500 mA I- = 2000 mA  y * = 6.5 mm  x * = 50 cm Crossing angle = 0 to 4 mrad (?) Beam-beam parameters = 0.10 N = 1700 bunches (every second bucket) L = 2-3 x cm -2 s -1

This talk will concentrate on power losses For the parameters in the previous slide : Losses due to synchrotron radiation are about 7.2 MW are the HER and 3 MW for the LER. The resistive wall losses for the whole ring are 56 kW for the LER and 15 kW for the HER. The cavity higher order mode losses are 14 kW for the LER and 3 kW for the HER. Total PEP-II power is, thus, about 25 MW and for the whole site 45 MW.

Advanced B Factory using PEP-II RF Frequency Keep present RF frequency = 476 MHz. Go to 8 x 3.5 GeV with 11 A x 4.8 A. HER current limited to 4.8 Amps using present vacuum chamber. New LER vacuum chambers with antechambers for higher power (x 4). LER current limited to 11 Amps to match HER beam-beam. Keep present arc magnets but add magnets to soften losses. New bunch-by-bunch feedback for 3400 bunches (every bucket) at 2 nsec spacing. (We are presently designing a feedback system for nsec spacing. [Fox, Teytelman,…]) Push  y * to 2.2 mm: need new IR (SC quadrupoles, [Parker, …])  Save on costs by adding to present RF, keeping HER/LER magnets (with some additions). Same HER vacuum system.

Advanced B Factory with 476 MHz RF Frequency E - = 8 GeV E + = 3.5 GeV I- = 4.8 A I+ = 11 A  y * = 2.2 mm  x * = 15 cm Bunch length = 2.5 mm Crossing angle = ~15. mrad Beam-beam parameters = 0.15 –(Needs some testing but 0.12 now!) N = 3450 bunches L = 5 x cm -2 s -1 Site power with linac and campus = ~120 MW.

IR for a B-Factory From M. Sullivan

Advanced B Factory with New RF Frequency Higher RF frequency provides for more bunches. Better for resistive wall losses, Touschek lifetime, single bunch instabilities, lower beam emittance, perhaps lower parasitic beam-beam effects, less peak synchrotron radiation heat stress, … Choose frequency related to linac frequency 2856 MHz: –238, 476, 714, 952, 1190, 1448, … MHz –For today we choose 952 MHz.

Advanced B Factory with 952 MHz RF Frequency E + = 8 GeV E - = 3.5 GeV I+ = 6.8 A I- = 15.5 A  y * = 1.5 mm  x * = 15 cm Bunch length = 1.8 mm Crossing angle = ~15. mrad Beam-beam parameters = 0.15 N = 6900 bunches L = 1.0 x cm -2 s -1 Site power with linac and campus = ~120 MW.

Calculation of the Total Site Power vs Luminosity and RF frequency Assume the Campus, SPEAR, Linac plus PEP-II magnets sums to 40 MW (~35 MW now). Beam power losses come from the resistive wall effect, synchrotron radiation, and higher order mode losses in the cavities and other chambers. Assume bunch lengths are fixed. Assume the number of bunches are fixed. Scale the currents linearly with the luminosity adjusting the emittance to keep the beam-beam parameters at Assume the RF power supply and RF klystron have a combined efficiency of 45% and that a klystron delivers 450 kW to each cavity.

Scaling of the power losses Luminosity ~ I beam (after correcting the beam-beam parameter with emittance changes) Resistive wall losses ~N bunches x I 2 bunch = I bunch x I total HOM losses ~I bunch x I total Number of RF cavities = total losses/(450 kW-100kW/cav losses-HOM losses/cav)  Three non-linearities!

HOM Calculation for a 476 MHz Cavity with a larger beam opening (Novokhatski)

Shintake Cavity

Further Higher Order Mode Calculations (Novokhatski)

Site Power including Linac and Campus for Two Different RF Frequencies for the Super-B-Factory 476 MHz 952 MHz (Linac, PEP-II magnets and campus power = 40 MW)

Future BF activities Planned workshops: –October 13-16, 2003 at SLAC: ICFA Workshop on e+e- High Luminosity Colliders. –Super-B 10^36 Particle Physics Workshop at SLAC October –Joint KEK/SLAC Super-B-Factory workshop in January 19-22, 2004 in Oahu, Hawaii. –

Conclusions The parameters of a Super-PEP-II were studied with RF frequencies of 476 MHz.and 952 MHz. At the present, for about 120 MW of total power, linac and campus included: 476 MHz provides a luminosity of about 5E35 and 952 MHz provides a luminosity of about 1E36 with beam-beam parameters of Coupled-bunch beam-dynamics effects, IR design, and vacuum systems will be studied next.