Beam pipes M Sullivan Detector Beam Pipe Diameter

Beam pipes M. Sullivan Detector Beam Pipe Diameter Discussion M. Sullivan Super-B Factory Workshop Hawaii January 19 -22, 2004 Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan Detector Beam Pipe Constraints and Desires ØVertex Desires Thinnest, lowest Z material Smallest possible radius ØSR masking or shielding Many k. Ws of SR power in the super. B designs Ø I 2 R Can the beam pipe absorb all of the power from I 2 R losses? ØHOM Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan Vertexing Desires ØBe is usually the material of choice for the beam pipe §Exotic suggestions: Diamond (probably more multiple scattering) Silicon (detector beam pipe) …? ØDouble layer (unfortunately) with water to cool the pipe (water layer increases effective thickness – more multiple scattering) ØSmallest possible radius (see next talk) Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan SR Masking and Shielding ØSynchrotron radiation fans from upstream magnets need to be kept to a minimum in order to allow for small radius beam pipes ØQuadrupole radiation from the final focus quads (Next slide) also sets a limit on how small a beam pipe can be (there is a wall of x-rays down there!) Ø ØAn accelerator design with many bunches and low beam emittance helps keep the beam size small in the final focus quads Important rule of thumb: 1 Watt of x-rays 1 Mrad/s Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan Assumed beam-tails for SR background calculations for PEP-II SR masking usually concentrates on blocking x-rays from the high sigma particles in the beam tails where the particle density is relatively low. However, as the beam pipe radius shrinks the masking must block x-rays that are coming from the core particles (keep in mind the beam size in the upstream final focus quads is 50 -500 times larger than at the IP) Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan I 2 R power 2 1035 PEP-II now Itotal = 1. 3+1. 9 = 3. 2 A r 1 = 2. 5 cm nb = 1320 sz = 12 mm P = 8 W for a 20 cm long pipe Observed power is about ~600 W KEKB observed power is 100 W Itotal = 4. 8+11 = 15. 8 A (x 25) r 1 = 2. 0 cm? (x 1. 25) nb = 3400 (x 0. 39) sz = 4 mm (x 5) Power should be about 60 times higher than now or ~ 480 W 1 1036 PEP-II Itotal = 10+23 = 33 A (x 106) r 1 = 1. 0 cm? (x 2. 5) nb = 6800 (x 0. 19) sz = 1. 5 mm (x 22. 6) Power should be about 1100 times higher than now or ~ 8800 W Resistive wall pwr ~ I 2 total/r 1/nb/sz 3/2 Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan HOM power ØThe I 2 R losses grow rapidly with shrinking bunch length and increasing beam currents, but both PEP-II and KEKB see much more power than I 2 R already. Must be HOM power. ØMore difficult to predict and quantify. HOM power is also a strong function of the bunch length and beam currents. ØAssuming a similar dependence as the I 2 R losses then the 2 x 1035 PEP-II machine would see 36 k. W of power and the 1 x 1036 PEP-II would see 660 k. W of power WOW! Super-B Factory Workshop January 19 -22, 2004

Beam pipes M. Sullivan Summary ØThe minimum detector beam pipe radius is largely controlled by the size of the beam upstream of the IP. As the beam size at the collision point gets smaller the size of the beam upstream of the IP gets larger. (At the high beam currents of the super B designs even quadrupole radiation has k. Ws of power). ØSR generated by the final focus upstream magnets at some point produces a “wall” of x-rays as the beam pipe radius gets smaller when SR from the core beam (3 -5 s) particles starts to be intercepted ØI 2 R losses increase with increasing beam currents and shorter beam bunches but making the beam pipe shorter as the radius decreases can help ØMore difficult to predict and quantify, HOM power may be a bigger problem. Present machine beam pipes see significantly more power (10 -50 times more) than calculated from just resistive wall losses. Super-B Factory Workshop January 19 -22, 2004