Linac possibilities for a Super-B Sasha Novokhatski SLAC, Stanford University WG2 - Linac/RF, Positron Source, Injection/Extraction March 17, 2006

Long history of electron-positron colliders Go to “Google” and find hundreds of projects A.M.Budker, International High Energy Physics Conference, Kiev, Russia, 1970 Ugo Amaldi,1978

Linearly colliding Super-B Factory layout Why linear collider scheme? We believe that luminosity in single collisions can be higher and we can cool the beams to smaller emittance in the damping ring

Possible limitation for damping ring energy “Space charge problem in the TESLA Damping Ring” W.Decking, R.Brinkmann, EPAC’2000 At lower energies (< 3 GeV) the space-charge can lead to emittance growth, and potentially to particle loss. The space charge tune shift may be noticeable. Estimation for round beams Maximum gradient of the force Flat beams

Space charge tune shift Incoherent tune shift Better to go to higher energy in damping ring

Linear Super B (may be the cheapest option) IP 4 GeV e- SC linac Bunch compressor e- Gun Positron target Decompressor monochromator 1GeV e+ linac 1GeV e+DR 6 GeV e+ SC linac without klystrons e- Dump 7GeV e+ DR

Damping Ring Energy 7GeV Beam current 1.6E-8 / 2.1E-9=7.6A Circumference 10000*0.63m=6.3km Damping time 8.3msec Injection/ejection by mini trains of 1000 bunches with frequency of 1.2 kHz RF power 2.2MeV*7.6=16.7 MW +HOMs(10%)+Resistive wall Collision time structure 8.3 msec 2.1nsec*1000=2.1 msec

Accelerator Physics Issues Electron gun Beam transfer lines Buncher (compressor) Debuncher-Monochromator HOM loads Beam Loss Single-bunch instability Adiabatic anti-damping Multi-bunch Instabilities Two beams of different energies must remain confined in the same focusing channel (not so difficult in linacs)

Linac 4 GeV is a TESLA-type linac, with higher repetition rate TESLA Linear Collider

Wake fields in Tesla cavities 0.2 mm bunch Wake potential in the last cell

Accelerating gradient and HOM power loss

Preliminary Super-B Factory parameters Collision parameters Linacs parameters Parameter LEB HEB Beam Energy (GeV) 4 7 Number of bunches 10000 Collision freq/bunch (Hz) 120 IP energy spread (MeV) 5 Particles /bunch x 1010 10 Time between collisions (msec) 8.3 by* (mm) 0.5 bx* (mm) 22 Emittance (x/y) (nm) 0.7/0.0016 sz (mm) 0.35 Lumi enchancement Hd 1.07 Crossing angle(mrad) IP Horiz. size (mm) IP Vert. size (mm) 0.028 Horizontal disruption 1.7 0.9 Vertical disruption 244 127 Luminosity (x1034/cm2/s) 100 Parameter LEB HEB Linac Energy [GeV] 4 6+1 Number of bunches per cycle 10*1000 10*10 Repetition rate [Hz] 1200 Final energy spread [MeV] 5 7 Particles /bunch x 1010 10 1 Bunch spacing [nsec] 2.1 RF Frequency [MHz] 1428 Norm. Emittance (x/y) [mm*mrad] 5.48/0.0125 9.59/0.022 Bunch length at injection [mm] 3 Final bunch length sz [mm] 0.35 Accelerating gradient [MV/m] 20 Accelerator length [m] 200 300 Energy spread after collision [MeV] 15 Average current [mA] 19.2 0.19 Energy recovery efficiency [%] n/a 95 RF power (40% efficiency) [MW] 192 ~0 Relative particle loss [1/sec] 0.001