Sasha%20Novokhatski

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Linac possibilities for a Super-B

• Sasha Novokhatski
• SLAC, Stanford University
• WG2 - Linac/RF, Positron Source,
  Injection/Extraction
• March 17, 2006

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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
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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
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Possible limitation for damping ring energy
Space charge problem in the TESLA Damping
Ring W.Decking, R.Brinkmann, EPAC2000 At
lower energies (lt 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

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Space charge tune shift
Incoherent tune shift

Better to go to higher energy in damping ring
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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 eDR
6 GeV e SC linac without klystrons
e- Dump
7GeV e DR
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Damping Ring

• Energy 7GeV
• Beam current 1.6E-8 / 2.1E-97.6A
• Circumference 100000.63m6.3km
• Damping time 8.3msec
• Injection/ejection by mini trains of 1000 bunches
  with frequency of 1.2 kHz
• RF power 2.2MeV7.616.7 MW HOMs(10)Resistive
  wall
• Collision time structure

8.3 msec
2.1nsec10002.1 msec
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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)

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Linac 4 GeV is a TESLA-type linac, with higher
repetition rate
TESLA Linear Collider
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Wake fields in Tesla cavities
0.2 mm bunch Wake potential in the last cell
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Accelerating gradient and HOM power loss
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Preliminary Super-B Factory parameters
Collision parameters
Linacs parameters
Parameter LEB HEB
Beam Energy (GeV) 4 7
Number of bunches 10000 10000
Collision freq/bunch (Hz) 120 120
IP energy spread (MeV) 5 7
Particles /bunch x 1010 10 10
Time between collisions (msec) 8.3 8.3
by (mm) 0.5 0.5
bx (mm) 22 22
Emittance (x/y) (nm) 0.7/0.0016 0.7/0.0016
sz (mm) 0.35 0.35
Lumi enchancement Hd 1.07 1.07
Crossing angle(mrad) 0 0
IP Horiz. size (mm) 4 4
IP Vert. size (mm) 0.028 0.028
Horizontal disruption 1.7 0.9
Vertical disruption 244 127
Luminosity (x1034/cm2/s) 100 100
Parameter LEB HEB
Linac Energy GeV 4 61
Number of bunches per cycle 101000 1010
Repetition rate Hz 1200 1200
Final energy spread MeV 5 7
Particles /bunch x 1010 10 1
Bunch spacing nsec 2.1 2.1
RF Frequency MHz 1428 1428
Norm. Emittance (x/y) mmmrad 5.48/0.0125 9.59/0.022
Bunch length at injection mm 1 3
Final bunch length sz mm 0.35 3
Accelerating gradient MV/m 20 20
Accelerator length m 200 300
Energy spread after collision MeV 15 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 n/a 0.001