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

2. 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

3. 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

4. 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

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

6. 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

7. 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

8. 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)

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

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

11. Accelerating gradient and HOM power loss

12. 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