1. BINP Tau-Charm Project
E.Levichev
For the BINP C-Tau team
International Workshop on e+e- collisions from Phi to Psi (13-16 October 2009)
IHEP, Beijing

2. Outline 1. Introduction of Crab Waist collision approach 2
Outline 1. Introduction of Crab Waist collision approach 2. Scientific program and specifications 3. Optics 4. FF and QD0 5. Polarization insertions 6. Energy calibration

3. Crab Waist in 3 Steps Large Piwinski’s angle F = tg(q)sz/sx
Vertical beta comparable with overlap area by sx/q
Crab waist transformation y = xy’/(2q)
1. P.Raimondi, 2° SuperB Workshop, March 2006
2. P.Raimondi, D.Shatilov, M.Zobov, physics/
M.Zobov, Tau08, Novosibirsk

4. Crabbed Waist Scheme Sextupole IP (Anti)sextupole Sextupole strength
Equivalent Hamiltonian
M.Zobov, Tau08, Novosibirsk

5. Collisions without Crab Sextupoles
Bigger blowup
Sharp lifetime reduction for bunch currents > mA
February 2009
Courtesy G. Mazzitelli

6. Scientific case for the BINP C-tau project
► D-Dbar mixing
► CP violation searches in charm decays
► Rare and forbidden charm decays
► Standard Model tests in  leptons decays
► Searches for lepton flavor violation t→mg
► CP/T violation searches in  leptons decays
► Production of the polarized anti-nucleons E = 1 GeV (may be with reduced luminosity)
Requirements: L > 1034 cm-2 s-1, longitudinal polarization, beam energy range from 1 GeV to 2.5 GeV

7. Specifications
► Variable energy Ecm= 2 – 5 GeV ► Luminosity L = 1÷2×1035 cm-2s-1 ► Electrons are polarized longitudinally at IP ► No energy asymmetry ► No beam monochromatization ► Energy calibration with medium accuracy is sufficient (Compton backscattering)

8. Facility key features and principles
► Two rings with a single interaction point ► Crab waist collision ► SC wigglers to keep the same damping and emittance in the whole energy range (optimal luminosity) ► Polarized e- injector and spin control to get the longitudinally polarized electron beam at IP ► Wide re-using of the existing structures and facilities to save the cost

9. Layout Injection facility exists
Tunnel for the linac and the technical straight section of the factory is ready

10. Main ring

11. Main ring: tunnel Ready-built tunnel FF region
Technical reg. (RF and injection)
Damping wiggler sections

12. Main accelerator parameters
Energy
1.0 GeV
1.5 GeV
2.0 GeV
2.5 GeV
Circumference m
Emittance hor/ver
10 nm/0.15 nm
10 nm/0.09 nm
10 nm/0.05 nm
Longitudinal damping time
30 ms
15 ms
Natural bunch length
10 mm
Energy spread
8.5·10-4
10.5·10-4
8.8·10-4
7.4·10-4
Energy loss/turn
84 keV
251 keV
335 keV
420 keV
Betatron tunes hor/ver
29.53/21.57
Momentum compaction
1.137·10-3
1.127·10-3
1.118·10-3
1.115·10-3
Synchrotron tune
0.012
0.014
0.010
Wiggler field
4.4 T
4.8 T
3.3 T
RF frequency
500 MHz
Harmonic number
1260
Particles/bunch
5·1010
7·1010
Number of bunches
416
312
Bunch current
3.18 mA
4.45 mA
Total beam current
1.32 A
1.39 A
8 m of the SC wigglers with 20-cm-period are used to control the beam parameters at different energies

13. FODO but close to the theoretical minimum emittance
Main ring: arc cell
FODO but close to the theoretical minimum emittance 
bx, by

14. Main ring: injection section
bx, by

15. IR optics
bx, by
L1/2 = 85 m

16. QD0 SC iron yoke twin aperture magnet Excitation current 1150 A
Single aperture 2 cm
Gradient 150 T/m

17. Luminosity
D.Shatilov
y=760 mm, Θ=34, mrad, σz=1cm, x=10 nm·rad, 1% coupling

18. Polarization scheme
At the nominal energy the magnets rotate the spin around the field direction by (2k+1), k is integer. Solenoids rotate the spin by /2 around the velocity vector: a polarization vector is longitudinal at IP and transverse outside the polarization insertion.

19. Polarization vs energy
Longitudinal polarization degree, averaged on time and particle ensemble

20. Damping wigglers
The damping wigglers keep the damping time tx =30 ms and the
horizontal emittance (10 nm) in the energy range 1.5 – 2.5 GeV
Field amplitude at 1.5 GeV
4.3 T
Period length
0.2 m
Total length
8 m
Damping integral i2 at 1.5 GeV
2.76 m-1
Excitation integral i5 at 1.5 GeV
0.01 m-1
Wiggler with similar parameters produced by BINP
Wiggler field amplitude vs energy

21. Na24 (1)=1368.625 keV Na24 (2)=2754.008 keV Na24 (1+2)=4122.633 keV
Energy calibration
Compton backscattering E
calibration (~10-410-5)
Na24 (1)= keV Na24 (2)= keV Na24 (1+2)= keV
Spectrum edge

22. Injection facility

23. Injection facility upgrade
Today:
21010 e-/pulse  (1.5% conversion)  3 108 e+/pulse
 50 Hz = 1.51010 e+/s
Upgrade:
e- current increase ( 3)
Better focusing in positron linac ( 1.5)
Debuncher usage ( 2)
= 1.351011 e+/s
Reserve: electron energy can be increased by 100 MeV ( 1.3)

24. Summary
► Crab Waist collision seems a very promising idea to enhance a circular colliders luminosity beyond the present value by factor of without current increase. Three projects (SuperB, SuperKEKB and BINP-SuperCT) adopt CW as a basic idea of design.
► CW approach was successfully proved experimentally at DAFNE in the end of 2008
► Novosibirsk SuperCT project is under way. The key issues like IR design, DA optimization, polarization scheme, QD0 design, etc. seem solved successfully
► In the end of 2009 we hope to prepare a CDR of the project and in 2010 clear the project funding with Russian Government. In parallel a TDR will be prepared