1. Recommissioning and Perspectives of VEPP-2000 e+e Collider
Dmitry Shwartz
BINP, Novosibirsk
on behalf of VEPP-2000 team
August 4, 2016
ICHEP’2016

2. Round beams at e+e- collider
Luminosity increase scenario:
Number of bunches (i.e. collision frequency)
Bunch-by-bunch luminosity
Round Beams:
Geometric factor:
Beam-beam limit enhancement:
IBS for low energy? Better life time!
02/21

3. The concept of Round Colliding Beams
Axial symmetry of counter beam force together with x-y symmetry of transfer matrix should provide additional integral of motion (angular momentum Mz = xy - xy). Particle dynamics remains nonlinear, but becomes 1D.
Lattice requirements:
Head-on collisions
Small and equal β-functions at IP:
Equal beam emittances:
Equal fractional parts of betatron tunes:
Round beam
Mx = My
V.V.Danilov et al., EPAC’96, Barcelona, p.1149, (1996)
03/21

4. Historic beam-beam simulations
“Weak-Strong”
“Strong-Strong”
I.Nesterenko, D.Shatilov, E.Simonov, in Proc. of Mini-Workshop on “Round beams and related concepts in beam dynamics”, Fermilab, December 5-6, 1996.
Beam size and luminosity vs. the nominal beam-beam parameter (A. Valishev, E. Perevedentsev, K. Ohmi, PAC’2003 )
04/21

5. VEPP-2000 main design parameters @ 1 GeV
VEPP-2000 layout ( )
13 T final focusing
solenoids
max. production rate:
2×107 e+/s
VEPP-2000 main design 1 GeV
Circumference m
Energy range
150  1000 MeV
Number of bunches 1
Number of particles
11011
Betatron tunes
4.1/2.1 IP
8.5 cm
Beam-beam parameter
0.1
Luminosity
11032 cm-2s-1

6. VEPP-2000
06/21

7. Beam size measurement by CCD cameras
07/21

8. Experimental program (CMD-3 detector)
Precision measurement of 𝑅=( 𝑒 + 𝑒 − →ℎ𝑎𝑑𝑟𝑜𝑛𝑠)/ 𝜎( 𝑒 + 𝑒 − → 𝜇 + 𝜇 − )
exclusive approach, up to <1% for major modes
Study of hadronic final states:
𝑒 + 𝑒 − →2ℎ, 3ℎ, 4ℎ,… ℎ=𝜋,𝐾,𝜂
Study of vector mesons and theirs excitations:
’, ’’, ’, ’,…
Comparison of cross-sections 𝑒 + 𝑒 − →ℎ𝑎𝑑𝑟𝑜𝑛𝑠 (𝑇=1) with spectral functions of 𝜏-decays
Study of nucleon electromagnetic formfactor at threshold
𝑒 + 𝑒 − →𝑝 𝑝 , 𝑛 𝑛
Measurement of the cross-sections using ISR
Study of higher order QED processes
Overall, we plan to collect at least 1 fb-1
Dedicated talk by I. Logashenko (today, 18:05, Superior A):
Measurement of hadronic cross-sections at VEPP-2000
08/21

9. Luminosity vs. beam energy 2010-2013
Peak luminosity overestimate for “optimal” lattice variation
*  , L  2
CMD-3 luminosity, averaged over 10% of best runs
Fixed lattice energy scaling law: L  4
Historic VEPP-2M data
Energy ramping
e+ deficit
Beam-beam effects
DA, IBS lifetime
09/21

10. Beam-beam parameter  = 0.175   = 0.125/IP   Е = 392.5 MeV
Beam-beam parameter extracted from luminosity monitor data
Coherent oscillations spectrum  
BB-threshold improvement with beam lengthening:
Е = 392.5 MeV
Urf = 35 kV (purple)
Urf = 17 kV (blue)
 =   = 0.125/IP
10/21

11. “Flip-flop” effect   e+ e TV
Pickup spectrum of the coherent oscillations
regular e
0.17
0.2
0.25
E = 240 MeV,
Ibeam ~ 55 mA
flipped e
0.17
0.2
Coherent beam-beam -mode interaction with machine nonlinear resonances?
flipped e+
0.17
0.2
11/21

12. Bunch lengthening: microwave inst.
Bunch length measurement with phi-dissector as a function of single beam current for different RF 478 MeV.
Energy spread dependence, restored from beam transverse profile measurements. 12
12/21

13. Beam sizes data analysis @ 392.5 MeV
URF= 35 kV
I = 15 mA corresponds to  ~ 0.1
And we should keep in mind that bunch lengthening is current-dependent…
URF= 17 kV
13/21

14. Delivered integral luminosity L = 60 pb-1/detector
Data collection
𝑛 𝑛
PRD 90 (2014)
Delivered integral luminosity L = 60 pb-1/detector 𝜔𝜂
3( 𝜋 + 𝜋 − )
arXiv:
PLB 723 (2013) 82
I. Logashenko (18:05, Superior A): Measurement of hadronic cross-sections at VEPP-2000
14/21

15. VEPP-2000 upgrade: 2013 >> 2016
VEPP-2000 complex
K-500 beam transfer channel
BINP Injection complex
e+, e beams from new BINP Injection Complex (IC):
high intensity
higher energy (400 MeV);
high quality (!);
Booster BEP upgrade to 1 GeV.
Transfer channels BEP  VEPP to 1 GeV.
VEPP-2000 ring modifications.
15/21

16. BEP reconstruction New pulsed injection septum
New RF-system (110 kV, MHz, q = 13)
Magnets yokes reprofiling (gap reduction, etc.). Fed in series all magnets has to follow single saturation curve. As well as chromatic sextupoles embedded into quads profile.
New correction coils
Vacuum chamber local deformation within reduced gaps
New pulse “bump” magnets extraction)
New SR outlet
Dipoles excitation curve
1 GeV:
H = 26 kGs,
I = 10.2 kA
RF cavity
Booster BEP
16/21

17. VEPP-2000 modifications
New vacuum chambers in two dipoles with additional kicker electrodes 1 GeV)
Original kicker electrodes
Scraper 2
Scraper 1
Additional
kicker electrodes
New SR mirrors for beam diagnostics:
17/21

18. Beam commissioning
K-500 transfer channel and scintillator screen
Timeline
Jan 16, 2016 – BEP assembly finished
Jan 27, 2016 – First e beam captured to BEP
Mar 21, 2016 – BEP-VEPP transfer channel assembly finished.
Apr 22, 2016 – First e beam captured to VEPP-2000
Jun 23, 2016 – e+ beam captured to BEP
Jun 30, 2016 – e+ beam delivered to VEPP-2000
Jul 28, 2016 – Shutdown
Image current K-500 transfer channel
18/21

19. BEP commissioning
Stacking rate of 2× MeV is obtained (gain factor of 10 in comparison to old production system)
500 mA of circulating multi-bunch e beam during beam scrabbing
Low-intensity beam accelerated to 1 GeV (RF system commissioning is not finished, new pre-amplifier under construction)
Beam 980 MeV with existing kickers
First beam BEP
I, mA
BEP-VEPP transfer channel (510 MeV)
19/21

20. VEPP-2000 ring re-commissioning
Storage ring re-commissioned in “warm” regime (FF solenoids turned off)
Beam scrubbing in both 510 MeV is done (e: 20 A*h, e+: 5.5 A*h)
Two beams (low-intensive) obtained, beam image monitors aligned and tuned
SND and CMD-3 detectors made test runs with cosmic data and beam background. Now ready for data taking.
I, mA
e+ e test beams
@ VEPP-2000
Beam VEPP-2000
20/21

21. Thank you for your attention
Summary
Round beams give a serious luminosity enhancement.
The achieved beam-beam parameter value at middle energies amounts to  ~ 0.1–0.12 during regular operation.
VEPP-2000 scanned all energy range of 160–1000 MeV with data taking. Achieved luminosity value five times higher comparatively to VEPP-2M. Total luminosity integral collected by both detectors is about 120 pb-1.
Injection chain of VEPP-2000 complex was upgraded and commissioned to provide the design luminosity at top energy.
VEPP-2000 passed through beam scrabbing procedure and is ready to start data taking with both detectors at designed luminosity level.
Thank you for your attention
21/21

22. Backup slides

23. Round Beams Options for VEPP-2000
Round beam due to coupling resonance?
The simplest practical solution!
Both simulations and experimental tests showed insufficient dynamic aperture for regular work in circular modes options.
Flat to Round or Mobius change needs polarity switch in solenoids and new orbit correction.
08/19

24. Dynamic beta, emittance and size
Simulations for E = 500 MeV.
50 mA corresponds to  ~ 0.1.
Invariance of beam IP is the essential VEPP-2000 lattice feature.
09/19

25. Dynamic sizes at the beam-size monitors
nom ~ 0.12
10/19

26. Beam-beam parameter evolution
537.5 MeV,
June-2011
392.5 MeV,
June-2013
0.07
511.5 MeV,
May-2013
0.08
0.09 (purple points)
13/19

27. Integrable round beam? (Danilov, Perevedentsev, 1997)
Proper profile of longitudinal distribution together with  = n betatron phase advance between IPs makes the Hamiltonian time-independent, i.e. integral of motion.
Synchrotron motion destroys full integrability
as = 0.0
as = 1.0
* = 5cm
s = 5cm
 = 0.15
D.Shatilov, A.Valishev, NaPAC’13
17/19

28. Working points for different options
“Flat”
“Normal
Round”
“Flat” &
“Normal round”
“Single möbius”
“Single möbius”
“Double möbius”
“Double möbius”

29. Luminosity: energy scaling approach
*  
  
*  
L  2
* = const
  2
*  
L  4

30. LIFETRAC simulations (weak-strong)
30 mA
40 mA
50 mA
20 mA
On resonance
(ν1 + ν2)/2 = 0.10
Detuned by +0.01
Detuned by –0.01

31. LIFETRAC predictions
Very high  threshold values for ideal linear machine lattice, th ~ 0.25.
Chromatic sextupoles affect significantly on bb-effects decreasing threshold down to th ~ 0.15. (Break of the angular momentum conservation by nonlinear fields asymmetric to x-y motion)
Working point shift from coupling resonance under diagonal (x > z) preferable than vise versa. (Emittances parity breaking.)
Uncompensated solenoids acceptable in wide range (x,z ~ 0.02) while coupling in arcs provided by skew-quadrupole fields should be avoided. (Angular momentum conservation break by skew-quads, breaking x-y symmetry of transport matrix.)
Inequality of x-y beta-functions in IP within 10 % tolerance does not affect on bb- effects.
Bb-effects do not cause emittance blow-up but reduce beam lifetime via non- Gaussian “tails” growth in transverse particles distribution.
Beam lifetime improves with working point approach to the integer resonance.
Qualitative agreement of all predictions with experimental experience.

32. Luminosity measurement via beam sizes @ CCD cameras
SND and CMD-3 luminosity monitors:
Slow (1 measurement ~ 1/2 minute)
Large statistical jitter at low beams intensities
Needed:
Beams current measurement e+, e (ФЭУ)
4 beam sizes * (with current dependent dynamic * and emittance)  reconstruction from 16 beam profile monitors.
Assumptions:
Lattice model well known (transport matrices)
Focusing distortion concentrated within IP vicinity.
Beam profile preserve Gaussian distribution.
2  4 = 8 parameters /
8  2  2 = 32 measured values.

33. Luminosity monitor
800 MeV
180 MeV