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

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

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

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

VEPP-2000 main design parameters @ 1 GeV VEPP-2000 layout (2010-2013) 13 T final focusing solenoids max. production rate: 2×107 e+/s VEPP-2000 main design parameters @ 1 GeV Circumference 24.388 m Energy range 150  1000 MeV Number of bunches 1 Number of particles 11011 Betatron tunes 4.1/2.1 Beta-functions @ IP 8.5 cm Beam-beam parameter 0.1 Luminosity 11032 cm-2s-1

VEPP-2000 06/21

Beam size measurement by CCD cameras 07/21

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

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

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)  = 0.175   = 0.125/IP 10/21

“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

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

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

Delivered integral luminosity L = 60 pb-1/detector Data collection 2010-2013 𝑛 𝑛 PRD 90 (2014) 112007 Delivered integral luminosity L = 60 pb-1/detector 𝜔𝜂 3( 𝜋 + 𝜋 − ) arXiv:1607.00371 PLB 723 (2013) 82 I. Logashenko (18:05, Superior A): Measurement of hadronic cross-sections at VEPP-2000 14/21

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

BEP reconstruction New pulsed injection septum New RF-system (110 kV, 174.382 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 (COD @ extraction) New SR outlet Dipoles excitation curve 1 GeV: H = 26 kGs, I = 10.2 kA RF cavity Booster BEP 16/21

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

Beam commissioning K-500 transfer channel and beam @ 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 BPMs @ K-500 transfer channel 18/21

BEP commissioning Stacking rate of 2×108 e+/sec @ 390 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 extracted @ 980 MeV with existing kickers First beam SR @ BEP I, mA BPMs @ BEP-VEPP transfer channel (510 MeV) 19/21

VEPP-2000 ring re-commissioning Storage ring re-commissioned in “warm” regime (FF solenoids turned off) Beam scrubbing in both directions @ 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 scrubbing @ VEPP-2000 20/21

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

Backup slides

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

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

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

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

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

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

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

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

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.

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.

Luminosity monitor 800 MeV 180 MeV