The VEPP-4M electron-positron collider

Magnet lattice
(in MAD-8 format)

The VEPP-4 electron-positron collider with the maximal beam energy of 6 GeV has been commissioned in 1979. In 1979-1985, a range of high-energy physics experiments with the MD-1 detector has been performed, including ypsilon-meson study and two-photon physics. To increase the collider luminosity, a modernization has been done in 1986-1994.

Principal modifications of the VEPP-4M against the VEPP-4:

  • ring symmetrization about an axis passing through the centers of the experimental and the technical straight sections;
  • inserts with increased aperture and electrostatic separators installed in the middle of semi-rings to provide 2x2-bunch operation and SR output for users;
  • modification of the experimental straight section magnet lattice for operation with the detector KEDR longitudinal magnetic field;
  • development of the distributed spectrometer for the system of scattered electrons registration;
  • the ROKK-1M facility for gamma-quantum beam production by Compton back-scattering.

The VEPP-4M layout in the PDF format is  here.

Main parameters

Perimeter366.075 m
Revolution frequency818.924 kHz
Beam energy1.5-5.5 GeV
Momentum compaction factor0.0168
Betatron tunes, horizontal/vertical8.54/7.58
Natural chromaticity, horizontal/vertical-14.5/-20.3
Beta-function, maximum/minimum

132.25/0.70 m
122.20/0.05 m
Horizontal dispersion,

1.99/-1.48 m
Aperture in semi-rings60x30 mm2
Accelerating RF system
Frequency181.10165 MHz
Harmonic number222
Number of cavities5
Maximal amplitude voltage per cavity1000 kV
Maximal RF generator power700 kW
Design beam parameters (E = 1850 MeV)
Damping time of
  ver. betatron oscillation
  hor. betatron oscillation
  phase oscillation

134 ms
139 ms
71 ms
Horizontal emittance24.6 nm·rad
Energy spread dE/E, r.m.s.3.22·10-4
Bunch length, r.m.s.3 см
Energy loss per turn32 keV
Synchrotron tune0.011 (9.26 kHz)

At present, the main high-energy physics experiment at the VEPP-4M is precise measurement of the tau-lepton mass at its production threshold. Experiments for accuracy improvement of the measured masses of the psi(2s) and psi(3770) mesons are also continued (the beam energy range is 1840-1900 MeV). In the low energy range (1.5-3.0 GeV), peak luminosity of the collider is 2·1030cm-2s-1. Average rate of KEDR data collection is about 300 nb-1 per week.

Design luminosity at the 6 GeV energy is 4·1031cm-2s-1 with natural beam size; 7·1031см-2с-1 with superconducting damping wigglers; 1032см-2с-1 with additional superconducting RF cavity to decrease bunch length and beta-fuction at the interaction point.