OPERATION AT LOW ENERGY* A w o m p m p p a t p s a o m t h

bstract During the last few years the e+e − collider VEPP-4M as operating in the low energy range E = 1.5–2 GeV in rder to study ψ- and τ-physics. Recently another easurement of the ψ- and ψ′-meson masses was erformed at VEPP-4M with the detector KEDR, and the easurement accuracy was 3 times as high as that of the revious precise experiments. The paper covers the recise energy measurement results obtained at VEPP-4M s well as other issues of the accelerator physics including he low energy luminosity, influence of wigglers on beam arameters, experimental non-linear beam dynamics tudy etc. Figure1: The change of the intrabeam scattering count rate. The electron beam polarizes in the 2 GeV booster storage ring VEPP-3 and two bunches (polarized and reference) are injected one after another into the VEPP-4M vacuum chamber. RF voltage applied to the exciter electrodes sweeps some frequency range close to the spin precession frequency, and special counters inserted inside the vacuum chamber registered Touschek electrons. Since the intrabeam scattering depends on the particle spin, the ratio 21 /1 NN − increases step-wise (see Fig.1) when the test bunch is depolarized and the frequency of the RF voltage gives us the beam energy [3]