VEPP-2000 electron-positron collider operating in the beam energy range of 150-1000 MeV is the only machine originally designed for and successfully exploiting Round Beams Concept. After injection chain upgrade including link to the new BINP injection complex VEPP-2000 proceeded with data taking since 2017 with luminosity limited only by beam-beam effects. At the low energies (300-600 MeV/beam) the novel technique of effective emittance controlled increase by weak coherent beam shaking allowed to suppress the limiting flip-flop effect and resulted in additional luminosity gain factor of 4. The averaged delivered luminosity at the omega-meson production energy (2×391 MeV) achieved L =2×1031 cm2s1/IP. At the top energies above nucleonantinucleon production threshold the stable operation with luminosity of L = 5×1031 cm2s1/IP resulted in high average data taking rate of 2 pb1/day in 2020.

VEPP-5 Injection Complex was designed as a powerful source of intense electron and positron bunches at the energy of 510 MeV. Now Complex is very close to start full scale commissioning. The most important subsystems of Injection Complex (high intensity driving electron linac and positron production system) have been put in operation at designed parameters. The results of positron production system commissioning are presented in this paper.

VEPP-2000 is the only electron-positron collider operating with round beams that allow to enhance beam-beam limit. VEPP-2000 with SND and CMD-3 detectors carried out two successful data-taking runs after new BINP injection complex was commissioned. The 2016/2017 run was dedicated to high energy range (640-1000 MeV per beam) while the 2017/2018 run was focused at 275-600 MeV/beam energies. With sufficient positron production rate and upgraded full-energy booster the collider luminosity was limited by beam-beam effects, namely flip-flop effect. Thorough machine tuning together with new ideas introduced to suppress flip-flop allowed to establish new world record for beam-beam parameter and bunch-by-bunch luminosity values at specific beam energies. The achieved luminosity increased 2-5 times in a whole energy range in comparison to phase-1 operation (2010-2013).

Two BINP colliders VEPP-4M and VEPP-2000 e+ecolliders are under operation with the beams feeding from VEPP-5 Injection Complex via newly constructed K-500 beam transfer line. Upgraded injection chain demonstrated ability to provide designed luminosity both to VEPP4M and VEPP-2000 and techniques of reliable operation are under development now. The design and operation experience of Injection Complex and transfer lines are presented. INTRODUCTION Two electron-positron colliders at Budker Institute of Nuclear Physics (Novosibirsk, Russia) are under operation: VEPP-2000 [1, 2, and 3] and VEPP-4M [4]. Both colliders are fed with the electron and positron beams from VEPP-5 Injection Complex [5, 6]. The infrastructure of BINP accelerator facilities are presented in Fig. 1. VEPP-5 Injection Complex and collider facilities are connected with the Beam Transportation Channels (K-500 Channels) [7]. Figure 1: BINP Accelerator Facility layout. INJECTION COMPLEX VEPP-5 VEPP-5 Injection Complex consists of electron gun, 270 MeV driving electron Linac, 510 MeV positron Linac and dumping ring. Damping ring stores and cools down both electron and positron beams for the next extraction to K-500 beam transfer line (see Fig. 2). Repetition rate is decided to be kept under 12.5 Hz due to VEPP-5 operation experience: some subsystems, like injection/extraction system, require more powerful cooling and some radiation aspects should be reconsidered before planned repetition rate increasing. Nevertheless, 1.2·10 of the particles corresponds to 200 mA circulating beam in the Damping Ring – it exceeds VEPP-5 project parameters more than twice [6, 8]. Figure 2: VEPP-5 Injection Complex layout. Table 1: VEPP-5 Beam Production Parameter Value Energy (2016/17 runs) 385 – 420 MeV Electrons storage rate 2·10/s Positrons storage rate 2·10/s Repetition rate up to 12.5 Hz Maximum e extraction: up to 1.2·10 Maximum e extraction: up to 1.2·10 K-500 BEAM TRANSFER LINE The K-500 beam transfer line was turned into operation at BINP in the end of 2015 [7, 8]. This beamline to VEPP2000 facility was designed to the energy of 510 MeV, it has the length of approximately 250 meters to VEPP-2000 side and 120 meters to VEPP-4M side. K-500 and consists of five sections: descent from Damping Ring to K500 tunnel, regular FODO structure in the tunnel both to VEPP-2000 and VEPP-4M, and two lifting to the both collider facilities. The fragment of the transfer line are shown in Fig. 3. ___________________________________________ † d.e.berkaev@inp.nsk.su WEPIK026 Proceedings of IPAC2017, Copenhagen, Denmark ISBN 978-3-95450-182-3 2982 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs 01 Circular and Linear Colliders T12 Beam Injection/Extraction and Transport Figure 3: VEPP-5 – VEPP-2000 beam transfer line (right down corner – view of the beam at the phosphor screen at the end of transfer line). DAMPING RING INJECTION AND EXTRACTION The cycle of injection/extraction in/from Damping Ring consists from several cycles of beam injection and one extraction action. Extraction channels are presented in Fig. 4. They consist from extraction “bridges” and 900 turns: DC powered solid yoke dipole and quadrupole magnets (green and grey correspondingly in Fig. 6), and descending beam line with VEPP-2000/VEPP-4M separation: DC powered dipoles and pulsed quads. Such a mixture of techniques appeared during long (the project started in 1993) and staged construction and commissioning of the VEPP-5 IC. EXTRACTION AND TRANSFER MODES VEPP-5 IC has four modes of operation: electrons and positrons to two directions. Figure 4: Extraction lines from Damping Ring. Thus, one need to configure 12 different switch processes (see Fig. 6). In the simplest cases, only type of particles is changing. For the other cases one need to magnetize ex-traction magnet system using the opposite type of particles first. Nevertheless, the last rule has the exception: for the transfer of the particles to VEPP-4M direction mag-nets 6M1-4 has to be turned off (see Fig. 5a). So it is very important the state before zero current setup. In our case, positron mode to VEPP-2000 was chosen for both transitions from VEPP-2000 to VEPP-4M directions for stable operation. Each single changing of the magnets fields lasts 30 seconds due to parameters of DC power converters and the inductance of their loads. Therefore, the maximum time of mode change is 60 seconds. a) operation with VEPP-4M facility. b) operation with VEPP-2000 facility. Figures 5 a) and 5 b): IC VEPP-5 Operation Modes. All mode switching as a mode saving and restoring are provided with the special designed infrastructure [9] based on CX modular accelerators modular control system [10]. Proceedings of IPAC2017, Copenhagen, Denmark WEPIK026 01 Circular and Linear Colliders T12 Beam Injection/Extraction and Transport ISBN 978-3-95450-182-3 2983 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs Figure 6: IC VEPP-5 extraction matrix of modes. TWO COLLIDERS OPERATION Common cycle based on the current operation experience starts from the positrons to VEPP-4M mode. Ten minutes are enough to fill the facility booster with 60-90 mA of circulating currents (see the Table 2 for BINP accelerator rings parameters comparison). Than VEPP-4M performs own cycle of boosting and injection to the collider. For this time, IC VEPP-5 is switched to VEPP2000 direction and provides the required particles for another collider. Own VEPP-4M cycle lasts about 15 minutes, then, IC VEPP-5 is turned back to VEPP-4M direction but in the electron mode. Than the common cycle repeats. Typical IC VEPP-5 switching modes are presented in Fig. 7. Figure 7: Status page of IC VEPP-5 [11]. Table 2: Comparison of the Number of Particles and Beam Currents for Different BINP Accelerator Rings VEPP5 DR BEP VEPP2000 VEPP3 VEPP4M N/P,m 27.40 22.35 24.18 74.39 366.1 1•109 1.75 2.15 1.99 0.65 0.13 5•109 8.76 10.74 9.93 3.23 0.66 1•1010 17.52 21.48 19.85 6.45 1.31 5•1010 87.59 107.38 99.26 32.26 6.56 1•1011 175.18 214.77 198.51 64.52 13.11 CONCLUSION At the present, Injection Complex VEPP-5 are routinely provide both types of particles to both BINP Colliders with the efficiency up to 80% VEPP-2000 and VEPP-4 colliders are under operation for the experiments according to their scientific programs.