Brief accelerator description.

INR accelerator was developed and constructed as a multi-purpose tool for both applied and fundamental research in nuclear and elementary particle physics. It consists of the following main facilities:

• High intensity linear accelerator.
• Experimental facility.
• Isotope production facility.
• Conventional and auxiliary facilities.

High intensity linear accelerator forms the basis of the meson factory. The INR linac is foreseen to accelerate protons and Н^- ions up to 600 MeV with the average current up to 500 μA. Pulse current is 50 mA, beam pulse duration - 100 μs and beam pulse repetition rate - 100 Hz. The linac includes the injector complex, the initial part of the accelerator (up to 100 MeV) and the high energy part (up to 600 MeV). The intermediate energy beam extraction is foreseen at 160 MeV.

The injector complex includes two injectors - protons and Н^- ions, - and the corresponding injection lines. Both injectors use accelerating tubes and HV pulse transformers initially providing the energy of 750 keV.

The pulse current at the exit of the injectors is tens mA, beam pulse duration - 100 μs, repetition rate - 50 Hz. Three 45⁰ bending magnets enable to coincide both beams at the third area of injection line. This area has been reconstructed and a booster RFQ operating at 198.2 MHz has been additionally installed to provide acceleration from 400 keV to 750 keV. Using of the booster RFQ enabled to decrease the energy of the injectors to 400 keV thus resulting in improvement of injector reliability for the repetition rates up to 100 Hz as well as in increasing of the beam pulse duration up to 200 μs without pulse transformer core saturation.

Due to economic reasons the only proton beam was accelerated till the end of 2006. The Н^- injector and the corresponding injection line has been commissioned in December 2006 and the Н- beam has been accelerated in the initial part of the accelerator.

The beam macro pulse at the exit of the RFQ includes about 4*10⁴ bunches of approximately 0.8 ns duration. Six dimensional beam matching with the downstream accelerator acceptance is provided with the four quadrupole lenses and the buncher cavity operating at 198.2 MHz. To increase the RFQ beam capture one more buncher cavity is installed in front of the RFQ entrance. The matched beam is injected into the initial part of the accelerator consisting of five drift tube tanks Р₁-Р₅, operating at 198.2 MHz. After being accelerated up to 100.1 MeV the beam is injected into the high energy part of accelerator consisting of 27 disc and washer type (DAW) accelerating cavities Р₆-Р₃₂ operating at 991 MHz. The DAW cavities are grouped in three accelerator sections from the point of view of control and power supply, 9 cavities in each section, with the exit energies of 247.32 MeV, 423.04 MeV and 602.03 MeV. RF power is generated by 6 triode generators and 32 klystron generators with the output power of 3 MW and 4.7 MW correspondingly.

For beam focusing 196 quadrupole lenses are foreseen in drift tubes of five DTL tanks of initial part of the accelerator. High energy part utilizes 120 quadrupole doublets located between the accelerating sections. The average pressure in the beam line is about 5*10^-8 torr. Total length of the accelerator is 450 m.

During the step-by-step commissioning the beam was accelerated up to 500 MeV. At present the energy is limited by the amount of klystrons available and capabilities of their production in industry. The rest of the cavities up to final energy have been conditioned with a movable klystron.

The main criterion of proper accelerator tuning is minimum beam loss. Usually the value of beam loss must not exceed few tenth of per cent in the main part of the accelerator. The system to observe and monitor beam loss provides a possibility to decrease the loss to about 0.1 % thus enabling operation of the accelerator with beam intensities up to 120 μA. The pulse intensity is about 20 mA.

A variety of beam tuning techniques has been developed and implemented: acceptance scan, delta-T procedure, beam correction and matching procedure etc. The method of fine energy adjustment with accurate time of flight measurements, about ±0.2%, has also been developed and implemented. A detector for longitudinal beam profile measurement has been developed. This detector has been also developed for several accelerator laboratories in Germany, USA, Japan and CERN.

To provide time of flight neutron measurement as well as the measurement in a spectrometer on slowing-down in lead generation of beam short pulses is provided using a traveling wave beam deflector installed in injection line. One or two pulses with adjustable duration within the range from 0.3 μs to 50 μs and adjustable delay can be provided.

The beam line to extract the beam to the isotope production facility at 160 MeV has been designed and built. The beam is deflected by two dipole magnets and approximately 15 mm diameter spot is formed on the target with two quadrupole doublets. To decrease heat loading of the target as well as that of the extraction window a 120 μA beam is continuously rotated with the amplitude of 5 mm with two steering magnets.

For experimental physics use the beam is transported to the experimental facility downstream of the exit of the accelerator. The energy and the intensity in this case depend on requirement of particular experiment and the number of klystrons available.

Regular accelerator operation started in 1993. Since that time till the end of 2014 113 accelerator runs with total duration of 42000 hours have been carried out.

The results of accelerator development and building are rated highly by scientific community and Russian Government. The 2001 Prize of the Government of Russian Federation in science and technology was awarded for the work on development, construction and commissioning of the accelerator.