Joint Institute for Nuclear Research
Dzhelepov Laboratory of Nuclear Problems




operating console

The Laboratory of Nuclear Problems is the oldest laboratory of the physics research centre in Dubna. It was set up in 1947, when one began the construction of a 5-metre synchrocyclotron for energy of 560 MeV, the largest accelerator at that time. The initial operation of the accelerator took place on 14 December 1949. To carry out investigations at the synchrocyclotron, the Institute of Nuclear Problems of the USSR Academy of Sciences was established.
In 1956 the Soviet Government placed the synchrocyclotron and the staff of the INP at the disposal of the Joint Institute for Nuclear Research (JINR), which was established in Dubna.
In 1979-1984 the synchrocyclotron was converted into a space-varying field phasotron. The conversion allowed a 20-25-fold increase in the intensity of the ejected proton beam.
Investigations are carried out with ejected proton beams. The phasotron has 10 beam channels employed for experiments with pi-mesons, muons, neutrons and protons. Five secondary beams are intended for medical research, mainly in oncotherapy.

The main directions in the research at the phasotron are as follows:

- nuclear spectroscopy at the YASNAPP complex;
- mu-catalysis investigations;
- study of rare particle decays;
- µSR study of condensed matter properties;
- medico-biological research.


The phasotron has an effective ejection system based on an iron-current channel.
- The fast ejection efficiency is 50-60%.
- Slow ejection (stretching) allows an almost continuous beam to be extracted from the phasotron.

The general view of the phasotron:

Figure 2. Schematic view of the phasotron at the Laboratory of Nuclear Problems, JINR.
1 - magnet body; 2 - vacuum chamber; 3 dee; 4 - ejection channel; 5 - SI electrode for beam stretching; 6 - intermediate chamber; 7 - rotating capacitor; 8 - RF generator; 9 - vacuum pumps; 10 probes; 11 - ion source Rod; 12 - first magnetic elements of proton beam line; 13 - spiral shims for magnetic field variation in space; 14 - magnet excitation coil

Basic parameters of the phasotron

Energy of accelerated protons = (659 6) e
Energy dispersion ? = (3,1 0,8) e
Frequency of proton acceleration cycles (modulation frequency) 250 Hz
Emittance on boundary of scattered magnetic field of phasotron:  
e = ?(5,1 2,3) m*mrad
ey = ?(3.4 1.4) m*mrad
Ejected proton beam intensity in "fast" ejection mode (pulse duration is 30 µs) (2-2,5) µ
Ejected proton beam intensity in "slow" ejection mode (Time-stretched beam within 85% of modulation period duration (~ 4 ms) (1,6-2,0) µ
The ejected proton beam has a micro-structure: particle bunches of 10 ns duration follow each other with an interval about 70 ns.


The layout of the phasotron beam channels is shown in Fig. 3. Channels I, II, III, IX are used for meson beam formation; other channels, for nucleon beam formation.

Meson channels I and II are designed for obtaining separated and non-separated muon, pion and electron beams in the energy range from 30 to 300 MeV.
Channel II is mainly intended for meson beam formation in a low-background hall.
Channel III is used to obtain pion beams of energy 50-250 MeV.
Channel VIII serves for obtaining slowed-down proton beams of energy 100, 130 and 200 MeV.
Channel IX allows intense meson beams to be obtained by means of a wide-angle magnetic lens.
Channel X is used for neutron beam formation.
Channel XI allows narrow proton beams (5- 20 mm in diameter).
Channel XII is used for proton beam transport to the YASNAPP building.

Targets for radio-chemical investigations are irradiated in the internal beam of the phasotron at energies from 70 MeV to 660 MeV with intensities up to 6 mkA, and in the KOBRA installation at the end of channel IX.


In the Soviet Union (now the CIS) the first proton beam exhibiting the necessary parameters for radiation therapy was produced on proposal of Prof. Dzhelepov V.P. in the Laboratory of Nuclear Problems of the JINR (Dubna) at the 6S0 MeV phasotron in 19CT [2]. All work with this beam was carried out jointly by researchers of the Institute of Experimental and Clinical Oncology of the Academy of Medical Sciences of the USSR (now the Oncological Scientific Centre of the Russian Academy of Medical Sciences) and a group of physicists of the Laboratory of Nuclear Problems of the JINR. Clinical studies were initiated after the completion of a series of physico-dosimetrical and ra-diobiological experiments. Studies were carried out at the medical proton beam of the JINR LNP between 1968 and 1974 (and were suspended when the accelerator was reconstructed and the six-cabin medical facility was constructed).

For implementation of the adopted research program the construction was completed by the end of 1985 of a six-cabin medical facility at the JINR Laboratory of Nuclear Problems, including:
* four proton medical beams intended for irradiation of deeply lying tumours with broad and narrow proton beams of various energies (between 100 and 660 MeV);
* a medical pion channel for beam therapy using high-intensity negative pion beams with energies between 30 and 80 MeV;
* a neutron channel for medical purposes (the average energy of neutrons in the beam is approximately 350 MeV) for irradiation of large radioresistant tumours;
* a therapeutic gamma unit to be utilized as a spare source of radiation and for telegaramatherapy for combined irradiation methods are applied.

renovation: July 16, 2007 14:40
Anatoli Chirkov, Copyright, 2003