Laboratory of High Energies,
Joint Institute for Nuclear Research,
141980 Dubna, Russia
The first superconducting synchrotron named Nuclotron based on a miniature iron- shaped field SC-magnets was designed, constructed and put into operation at the LHE. Five runs of a total duration of about 1400 hours have been provided by the present time. Unique experimental results on the cryomagnetic system of a novel type as well as new data on nuclear collisions using internal target have been obtained. Successful experience of the Nuclotron building gives no doubt in further applications of such a low cost reliable technology for future accelerators both as for superhigh energies or high intensity beams production.
It is my great
privilage to present this talk at the Anniversary symposium devoted to the
discovery of the phase stability principle. Fifty years were passing after
V.I.Veksler's famous paper was published in 1944 .
Revolutionary progress of high energy nuclear and elementary particle physics as
well as the progress of high technologies in different directions of human
activity are connected with the development of accelerators based on this
Since 1957 the major research facility of the LHE JINR is 10-GeV proton Synchrophasotron built under the leadership of V.I.Veksler. The proposal of the Nuclotron construction as well as the synchrophasotron upgrade program were unitiated by A.M.Baldin in the beginning of 70s [2,3]. The ideas of relativistic nuclear physics aimed at the study of colour degrees of freedom in nuclei, QCD of large distances and fundamental properties of highly exited nuclear matter defined the prospects for the LHE accelerator complex development as relativistic nuclei and polarized beam facility. In accordance with this concept the following main problems were solved during the past years:
2. THE LHE ACCELERATOR COMPLEX
composition of the accelerators and experimental areas at the Laboratory of High
Energies is shown in Fig.1.
Fig.1. Accelerator Centre of the Laboratory of High Energies.
( Also, sensitive map of LHE Accelerator Complex is available. )
|Accelerated particles||Intensity charge/pulse||Pulse duration||Type of the source||Comments|
index and value Pzz=0.54±0.08
Nd-glass laser was first used to obtain relativistic carbon nuclei at our
accelerator complex in 1976 . The
LDS based on a CO2 laser was developed and put into operation several
years later .
The electron-beam ionizer - KRION was suggested by Donets in 1967 . The highest value of the ionization factor is provided by the KRION-type source. Since 1977, the sources of this type is used at the LHE accelerator complex. The heaviest nuclei accelerated at the synchrophasotron was sulphur . This experiment was carried out in accordance with the request of the users to be interested in the mostly complete experimental data on sulphur nuclei interactions over energy range of 1-200 GeV. But acceleration of the ions even as sulphur at the synchrophasotron is inefficient due to a big losses of the beam intensity caused mainly by unsufficient vacuum, low energy of injection and low accelerating r.f. voltage. The progress of the LHE relativistic heavy ion program is connected with the Nuclotron operation and proposed development of the injector complex. The EBIS-type ion sources are considered as one of the basic devices in the frames of this program.
Beams of polarized deuterons were obtained in 1981 after a special cryogenic source "Polaris" was developed and put into operation . The maximal momentum and intensity of accelerated beam are: p=4.5 GeV/c and N=5·109part./pulse. Investigations of spin phenomena using polarized beams and the development of experimental facilities for this researches are the subject of particular interest.
There are two directions (labeled MV-1 and MV-2 in Fig.1) of beam extraction from the Synchrophasotron. Along the MV-1 the beams are extractred slowly (Textr 500 ms) and transported to the main experimental area - hall 205 which has been built during the end of the 70s. Efficiency of slow extraction at maximal beam energy of about 95%. Along the MV-2 both as slow or fast (Textr 1 ms) beam extraction modes are available.
Eight beam transfer lines, namely the main one VP-1 and seven lateral 1V7V can provide ten physics setups with beams in hall 205. During the past few years the MV-2 direction of beam extraction was operated less intensively but the using of an "old" experimental area - hall 1A is included into the full scale prospect of the Nuclotron userôs policy. More detailed description of the synchrophasotron external beams was presented for example in paper . Notice, that using of existing experimental areas was one of the conditions under the Nuclotron design.
Normally the total running time of the synchrophasotron up to 1991 was about 4000 hours per year. Later, disbalance between budget funding and prices for electric power led to catastrofic decreasing of the accelerator running time. Only about 1000 hours per year were available for the users in 1991 and in 1992. Starting from 1993 the Nuclotron is under operation. It seems realistic to support total running time (Synchrophasotron + Nuclotron) at the level of about 2000- 2500 hours per year during several next years. The synchrophasotron will be used mainly to obtain polarized beams. The efforts should be concentrated also at the problem of beam extraction from the Nuclotron.
3. NUCLOTRON DESIGN AND CONSTRUCTION
conceptual design proposal of development of the LHE accelerator centre was
published in 1973. The "Nuclotron", a superconducting strong focusing
accelerator of relativistic nuclei, was considered as a three-stage accelerating
facility, consisting of: 10 MeV/u linac, 750 MeV/u booster ring (both
conventional and superconducting ones were considered) and 2025 GeV/u main ring .
Pulsed superconducting dipoles of a cos - type with a peak magnetic field of 6 T
were suggested to be used for the Nuclotron main ring. However, after the first
tests of cos - type high field SC
magnets had been performed, further R& D works were reoriented at the
investigation of a miniature iron-shaped field SC-magnets. It was the only
feasible way of constructing a new accelerator at LHE because of very limited
funs allocated to the relativistic nuclear physics program. The final option of
the Nuclotron was developed to the 80s ,and
the project: "Reconstruction of the synchrophasotron magnetic system to the
superconducting one - Nuclotron" was approved in December 1986.
The proposal of the using a pulse 2-2.5 T magnets based on a window- frame type iron yoke and SC-coils for a relatively small synchrotrons was made by I.Shelaev. Five modifications of such type magnets with the SC-coils made of plane SC-cable a immerse type of cooling were fabricated and tested at LHE up to 1978 . New magnets had very attractive parameters such as: low cost, low stored energy, high quality of the magnetic field over the aperture, the lowest specific weight (only 30 kg/m). The question was: "Is the peak beam energy of 6 GeV/u instead of 20 GeV/u enough for the problems to be solved in the frames of basic physics program at Nuclotron?". According to general representation developed by A.M.Baldin  - relative 4-velocity between colliding particles (hadrons, nuclei) should be bI,II >> 1. In this case the nucleons cannot considered as quasi-particles of nuclear matter and the influence of quark-gluon degrees of freedom in interactions of hadrons and or nuclei should be observed. The basic quantitives bik which the probability distribution in the process of multiple particle production
I + II 1 + 2 + 3 + ...
where pi , pk - 4-momenta of partciles i and k ; mi , mk - their masses; ui , uk - 4- velocities.
Fig.2. The Nuclotron dipole magnet inside its cryostat near the synchrophasotron.
The nuclotron ring is installed in the tunnel around the synchrophasotron. This tunnel was originally built for cable communications and the equipment of the synchrophasotron vacuum system. The Nuclotron median plane is at 3.7 m below the synchrophasotron one. The picture of the Nuclotron in the tunnel is presented in the talk by A.M.Baldin.
The Nuclotron lattice is typical for a strong-focusing separated function synchrotrons. It contains 8 superperiods and 8 stright sections, one of which is "warm". Different targets for the experiments at internal beam can be installed more easy using this place.
Fig.3. The Nuclotron quadrupole lens.
Fig.4. General scheme of the Nuclotron cryogenics. 1 - vacuum
shell; 2 - heat shield; 3 - suuply header;
4 - return header; 5 - dipole magnet; 6 - quadrupole magnet; 7 - subcooler; 8 - separator; 9 - refrigerator;
10 - gas bag; 11 - storage vessel; 12,14,15,17 - compressors; 13,16 - purifiers.
4. FIRST BEAMS AND EXPERIMENTS AT NUCLOTRON
During the first
test run (March 17th-26th, 1993) the Nuclotron ring was cooled down to 4.5 K (it
took about 110 hours), the dipoles and quadrupoles were supplied by dc-current
and a 5 MeV/u deutron beam was injected. Soon after tuning the levels of
magnetic field and gradient, we observed the first turns of particles in the
vacuum chamber. This result was reported at the CERN PS Seminar and caused very
big interest .
Deuteron beam acceleration up to an energy of 0.2 GeV/u and internal target
irradiation were performed during the second run in June 26th -July 6th [9,10]. The
intensity of the accelerated deuteron beam was up to 2·109 per cycle.
Beam dynamics was stable enough, and a maximum beam energy was limited by the
run program. Additional adjustment of the magnets power supply sources and
quench protection system should be provided before the next step.
New results on acceleration of heavier ions were obtained at Nuclotron in December 1993 run. The cryogenic electron beam ion source "KRION-S" was installed at the linac. Beams of argon and krypton ions were obtained and accelerated to an energy of 5 MeV/u at the linac and the krypton beam was injected into the Nuclotron ring.
But we were forced to interupt this run due to failure the cathode of the electron gun at the KRION. The run was continued after the KRION was replaced by the laser drive source. An accelerated beam of carbon ions with the intensity of ~109 per cycle was obtained at Nuclotron using the LDS. So, operation of LDS with the Nuclotron system was tested .
The Nuclotron is excelent tool for the experiments at internal target (Fig.5) due to the possibility of a beam energy variation starting from injection (5 MeV/u) up to maximum value (6 GeV/u) with very fine steps. The step of guiding magnetic field rise is 1 G. So, the energy variation of 10-4 can be provided for the experiments over energy range of (16) GeV/u.
The first physics experiments with relativistic deuterons were carried out during the fourth Nuclotron run in March 17-29. The run began just after the completion of a Synchrophasotron polarized deuteron run. In accordance with the program, a polarized deuteron beam injection and acceleration (up to 100 MeV/u) were provided. After that the polarized deuteron source "Polaris" was replaced by a duoplasmatron and the Nuclotron continued to operate for physics program.The parameters of the magnetic field cycles were 6, 8.5 and 10 kGs with a rise of 6 kGs/s. The beam dynamics was stable and no particle losses were observed during the acceleration time after 50 ms. Thus, the maximum momentum of deuterons of 3.5 A GeV/c at beam intensity of 2·109 per cycle has been reached.
Fig.5. The fragment of the Nuclotron ring and "warm" streight section where the box with internal target inside.
The example of beam-target interaction is shown in Fig.6. Observable time of interaction is about 400 ms. It is easy to show that the luminosity level of about 3.1033 cm-2.s-1 for dC- interactions was obtained in that experiment.
Fig.6. Beam-target interaction at the Nuclotron internal beam.
Ultraviolet and X-ray radiation produced in interactions of beam particles with target material has been applied to study the radiofrequency structure of accelerated beam.
The accelerated beam microstructure for different conditions is shown in Fig.7. The upper diagram shows a time structure of accelerated beam just before the beginning of the flat top (plato) of the magnetic field cycle. The middle one is correspond to the moment when r.f. voltage has been switch off. A typical bunch structure of the beam is observed in this case. The last diagram demonstrate longitudinal beam density in the process of the particles circulation at the plato of magnetic field after the r.f. voltage was switch off. There are no bunches and longitudinal beam density is quite uniform.This mode of operation is the most attractive for data taken.
Fig.7. Microstructure of accelerated beam.
operation and development of the synchrophasotron, design and construction of
the new superconducting accelerator Nuclotron would not be possible without
great efforts of many people. I feel my duty to express gratitudes to
L.P.Zinoviev, L.G.Makarov, I.N.Semenyushkin, I.B.Issinsky, Yu.D.Beznogikh,
S.A.Averichev, A.A.Smirnov, K.V.Chekhlov, A.I.Mikhailov, A.P.Tsarenkov,
V.A.Monchinsky, V.I.Volkov, B.D.Omelchenko, N.N.Agapov, H.G.Khodgibagiyan,
M.A.Voevodin, V.A.Mikhailov, A.I.Malakhov, V.M.Slepnev, O.I.Brovko and all
engineering and operational stuff of the LHE Accelerator complex.
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18. A.M.Baldin and A.D.Kovalenko. CERN bulletin, 14/93, no.4, (1993).
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20. A.M.Baldin et al.Nucl.Phys. A583, p.637-640, (1995).
NUCLOTRON: FIRST BEAMS AND EXPERIMENTS AT THE SUPERCONDUCTING SYNCHROTRON IN DUBNA