V. V. Kol'ga

A Cyclotron Complex for Accelerating Multicharged Ions up to Relativistic Energies

The accelerating complex for the production of the multicharged ion beams up to uranium with a final energy of 300 MeV/amu is described. It is supposed to use a Wideroe type accelerator at the first stage of acceleration (up to 0.59 MeV/amu), a conventional isochronous cyclotron at the second stage (up to 10 MeV/amu), and an isochronous cyclotron with superconducting magnet coils at the final stage. Such a structure of the accelerating complex provides high beam intensity at the full energy of 300 MeV/amu (about 1013 particles per second for uranium), and the intermediate energy of 10 MeV/amu (about 1014 particles per second for uranium). Some preliminary parameters of the accelerator are presented.

Problems of theory and modelling of a ring-shaped phasotron with spiral field distribution

Abstract Some problems related to the construction of the model of a ring-shaped phasotron with spiral magnetic field structure is considered in this paper. Basic parameters of the designed model are given and the sections of the magnetic system and the accelerator-injector of the model of the ring-shaped phasotron are described.

Experimental Research of the Closed Orbit Expansion Effect in the Strong Focusing Cyclotron

The theoretical and experimental study of beam extraction method using the closed orbit expansion effect is described. The steep slope of the magnetic field variation magnitude is used to change the momentum compaction factor for the limit radial area. The orbit separation is found by computing the dynamical equations, since the behaviour of the betatron oscillation frequencies and the beam phase are investigated in this radial region. The experimental study of the effect is carried out with the ring cyclotron electron model, which is a strong focusing eight sector isochronous cyclotron. Calculated orbit separation in the extraction area is about 2+4 cm. The magnet system which is to obtain the proper gradient of the magnetic field variation and the magnet measurements results are described. The measured value of the orbit separation equals 4 cm. At the same time the space between two orbits without current (free of particles) is about 2 cm and the full current on the separated orbit is equal to that before separation. The theoretically predicted beam phase shift is found to be equal to 30+40°. The obtained results confirm the possibility of the 100% beam extraction from the accelerator with space magnetic field variation.

Study of the Modified Resonance Extraction Method from a Relativistic Cyclotron

The highly ef fec t ive ext rac t ion of accelerated p a r t i c l e s from a r e l a t i v i s t i c cyclotron (RC) i s one of the basic problems since the successful use of the RC a high energy physics instrument and i ts normal employment are possible only when p rac t i ca l ly a l l the p a r t i c l e s a re extracted from the chamber and external t a rge t s a re used. The most e f fec t ive methods f o r beam extraction from cycl ic accelerators having constant magnetic f i e l d s are based on resonance coupling between azimuthal and r a d i a l degrees of freedom of the accelerated pa r t i c l e a t the given radius. I n t h i s case it is necessary t o provide conditions of the absence of cou l i n g with a x i a l o sc i l l a t ions of part i c f e s . The s p i r a l s t ruc ture of the magneti c f i e l d of the RC causes in t e rna l nonl i n e a r resonance a t t h e frequency of r a d i a l o sc i l l a t ions Q =N/q, where N is the number of spirals: 9 is an in t eg ra l ( the resonance order). With N=8 the nonl i n e a r resonance of t h e 4-th order (Q = 2) correspgnds t o about 820 MeV. ~ h h O p Ridge MC cyclotron design (USA) envisages the use of the nonlinear resonance Qr=8/4 t o construct the extract i o n system with a 9% eff ic iency obtained with the electron analogue of t h i s accelerator. The f i n a l RC energy i s 700 MeV according t o the conversion design of the Dubna synchrocyclotron . I n t h i s case Q, = 1.8 and the d i r ec t use of the reson-

The effect of space charge on the frequency of the free oscillations of the particles in an isochronous cyclotron

The theoretical and experimental results of an investigation into the effect of the space charge of the ions on the frequency of the free axial oscillations in an isochronous cyclotron are discussed. The frequency of the axial oscillations was determined by using an external electric field to excite a resonance of the free oscillations. It is shown that the axial oscillation frequency varies with the space charge density in accord with the theoretical predictions. The azimuthal extent of the bunch of accelerated particles has been determined experimentally at various radii. The work was carried out at the Laboratory for Nuclear Problems at the Joint Institute for Nuclear Research on a cyclotron with an azimuthal magnetic field variation.

Free particle oscillation frequency in an isochronous cyclotron as affected by space charge

Theoretical and experimental results are presented from a study of the effect of ionic space charge on the frequency of the free axial oscillations in an isochronous synchrotron. The axial oscillation frequency was determined by resonance excitation of free oscillations with an external electric field. It is shown that the change in frequency of the axial oscillations as a function of space charge density agrees with the results of the theoretical treatment. An experimental determination was made of the azimuthal dimension of the accelerated particle burst at different radii. The studies were made in the Nuclear Problems Laboratory of the United Institute of Nuclear Studies, on a cyclotron with spatial variation of the magnetic field.

A CYCLOTRON WITH A SPATIALLY VARYING MAGNETIC FIELD

This article is devoted to the design of a cyclotron with a spatially varying magnetic field. The basic conclusions of the linear theory of motion of charged particles in a magnetic field of periodic radial and azimuthal structure are given. The theoretical and experimental results of the study of nonlinear resonance close to the center of the accelerator are presented. Formulas are obtained for the calculation of required magnetic field configurations. Methods of shimming, measurement, and stabilization of the magnetic field are suggested. An accelerator designed with pole faces of diameter 120 cm was used for modeling the ion phase motion and for investigating spatial stability. Deuterons were accelerated to an energy of 13 Mev at an accelerating voltage of 5 kv.

On the particle loss at a synchrocyclotron limit radius

Abstract Resonance interaction of radial and vertical oscillations near n = 0.25 is considered. This resonance is shown to be more dangerous than a parametric excitation of vertical oscillations which is caused by the first harmonic in the magnetic field structure.

Starting up of the cyclotron with space variation of the magnetic field

The mean magnetic field increase along the radius in accordance with relativistic mass increase of the accelerating ions is discussed. The magnetic field increase is necessary for the elimination of non-linear resonance effects at the center of the accelerator. Measurements of the magnetic field were made with an accuracy of plus or minus 1.5 gauss by a nuclear magnetometer. Deuterons were accelerated to an energy of 12 Mev and alpha particles of 24 Mev when the minimum amplitude of the accelerating voltage on the dee was 8 kv. All measurements were carried out with the intensity of the internal beam close to 1 mu a. (B.O.G.)