Beam dynamics in a C253-V3 cyclotron for proton therapy

In recent years, oncologic diseases have become a severe issue in developed countries. Proton therapy is viewed as one of the most efficient methods of treating oncologic diseases. The results of computing the beam dynamics in a C235 medical cyclotron intended for proton therapy are presented. The cyclotron was modified by teams of researchers at the Joint Institute for Nuclear Research and Ion Beam Application (IBA Group, Belgium). Possible reasons for losses in the beam under acceleration are considered, and the influence of the magnetic field radial component in the median plane of the accelerator is studied. The results of analysis and upgrading of the beam extraction system are presented. Based on analytical data, the design of the commercial C235 cyclotron is considerably modified. A new version of the C235-V3 cyclotron will be placed in commission at the Dimitrovgrad center of radiation medicine.     

Effect of the magnetic field from the accelerating system on the beam dynamics in the cyclotron

Magnetic components of the HF field in a cyclotron can change the transverse beam size and the phase width of bunches during acceleration. As a consequence, the phase portraits of the beam at the entrance to the electrostatic deflector and thus the efficiency of the extraction system can change. Expressions are obtained for the components of the magnetic field from the HF system in the vicinity of the cyclotron median plane. The effect of this field on the beam parameters during acceleration and at the entrance to the electrostatic deflector is shown by numerical simulation. For the C235 proton cyclotron, the beam parameter variation is as large as 50%.     

Beam dynamics study in the C235 cyclotron for proton therapy

A study of the beam dynamics in the C235 (T06) cyclotron made for proton therapy is presented. Results of the computer simulations of the particle motion in the measured magnetic field are given. A study of the resonance influence on the acceleration process was carried out. The corresponding tolerances on the magnetic field imperfections and transverse beam parameters were defined using these simulations. The text was submitted by the authors in English.     

Simulation of beam extraction from C235 cyclotron for proton therapy

The extraction of an accelerated beam from C235 cyclotron (IBA, Belgium) for proton therapy is simulated. The results of optimizing the parameters of the extraction system to increase the beam extraction efficiency are presented. Our theoretical results agree well with the experimental data. A new configuration of electrostatic deflector is proposed based on the numerical results; using this configuration essentially increases the efficiency of the cyclotron extraction system.     

C235-V3 cyclotron for a proton therapy center to be installed in the hospital complex of radiation medicine (Dimitrovgrad)

Proton therapy is an effective method of treating oncologic diseases. In Russia, construction of several centers for proton and ion therapy is slated for the years to come. A proton therapy center in Dimitrovgrad will be the first. The Joint Institute for Nuclear Research (Russia) in collaboration with Ion Beam Application (IBA) (Belgium) has designed an C235-V3 medical proton cyclotron for this center. It outperforms previous versions of commercial IBA cyclotrons, which have already been installed in 11 oncologic hospital centers in different countries. Experimental and calculation data for the beam dynamics in the C235-V3 medical cyclotron are presented. Reasons for beam losses during acceleration are considered, the influence of the magnetic field radial component in the midplane of the accelerator and main resonances is studied, and a beam extraction system is designed. In 2011–2012 in Dubna, the cyclotron was mounted, its magnetic field was properly configured, acceleration conditions were optimized, and beam extraction tests were carried out after which it was supplied to Dimitrovgrad. In the C235-V3 cyclotron, an acceleration efficiency of 72% and an extraction efficiency of 62% have been achieved without diaphragming to form a vertical profile of the beam.     

磁边界效应对径向磁场中等离子体束流运动轨迹的影响

根据离子与径向磁场的约束关系,用面向对象的单元粒子法模拟了极向偏转器中等离子体束流在均匀和非均匀径向磁场中的运动情况,得到了在磁边界效应下极向偏转器内部畸变电场的分布,分析了对质量分离的影响。模拟成果对质量分离器、质谱分析仪及材料提纯等装置的研制、特殊位形电磁场控制多质量束流等相关领域的研究有参考价值。     

Modeling beam dynamics in magnetic field of the helical coil

In this report, the beam dynamics in the magnetic field defined by the integral expression of the vector potential is considered. The influence of transverse components of the magnetic field on the shift of the beam trajectory in the helical solenoid of the LUE-200 accelerator of the IREN setup (Joint Institute for Nuclear Research, Dubna) is analyzed.     

Behavior of the fast cyclotron wave in a nonuniform magnetic field

The fast cyclotron wave becomes unstable and is excited in a spiral electron beam-plasma system when the perpendicular energy component of the beam is sufficiently large. When a nonuniform magnetic field is applied to the system, the cyclotron frequency as well as the parallel velocity component of the beam vary spatially. It is confirmed experimentally, that the variation affects the excited wave and results in a spatial variation of its wavenumber in the way predicted by the dispersion relation of the fast cyclotron wave.     

Effect of a planar magnetic field on the domain wall dynamics in a double-layer uniaxial magnetic film

Motion of an isolated domain wall in a double-layer uniaxial magnetic film, where the film layers differ in characteristic length, saturation magnetization and damping parameter, is investigated by solving the Slonczewski equation. A planar magnetic field is applied normal to the domain-wall plane. The dependences of the threshold field and limiting velocity of disruption of the steady-state motion of the domain wall on the planar magnetic field value are obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 60–63, December, 2008.     

Measurements of spatial cyclotron damping in a uniform magnetic field

The dispersion and damping of whistler waves has been measured in an essentially collisionless plasma at frequencies up to 0.92ω_c, the electron cyclotron frequency. The experimental results agree to within ± 10% of the plane wave hot plasma dispersion relation.     

Nonlinear cyclotron resonant wave-particle interaction in a nonuniform magnetic field

Quasilinear analysis of wave-particle interactions is presented for plasma flowing in a weakly nonuniform magnetic field configuration. The method presented is based on a scale separation between the length scales of quasilinear relaxation and the magnetic field inhomogeneity, allowing one to obtain large scale solutions for both particle distribution functions and wave spectra, without going into the details of the small scale quasilinear relaxation. The numerical example shows the existence of a secondary instability for an initially stable particle distribution function.     

Effect of a pulsed magnetic field on the nonlinear dynamics of vortexlike domain walls in magnetic films

The Landau-Lifshitz equation is numerically solved to study the nonlinear dynamic behavior of domain walls with the 2D vortexlike magnetization distribution in magnetically uniaxial films that have in-plane anisotropy and are exposed to a pulsed magnetic field. It is shown that a pulsed magnetic field H _p may induce transitions between various steady wall motions that differ in magnetization distribution. Solitary rectangular pulses, as well as a regular train of rectangular pulses, may be used to control the period of nonlinear dynamic transformations of the wall internal structure and the related period of variation of the wall velocity.     

Formation and dynamics of a virtual cathode in a tubular electron beam placed in a magnetic field

Mechanisms underlying the formation and dynamics of a virtual cathode (VC) in a tubular electron beam subjected to a magnetic field are studied using a numerical 2D model. Two qualitatively different competing types of space charge dynamics near the VC are discovered. Which of them predominates depends on the magnetic field strength. The beam current critical density at which a nonstationary VC forms in the system is also strongly dependent on the magnetic field. It is shown that the optimal strength of the magnetic field that minimizes the beam current critical density depends on the Brillouin magnetic field.     

Basic features of a charged particle dynamics in a laser beam with static axial magnetic field

In this paper, the trajectory and kinetic energy of a charged particle, subjected to interaction from a laser beam containing an additionally applied external static axial magnetic field, have been analyzed. We give the rigorous analytical solutions of the dynamic equations. The obtained analytical solutions have been verified by performing calculations using the derived solutions and the well known Runge-Kutta procedure for solving original dynamic equations. Both methods gave the same results. The simulation results have been obtained and presented in graphical form using the derived solutions. Apart from the laser beam, we show the results for a maser beam. The obtained analytical solutions enabled us to perform a quantitative illustration, in a graphical form of the impact of many parameters on the shape, dimensions and the motion direction along a trajectory. The kinetic energy of electrons has also been studied and the energy oscillations in time with a period equal to the one of a particle rotation have been found. We show the appearance of, so-called, stationary trajectories (hypocycloid or epicycloid) which are the projections of the real trajectory onto the (x, y) plane. Increase in laser or maser beam intensity results in the increase in particle’s trajectory dimension which was found to be proportional to the amplitude of the electric field of the electromagnetic wave. However, external magnetic field increases the results in shrinking of the trajectories. Performed studies show that not only amplitude of the electric field but also the static axial magnetic field plays a crucial role in the acceleration process of a charged particle. At the authors of this paper best knowledge, the precise analytical solutions and theoretical analysis of the trajectories and energy gains by the charged particles accelerated in the laser beam and magnetic field are lacking in up to date publications. The authors have an intention to clarify partly some important aspects connected with this process. The presented theoretical studies apply for arbitrary charged particle and the attached figures-for electrons only.     

Optimization of the magnetic field in the analyzing magnet of the axial injection beam line of the cyclotron DC-280

The optimization of the field distribution of the analyzing magnet installed in the axial injection beam line of the cyclotron DC-280 is carried out. This optimization is done on the basis of a three-dimensional calculation of the magnet field. The optimum value of the basic geometrical characteristics of the magnet influencing the form of the field distribution is found.     

Transverse dynamics of a low-density relativistic electron beam propagating in the plasma along an external magnetic field

It is shown that a low-density relativistic electron beam can be transported under conditions of (i) periodic oscillation of the beam radius, (ii) unlimited beam expansion, and (ii) pinching. Analytical expressions for the radial evolution of the beam under these transport condition are obtained.     

Effect of a constant magnetic field on the photoconductivity of single-crystal C60

Magnetic fields with induction B<1 T are found to affect the photocurrent in single-crystal C₆₀. This effect does not reduce to the Hall effect. The effect of the field on the multiplicity of short-lived pairs consisting of mobile carriers and their traps is proposed as a possible explanation for the observed phenomenon. Fiz. Tverd. Tela (St. Petersburg) 41, 2097–2099 (November 1999)     

Effect of a pulsed magnetic field on the microhardness of C60 single crystals

Magnetic-field pulses with induction greater than 10 T were observed to influence the microhardness of C₆₀ single crystals. It was established that the magnetic field reversibly alters the bulk properties of the material. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 110–113 (25 January 1999)