Computer modeling of the acceleration of low-charge krypton ions in the CYTRACK cyclotron

The basic results of numeric simulations of krypton ion motion with decreased charge in the CYTRACK cyclotron are presented. CYTRACK is the world??s first industrial cyclotron dedicated to the production of track membranes. Computer modeling confirms the possibility of Kr ₈₄ ⁺¹¹ ion acceleration in the magnetic field with an increase in the level of the magnetic field by 1.6% on the 6 harmonic of the accelerating system. The beam energy will be sufficient for the exposure of a film with a thickness of 10 ??m.     

Development of radiation medicine at DLNP, JINR

The Dzhelepov Laboratory of Nuclear Problems’ activity is aimed at developing three directions in radiation medicine: 3D conformal proton therapy, accelerator techniques for proton and carbon treatment of tumors, and new types of detector systems for spectrometric computed tomography (CT) and positron emission tomography (PET). JINR and IBA have developed and constructed the medical proton cyclotron C235-V3. At present, all basic cyclotron systems have been built. We plan to assemble this cyclotron at JINR in 2011 and perform tests with the extracted proton beam in 2012. A superconducting isochronous cyclotron C400 has been designed by the IBA-JINR collaboration. This cyclotron will be used for radiotherapy with proton, helium and carbon ions. The ¹²C⁶⁺ and ⁴He²⁺ ions will be accelerated to an energy of 400 MeV/amu, the protons will be extracted at the energy 265 MeV. The construction of the C400 cyclotron was started in 2010 within the framework of the Archarde project (France). Development of spectrometric CT tomographs may allow one to determine the chemical composition of a substance together with the density, measured using traditional CT. This may advance modern diagnostic methods significantly. JINR develops fundamentally new pixel detector systems for spectrometric CT. The time-of-flight (TOF) system installed in the positron emission tomograph (PET) permits essential reduction in the detector noise from occasional events of different positron annihilations. The micropixel avalanche photodiodes (MAPDs) developed at JINR allow a factor of 1.5 reduction in the resolution time for the PET TOF system and suppression of the noise level as compared to commercial PET. The development of a combined PET/MRI is of considerable medical interest, but it cannot be made with the existing PET tomographs based on detectors of compact photomultipliers due to strong alternating magnetic field of MRI. Change-over to detectors of micropixel avalanche photodiodes permits making a combined PET/MRI.     

H− superconducting cyclotron for PET isotope production

The scientific design of a 14-MeV H^? compact superconducting cyclotron for producing of the ¹⁸F and ¹³N isotopes has been developed. Main requirements to the facility as a medical accelerator are met in the design. In particular, the main requirement for the cyclotron was the smallest possible size due to the superconducting magnet. The calculations show that the proposed cyclotron allows extracted beam intensity over 500 μA. To increase system reliability and production rates, an external H^? ion source is applied. The choice of the cyclotron concept, design of the structure elements, calculation of the electromagnetic fields and beam dynamics from the ion source to the extraction system were performed.     

Giant magnetoresistance oscillations induced by microwave radiation and a zero-resistance state in a 2D electron system with a moderate mobility

The effect of a microwave field in the frequency range from 54 to 140 GHz on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than 10⁶ cm²/V s is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in the magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-GHz microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than 10⁶ cm²/V s does not prevent the formation of zero-resistance states in a magnetic field in a two-dimensional system under the effect of microwave radiation.     

On the possible separation of the phase enriched with Nb in superconducting intermetallic Nb<Subscript>3</Subscript>Sn irradiated with fast protons

The results of the study of magnetization and dynamic magnetic susceptibility are correlated with changes in the microstructure of superconducting intermetallic Nb₃Sn plates irradiated at the Kurchatov Institute cyclotron with fast protons with an energy of 12.8 MeV to a fluence of 1 · 10¹⁸ cm^?2. The dependence of the superconducting transition temperature on the total irradiation dose is determined. For one of the samples, the dynamic magnetic susceptibility exhibits several steps corresponding to superconducting transitions at different temperatures. It is assumed that a Nb-enriched phase is separated in the region of maximum radiation damages. A microstructural analysis shows the appearance of randomly oriented Nb-enriched regions from 0.1 to 0.5 μm in size.     

Positron emission isotope production cyclotron in DLNP JINR (Status Report)

A C10-cyclotron for radioisotope production is under construction at the Dzhelepov Laboratory of Nuclear Problem, Joint Institute for Nuclear Research (DLNP JINR). It is a compact isochronous cyclotron for accelerating H⁻ ions to the energy of about 10 MeV. The magnetic system, vacuum chamber and accelerating system is being built now. Results of the calculation and forming of the cyclotron magnetic field and the study of the beam dynamics from an ion source to an extraction system in calculated magnetic field are presented. The text was submitted by the authors in English.     

A Superconducting Quantum Interference Device Measurement System for Ultra Low-Field Nuclear Magnetic Resonance

We describe a superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) spectrometer operating at ultralow magnetic fields far below the Earth’s field. The spectrometer consists of a helium-cooled magnetic sensor system and two Helmholtz coils, one for pre-polarizing the sample by fields of up to 5 mT, and one for the detection in fields of the nanotesla and microtesla range. The spectrometer represents the current state of the art in ultralow-field NMR and enables the observation of phenomena that are difficult or impossible to achieve by a conventional NMR setting. In particular, one can obtain broad band spectra covering different nuclei, such as ¹H and ³¹P, with a frequency resolution in the millihertz range, observe the variation of their heteronuclear coupling with the detection field strength, and investigate relaxation processes that reflect molecular dynamics in the millisecond range.     

Stability of electrostatic ion cyclotron waves in a multi-ion plasma

We have studied the stability of the electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H⁺) and temperature-anisotropic positively (O⁺) and negatively (O⁻) charged oxygen ions, with the electrons drifting parallel to the magnetic field. Analytical expressions have been derived for the frequency and growth/damping rate of ion cyclotron waves around the first harmonic of both hydrogen and oxygen ion gyrofrequencies. We find that the frequencies and growth/damping rates are dependent on the densities and temperatures of all species of ions. A detailed numerical study, for parameters relevant to comet Halley, shows that the growth rate is dependent on the magnitude of the frequency. The ion cyclotron waves are driven by the electron drift parallel to the magnetic field; the temperature anisotropy of the oxygen ions only slightly enhance the growth rates for small values of temperature anisotropies. A simple explanation, in terms of wave exponentiation times, is offered for the absence of electrostatic ion cyclotron waves in the multi-ion plasma of comet Halley.     

分离扇回旋加速器的接受度及效率

以9.7MeV/u的238U36+,5.62MeV/u的70Zn10+为典型离子,分析并模拟了分离扇回旋加速器(SSC)的注入、加速和引出,得到了SSC在理论等时场下横向和纵向的接受度。为了研究SSC在实际情况下的接受度,在实测场的基础上采用Kr-Kb方法以及Lagrange插值方法建立了与实际比较符合的等时场,计算了该等时场下SSC横向和纵向的接受度,发现了导致SSC实际接受度和传输效率低的主要原因在于注入系统中的MSI3元件和引出系统中的MSE3元件设计存在缺陷。模拟结果显示,通过改变MSI3和MSE3的曲率或者垫铁改变元件内部的场分布可以改善SSC的实际接受度和传输效率。     

Excitation of ion cyclotron waves at the difference frequency of two microwave beams in a semiconductor

This paper presents an investigation of the resonant excitation of the electrostatic ion cyclotron wave at the difference frequency of two microwave beams propagating in a magnetoactive solid state plasma, viz. n InSb. The resonant excitation of the electrostatic ion cyclotron wave occurs when the difference frequency of the two microwave beams and the difference of their propagation vectors satisfy the dispersion relation corresponding to the electrostatic ion cyclotron wave. For typical plasma parameters of n InSb and microwave beams of power densities 1 MW cm^?2, the power density of the excited ion cyclotron wave is 0.40 kW cm^?2 when external magnetic field is $\text{1.46 kG (}\text{Ω}{}_{\mathrm{c}}\text{ω}\text{) = 0.1)}$. The power density of the excited ion cyclotron wave increases with the magnetic field. This study may provide new means for the characterisation and diagnostic of semiconductors.     

Magneto-optical measurements with a hybrid magnet

An FFT spectrometer has been constructed to measure magneto-optical spectra in the far-infrared region (3 to 40 cm^–1) with a hybrid magnet system. The magneto-absorption was studied in the spin-Peierls cuprate CuGeO₃ at various magnetic fields. Coil constants of superconducting magnet and resistive one, of which a hybrid magnet consists, were calibrated by ESR spectra at the constant field.     

金属玻璃Zr78Co22中的弱局域化效应

测量了超导金属玻璃Zr₇₈Co₂₂的磁阻和上临界磁场H_c2。磁阻的实验结果定性地与包含自旋-轨道散射的三维弱局域化理论相符,而定量则有明显的偏差,其偏差主要来源于超导涨落效应。在所测量的温区内,上临界磁场H_c2随温度呈线性变化,同时还得出超导金属玻璃Zr₇₈Co₂₂中的非弹性散射主要来源于电子-声子相互作用,其散射几率τ_i^-1=1.3×1O¹⁰T²,略小于Bergmann理论所预言的值。 关键词：     

Quantum transport in GaInAs-AlInAs heterojunctions,and the influence of intersubband scattering

Shubnikov-de Haas and cyclotron resonance results are presented for GaInAs-AlInAs heterojunctions in both perpendicular and tilted magnetic fields. Two electric subbands are occupied in zero magnetic field. Magnetic depopulation of the higher (E₁) subband is observed in both perpendicular and tilted orientations. This enables a demonstration of the importance of intersubband scattering in both resistivity and cyclotron resonance. A shift of the relative positions of the E_o and E₁ subbands by parallel magnetic fields is measured to be 0.26 meV/T².     

Discrete accidental symmetry for a particle in a constant magnetic field on a torus

A classical particle in a constant magnetic field undergoes cyclotron motion on a circular orbit. At the quantum level, the fact that all classical orbits are closed gives rise to degeneracies in the spectrum. It is well-known that the spectrum of a charged particle in a constant magnetic field consists of infinitely degenerate Landau levels. Just as for the 1/r and r² potentials, one thus expects some hidden accidental symmetry, in this case with infinite-dimensional representations. Indeed, the position of the center of the cyclotron circle plays the role of a Runge-Lenz vector. After identifying the corresponding accidental symmetry algebra, we re-analyze the system in a finite periodic volume. Interestingly, similar to the quantum mechanical breaking of CP invariance due to the θ-vacuum angle in non-Abelian gauge theories, quantum effects due to two self-adjoint extension parameters θ_x and θ_y explicitly break the continuous translation invariance of the classical theory. This reduces the symmetry to a discrete magnetic translation group and leads to finite degeneracy. Similar to a particle moving on a cone, a particle in a constant magnetic field shows a very peculiar realization of accidental symmetry in quantum mechanics.     

Local probe (170Yb3+) measurements of magnetic fields in YBa2Cu3Ox

We introduce the technique of studying the field dependence of the electro-nuclear energy levels of a rare earth to measure the magnetic field present at the rare earth/yttrium site in YBa₂Cu₃O_x. Measurements were made by¹⁷⁰Yb Mössbauer spectroscopy. The hyperfine spectrum of the ground state Kramers doublet for Yb³⁺ ions diluted into this matrix is sensitive to fields in the range 100 to 2000G. Flux penetration and trapping at the local site level have been measured in superconducting samples. A molecular field exists on the rare earth site in non superconducting samples suggesting that the ordered Cu2 magnetic moments are intrinsically non colinear.     

Alignment of Anisotropic Particles by Magnetic Field as Seen by NMR

We applied ¹³C and ²⁰⁵Tl NMR for studying alignment of particles of graphene and high temperature superconductor (Tl_0.5Pb_0.5)(Ba_0.2Sr_0.8)₂Ca₂Cu₃O_y caused by magnetic field. These compounds have layered structure and reveal anisotropic magnetic susceptibility. We found that the field of 8 T causes minor alignment of powder graphene and somewhat better alignment of fluffy graphene particles. Herewith the effect of alignment is well pronounced in ²⁰⁵Tl spectra of the superconducting particles fixed in epoxy in the field of 8 T. This effect is reflected in the ²⁰⁵Tl line shape measured in a magnetic field of 1.17 T and becomes much more pronounced in measurements made in high magnetic field of 8 T. Spectra simulations allow determining the degree of the particles’ alignment.     

DC-60 heavy ion cyclotron complex: The first beams and project parameters

The construction of the DC-60 Heavy Ion Cyclotron for the Interdisciplinary Scientific Research Complex (ISRC) in Astana started in early 2004. The cyclotron was manufactured and tested at the Flerov Laboratory of Nuclear Reactions (FLNR) in Dubna. The main units were delivered to Astana and assembled in the ISRC building in the summer of 2006. The cyclotron was turned on in September, 2006. The first heavy ion beams in the whole A/Z and energy ranges were accelerated and extracted in December, 2006. The complex, based on the DC-60 cyclotron, is intended for applied and fundamental research using accelerated heavy ion beams ranging from Carbon to Xenon with energies in the range of 0.34–1.77 MeV/nucleon, as well as for experiments on the channel of low energy ion beams, where the ion extraction voltage supplied by the ECR source reaches 25 kV. The energy variation of the accelerated ions is accomplished by changing the ion charge. The possibility of smoothly tuning the ion energy by ±30% of its nominal value can be seen by changing the cyclotron magnetic field. Within the framework of commissioning the DC-60 cyclotron, a number of experiments were carried out with accelerating charged particle beams in the main points of the working diagram

Effective mass of the 2-dimensional electron gas in an Al0.6Ga0.4Sb/InAs single quantum well

The 2-dimensional electron gas (2DEG) in an Al_0.6Ga_0.4Sb/InAs single quantum well is studied using cyclotron resonance and Shubnikov - de Haas (SdH) techniques. The effective mass (m^*) of the 2DEG was obtained from the peak positions of the cyclotron resonance transmission spectra. The results exhibit oscillatory behavior as a function of the magnetic field strength (B). The m^* value extracted from the temperature dependence of the SdH oscillations is in good agreement with the average value of m^* obtained from cyclotron resonance measurements. The effective mass is calculated as a function of B using an electron self-energy model based on the Hartree-Fock approximation. The calculated m^* values also show oscillatory behavior similar to that of the measured cyclotron resonance m^*. Both experiment and theory show that m^* maxima are shifted from the integral values (both odd and even) of the filling factors.