Proton Cyclotron Research Articles

Design of an EBIS charge breeder system for rare-isotope beams

Rare-isotope beams will be produced by using the isotope separation on-line (ISOL) system at the Rare Isotope Science Project (RISP). A proton cyclotron is the driver accelerator for ISOL targets, and uranium carbide (UCx) will be a major target material. An isotope beam of interest extracted from the target will be ionized and selected by using a mass separator. The beam emittance will then be reduced by using a radio-frequency quadrupole (RFQ) cooler before the beam is injected into the electron-beam ion-source (EBIS) charge breeder (CB). The maximum electron beam current of the EBIS is 3 A from a cathode made of IrCe in an applied magnetic field of 0.2 T. The size of the electron beam is compressed by magnetic fields of up to 6 T caused in the charge-breeding region by a superconducting solenoid. The design of EBIS-CB was performed by using mechanics as well as beam optics. A test stand for the electron gun and its collector, which can take an electron-beam power of 20 kW, are under construction. The gun assembly was first tested by using a high-voltage pulse so as to measure its perveance. The design of the EBIS, along with its test stand, is described.

Acoustic time-of-flight for proton range verification in water.

Measurement of the arrival times of thermoacoustic waves induced by pulsed proton dose depositions (protoacoustics) may provide a proton range verification method. The goal of this study is to characterize the required dose and protoacoustic proton range (distance) verification accuracy in a homogeneous water medium at a hospital-based clinical cyclotron. Gaussian-like proton pulses with 17 μs widths and instantaneous currents of 480 nA (5.6 × 10(7) protons/pulse, 3.4 cGy/pulse at the Bragg peak) were generated by modulating the cyclotron proton source with a function generator. After energy degradation, the 190 MeV proton pulses irradiated a water phantom, and the generated protoacoustic emissions were measured by a hydrophone. The detector position and proton pulse characteristics were varied. The experimental results were compared to simulations. Different arrival time metrics derived from acoustic waveforms were compared, and the accuracy of protoacoustic time-of-flight distance calculations was assessed. A 27 mPa noise level was observed in the treatment room during irradiation. At 5 cm from the proton beam, an average maximum pressure of 5.2 mPa/1 × 10(7) protons (6.1 mGy at the Bragg peak) was measured after irradiation with a proton pulse with 10%-90% rise time of 11 μs. Simulation and experiment arrival times agreed well, and the observed 2.4 μs delay between simulation and experiment is attributed to the difference between the hydrophone's acoustic and geometric centers. Based on protoacoustic arrival times, the beam axis position was measured to within (x, y) = (-2.0, 0.5) ± 1 mm. After deconvolution of the exciting proton pulse, the protoacoustic compression peak provided the most consistent measure of the distance to the Bragg peak, with an error distribution with mean = - 4.5 mm and standard deviation = 2.0 mm. Based on water tank measurements at a clinical hospital-based cyclotron, protoacoustics is a potential method for measuring the beam's position (x and y within 2.0 mm) and Bragg peak range (2.0 mm standard deviation), although range verification will require simulation or experimental calibration to remove systematic error. Based on extrapolation, a protoacoustic arrival time reproducibility of 1.5 μs (2.2 mm) is achievable with 2 Gy of total deposited dose. Of the compared methods, deconvolution of the excitation proton pulse is the best technique for extracting protoacoustic arrival times, particularly if there is variation in the proton pulse shape.

Coupling of electrostatic ion cyclotron and ion acoustic waves in the solar wind

The coupling of electrostatic ion cyclotron and ion acoustic waves is examined in three component magnetized plasma consisting of electrons, protons, and alpha particles. In the theoretical model relevant to solar wind plasma, electrons are assumed to be superthermal with kappa distribution and protons as well as alpha particles follow the fluid dynamical equations. A general linear dispersion relation is derived for such a plasma system which is analyzed both analytically and numerically. For parallel propagation, electrostatic ion cyclotron (proton and helium cyclotron) and ion acoustic (slow and fast) modes are decoupled. For oblique propagation, coupling between the cyclotron and acoustic modes occurs. Furthermore, when the angle of propagation is increased, the separation between acoustic and cyclotron modes increases which is an indication of weaker coupling at large angle of propagation. For perpendicular propagation, only cyclotron modes are observed. The effect of various parameters such as number density and temperature of alpha particles and superthermality on dispersion characteristics is examined in details. The coupling between various modes occurs for small values of wavenumber.

Characteristics of quasi‐monochromatic ULF waves in the Venusian foreshock

AbstractThe statistical properties of ULF waves observed upstream of Venus foreshock are investigated. The study is restricted to waves which are observed well below the local proton cyclotron frequency. Using the magnetic field observations from Venus Express between May 2006 and February 2012, 115 quasi‐monochromatic ULF wave trains have been identified. Statistical results show that the wave periods are mainly from 20 to 30 s in the spacecraft frame, which is about 2–3 times of the local proton cyclotron period. The transverse power dominates the power spectrum, and most of the waves display nearly circular or slightly elliptical polarization in the spacecraft frame. Moreover, these ULF waves mainly have small relative amplitudes with respect to the ambient field magnitude B0 for parallel component (δB||/B0 less than 0.3), while the range of relative amplitudes for perpendicular component δB⊥/B0 is from ~0.1 to ~1.0. Wave propagation angles are mainly less than 30° with respect to the mean magnetic field direction. The obtained results are very similar to the wave properties seen for ULF waves present in the terrestrial foreshock, which suggests that backstreaming ions in the Venusian foreshock form an important energy source for the generation of the waves.

Propagation of equatorial noise to low altitudes: Decoupling from the magnetosonic mode

AbstractEquatorial noise (often phenomenologically described as magnetosonic waves in the literature) is a natural electromagnetic emission, which is generated by instability of ion distributions and which can interact with electrons in the Van Allen radiation belts. We use multicomponent electromagnetic measurements of the DEMETER spacecraft to investigate if equatorial noise propagates inward down to the Earth. Analysis of a selected event recorded under disturbed geomagnetic conditions shows that equatorial noise can be observed at an altitude of 700 km, while propagating radially downward as a superposition of spectral lines from different distant sources observed at frequencies both below and above the local proton cyclotron frequency. Changes in the local ion composition encountered by the waves during their inward propagation disconnect the identified wave mode from the low‐frequency magnetosonic mode. The local ion composition also induces a cutoff which prevents the waves from propagating down to the ground.

Ion Bernstein instability dependence on the proton‐to‐electron mass ratio: Linear dispersion theory

AbstractFast magnetosonic waves, which have as their source ion Bernstein instabilities driven by tenuous ring‐like proton velocity distributions, are frequently observed in the inner magnetosphere. One major difficulty in the simulation of these waves is that they are excited in a wide frequency range with discrete harmonic nature and require time‐consuming computations. To overcome this difficulty, recent simulation studies assumed a reduced proton‐to‐electron mass ratio, mp/me, and a reduced light‐to‐Alfvén speed ratio, c/vA, to reduce the number of unstable modes and, therefore, computational costs. Although these studies argued that the physics of wave‐particle interactions would essentially remain the same, detailed investigation of the effect of this reduced system on the excited waves has not been done. In this study, we investigate how the complex frequency, ω = ωr+iγ, of the ion Bernstein modes varies with mp/me for a sufficiently large c/vA (such that ) using linear dispersion theory assuming two different types of energetic proton velocity distributions, namely, ring and shell. The results show that low‐ and high‐frequency harmonic modes respond differently to the change of mp/me. For the low harmonic modes (i.e., ωr∼Ωp), both ωr/Ωp and γ/Ωp are roughly independent of mp/me, where Ωp is the proton cyclotron frequency. For the high harmonic modes (i.e., , where ωlh is the lower hybrid frequency), γ/ωlh (at fixed ωr/ωlh) stays independent of mp/me when the parallel wave number, k∥, is sufficiently large and becomes inversely proportional to (mp/me)1/4 when k∥ goes to zero. On the other hand, the frequency range of the unstable modes normalized to ωlh remains independent of mp/me, regardless of k∥.

Collimator design for spatially-fractionated proton beams for radiobiology research

Preclinical and translational research is an imperative to improve the efficacy of proton radiotherapy. We present a feasible and practical method to produce spatially-modulated proton beams for cellular and small animal research for clinical and research facilities. The University of Washington (UW) 50.5 MeV proton research beamline hosting a brass collimation system was modeled using Monte Carlo simulations. This collimator consisted of an array of 2 cm long slits to cover an area of 2 × 2 cm2. To evaluate the collimator design effects on dose rate, valley dose and the peak-to-valley dose ratios (PVDR) the following parameters were varied; slit width (0.1–1.0 mm), peak center-to-center distance (1–3 mm), collimator thickness (1–7 cm) and collimator location along the beam axis. Several combinations of slit widths and 1 mm spacing achieved uniform dose at the Bragg peak while maintaining spatial modulation on the beam entrance. A more detailed analysis was carried out for the case of a slit width of 0.3 mm, peak center-to-center distance of 1 mm, a collimator thickness of 5 cm and with the collimator flush against the water phantom. The dose rate at 5 mm depth dropped relative to an open field by a factor of 12 and produced a PVDR of 10.1. Technical realization of proton mini-beams for radiobiology small animal research is demonstrated to be feasible. It is possible to obtain uniform dose at depth while maintaining reasonable modulation at shallower depths near the beam entrance. While collimator design is important the collimator location has a strong influence on the entrance region PVDRs and on dose rate. These findings are being used to manufacture a collimator for installation on the UW cyclotron proton beam nozzle. This collimator will enable comparative studies on the radiobiological efficacy of x-rays and proton beams.

Magnet Design of an 800 MeV High Power Proton Cyclotron

The high-power proton beam has wide applications in neutron and neutrino physics, radioactive ion-beam production, ADS systems, proton radiography, and nuclear data measurement, etc. Cyclotrons are intrinsic in continuous-wave beam mode, which has the characteristics of high efficient power conversion rate, compact structure, and relatively low construction cost. A high-power 800-MeV proton cyclotron was proposed by CIAE, and the prestudy on the cyclotron was carried out since the year of 2009. The main magnet is among the most crucial and challenging subsystems. In contrast to low beam current cyclotron, the main magnet system of high beam current cyclotron needs to provide very strong vertical focusing force to avoid the beam blowup caused by dangerous resonances and space charge effects. In this paper, the 3-D modeling and optimizing work on this large-scale magnet system are presented in detail.

Effects of electron temperature anisotropy on proton mirror instability evolution

AbstractProton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here we use particle‐in‐cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron‐free energy so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability.

Conceptual design of the superconducting magnet for the 250MeV proton cyclotron.

BackgroundThe superconducting cyclotron is of great importance to treat cancer parts of the body. To reduce the operation costs, a superconducting magnet system for the 250 MeV proton cyclotron was designed to confirm the feasibility of the superconducting cyclotron.FindingsThe superconducting magnet system consists of a pair of split coils, the cryostat and a pair of binary high temperature superconductor current leads. The superconducting magnet can reach a central magnetic field of about 1.155 T at 160 A. The three GM cryocooler with cooling capacities of 1.5 W at 4.5 K and 35 W at 50 K and one GM cryocooler of 100 W at 50 K were adopted to cool the superconducting magnet system through the thermosiphon technology.ConclusionThe four GM cryocoolers were used to cool the superconducting magnet to realize zero evaporation of the liquid helium.

Survey of the frequency dependent latitudinal distribution of the fast magnetosonic wave mode from Van Allen Probes Electric and Magnetic Field Instrument and Integrated Science waveform receiver plasma wave analysis

AbstractWe present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 21 September 2012 to 1 August 2014. We show that statistically, the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (fcP) has a distinct funnel‐shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extra‐ordinary (whistler) mode at wave normal angles (θk) near 90°. Performing polarization analysis on synthetic waveforms composed from a superposition of extra‐ordinary mode plane waves with θk randomly chosen between 87 and 90°, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to θk of 60°, suggesting that another approach is necessary to estimate the true distribution of θk. We find that the histograms of the synthetically derived ellipticities and θk are consistent with the observations of ellipticities and θk derived using polarization analysis. We make estimates of the median equatorial θk by comparing observed and model ray tracing frequency‐dependent probability occurrence with latitude and give preliminary frequency dependent estimates of the equatorial θk distribution around noon and 4 RE, with the median of ~4 to 7° from 90° at f/fcP = 2 and dropping to ~0.5° from 90° at f/fcP = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies.

Understanding the growth rate patterns of ion Bernstein instabilities driven by ring‐like proton velocity distributions

AbstractFast magnetosonic waves in Earth's inner magnetosphere, which have as their source ion Bernstein instabilities, are driven by hot proton velocity distributions (fp) with ∂fp(v⊥)/∂v⊥>0. Two typical types of distributions with such features are ring and shell velocity distributions. Both have been used in studies of ion Bernstein instabilities and fast magnetosonic waves, but the differences between instabilities driven by the two types of distributions have not been thoroughly addressed. The present study uses linear kinetic theory to examine and understand these differences. It is found that the growth rate pattern is primarily determined by the cyclotron resonance condition and the structure of the velocity distribution in gyroaveraged velocity space. For ring‐driven Bernstein instabilities, as the parallel wave number (k∥) increases, the discrete unstable modes approximately follow the corresponding proton cyclotron harmonic frequencies while they become broader in frequency space. At sufficiently large k∥, the neighboring discrete modes merge into a continuum. In contrast, for shell‐driven Bernstein instabilities, the curved geometry of the shell velocity distribution in gyroaveraged velocity space results in a complex alternating pattern of growth and damping rates in frequency and wave number space and confines the unstable Bernstein modes to relatively small k∥. In addition, when k∥ increases, the unstable modes are no longer limited to the proton cyclotron harmonic frequencies. The local growth rate peak near an exact harmonic at small k∥ bifurcates into two local peaks on both sides of the harmonic when k∥ becomes large.

High intensity proton beam transportation through fringe field of 70 MeV compact cyclotron to beam line targets

From the stripping points, the high intensity proton beam of a compact cyclotron travels through the fringe field area of the machine to the combination magnet. Starting from there the beams with various energy is transferred to the switching magnet for distribution to the beam line targets. In the design of the extraction and transport system for the compact proton cyclotron facilities, such as the 70MeV in France and the 100MeV in China, the space charge effect as the beam crosses the fringe field has not been previously considered; neither has the impact on transverse beam envelope coupled from the longitudinal direction. Those have been concerned much more with the higher beam-power because of the beam loss problem. In this paper, based on the mapping data of 70MeV cyclotron including the fringe field by BEST Cyclotron Inc (BEST) and combination magnet field by China Institute of Atomic Energy (CIAE), the beam extraction and transport are investigated for the 70MeV cyclotron used on the SPES project at Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro (INFN–LNL). The study includes the space charge effect and longitudinal and transverse coupling mentioned above, as well as the matching of beam optics using the beam line for medical isotope production as an example. In addition, the designs of the ±45° switching magnets and the 60° bending magnet for the extracted beam with the energy from 35MeV to 70MeV have been made. Parts of the construction and field measurements of those magnets have been done as well. The current result shows that, the design considers the complexity of the compact cyclotron extraction area and fits the requirements of the extraction and transport for high intensity proton beam, especially at mA intensity levels.

Scalings of Alfvén‐cyclotron and ion Bernstein instabilities on temperature anisotropy of a ring‐like velocity distribution in the inner magnetosphere

AbstractA ring‐like proton velocity distribution with ∂fp(v⊥)/∂v⊥>0 and which is sufficiently anisotropic can excite two distinct types of growing modes in the inner magnetosphere: ion Bernstein instabilities with multiple ion cyclotron harmonics and quasi‐perpendicular propagation and an Alfvén‐cyclotron instability at frequencies below the proton cyclotron frequency and quasi‐parallel propagation. Recent particle‐in‐cell simulations have demonstrated that even if the maximum linear growth rate of the latter instability is smaller than the corresponding growth of the former instability, the saturation levels of the fluctuating magnetic fields can be greater for the Alfvén‐cyclotron instability than for the ion Bernstein instabilities. In this study, linear dispersion theory and two‐dimensional particle‐in‐cell simulations are used to examine scalings of the linear growth rate and saturation level of the two types of growing modes as functions of the temperature anisotropy T⊥/T|| for a general ring‐like proton distribution with a fixed ring speed of 2vA, where vA is the Alfvén speed. For the proton distribution parameters chosen, the maximum linear theory growth rate of the Alfvén‐cyclotron waves is smaller than that of the fastest‐growing Bernstein mode for the wide range of anisotropies (1≤T⊥/T||≤7) considered here. Yet the corresponding particle‐in‐cell simulations yield a higher saturation level of the fluctuating magnetic fields for the Alfvén‐cyclotron instability than for the Bernstein modes as long as . Since fast magnetosonic waves with ion Bernstein instability properties observed in the magnetosphere are often not accompanied by electromagnetic ion cyclotron waves, the results of the present study indicate that the ring‐like proton distributions responsible for the excitation of these fast magnetosonic waves should not be very anisotropic.

SPES and the neutron facilities at Laboratori Nazionali di Legnaro

The SPES Radioactive Ion Beam (RIB) facility, now in the construction phase at INFN-LNL, has the aim to provide high-intensity and high-quality beams of neutron-rich nuclei for nuclear physics research as well as to develop an interdisciplinary research center based on the cyclotron proton beam. The SPES system is based on a dual-exit high-current cyclotron, with tunable proton beam energy 35-70MeV and 0.20-0.75mA. The first exit is used as proton driver to supply an ISOL system with an UCx Direct Target able to sustain a power of 10kW. The expected fission rate in the target is of the order of \( 10^{13}\) fissions per second. The exotic isotopes will be re-accelerated by the ALPI superconducting LINAC at energies of 10 A MeV and higher, for masses around \( A=130\) amu, with an expected beam intensity of \( 10^7\) - \( 10^9\) pps. The second exit will be used for applied physics: radioisotope production for medicine and neutrons for material studies. Fast neutron spectra will be produced by the proton beam interaction with a conversion target. A production rate in excess of \( 10^{14}\) n/s can be achieved: this opens up the prospect of a high-flux neutron irradiation facility (NEPIR) to produce both discrete and continuous energy neutrons. A direct proton beam line is also envisaged. NEPIR and the direct proton line would dramatically increase the wide range of irradiation facilities presently available at LNL. We also present LENOS, a proposed project dedicated to accurate neutron cross-sections measurements using intense, well-characterized, broad energy neutron beams. Other activities already in operation at LNL are briefly reviewed: the SIRAD facility for proton and heavy-ion irradiation at the TANDEM-ALPI accelerator and the BELINA test facility at CN van de Graaff accelerator.

Design and Characterization of a Thermal Neutron Source Based on a 13 MeV Proton Cyclotron

Design and Characterization of a Thermal Neutron Source Based on a 13 MeV Proton Cyclotron

Generation of magnetosonic waves over a continuous spectrum

AbstractMagnetosonic waves, also known as equatorial noise emission, were found to have discrete frequency structures, which is consistent with instability caused by proton ring distribution. Nonetheless, nondiscrete structure, i.e., a broadband spectrum over a continuous frequency range, has been reported. We investigate the question whether proton ring distribution can generate nondiscrete spectra for perpendicularly propagating magnetosonic waves. We propose discrete and nondiscrete characteristics of the local instability for explaining the observation of discrete, continuous, and mixed spectra. The criterion for transition from discrete and continuous instability is given, γ >∼ Ωh/2, where γ is wave growth rate and Ωh is proton cyclotron frequency. The condition is verified by particle‐in‐cell simulation using more realistic electron‐to‐proton mass ratio and speed of light than in previous studies. Such criterion of generating a continuous spectrum can be tested against simultaneous in situ measurement of wave and particle. We also find that the modes at low Ωh harmonics, including the fundamental Ωh, can be still excited through nonlinear wave‐wave coupling, even when they are neutral modes (γ = 0) according to the linear kinetic theory. Comparison with magnetosonic waves in cold plasma limit and electromagnetic ion Bernstein mode is also discussed.

The beam commissioning of BRIF and future cyclotron development at CIAE

As an upgrade project of the existing HI-13 tandem accelerator facility, the Beijing Radioactive Ion-beam Facility (BRIF) is being constructed in China Institute of Atomic Energy (CIAE). This project consists of an 100MeV proton compact cyclotron, a two-stage ISOL system, a superconducting linac booster and various experimental terminals. The beam commissioning of the cyclotron was launched by the end of 2013 and on July 4, 2014 the first 100MeV proton beam was received on a temporary target which was positioned at the outlet of the cyclotron. The beam current was stably maintained at above 25μA for about 9h on July 25, 2014 and the cyclotron is now ready for providing CW proton beam on target-source for RIB production. The beam current is expected to be increased to 200–500μA in the coming years. The installation of the ISOL system is finished and the stable ion beam test shows it can reach a mass resolution better than 10,000. It is expected to generate dozens of RIB by 100MeV proton beam. In addition, this paper also introduces the recent progress of the pre-study of an 800MeV, 3–4MW separate-sector proton cyclotron, which is aimed to provide high power proton beam for various applications, such as neutron and neutrino physics, proton radiography and nuclear data measurement and ADS system.

Analysis of the radiation shielding of the bunker of a 230 MeV proton cyclotron therapy facility; comparison of analytical and Monte Carlo techniques

The neutron ambient dose equivalent outside the radiation shield of a proton therapy cyclotron vault is estimated using the unshielded dose equivalent rates and the attenuation lengths obtained from the literature and by simulations carried out with the FLUKA Monte Carlo radiation transport code. The source terms derived from the literature and that obtained from the FLUKA calculations differ by a factor of 2–3, while the attenuation lengths obtained from the literature differ by 20–40%. The instantaneous dose equivalent rates outside the shield differ by a few orders of magnitude, not only in comparison with the Monte Carlo simulation results, but also with the results obtained by line of sight attenuation calculations with the different parameters obtained from the literature. The attenuation of neutrons caused by the presence of bulk iron, such as magnet yokes is expected to reduce the dose equivalent by as much as a couple of orders of magnitude outside the shield walls.

The outburst decay of the low magnetic field magnetar SWIFT J1822.3−1606: phase-resolved analysis and evidence for a variable cyclotron feature

We study the timing and spectral properties of the low-magnetic field, transient magnetar SWIFT J1822.3-1606 as it approached quiescence. We coherently phase-connect the observations over a time-span of ~500 days since the discovery of SWIFT J1822.3-1606 following the Swift-BAT trigger on 2011 July 14, and carried out a detailed pulse phase spectroscopy along the outburst decay. We follow the spectral evolution of different pulse phase intervals and find a phase and energy-variable spectral feature, which we interpret as proton cyclotron resonant scattering of soft photon from currents circulating in a strong (10^14 G) small-scale component of the magnetic field near the neutron star surface, superimposed to the much weaker (~3 x 10^13 G) magnetic dipole field. We discuss also the implications of the pulse-resolved spectral analysis for the emission regions on the surface of the cooling magnetar.