Proton Cyclotron Research Articles

Proton Cyclotron Waves and Pickup Ion Ring Distribution Instabilities Upstream of Mars

AbstractProton cyclotron waves (PCWs) upstream of Mars are thought to be associated with the instabilities of pickup ions. The instabilities of pickup ions of ring distributions have larger maximum growth rates compared with beam distributions. However, observations revealed a notably‐reduced occurrence rate of PCWs for pickup ions of ring distributions. Linear instability analysis and a corresponding two‐dimensional particle‐in‐cell (PIC) simulation are performed to investigate the instabilities of pickup ion ring distributions upstream of Mars. Linear instability analysis indicates that a pickup ion ring distribution is unstable to the ion cyclotron, ion Bernstein, and mirror instabilities. The corresponding PIC simulation confirms the linear analysis results and further demonstrates that the pickup ions are scattered toward an isotropic shell distribution by the waves excited. Interestingly, the saturation energy of the waves is much lower than that driven by a corresponding pickup ion beam distribution, and mirror waves eventually dominate the system.

Quiescent Solar Wind Regions in the Near-Sun Environment: Properties and Radial Evolution

Regions of magnetic fields with near-radial, Parker-spiral-like geometry known as quiescent regions have been observed in Parker Solar Probe data. These regions have very low δ B/〈∣B∣〉 compared to nonquiescent solar wind at the same heliocentric distances. Quiescent regions are observed to have lower solar wind bulk speeds, lower proton temperatures, and lower proton density. Inside of 15 solar radii ( R ⊙ ), identified quiescent regions show distinct thermal properties, having higher proton temperature anisotropies and lower parallel plasma betas compared to switchback patches observed at the same heliocentric distances. When placed on R -versus-β ∥p plots (where R is the proton temperature anisotropy), quiescent region solar wind is shown to be more stable to proton cyclotron and firehose instabilities than nonquiescent solar wind at the same heliocentric distances. It is shown that quiescent regions evolve similarly to the surrounding nonquiescent solar wind, but quiescent solar wind begins at a different location in the R -versus-β ∥p parameter space, suggesting that these regions have separate origins from the more turbulent nonquiescent solar wind. Namely, enhanced temperature anisotropies and enhanced magnetic field strength may be consistent with magnetic field lines that have undergone less magnetic field expansion compared to nonquiescent wind at the same heliocentric distances.

Role of nonthermal solar wind protons in the excitation of electromagnetic proton-cyclotron instability: a kinetic theory based exact numerical investigation

Free transverse kinetic energy i.e. perpendicular temperature anisotropy of protons excite the electromagnetic ion/proton cyclotron instability which is pertained to waves associated with prevalent electromagnetic ion/proton cyclotron emissions in various natural regions of plasmas. The transverse dielectric response function of left hand circularly polarized electromagnetic proton cyclotron (EPC) instability is calculated for two models of nonthermal Cairns distributed plasmas. These models are distinguished according to the effective thermal velocities of protons. For the energetic nonthermal protons populations, nonthermality dependent effective temperature model is proposed which significantly contributes in the excitation of aforementioned plasma mode and cause an appreciable enhancement in the instability growth rate. Exact numerical solution of dispersion relation yields oscillatory real frequency and growth rate of instability. A comparative analysis is also carried out to examine the instability behavior in distinct nonthermal and thermal plasma models. Contemporary numerical investigations are highly beneficial to understand the intricate dynamics of space plasmas.

Anisotropic Heating and Cooling within Interplanetary Coronal Mass Ejection Sheath Plasma

This study presents the first comprehensive investigation of the relationship between heating and cooling, temperature anisotropy, turbulence level, and collisional age within interplanetary coronal mass ejection (ICME) sheaths, which are highly compressed, heated, and turbulent. Using Wind spacecraft data, we analyze 333 ICME sheaths observed at 1 au from 1995 to 2015. The proton temperature within the ICME sheaths has a log-normal probability distribution. Irrespective of instability growth rates, plasma unstable to proton-cyclotron (PC) and firehose instabilities appear to be statistically hotter, at least by a factor of 5 to 10, compared to stable plasma. We also observe relatively enhanced magnetic fluctuations and low collisional age, especially in regimes unstable to PC and firehose instabilities at low proton betas β p ≤ 2. In the case of high beta β p ≥ 2, we observe high magnetic fluctuations close to the instabilities and less collisional age to the plasma unstable to firehose instability rather than near the mirror mode and PC threshold. Our findings suggest that heating processes dominate over cooling processes in producing proton temperature anisotropy in the ICME sheath region. Moreover, collisional age and magnetic fluctuations are critical in maintaining anisotropic and isotropic conditions.

Magnetosonic waves in the Martian ionosphere driven by upstream proton cyclotron waves: Two-point observations by MAVEN and Mars Express

Recent observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express (MEX) spacecraft have suggested that pressure pulses originating from upstream proton cyclotron waves (PCWs) can “ring” the Martian magnetopause at the same frequency and drive magnetosonic waves in the upper ionosphere of Mars, thereby transporting energy from the solar wind into the ionosphere. However, the limitation of single-spacecraft measurements prevents simultaneous observations of the driver and response of this “ringing” process of the Martian magnetosphere. Here we utilize two-point measurements from MAVEN and MEX to characterize the ringing probability at which upstream PCWs drive compressional fluctuations in the ionospheric magnetic field. We develop an algorithm to identify PCW-driven magnetosonic waves in the upper ionosphere of Mars from the two-point magnetic field data. The derived ringing probability is higher on the dayside, outside strong crustal magnetic fields, and under high solar wind density conditions. We also show that the median power of dayside ionospheric magnetic field fluctuations is enhanced by a factor of ∼2 at corresponding frequencies in the presence of upstream PCWs compared to the median power in the absence of upstream PCWs. These results demonstrate the prevalence of energy deposits into the dayside Martian ionosphere from the solar wind mediated by the PCW-driven ringing of the magnetosphere. Future studies, possibly with new multi-point observations, should address the detailed processes of wave propagation and energy transport through the system and the long-term impact of this chain of processes on the planetary ion heating in the ionosphere and atmospheric loss from Mars.

Magnetosonic Waves Excited by Maxwellian Ring Protons in Space Plasma Environment

A comprehensive theoretical model for a homogeneous plasma system of hot, tenuous Maxwellian ring-distributed protons and the cold background of Maxwellian ions and electrons is used to study the resonant instabilities of magnetosonic (MS) waves. The perpendicular velocity integrals associated with the Maxwellian ring distribution have no analytical solution, hence, are solved numerically, while the parallel velocity integrals are solved analytically by invoking series expansion of the plasma dispersion function. For the plasma parameters relevant to Earth’s inner magnetosphere, the theoretical model generates MS waves with frequencies from 5 times the local proton cyclotron frequency to above the lower hybrid frequency for a propagation angle of 89.5°. Hydrogen (H+) band electromagnetic ion cyclotron waves are also excited by the Maxwellian ring protons for the same set of plasma parameters. A detailed analysis reveals that a sufficiently large ring velocity, as well as a smaller perpendicular and parallel thermal velocity, can enhance the MS wave growth. The study also explores the role of background plasma parameters in modulating the waves. The present theoretical model reproduces the harmonics of the MS waves observed by the Van Allen Probes in the Earth’s inner magnetosphere. Further, the model can generate MS waves in other plasma environments, e.g., Mars, where the presence of ring protons has been established by MAVEN in connection with the MS wave observations.

Automatic Detection of Quasi-Periodic Emissions from Satellite Observations by Using DETR Method

The ionospheric quasi-periodic wave is a type of typical and common electromagnetic wave phenomenon occurring in extremely low-frequency (ELF) and very low-frequency ranges (VLF). These emissions propagate in a distinct whistler-wave mode, with varying periodic modulations of the wave intensity over time scales from several seconds to a few minutes. We developed an automatic detection model for the QP waves in the ELF band recorded by the China Seismo-Electromagnetic Satellite. Based on the 827 QP wave events, which were collected through visual screening from the electromagnetic field observations, an automatic detection model based on the Transformer architecture was built. This model, comprising 34.27 million parameters, was trained and evaluated. It achieved mean average precision of 92.3% on the validation dataset, operating at a frame rate of 39.3 frames per second. Notably, after incorporating the proton cyclotron frequency constraint, the model displayed promising performance. Its lightweight design facilitates easy deployment on satellite equipment, significantly enhancing the feasibility of on-board detection.

Coexistence of Antisunward and Sunward Ion Cyclotron Waves in the Near-Sun Solar Wind: Excitation by the Proton Cyclotron Instability

Based on observations from the Parker Solar Probe in the near-Sun solar wind, this study identifies an ion-scale wave event characterized by two distinct frequency bands. The lower-band waves exhibit right-hand polarization, while the upper-band waves have left-hand polarization. Alongside these waves, there are clear indications of the existence of both proton core and beam components, with the perpendicular temperature being higher than the parallel temperature in the measured proton velocity distribution functions (VDFs). Utilizing the plasma parameters derived from typical proton VDFs, instability analyses are conducted to investigate the mode nature of the observed waves and their excitation mechanism. The lower-band waves are identified as sunward ion cyclotron waves (ICWs), generated through the proton beam cyclotron instability; the upper-band waves are recognized as antisunward ICWs, induced by the proton core cyclotron instability. This study provides the first direct observational evidence confirming the presence of counterpropagating ICWs and proton cyclotron instability in the solar wind.

Development of a fast neutron monitoring detector for the NDPS neutron TOF facility by using Parallel Plate Avalanche Counters

A Parallel Plate Avalanche Counter (PPAC) neutron monitoring detector was developed and manufactured to monitor fast neutrons with energies greater than ∼1 MeV for use in the Nuclear Data Production System (NDPS), a neutron Time-of-Flight (TOF) facility of RAON. The detectors designed for monitoring fast neutrons comprise two sets of PPACs and a fast neutron converter. The performance of the detector was tested by using a241Am alpha source and neutron beams from a proton cyclotron. For the fast neutron converter, a thin thorium coating with a diameter of 60 mm was prepared by using the electrodeposition method. The areal density of thorium deposited on a thin aluminium layer with a thickness of 2 μm was determined by alpha spectrometry and measured to be 306 ± 7.65 μg/cm2. For the neutron beam test, neutrons were generated through the 9Be (p,n)9B reaction in a proton cyclotron facility. These generated neutrons were detected by using our PPAC neutron detector, and the experimentally measured count rate (1.74 ± 0.18 counts/s) agreed with the count rate (1.68 counts/s) calculated by PHITS v3.16 and GEANT4 v10.7 simulations. The timing resolution of the detector was estimated to be σ = 550 ps.

New Regime of Inertial Alfvén Wave Turbulence in the Auroral Ionosphere.

We investigate a new regime of inertial Alfvén wave turbulence observed in the very low beta plasma of the auroral ionosphere using electric and magnetic field measurements by the TRICE-2 sounding rocket. Combining the observed features of the electric and magnetic field frequency spectra with the linear properties of inertial Alfvén waves, we deduce the path of the anisotropic turbulent cascade through wave vector space. We find a critically balanced cascade through the magnetohydrodynamic scales of the inertial range down to the perpendicular scale of the plasma skin depth, followed by a parallel cascade to the ion inertial length. We infer damping of the cascade by a combination of proton cyclotron damping and electron Landau damping.

Navigating the straits: realizing the potential of proton FLASH through physics advances and further pre-clinical characterization.

Ultra-high dose-rate 'FLASH' radiotherapy may be a pivotal step forward for cancer treatment, widening the therapeutic window between radiation tumour killing and damage to neighbouring normal tissues. The extent of normal tissue sparing reported in pre-clinical FLASH studies typically corresponds to an increase in isotoxic dose-levels of 5-20%, though gains are larger at higher doses. Conditions currently thought necessary for FLASH normal tissue sparing are a dose-rate ≥40 Gy s-1, dose-per-fraction ≥5-10 Gy and irradiation duration ≤0.2-0.5 s. Cyclotron proton accelerators are the first clinical systems to be adapted to irradiate deep-seated tumours at FLASH dose-rates, but even using these machines it is challenging to meet the FLASH conditions. In this review we describe the challenges for delivering FLASH proton beam therapy, the compromises that ensue if these challenges are not addressed, and resulting dosimetric losses. Some of these losses are on the same scale as the gains from FLASH found pre-clinically. We therefore conclude that for FLASH to succeed clinically the challenges must be systematically overcome rather than accommodated, and we survey physical and pre-clinical routes for achieving this.

First Observation of Harmonics of Magnetosonic Waves in Martian Magnetosheath Region

AbstractThe present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (fci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of fci. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left‐hand (LH), and higher frequency harmonics are associated with the right‐hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi‐perpendicular directions to the ambient magnetic field. The results of linear theory and Particle‐In‐Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.

Pickup Ion Modulation on Plateau-like Turbulence in the Martian Magnetosheath

The distribution of magnetic energy across scales, represented by the turbulence spectrum, provides insights into magnetic field dynamics in astrophysical and space plasma. While the Earth’s magnetosheath exhibits a conventional two-slope spectrum, the Martian magnetosheath often displays a prominent plateau-like spectrum. However, the underlying physical mechanism remains unresolved. Based on MAVEN observations, we present appealing evidence of pickup ions (PUIs) modulating the plateau-like spectrum through proton cyclotron waves (PCWs). PCWs, driven by unstable pickup H+ ion distributions, significantly influence the formation of plateau-like spectra. Both case and statistical studies suggest that the spectral evolution is affected by the relative abundance of pickup O+ ions. A substantial presence of pickup O+ ions can suppress PCWs driven by pickup H+ ions, resulting in a decline in the slope of the plateau spectrum. Particle-in-cell simulations confirm the role of PUI-modulated PCWs in the plateau-range energy injection. Our results provide new insight into the impact of PUIs on magnetic turbulence evolution and associated energy transfer processes in space and astrophysical plasma.

Predicting ion cyclotron emission from neutral beam heated plasmas in Wendelstein7-X stellarator

Measurements of ion cyclotron emission (ICE) are planned for magnetically confined fusion plasmas heated by neutral beam injection (NBI) in the Wendelstein 7-X stellarator (W7-X). Freshly injected NBI ions in the edge region, whose velocity-space distribution function approximates a delta-function, are potentially unstable against the magnetoacoustic cyclotron instability (MCI), which could drive a detectable ICE signal. Prediction of ICE from NBI protons in W7-X hydrogen plasmas is challenging, owing to the low ratio of the ions’ perpendicular velocity to the local Alfvén speed, v⊥(NBI)/VA≃0.14 . We address this from first principles, using the particle-in-cell kinetic code EPOCH. This self-consistently solves the Lorentz force equation and Maxwell’s equations for tens of millions of computational ions (both thermal majority and energetic NBI minority) and electrons, fully resolving gyromotion and hence capturing the cyclotron resonant phenomenology which gives rise to ICE. Our simulations predict an ICE signal which is predominantly electrostatic while incorporating a significant electromagnetic component. Its frequency power spectrum reflects novel MCI physics, reported here for the first time. The NBI ions relaxing under the MCI first drive broadband field energy at frequencies a little below the lower hybrid frequency ωLH, across the wavenumber range kωc/VA=40 –60, where ω c and VA denote ion cyclotron frequency and Alfvén velocity. Nonlinear coupling between these waves then excites spectrally structured ICE with narrow peaks, at much lower frequencies, typically the proton cyclotron frequency and its lower harmonics. The relative strength of these peaks depends on the specifics of the NBI ion velocity-space distribution and of the local plasma conditions, implying diagnostic potential for the predicted ICE signal from W7-X.

Comprehensive beam delivery latency evaluation for gated proton therapy system using customized multi-channel signal acquisition platform.

Beam delivery latency in respiratory-gated particle therapy systems is a crucial issue to dose delivery accuracy. The aim of this study is to develop a multi-channel signal acquisition platform for investigating gating latencies occurring within RPM respiratory gating system (Varian, USA) and ProBeam proton treatment system (Varian, USA) individually. The multi-channel signal acquisition platform consisted of several electronic components, including a string position sensor for target motion detection, a photodiode for proton beam sensing, an interfacing board for accessing the trigger signal between the respiratory gating system and the proton treatment system, a signal acquisition device for sampling and synchronizing signals from the aforementioned components, and a laptop for controlling the signal acquisition device and data storage. RPM system latencies were determined by comparing the expected gating phases extracted from the motion signal with the trigger signal's state turning points. ProBeam system latencies were assessed by comparing the state turning points of the trigger signal with the beam signal. The total beam delivery latencies were calculated as the sum of delays in the respiratory gating system and the cyclotron proton treatment system. During latency measurements, simulated sinusoidal motion were applied at different amplitudes and periods for complete beam delivery latency evaluation under different breathing patterns. Each breathing pattern was repeated 30 times for statistical analysis. The measured gating ON/OFF latencies in the RPM system were found to be 104.20±13.64ms and 113.60±14.98ms, respectively. The measured gating ON/OFF delays in the ProBeam system were 108.29±0.85ms and 1.20±0.04ms, respectively. The total beam ON/OFF latencies were determined to be 212.50±13.64ms and 114.80±14.98ms. With the developed multi-channel signal acquisition platform, it was able to investigate the gating lags happened in both the respiratory gating system and the proton treatment system. The resolution of the platform is enough to distinguish the delays at the millisecond time level. Both the respiratory gating system and the proton treatment system made contributions to gating latency. Both systems contributed nearly equally to the total beam ON latency, with approximately 100ms. In contrast, the respiratory gating system was the dominant contributor to the total beam OFF latency.

Wave Generation by Flare-accelerated Ions and Implications for 3He Acceleration

The waves generated by high-energy proton and alpha particles streaming from solar flares into regions of colder plasma are explored using particle-in-cell simulations. Initial distribution functions for the protons and alphas consist of two populations: an energetic, streaming population represented by an anisotropic (T ∥ > T ⊥), one-sided kappa function and a cold, Maxwellian background population. The anisotropies and nonzero heat fluxes of these distributions destabilize oblique waves with a range of frequencies below the proton cyclotron frequency. These waves scatter particles out of the tails of the initial distributions along constant-energy surfaces in the wave frame. Overlap of the nonlinear resonance widths allows particles to scatter into near-isotropic distributions by the end of the simulations. The dynamics of 3He are explored using test particles. Their temperatures can increase by a factor of nearly 20. Propagation of such waves into regions above and below the flare site can lead to heating and transport of 3He into the flare acceleration region. The amount of heated 3He that will be driven into the flare site is proportional to the wave energy. Using values from our simulations, we show that the abundance of 3He driven into the acceleration region should approach that of 4He in the corona. Therefore, waves driven by energetic ions produced in flares are a strong candidate to drive the enhancements of 3He observed in impulsive flares.

Linear Theory Analysis and One‐Dimensional Hybrid Simulations of High‐Frequency EMIC Waves in a Dipole Magnetic Field

AbstractNarrowband (Δf ≲ 0.1fcp), high‐frequency (0.9fcp ≲ f < fcp) electromagnetic ion cyclotron (EMIC) waves, or HFEMIC waves for short, are a relatively new type of EMIC waves, where fcp is the proton cyclotron frequency. Here, we investigate the instability threshold conditions and the nonlinear evolution of HFEMIC waves at parallel propagation. First, linear theory analysis is extended to a regime relevant to HFEMIC waves (parallel proton beta β‖p < 0.01). The instability threshold follows a similar anisotropy‐β‖p relation and requires a large value of anisotropy (T⊥p/T‖p ≳ 10) for wave growth. As a result of decreasing group velocity, the convective growth rate at a fixed threshold exhibits a similar inverse relation with β‖p. Heavy ions affect the instability only weakly, primarily through the introduction of stop bands. Second, we carry out one‐dimensional hybrid simulations in a parabolic background magnetic field, with initial parameters constrained by observation. Despite the narrow source region (within about ±3° latitude), HFEMIC waves can grow well above the thermal noise level due in large part to a small group velocity of HFEMIC waves. The saturation level is well within the range of observational amplitudes, and the quasilinear process primarily determines the wave evolution. Finally, we demonstrate that the present results compare favorably to the recent statistical results, thereby supporting anisotropic low‐energy protons as free energy source for HFEMIC waves.

Conjugate Observations of Magnetospheric and Ionospheric Phenomena During a Substorm Event

AbstractThis study investigates the comprehensive magnetospheric and ionospheric phenomena during a substorm event on 14 December 2013. The methodology involves analyzing data from satellites located within the plasmasphere at dusk‐side of the Earth, as well as data from ionospheric satellites mapped in the subauroral region. Magnetospheric data were analyzed to identify key features during the substorm event. Proton injection into the ring current, presence of proton and helium band electromagnetic ion cyclotron (EMIC) waves with different polarization characteristics, and harmonic structures in these EMIC waves were identified. These harmonic structures coincided with the appearance of magnetosonic waves characterized by rising tone structures and heating of low‐energy protons (<100 eV). Ionospheric satellites (DMSP F17 and POES 15) recorded enhanced proton precipitation contributing to the intensification of subauroral proton arcs. The analysis revealed that these enhanced proton fluxes were associated with variations in field‐aligned currents (FACs) and drove dynamics within the Sub‐Auroral Polarization Streams (SAPS). By combining and analyzing the magnetospheric and ionospheric data sets, this study provides a comprehensive understanding of magnetosphere‐ionosphere coupling during substorms, particularly on the duskside. The complex interdependence and causal relationships among EMIC waves, proton precipitation, subauroral proton arcs, FAC variations, and SAPS dynamics were highlighted.

Development and application analysis of high-energy neutron radiation shielding materials from tungsten boron polyethylene

The purpose of this study is to develop a high-energy neutron shielding material applied in proton therapy environment. Composite shielding material consisting of 10.00 wt% boron carbide particles (B4C), 13.64 wt% surface-modified cross-linked polyethylene (PE), and 76.36 wt% tungsten particles were fabricated by hot-pressure sintering method, where the optimal ratio of the composite is determined by the shielding effect under the neutron field generated in typical proton therapy environment. The results of Differential Scanning Calorimetry measurements (DSC) and tensile experiment show that the composite has good thermal and mechanical properties. In addition, the high energy-neutron shielding performance of the developed material was evaluated using cyclotron proton accelerator with 100 MeV proton. The simulation shows a 99.99% decrease in fast neutron injection after 44 cm shielding, and the experiment result show a 99.70% decrease. Finally, the shielding effect of replacing part of the shielding material of the proton therapy hall with the developed material was simulated, and the results showed that the total neutron injection decreased to 0.99‰ and the neutron dose reduced to 1.10‰ before the enhanced shielding. In summary, the developed material is expected to serve as a shielding enhancement material in the proton therapy environment.

A novel fiber-optic beam monitor

A novel beam monitor based on Ce-doped silica optical fibers is being presented. Four fibers are mounted on the outside of a beam transport pipe, at the location of a beam stop at a proton cyclotron. The secondary radiation caused by the proton beam interaction with the beam stop is measured by the optical fibers via Radiation-Induced Emission (RIE). The light signal in the individual fibers is correlated to the proton flux closest to the fiber and can therefore be used as a detector to monitor the position of the proton beam in the beam stop. Initial testing shows that monitoring of a 150 nA beam of 18 MeV protons into a beam dump is possible. The monitor can measure relative beam current and beam displacement in X and Y as a function of magnetic steering.