Loss of energetic particles due to feedback control of resistive wall mode in HL-3

Effects of three-dimensional(3D)magnetic field perturbations due to feedback control of an unstable n=1(n is toroidal mode number)resistive wall mode(RWM)on the energetic particle(EP)losses are systematically investigated for the HL-3 tokamak.The MARS-F(Liu et al 2000 Phys.Plasmas 73681)code,facilitated by the test particle guiding center tracing module REORBIT,is utilized for the study.The RWM is found to generally produce no EP loss for cocurrent particles in HL-3.Assuming the same perturbation level at the sensor location for the close-loop system,feedback produces nearly the same loss of counter-current EPs compared to the open-loop case.Assuming however that the sensor signal is ten times smaller in the close-loop system than the open-loop counter part(reflecting the fact that the RWM is more stable with feedback),the counter-current EP loss is found significantly reduced in the former.Most of EP losses occur only for particles launched close to the plasma edge,while particles launched further away from the plasma boundary experience much less loss.The strike points of lost EPs on the HL-3 limiting surface become more scattered for particles launched closer to the plasma boundary.Taking into account the full gyro-orbit of particles while approaching the limiting surface,REORBIT finds slightly enhanced loss fraction.

Solar energetic particles intensity variations associated with a tilted-dipole 3D corotating interaction region

The effect of a tilted-dipole three-dimensional corotating interaction region(CIR)on the transport and acceleration of solar energetic particles(SEPs)is studied.In this work,we discussed how the particle intensity longitudinal and radial dependence might be influenced by the background structures.Moreover,we investigate how the spectral index distribution is modulated by the CIR structure We use the focused transport equation(FTE)to describe the propagation and acceleration of SEPs in a tilt-dipole 3D CIR,generated by the high-resolution 3D magnetohydrodynamic(MHD)model.The forward stochastic differential method is used to solve the FTE.The protons with theE~(-4.4)spectrum from 0.5 to 15 MeV are injected uniformly at the heliographic equator of 0.15 AU.Physical quantities are extracted along each interplanetary magnetic field(IMF)line to show the results.In the tilted-dipole CIR background,if injected from the solar equator at the inner boundary,particles in the slow flow are transported to higher latitudes due to the extension of the IMF lines to higher latitudes.The longitudinal patterns of the particles are dominated by the density of IMF lines.The focusing effect modulates the longitudinal variation of the particle intensity and gives rise to new longitudinal intensity peaks.The adiabatic effect largely increases the intensity fluctuation along the longitude.The structure of the solar wind can also lead to the difference of the indexαin the empirical functionI_(max)=kR~(-α),describing the radial variation of peak intensity according to our simulation.Under the influence of the CIR structure,the indexαvaries from 1.9 to 3.4 at 0.3-1.0 AU.The variation of the solar wind speed should be considered when estimating the radial dependence of the SEP peak intensity.The spectra indices rise near the CIR boundaries and drop near the stream interface(SI).The adiabatic effect makes the spatial variability of the spectral index larger.The spectral index could be similar at different radial distances in the CIR structure.

Hybrid simulation of q=1 high-order harmonics driven by passing energetic particles in tokamak plasmas

High-order harmonics q(ψ_(s))=1 energetic particle modes(EPMs)have been observed in toroidal plasmas experiments with neutral beam injection.To investigate these phenomena,linear properties and nonlinear dynamics of these EPMs driven by passing energetic particles(EPs)are studied via the global hybrid kinetic-magnetohydrodynamic code M3D-K.Simulation results demonstrate that passing EPs'effects on high mode-number harmonics(q(ψ_(s))=m/n=2/2,3/3,4/4)instability are more obvious than the q(ψ_(s))=1/1 mode,especially when q-profile is sufficiently flat in the core region.Furthermore,the effects of the pitch angleΛ_0 and beam ion pressure P_(hot)/P_(total)on the features of high n components are also analyzed specifically.It is found that there exists only one resonant condition for these EPMs.In the nonlinear phase,these high mode-number harmonics can induce significant energetic ions redistribution and chirping up phenomena,which differs from the classical fishbone excited by passing EPs.These discoveries are conducive to better apprehend the underlying physical mechanisms of the highorder harmonics driven by passing EPs.

Validation of the current and pressure coupling schemes with nonlinear simulations of TAE and analysis on the linear stability of tearing mode in the presence of energetic particles

Both current and pressure coupling schemes have been adopted in the hybrid kinetic–magnetohydrodynamic code CLT-K recently.Numerical equivalences between these two coupling schemes are strictly verified under different approximations.First,when considering only the perturbed distribution function of energetic particles(EPs),the equivalence can be proved analytically.Second,when both the variations of the magnetic field and the EP distribution function are included,the current and pressure coupling schemes numerically produce the same result in the nonlinear simulations.On this basis,the influences of co-/counter-passing and trapped EPs on the linear stabilities of the m/n=2/1 tearing mode(TM)have been investigated(where m and n represent the poloidal and toroidal mode numbers,respectively).The results of scanningβh of EPs show that the co-passing and trapped EPs are found to stabilize the TM,while the counter-passing EPs tend to destabilize the TM.The behind(de)stabilization mechanisms of the TM by EPs are carefully analyzed.Furthermore,after exceeding critical EP betas,the same branch of the high-frequency mode is excited by co-/counterpassing and trapped EPs,which is identified as the m/n=2/1 energetic particle mode.

Alfvén Instabilities Excited by Energetic Particles in a Parameter Regime Similar to EAST Operation

The kinetic excitation of ideal magnetohydrodynamic （MHD） Alfvén instabilities is investigated for operations at the EAST tokamak. The instabilities include α-induced toroidal Alfvén eigenmodes （αTAE; here, α =-q2 Rdβ/dr, with q being the safety factor, β the ratio between the plasma and magnetic pressures, R the major radius, and r the minor radius）, toroidicity-induced Alfvén eigenmodes （TAE）, and the energetic particle continuum mode （EPM）. The αTAE, trapped by α-induced potential wells along the magnetic field line, can be readily destabilized by energetic particles due to negligible continuum damping via wave energy tunneling. It is shown for the geometry and the parameters similar to those of the EAST equilibrium that αTAE is different not only from the EPM by the potential-well determined frequency, but also from the TAE by the broad frequency spectrum outside the toroidal frequency gap.

Kinetic Theories of Geodesic Acoustic Modes：Radial Structure,Linear Excitation by Energetic Particles and Nonlinear Saturation＇

Geodesic acoustic modes（GAMs）are oscillating zonal mode structures unique to toroidal plasmas and are capable of regulating microscopic turbulence and associated transports.Inthispaper,three important aspects of GAM dynamics are investigated,namely（1） GAM continuous spectrum and its mode conversion to kinetic GAM （KGAM）;（2） 1inear excitation of energetic particle induced GAM （EGAM） and its coupling to the GAM continuum, and （3） nonlinear saturationofEGAMviawaveparticletrapping.TheanalogybetweentheGAM

Neutralized solar energetic particles for SEP forecasting:Feasibility study of an innovative technique for space weather applications

Energetic neutral atoms(ENAs)are produced by the neutralization of energetic ions formed by shock-accelerated gradual solar energetic particle events(SEP).These high-energy ENAs(HENAs)can reach the Earth earlier than the associated SEPs and thus can provide information about the SEPs at the lower corona.The HENA properties observed at Earth depend on the properties of the coronal mass ejection(CME)-driven shocks that accelerate the SEPs.Using a model of HENA production in a shock-accelerated SEP event,we semi-quantitatively investigate the energy-time spectrum of HENAs depending on the width,propagation speed,and direction of the shock,as well as the density and ion abundances of the lower corona.Compared to the baseline model parameters,the cases with a wider shock width angle or a higher coronal density would increase the HENA flux observed at the Earth,while the case with an Earthpropagating shock shows a softened HENA spectrum.The comparison of expected HENA fluxes in different cases with a flight-proven ENA instrument suggests that solar HENAs can feasibly be monitored with current technologies,which could provide a lead time of 2−3 hours for SEPs at a few MeV.We propose that monitoring of solar HENAs could provide a new method to forecast shock-driven SEP events that are capable of significant space weather impacts on the near-Earth environment.

Dust charging and levitating in a sheath of plasma containing energetic particles

The structure of the sheath in the presence of energetic particles is investigated in the multi-fluid framework. Based on the orbital motion limited（OML） theory, the dust grain charging inside the sheath of plasma containing energetic particles is examined for the carbon wall, and then the effect of the energetic particles on the stationary dust particle inside the sheath is discussed through the trapping potential energy. It is found that with the increase of energetic ion concentration or energy,the size of dust staying in levitation equilibrium decreases and the levitating position is much closer to the wall. In the case of deuterium ions as energetic ions, the bigger dust particle can be trapped by the sheath than in the case of hydrogen ions as energetic ions. When the energetic electron component is present, the levitating position of dust particle in the sheath depends strongly on the energetic electron. The levitating dust particle is closer to the wall as the energetic electron energy or concentration is increased. In addition, with the increase of temperature of thermal background ion, the size of dust particle trapped by the sheath decreases and the levitating positions of dust particles with the same size radius inside the sheath move toward the wall. Our results can be helpful in investigating the property of the sheath where the energetic particle component is present.

Analysis of the Energetic Particles Around the Chili Earthquake of M8.8

Based on the IDP data from the French DEMETER satellite,global distribution is shown,which corresponds to three precipitation zones:the aural precipitation zone,the mid-high latitude precipitation zone and the South Atlantic precipitation zone.Then the Chili earthquake with M8.8 which occurred on February 27,2010 is taken as an example.The IDP fluxes from repeat orbits are compared and the results show that there is a clear enhancement on February 26,2010,just one day ahead of the Chili earthquake.In the south zone with L=2.1～2.7,the flux on February 26 is higher than that on previous days.However in the north zone with L=2.1～2.7,there is no clear change during the day but great enhancement during the night,which is close to the time of the earthquake.At the same time,the flux on February 26 near the equator is far lower than that on previous days.

Experimental investigations of mechanical and reaction responses for drop-weight impacted energetic particles

Low-velocity drop-weight impact experiments on individual and multiple Cyclotetramethylene tetranitramine (HMX) energetic particles were performed using a modified drop-weight machine equipped with high-speed photography components. Multiple particles experienced more severe burning reactions than an individual particle. Comparisons between impacted salt and HMX particle show that jetting in HMX is mainly due to the motion of fragmented particles driven by gaseous reaction products. Velocity of jetting, flame propagation, and area expansion were measured via image processing, making it possible to quantify the chemical reaction or mechanical deformation violence at different stages.

Cross-calibration of high energetic particles data——A case study between FY-3B and NOAA-17

Cross-calibration of high energetic particle data is a primary requirement for the availability of multi-instrument, multi-spacecraft data. II also can provide a method to verify relative reliability of data from single satellite measurement. This pa- per presents a case study of energetic particles data cross-calibration between FY-3B and NOAA-17. A generally good agree- ment is acquired in the flux values and distribution trend of 2.5-6.9 MeV protons and 0.3-1.1 MeV electrons between FY-3B and NOAA-17 satellites. It suggests that the data observed by FY-3B is properly cross-calibrated. We can also confirm that energetic particles data observed by FY-3B satellite is available.

Linear hybrid simulations of low-frequency fishbone instability driven by energetic passing particles in tokamak plasmas

A linear simulation study of energetic passing particle-driven low-frequency fishbone instability in tokamak plasmas has been carried out using the global kinetic-MHD(magnetohydrodynamics)hybrid code M3D-K.This work is focused on the interaction of energetic passing beam ions and n=1 mode with a monotonic safety factor q profile and q_(0)<1.Specifically,the stability and mode frequency as well as mode structure of the n=1mode are calculated for scans of parameter values of beam ion beta,beam ion injection energy,beam ion orbit width,beam ion beta profile,as well as background plasma beta.The excited modes are identified as a low-frequency fishbone with the corresponding resonance of w_(φ)+w_(θ)=w,where w_(φ)is the beam ion toroidal transit frequency and w_(θ)is the beam ion poloidal transit frequency.The simulated mode frequency is approximately proportional to the beam ion injection energy and beam ion orbit width.The mode structure is similar to that of internal kink mode.These simulation results are similar to the analytic theory of Yu et al.

Preliminary results of the High Energetic Particle Package on-board the China Seismo-Electromagnetic Satellite

The high energetic particle package(HEPP) on-board the China Seismo-Electromagnetic Satellite(CSES) was launched on February 2, 2018. This package includes three independent detectors: HEPP-H, HEPP-L, and HEPP-X. HEPP-H and HEPP-L can detect energetic electrons from 100 keV to approximately 50 MeV and protons from 2 MeV to approximately 200 MeV. HEPP-X can measure solar X-rays in the energy range from 1 keV to approximately 20 keV. The objective of the HEPP payload was to provide a survey of energetic particles with high energy, pitch angle, and time resolutions in order to gain new insight into the space radiation environments of the near-Earth system. Particularly, the HEPP can provide new measurements of the magnetic storm related precipitation of electrons in the slot region, and the dynamics of radiation belts. In this paper, the HEPP scientific data sets are described and initial results are provided.The scientific data can show variations in the flux of energetic particles during magnetic storms.

Nonlinear dynamics of the reversed shear Alfvén eigenmode in burning plasmas

In a tokamak fusion reactor operated at steady state,the equilibrium magnetic field is likely to have reversed shear in the core region,as the noninductive bootstrap current profile generally peaks off-axis.The reversed shear Alfvén eigenmode(RSAE)as a unique branch of the shear Alfvén wave in this equilibrium,can exist with a broad spectrum in wavenumber and frequency,and be resonantly driven unstable by energetic particles(EP).After briefly discussing the RSAE linear properties in burning plasma condition,we review several key topics of the nonlinear dynamics for the RSAE through both wave-EP resonance and wave-wave coupling channels,and illustrate their potentially important role in reactor-scale fusion plasmas.By means of simplified hybrid MHD-kinetic simulations,the RSAEs are shown to have typically broad phase space resonance structure with both circulating and trapped EP,as results of weak/vanishing magnetic shear and relatively low frequency.Through the route of wave-EP nonlinearity,the dominant saturation mechanism is mainly due to the transported resonant EP radially decoupling with the localized RSAE mode structure,and the resultant EP transport generally has a convective feature.The saturated RSAEs also undergo various nonlinear couplings with other collective oscillations.Two typical routes as parametric decay and modulational instability are studied using nonlinear gyrokinetic theory,and applied to the scenario of spontaneous excitation by a finite amplitude pump RSAE.Multiple RSAEs could naturally couple and induce the spectral energy cascade into a low frequency Alfvénic mode,which may effectively transfer the EP energy to fuel ions via collisionless Landau damping.Moreover,zero frequency zonal field structure could be spontaneously excited by modulation of the pump RSAE envelope,and may also lead to saturation of the pump RSAE by both scattering into stable domain and local distortion of the continuum structure.

Effects of q-profiles of a weak magnetic shear on energetic ion excited q=1 mode in tokamak plasmas

In this paper, we study the effect of safety factor profiles, particularly with a very weak magnetic shear, on the m/n = 1 mode excited by energetic ions in tokamak plasmas. It is found that the profile plays a significant role in the onset of the mode, and the thresholds for the instability are also derived. The numerical results for configurations with conventional or reversed non monotonic magnetic shears are discussed. The effects of radial location of rational surfaces, edge q value, and flatness of q-profile on the energetic ion excited mode are further analyzed in detail.

Mode structure symmetry breaking of reversed shear Alfvén eigenmodes and its impact on the generation of parallel velocity asymmetries in energetic particle distribution

In this work,the gyrokinetic eigenvalue code LIGKA,the drift-kinetic/MHD hybrid code HMGC and the gyrokinetic full-f code TRIMEG-GKX are employed to study the mode structure details of reversed shear Alfvén eigenmodes(RSAEs).Using the parameters from an ASDEXUpgrade plasma,a benchmark with the three different physical models for RSAE without and with energetic particles(EPs)is carried out.Reasonable agreement has been found for the mode frequency and the growth rate.Mode structure symmetry breaking(MSSB)is observed when EPs are included,due to the EPs’non-perturbative effects.It is found that the MSSB properties are featured by a finite radial wave phase velocity,and the linear mode structure can be well described by an analytical complex Gaussian expressionФ(s)=e^(-σ(s-s_(0))^(2))with complex parametersσand s_(0),where s is the normalized radial coordinate.The mode structure is distorted in opposite manners when the EP drive shifted from one side of qminto the other side,and specifically,a non-zero average radial wave number with opposite signs is generated.The initial EP density profiles and the corresponding mode structures have been used as the input of HAGIS code to study the EP transport.The parallel velocity of EPs is generated in opposite directions,due to different values of the average radial wave number,corresponding to different initial EP density profiles with EP drive shifted away from the qmin.

Photometric and Statistical Analysis of Solar Energetic Particle (SEP) for the Peak of Solar Cycle 24

The major solar energetic particle events for the peak of solar cycle (24) for years (2012-2015) are analyzed by using the Energetic and Relativistic Nucleus and Electrons (ERNE) detectors and Large Angle and Spectrometric Coronagraph Experiment (LASCO) on board SOHO. It is found that the number of events which satisfies the required condition was 82 events. LASCO give information about Central Position Angle (CPA), Angular Width (AW), the speed of associated Coronal Mass Ejections (CMEs) and their basic features which cataloged in a data base SOHO/LASCO. The logarithmic intensity-time profile of SEP for the peak of solar cycle (24) was provided by ERNE, and from this profile the injection time, width, speed and onset time were estimated. All results that arise from these photometric analysis were statistically analyzed by using the statistical program SPSS (version 19). It have been concluded that 90% of these events were halo (360&deg;) CPA, 1% of North West, 4% South West and 2% North East and South East, as well as it was found that 39% gradual events and 29% impulsive events while 32% were not clear events, and also the acceleration of the energetic particle is not only in the interplanetary but also in the location of the event. We found from the statistical analysis for these events that the acceleration is inversely proportional to speed and the relationship between them is not relevant and also the speed increase in two regions, from year 2012 and 2014. This confirms that the peak of solar cycle (24) really is double peak. All these investigations were employed as data base for the space agencies to protect the solar wind.

Review of the experiments for energetic particle physics on HL-2A

This paper reviews the energetic particle（EP） experiments during electron cyclotron resonance heating（ECRH） and neutral beam injection in the HL-2 A tokamak.A number of important results are summarized,which relate to ITER physics,including the behavior of the multi-mode instability,the nonlinear interaction between wave-wave and wave-particles,the losses of EP induced by the instabilities,the effect of the EP instabilities on the thermal plasma confinement and the control of the EP instabilities by means of ECRH.Systematic experiments indicate that when the drive is great enough,the nonlinear effects and the multi-mode coexistence may play an important role,which affect the transport both of the EPs and the background plasma confinement,and these instabilities could be controlled.Some new phenomena about the EP induced instabilities discovered recently on the device,such as high frequency reversed shear Alfvén eigenmodes,Alfvénic ion temperature gradient modes,the geodesic acoustic mode induced by energetic electrons excited by interaction between tearing mode and beta induced Alfvén eigenmode and double e-fishbone in negative magnetic shear discharges etc,have also been presented in the paper.

Design of an energetic particle radiation diagnostic spectroscopy system based on national core chips and Qt on Linux in EAST

Energetic particle radiation diagnoses mainly detect the particles(such as neutrons,gamma rays,hard X-rays,and escaping electrons)that are radiated in the discharge process of the experimental advanced superconducting tokamak device to characterize the operating state of the plasma in real time.The upgrading of these diagnoses requires new instruments based on national(here,“national”means developed and produced by a Chinese company)core chips and open-source software with advanced digitization,a high sampling rate,and a high time resolution.The new spectroscopy system designed in this study adopts the national field-programmable gate array(FPGA)and an analog-to-digital converter as the core chip,and it is developed using Qt on Linux.The communication between the FPGA and embedded controller occurs via a high-speed peripheral component interconnect eXtension for instrument express protocol with a direct memory access mode.On this basis,the time resolution of the system is improved from 2 to 1 ms,the maximum channel address is increased to 4096,and the sampling rate is increased from 10 to 80 Msps.Calibration experiments of the spectroscopy system with 152Eu and 137Cs sources demonstrate that the best energy resolution is 0.27%and the measurement error is less than±0.5 keV.

Discrete Alfvén eigenmodes in the CFETR steady-state scenario

The stability features of discrete Alfvén eigenmodes(αTAEs) trapped by α-induced potential wells are explored in the China Fusion Engineering Test Reactor(CFETR) advanced steady-state operation environment, where α denotes a measure of the pressure gradient. For the reversed magnetic shear(RS) H-mode scenario with an enhanced internal transport barrier(ITB), the αTAEs are trapped in the electron cyclotron(EC) power deposition region and the effects of different pedestals on αTAEs are analyzed. For the negative off-axis magnetic shear scenario, the αTAEs are discussed, and the effect of different magnetic shears on the α TAEs is presented. Finally, the effects of beam energies and pitch-angle distributions onαTAE stability are also presented.