Bulletin of the Russian Academy of Sciences: Physics, 2013
ABSTRACT Spectra of solar cosmic rays on the Sun’s surface at a flare site and near Earth are mod... more ABSTRACT Spectra of solar cosmic rays on the Sun’s surface at a flare site and near Earth are modeled using the Monte Carlo method. Two of the most important mechanisms of energy accumulation by the particles are considered simultaneously: the regular acceleration of ions by the impulsive electric field of the current sheet and stochastic acceleration by the Alfvenic turbulence. This leads to substantial variations in the particle spectra in the low-energy region.
ABSTRACT The results of numerical simulation of stochastic acceleration of the heavy ions (3He, 4... more ABSTRACT The results of numerical simulation of stochastic acceleration of the heavy ions (3He, 4He, 16O, and 56Fe) are presented for the impulsive solar event of October 5, 2002. The energy spectra of the aforementioned particles have peculiarities (depressions) in the low-energy region (≤1 MeV nucleon−1). Coulomb losses in the flare plasma and adiabatic losses during interplanetary propagation are considered in the study as possible causes of such peculiarities.
Acceleration of iron ions by a spherical shock wave moving through the solar corona is considered... more Acceleration of iron ions by a spherical shock wave moving through the solar corona is considered. The energy dependence of the mean charge, (?) is determined by the characteristic acceleration time, Ta, and time for charge changes, Tq. The latter varies along with plasma number density during the propagation of the shock wave. An account of adiabatic energy changes and shock broadening is shown to insufficiently influence the dependence (?). According to our estimations the photoionizing processes do not affect the ionic states of the accelerated iron in gradual events in most cases.
Based on the recent data on charge state observations we deduce plasma parameters for the gradual... more Based on the recent data on charge state observations we deduce plasma parameters for the gradual solar energetic particle event of 6 November 1997. The dependence of the mean charge of several elements (C, O, Ne, Mg, Si and Fe) on energy is derived within the framework of charge-consistent acceleration model which is studied using Monte-Carlo approach. These simulations agree well with the experiment. The model incorporates ionisation and recombination processes during heavy ion propagation and acceleration by a parallel shock wave. To obtain good fits to observations we have to assume for the product of the characteristic acceleration time and number density TacN ∼ 10 s cm and temperature T = 10 K of a plasma, where the accelerated elements C, O, Ne, Mg, Si and Fe came from. However, a relatively abrupt increase in the Fe mean charge with energy is apparently in favour of admixture of this element originated from another (impulsive) event.
The energy spectra and charge distributions of heavy ions (using iron as an example) accelerated ... more The energy spectra and charge distributions of heavy ions (using iron as an example) accelerated at the front of a parallel shock are computed numerically. The Fe stripping by thermal electrons and protons during ion acceleration and propagation in plasma is taken into account. The computational results are compared with measurements of the mean charges qFe and energy spectra of iron in gradual solar-energetic-particle events. The theoretically derived Fe charge distributions could be of importance in light of new ACE spacecraft data which are expected to be obtained in the near future.
The spectra of stochastically accelerated heavy charged particles are determined, taking account ... more The spectra of stochastically accelerated heavy charged particles are determined, taking account of adiabatic deceleration and their escape from the acceleration region. The possibility that the ion charge may change as they move through a relatively dense and cold plasma is also taken into account. The stationary spectra in a two-level model (He(+) and He(2+)) are different near the injection momentum. Heavier ions (a multi-level model) have both energetic and charge distributions that are close to Gaussian, with a weak asymmetry relative to the mean charge. The dependence of the mean charge on the ion momentum provides a diagnostic for the acceleration region and the propagation of solar cosmic rays during solar flares.
We estimate the influence of photoionization processes on the charge states of heavy elements obs... more We estimate the influence of photoionization processes on the charge states of heavy elements observed from SEP events. Only the most powerful X-ray fluxes (X10 class events) could alter the ionic states of the elements. Majority of gradual and impulsive SEP events accompanied by soft X-rays cannot significantly ionize ions accelerated in flaring plasma.
ABSTRACT Acceleration of iron ions by a spherical shock wave moving through non-homogeneous solar... more ABSTRACT Acceleration of iron ions by a spherical shock wave moving through non-homogeneous solar corona is considered. The energy dependence of the mean charge of iron, [`(q)]\bar q Fe(E), is determined by the characteristic acceleration time, T a, trapping time, T tr, and time for charge changes, T q. The latter varies along with plasma number density during the propagation of the shock wave in the corona. Our calculations have demonstrated that adiabatic energy changes, Coulomb losses and shock broadening do not sufficiently influence the dependence [`(q)]\bar q Fe(E). According to our estimations, the photoionizing processes can scarcely affect the ionic states of accelerated iron, except probably for the most powerful X10 class events.
ABSTRACT The energy and charge spectra of Fe ions accelerated in gradual events are calculated nu... more ABSTRACT The energy and charge spectra of Fe ions accelerated in gradual events are calculated numerically. Our results are compared with the available observations. Stripping of Fe ions by thermal electrons and protons during ion acceleration in the solar corona results in the dependence of mean charge barq Feon energy. We consider the influence of varying plasma parameters (temperature T, number density N, and spectral index of turbulence S) on the charge distribution of iron. Our calculations indicate T106K and N(0.5–1)1010cm–3at the accelerating site, provided the characteristic acceleration time is about 1s. The calculated charge spectra for S>2 and S
ABSTRACT Using Monte Carlo method we have simulated solar cosmic ray spectra (3He, 4He, O and Fe)... more ABSTRACT Using Monte Carlo method we have simulated solar cosmic ray spectra (3He, 4He, O and Fe) at the flare site and at the Earth. It is shown that besides stochastic acceleration by Alfvenic turbulence an impulsive electric field of the current sheet significantly affects the ion energy spectra at low energies. Both mechanisms could explain some peculiarities in the energy spectra of heavy ions observed in experiments onboard ACE.
ABSTRACT This paper examines the possibility of using the energy spectra of accelerated solar cos... more ABSTRACT This paper examines the possibility of using the energy spectra of accelerated solar cosmic-ray ions and features formed by Coulomb losses to study the solar plasma (the power-law index S for the scattering turbulence, particle number density N, and temperature T of the background medium). For an individual solar flare, Coulomb losses can be manifest to different degrees in the spectra of different ions, providing a means to determine S. A comparison of theoretical spectra for H, He, C, O, and Fe ions with observed spectra for the prolonged solar flare of October 20, 1995 yields S≈3, N≈5×109 cm−3, and T≈106 K, assuming that the characteristic time scale over which these particles gain energy is about a second.
Bulletin of the Russian Academy of Sciences: Physics, 2013
ABSTRACT Spectra of solar cosmic rays on the Sun’s surface at a flare site and near Earth are mod... more ABSTRACT Spectra of solar cosmic rays on the Sun’s surface at a flare site and near Earth are modeled using the Monte Carlo method. Two of the most important mechanisms of energy accumulation by the particles are considered simultaneously: the regular acceleration of ions by the impulsive electric field of the current sheet and stochastic acceleration by the Alfvenic turbulence. This leads to substantial variations in the particle spectra in the low-energy region.
ABSTRACT The results of numerical simulation of stochastic acceleration of the heavy ions (3He, 4... more ABSTRACT The results of numerical simulation of stochastic acceleration of the heavy ions (3He, 4He, 16O, and 56Fe) are presented for the impulsive solar event of October 5, 2002. The energy spectra of the aforementioned particles have peculiarities (depressions) in the low-energy region (≤1 MeV nucleon−1). Coulomb losses in the flare plasma and adiabatic losses during interplanetary propagation are considered in the study as possible causes of such peculiarities.
Acceleration of iron ions by a spherical shock wave moving through the solar corona is considered... more Acceleration of iron ions by a spherical shock wave moving through the solar corona is considered. The energy dependence of the mean charge, (?) is determined by the characteristic acceleration time, Ta, and time for charge changes, Tq. The latter varies along with plasma number density during the propagation of the shock wave. An account of adiabatic energy changes and shock broadening is shown to insufficiently influence the dependence (?). According to our estimations the photoionizing processes do not affect the ionic states of the accelerated iron in gradual events in most cases.
Based on the recent data on charge state observations we deduce plasma parameters for the gradual... more Based on the recent data on charge state observations we deduce plasma parameters for the gradual solar energetic particle event of 6 November 1997. The dependence of the mean charge of several elements (C, O, Ne, Mg, Si and Fe) on energy is derived within the framework of charge-consistent acceleration model which is studied using Monte-Carlo approach. These simulations agree well with the experiment. The model incorporates ionisation and recombination processes during heavy ion propagation and acceleration by a parallel shock wave. To obtain good fits to observations we have to assume for the product of the characteristic acceleration time and number density TacN ∼ 10 s cm and temperature T = 10 K of a plasma, where the accelerated elements C, O, Ne, Mg, Si and Fe came from. However, a relatively abrupt increase in the Fe mean charge with energy is apparently in favour of admixture of this element originated from another (impulsive) event.
The energy spectra and charge distributions of heavy ions (using iron as an example) accelerated ... more The energy spectra and charge distributions of heavy ions (using iron as an example) accelerated at the front of a parallel shock are computed numerically. The Fe stripping by thermal electrons and protons during ion acceleration and propagation in plasma is taken into account. The computational results are compared with measurements of the mean charges qFe and energy spectra of iron in gradual solar-energetic-particle events. The theoretically derived Fe charge distributions could be of importance in light of new ACE spacecraft data which are expected to be obtained in the near future.
The spectra of stochastically accelerated heavy charged particles are determined, taking account ... more The spectra of stochastically accelerated heavy charged particles are determined, taking account of adiabatic deceleration and their escape from the acceleration region. The possibility that the ion charge may change as they move through a relatively dense and cold plasma is also taken into account. The stationary spectra in a two-level model (He(+) and He(2+)) are different near the injection momentum. Heavier ions (a multi-level model) have both energetic and charge distributions that are close to Gaussian, with a weak asymmetry relative to the mean charge. The dependence of the mean charge on the ion momentum provides a diagnostic for the acceleration region and the propagation of solar cosmic rays during solar flares.
We estimate the influence of photoionization processes on the charge states of heavy elements obs... more We estimate the influence of photoionization processes on the charge states of heavy elements observed from SEP events. Only the most powerful X-ray fluxes (X10 class events) could alter the ionic states of the elements. Majority of gradual and impulsive SEP events accompanied by soft X-rays cannot significantly ionize ions accelerated in flaring plasma.
ABSTRACT Acceleration of iron ions by a spherical shock wave moving through non-homogeneous solar... more ABSTRACT Acceleration of iron ions by a spherical shock wave moving through non-homogeneous solar corona is considered. The energy dependence of the mean charge of iron, [`(q)]\bar q Fe(E), is determined by the characteristic acceleration time, T a, trapping time, T tr, and time for charge changes, T q. The latter varies along with plasma number density during the propagation of the shock wave in the corona. Our calculations have demonstrated that adiabatic energy changes, Coulomb losses and shock broadening do not sufficiently influence the dependence [`(q)]\bar q Fe(E). According to our estimations, the photoionizing processes can scarcely affect the ionic states of accelerated iron, except probably for the most powerful X10 class events.
ABSTRACT The energy and charge spectra of Fe ions accelerated in gradual events are calculated nu... more ABSTRACT The energy and charge spectra of Fe ions accelerated in gradual events are calculated numerically. Our results are compared with the available observations. Stripping of Fe ions by thermal electrons and protons during ion acceleration in the solar corona results in the dependence of mean charge barq Feon energy. We consider the influence of varying plasma parameters (temperature T, number density N, and spectral index of turbulence S) on the charge distribution of iron. Our calculations indicate T106K and N(0.5–1)1010cm–3at the accelerating site, provided the characteristic acceleration time is about 1s. The calculated charge spectra for S>2 and S
ABSTRACT Using Monte Carlo method we have simulated solar cosmic ray spectra (3He, 4He, O and Fe)... more ABSTRACT Using Monte Carlo method we have simulated solar cosmic ray spectra (3He, 4He, O and Fe) at the flare site and at the Earth. It is shown that besides stochastic acceleration by Alfvenic turbulence an impulsive electric field of the current sheet significantly affects the ion energy spectra at low energies. Both mechanisms could explain some peculiarities in the energy spectra of heavy ions observed in experiments onboard ACE.
ABSTRACT This paper examines the possibility of using the energy spectra of accelerated solar cos... more ABSTRACT This paper examines the possibility of using the energy spectra of accelerated solar cosmic-ray ions and features formed by Coulomb losses to study the solar plasma (the power-law index S for the scattering turbulence, particle number density N, and temperature T of the background medium). For an individual solar flare, Coulomb losses can be manifest to different degrees in the spectra of different ions, providing a means to determine S. A comparison of theoretical spectra for H, He, C, O, and Fe ions with observed spectra for the prolonged solar flare of October 20, 1995 yields S≈3, N≈5×109 cm−3, and T≈106 K, assuming that the characteristic time scale over which these particles gain energy is about a second.
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