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1.
A new subgroup of 3He rich solar flares is found on reanalysing the global data. 3He/H ratio as a function of maximum proton flux at an energy of about 10 MeV shows a break-up of the data into two groups.
The first group follows the anticorrelation of 3He/H ratio with the proton flux, as expected in the plasma process acceleration models. But the second group has a constant 3He/H ratio as a function of maximum proton flux. This is not in conformity with the plasma process models. But this is expected
in models where the nuclear spallation reactions are responsible for the production of 3He. It is also found that the same break-up into two distinct groups follows if one plots the location of the flares in the
solar disc. The first group is more or less confined to the west limb of the Sun, whereas the second group is more widely
spread out across the solar disk.
Visiting Professor, Tata Institute of Fundamental Research, Bombay, August–September, 1983. 相似文献
2.
The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index, A
P ≥ 20 and the range of horizontal component of the Earth’s magnetic field H such that 250γ < H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data
(SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum
solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot
numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of
disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing
a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance of H
α
, X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e.,
SF during the period 1978-93. H
α
, X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. No H
α
, X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S,
the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number
of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares,
type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated
with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and
maximum activity lies between 58 and 118 h causing GMSs at the Earth. 相似文献
3.
Experimental studies on nonneutral (pure electron) plasmas of finite temperature, trapped in helical closed magnetic surfaces
have been conducted. The helical electron plasmas are produced with thermal electrons launched from the outside of the last
closed flux surface (LCFS). About 150 μs after the electron injection, the plasmas reach equilibrium state. Around the LCFS, a steep gradient of plasma space potential
φ
s
is formed. The corresponding radial electric field is about 2.5 kV/m. On the other hand, around the magnetic axis of helical
magnetic surfaces, φ
s
is almost constant, indicating that there are little electrons there. The volume-averaged electron density is on the order
of 10 13 m –3, smaller than the Brillouin density limit. The confinement time seems to be limited by a disruptive instability, and is so
far about 1.5 ms.
相似文献
4.
The influence of the escape of fast plasma electrons on the electron distribution function (EDF) in a low-voltage cesium Knudsen
arc is discussed. It is shown that even with a large Knudsen parameter l
e
/ h∼5–10 (where h is the gap and l
e
is the mean free path of electrons with energy of the order of the anode barrier) the electron flux from the plasma to the
anode is virtually identical to that calculated with a Maxwellian EDF.
Zh. Tekh. Fiz. 68, 61–64 (May 1998) 相似文献
5.
Summary We use experimental data to show that the amplitude A of the oscillations impressed upon upper atmospheric electrons by the electric field vectors of incident solar radiation
increases with the solar energy wavelength λ over the visible spectrum. Calculations based upon experimental data show that
the transmission coefficient T of the upper atmosphere for incident solar energy (say at intensity I
0) also increases with λ over the visible spectrum, implying that T increases with A over the latter range. Finally we show that I
0
1/2
λ 2 bears a positive linear relationship with T over the visible solar spectrum. The latter conclusion, which confirms theoretical results contained in a recent paper, is
then used to show that the 100 000 year eccentricity cycle effectively causes a maximum change in the total solar energy reaching
the lower atmosphere of approximately 4.5% which is enough to trigger an ice age. 相似文献
6.
Low pressure SF 6 with its isotopes in natural abundance was irradiated by a pulsed CO 2 laser operated on the P20 line (10.6 μm band). Dissociation yields of 32SF 6 and 34SF 6 were measured separately. If the radiation is focussed into the cell, the dissociation yield is proportional to the 3/2 power
of the laser energy, as was derived under general conditions and confirmed experimentally. The reaction probability P(Φ), the fraction of molecules dissociated by an energy flux Φ, was measured using parallel light. For both isotopes, P(Φ) saturates at high energy flux close to P=1. At a lower flux (2 J cm −2), the dissociation probability of 32SF 6 displays a threshold, whereas the dissociation probability of 34SF 6 is a very steep function of Φ over the whole range of fluxes. P(Φ) at the higher energy flux was measured in a cavity absorption cell, in which up to 80% of the molecules were dissociated
by a single pulse. Below 0.2 mbar SF 6 the dissociation yields for both isotopes are pressure independent. Above 2 mbar the isotopic selectivity is completely lost.
Addition of hydrogen always decreases the dissociation yields. 相似文献
7.
This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the
GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 10 17 cm −3 was created in the main plasma, whose density was 10 15 cm −3. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse
along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions.
Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released
in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which
is inhomogeneous in density and temperature, including the appearance of pressure waves.
Zh. éksp. Teor. Fiz. 113, 897–917 (March 1998) 相似文献
8.
The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability
(return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there
exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic
waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these
currents but the e.m. waves with frequencies, ω
2≪ Ω
e
2
≪ ω
pe
2
( Ω
e and ω
pe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic
field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence
generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma
due to the scattering of ion-sound waves by the electrons can be ∼ ω
pi
−1
( ω
pi being the plasma frequency for the ions). 相似文献
9.
Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated
by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimension d = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy
fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field,
and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately
equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤ r
A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies as d
1/3. For the normalized cross helicity σ c →1, the cascade rates are proportional to (1 − σ c)/(1 + σ c , and the Kolmogorov’s constants vary significantly with σ cc. 相似文献
10.
The low energy positron injector for the Low Energy Particle Toroidal Accumulator (LEPTA) accumulator was assembled at the
Joint Institute for Nuclear Research (JINR). Key elements of the injector have been tested. The cryogenic source of slow positrons
was tested with a test isotope 22Na of the initial activity of 0.8 MBk. A continuous slow positron beam intensity of 5.8 × 10 3 particle per second with an average energy of 1.2 eV and a spectrum width of 1 eV has been obtained. The achieved moderator
efficiency is about 1%. The accumulation process in the positron trap was investigated with electron flux. The lifetime of
the electrons in the trap, τ life ≥ 80 s and capture efficiency ɛ ∼ 0.4, were obtained. The maximum number of accumulated particles was N
exper = 2 × 10 8 at the initial flux of 5 × 10 6 electrons s −1.
The text was submitted by the authors in English. 相似文献
11.
The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 10 19 Wcm -2 laser pulses interacting with Al foils of thicknesses 10-200 μm. The fast electron beam characteristics and the foil temperature
were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths
in the optical domain, ≈407 nm (the second harmonic of the laser light) and ≈500 nm. The experimentally observed fast electron
distribution contains two components: one relativistic tail made of very energetic ( T
h
tail ≈ 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy),
and another, the bulk of the accelerated electrons, containing lower-energy ( T
h
bulk=500 ± 100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component
manifests itself by the coherent 2ω 0 emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target
heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms
of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons
with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of
100 eV per Joule of laser energy at 15 μm. Beyond that depth, because of the beam divergence, the incident current goes under
10 12 Acm -2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule
at 50 μm depth. 相似文献
12.
A search for the axioelectric absorption of 5.5-MeV solar axions produced in the p + d → 3He + γ (5.5 MeV) reaction was performed with two BGO detectors placed inside a low-background setup. Constraints on the axion-electron
coupling constant were obtained for axions with masses in the (0.1–1.0)-MeV range: g
Ae ≤ (1.8–9.0) × 10 −7. The solar positron flux from A → e − + e + decay was determined for axions with masses m
A
> 2 m
e. Using the existing experimental data on the interplanetary positron flux, a new constraint on the axion-electron coupling
constant for axions with masses in the (1.2–5.4)-MeV range was obtained: g
Ae ≤ (1–5) × 10 −17. 相似文献
13.
Summary Different fluxes and spectra of galactic cosmic rays (GCR) and solar cosmic rays result in a wide variety of radioactive and
stable-nuclides production rates. The records of cosmic-ray interactions, have been studied in terrestrial archives, in meteorites,
cosmic dust and lunar samples. We present here some results obtained in our laboratory on the study of cosmogenic radionuclides
produced in meteorites which fell in the last century. The laboratory is situated in the underground station of Monte dei
Cappuccini, Torino, at a depth of 70 m water equivalent to reduce the cosmic-ray background level. To measure γ-activity in
meteorites we have set up a highly efficient and selective Ge−NaI(Tl) γ-ray spectrometer surrounded by a passive shield. The
solar modulation affects the intensity of GCR and therefore the isotopes production rates in meteorites. The 11 y solar cycle
is well reproduced by the variations of 22Na ( T
1/2=2.6 y) in meteorites which fell during the past three solar cycles. The 44Ti ( T
1/2=66.6 y) activity measured in eight chondrites which fell in the last 110 y is qualitatively consistent with the century-scale
solar-activity variation, called the Gleissberg cycle. The increase is roughly four times higher, than expected (about 5%)
for a GCR flux calculated by a model in which the solar-activity modulation is determined solely by the sunspot number index R. This result suggests a much weakened modulation of GCR during the prolonged Gleissberg minimum during which highly ordered
magnetic fields set up in the heliosphere. 相似文献
14.
The space-based GAMMA-400 gamma-ray telescope will measure the fluxes of gamma rays in the energy range from ∼20 MeV to several TeV and cosmic-ray electrons and positrons in the energy range from several GeV to several TeV to investigate the origin of gamma-ray sources, sources and propagation of the Galactic cosmic rays and signatures of dark matter. The instrument consists of an anticoincidence system, a converter-tracker (thickness one radiation length, 1 X0), a time-of-flight system, an imaging calorimeter (2 X0) with tracker, a top shower scintillator detector, an electromagnetic calorimeter from CsI(Tl) crystals (16 X0) with four lateral scintillation detectors and a bottom shower scintillator detector. In this paper, the capability of the GAMMA-400 gamma-ray telescope for electron and positron measurements is analyzed. The bulk of cosmic rays are protons, whereas the contribution of the leptonic component to the total flux is ∼10−3 at high energy. The special methods for Monte Carlo simulations are proposed to distinguish electrons and positrons from proton background in the GAMMA-400 gamma-ray telescope. The contribution to the proton rejection from each detector system of the instrument is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of up to ∼1 × 104. 相似文献
15.
Experimental studies of the electron energy distribution function “EEDF” under well defined conditions in flowing afterglow
plasma, using a Langmuir probe are reported. The EEDF is measured in He 2
+ and Ar + dominated plasmas and in XeH + and XeD + dominated recombining plasmas. He is used as a buffer gas at medium pressures in all experiments (1600 Pa, 250 K). The deviation
of the measured EEDF from Maxwellian distribution is shown to depend on plasma composition and on the processes governing
the plasma decay. The influence of energetic electrons produced during the plasma decay on the body and tail of the EEDF is
observed. The mechanism of energy balance in afterglow plasma is discussed. 相似文献
16.
采用一维流体模型研究了含有杂质离子的等离子体与器壁材料相互作用给边界等离子体参量带来的影响.通过数值模拟,研究了分别选用碳和钨作为器壁材料时,器壁温度不同情形下热发射产生的电子对等离子体器壁电势、电场强度、热发射电子流以及沉积器壁离子动能流的影响.研究结果发现,当面向等离子体材料表面温度升高时,器壁电势和热发射产生的电流将增加,器壁电场强度和离子沉积器壁动能流则会减小,并且钨作为器壁材料要比碳作为器壁材料对于等离子体边界参量影响更明显.此外,研究了钨作为器壁材料时,碳杂质离子(浓度和电荷数)对等离子体器壁参量的影响. 相似文献
17.
Previously, we studied the ionospheric effects of the sequence of geomagnetic storms on September 9–14, 2005 using a global
self-consistent model “Thermosphere-Ionosphere-Protonosphere” (GSM TIP). Differences between the predicted and observed effects
of the ionospheric storms may be due to the use of the three-hour K
p
index of geomagnetic activity in modeling the time dependence of model input parameters, use of the dipole approximation
of the geomagnetic field, and disregard in simulations for solar flares that occurred during this period. We tried to eliminate
two of these three reasons. First, we used the A
E
index of geomagnetic activity with minute resolution in modeling the time dependence of the model input parameters. Second,
we took into account the effects of solar flares. In addition, GSM TIP model was supplemented by an empirical model describing
the precipitation of high-energy electrons. The results of the simulation of the behavior of various ionospheric parameters
over the Yakutsk, Irkutsk, Millstone Hill, and Arecibo stations on September 9 and 10, 2005 in the new formulation of the
problem, presented in the current work, are in better agreement with the available experimental data than the results of previous
calculations. 相似文献
18.
We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm 3 and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident
flux is assumed to have a Planck’s distribution over the spectrum with T
rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance
are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm 3 causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase
in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the
values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma
is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the
PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating
of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm 3 under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed. 相似文献
19.
The production of neutrinos with energies higher than 0.1 GeV in the solar atmosphere during solar flares is discussed. Neutrinos and muons are generated in decays of π+- mesons produced in nuclear interactions of accelerated solar flare protons with matter of the Sun. Muons themselves decay yielding neutrinos. These neutrinos could come to the Earth and be detected with neutrino telescopes. Estimations of fluxes of such neutrinos are given. 相似文献
20.
The first results from measuring the spectra of solar neutrons with energies of ~10–1000 MeV in the solar flares of 2006–2015 observed by the PAMELA international space experiment are presented. The PAMELA neutron detector with 3He counters and a moderator with an area of 0.18 m 2 allows us to estimate the flux of solar neutrons during solar flares. Solar neutrons with energies of ~10–1000 MeV likely occurred in 21 out of the 24 analyzed flares of 2006–2015. 相似文献
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