Variations in the X-ray Intensity of the Solar Corona and Heating of the Coronal Plasma in the Context of the Quantum Theory of Photon Pairs

Data obtained in the framework of the INTERBALL–Tail Probe (1995–2000) and RHESSI (from 2002 to the present) projects have revealed variations in the X-ray intensity of the solar corona in the photon energy range of 2?15 keV during the period of the quiet Sun. Previously, a hypothesis was proposed that this phenomenon could be associated with the effect of coronal heating. In the present study, a new mechanism of coronal plasma heating is proposed on the basis of the experimental data and the quantum theory of photon pairs that are produced from vacuum in the course of the Universe’s expansion. A similar mechanism based on the splitting of photon pairs in the interplanetary and intergalactic space is also proposed to explain the observed microwave background radiation.     

Reduction in the intensity of solar X-ray emission in the 2- to 15-keV photon energy range and heating of the solar corona

The time profiles of the energy spectra of low-intensity flares and the structure of the thermal background of the soft X-ray component of solar corona emission over the period of January–February, 2003, are investigated using the data of the RHESSI project. A reduction in the intensity of X-ray emission of the solar flares and the corona thermal background in the 2- to 15-keV photon energy range is revealed. The RHESSI data are compared with the data from the Interball-Geotail project. A new mechanism of solar corona heating is proposed on the basis of the results obtained.     

Small-Scale Structure of Thermal X-Ray Background of the Solar Corona and Microflares in the Photon Energy Range of 3-16 keV

The small-scale structure of the thermal X-ray background of the solar corona and microflares in the photon energy range from 3 to 16 keV according to the RHESSI data obtained on March–April 2003 is analyzed. The study of the reduction in the X-ray intensity in this spectral range is continued. A reduction and, in some cases, an increase in the X-ray intensity of the thermal background of the solar corona and microflares in narrow subranges of the X-ray spectrum of the quiet Sun are revealed in the photon energy range of 3–11 keV.     

Dynamics of accelerated ions in coronal loops and model of a gamma-ray source

The dynamics of ions accelerated to energies of 10–100 MeV/nucleon in an electric field of ～0.01–0.1 V/cm, which has a component directed along the magnetic field of solar coronal loops with a characteristic size of ～100000 km, is considered. The motion of fast ions trapped in a current-carrying magnetic loop that has a magnetic mirror at its base (the mirror trap model) is analyzed. The applicability of the obtained theoretical results to interpret gamma-ray bursts that, according to the data of the RHESSI space observatory, occurred on July 23, 2002 and October 28, 2003, is discussed. In those two bursts, a single and a pair gamma source displaced relative to the hard X-ray sources were localized in the 2.223-MeV neutron-capture line. On the basis of complex analysis of multi-wavelength (X-ray, gamma-ray, and optical) observations and the data on fast solar protons, a new topological model of the source of accelerated particles (of the mirror trap type) and a new scenario of the event that occurred on July 23, 2002 are proposed. Evidence of the possibility of particle acceleration by the electric field in coronal mass-ejection loops during large solar flares is obtained. The simulation results indicate that the gamma-ray source in the excitation lines (4.1–6.7 MeV) should coincide with the region where the accelerated ions interact with the background plasma of the solar atmosphere above the spot of the flare active region.     

Dynamics of an Al wire corona of a megaampere Z-pinch

It is shown that the development of instabilities in a Z-pinch plasma formed by loading a relatively thick Al wire (an initial diameter of 120 μm and a maximum discharge current of 2–3 MA) is slowed down due to the high plasma density in the wire corona. A cylindrically symmetric, regular, and stable corona surrounding the wire contains a helical formation with a dense, cold, and magnetized plasma. X-ray pulses with a photon energy of several keV and an FWHM duration of 10–20 ns are generated by a few imploded neck structures in the pinch phase of the corona evolution (70–100 ns after the current onset). The main part of X radiation emitted by individual bright spots in the photon energy range 1.5–2.4 keV (up to 40 J at a peak power of 4 GW) consists of the continuum and the bound-bound transition radiation from H-and He-like Al ions. A possible scenario for the axial magnetic field evolution during an X-ray pulse is outlined. __________ Translated from Fizika Plazmy, Vol. 28, No. 4, 2002, pp. 329–336. Original Russian Text Copyright ? 2002 by Kubeš, Renner, Krousky, Kravárik, Bakshaev, Blinov, Chernenko, Gordeev, Dan’ko, Korolev, Shashkov.     

Concerning mechanisms for the zebra pattern formation in the solar radio emission

The nature of the zebra patterns in continuous type-IV solar radio bursts is discussed. The most comprehensively developed models of such patterns involve mechanisms based on the double plasma resonance and plasma wave-whistler interaction. Over the last five years, there have appeared a dozen papers concerning the refinement of the mechanism based on the double plasma resonance, because, in its initial formulation, this mechanism failed to describe many features of the zebra pattern. It is shown that the improved model of this mechanism with a power-law distribution function of hot electrons within the loss cone is inapplicable to the coronal plasma. In recent papers, the formation of the zebra pattern in the course of electromagnetic wave propagation through the solar corona was considered. In the present paper, all these models are estimated comparatively. An analysis of recent theories shows that any types of zebra patterns can form in the course of radio wave propagation in the corona, provided that there are plasma inhomogeneities of different scales on the wave path. The superfine structure of zebra stripes in the form of millisecond spikes with a strict period of ～30 ms can be attributed to the generation of continuous radio emission in the radio source itself, assuming that plasma inhomogeneities are formed by a finite-amplitude wave with the same period.     

A review of projection radiography of plasma and biological objects in X-Pinch radiation

A review of studies on the X-pinch as a radiation source for X-ray projection shadow radiography (XPSR) and X-ray absorption spectroscopy (XAS) is presented. The ultimate capabilities of the techniques and ways of their achievement are considered. XPSR has been successfully used to study high-energy-density plasma objects, in particular, exploding wires and wire arrays. Using XPSR, the internal structure and dynamics of a wire explosion and wire array implosion have been investigated for the first time, which has made it possible to develop an adequate consistent theory of the processes occurring in the wire loads of generators with currents from several units of kiloamperes to a few tens of megamperes. The use of XAS for diagnostics of wire loads has allowed one for the first time to measure the parameters of matter in the wire core and plasma corona of the load. X-ray images of various biological objects have obtained, including those with the use of the phase contrast method. This review is a logical continuation of the review “Х-Pinch” [Plasma Phys. Rep. 41, 319, 493 (2015)], in which the Х-pinch as a physical object was considered.     

Compression zone of a magnetoplasma compressor as a source of extreme UV radiation

Results from experimental studies of extreme UV (EUV) radiation from the compression zone of a magnetoplasma compressor (MPC) operating with xenon are presented. Two MPC operating modes that differ in the method of xenon injection into the discharge were studied. It is shown that EUV radiation in the wavelength range of 5–80 nm is emitted from the compression zone. In the MPC operating mode with local xenon injection directly into the compression zone surrounded by helium plasma, the radiation power reaches it peak value of 16–18 kW in the wavelength range of 12.2–15.8 nm.     

Weak solar events

Soft X-ray solar bursts were investigated in the framework of the Interball—Tail Probe project by using an RF-15I-2 X-ray photometer. When studying microflares over the period from September to December 1995, weak bursts with intensities of less than 10^?8 W/m² were detected. All these data are confirmed by observations performed in the framework of the GOES project. The characteristics of solar microflares were determined, and the physical mechanism of weak solar events was considered. The distribution of microflares over their intensities was obtained. It is found that the distribution of solar flares over released energies do not obey a power law, and a lower limit is revealed in this distribution. This result is confirmed by the data obtained in the framework of the RHESSI project. Correlation between the daily average values of the maximum intensities of X-ray bursts of different classes of microflares and the daily average values of the thermal background of the solar corona is revealed.     

Coronal oscillations and internal loop structure

The transverse oscillations of a coronal magnetic loop whose ends are rigidly fixed in the photosphere are investigated. The loop is assumed to be inhomogeneous and to comprise two internal structural components: a central dense hot filament and a coaxial rarefied shell around it, in which the plasma density is lower than the density of the surrounding coronal plasma. The Alfvén speed in the shell, V_Am, is higher than that in the central filament and in the corona: V_Am>V_Ae>V_Ai. It is shown that, in the perfectly conducting plasma approximation, such a loop can generate two fast magnetosonic waves. The higher velocity wave is emitted in a radial direction, thereby ensuring the effect of the radiative damping of oscillations at the frequency of the m=1 cylindrical mode. The results of calculating the effect of radiative losses show that, for typical loop parameters (corresponding to those of the loops observed in the solar corona), the quality factor of oscillations may be fairly low (Q≈40). Under the conditions in question, the second (lower velocity) fast magnetosonic wave is not emitted (in contrast to the first) but rather turns out to be trapped in the magnetic flux tube.     

EUV spectroscopy of plasmas created in the final anode-cathode gap of the Z-Machine high-current pulsed generator (SNL)

The effect of short-circuit across the final anode-cathode gap of powerful pulsed current generators could hamper efficient power delivery to the Z-pinch plasma. To study this effect, a novel EUV diagnostics of plasmas created in the final section of the transmission line (the anode-cathode gap near the main load) of the Z-Machine high-current generator (Sandia National Laboratories, United States) was developed. The work included developing spectroscopic instruments, theoretical and experimental studies of EUV spectra of iron ions in well-diagnosed laser-produced plasmas, and a comparison of these spectra with those of plasmas created in the final anode-cathode gap of the transmission line. The EUV spectra of highly charged Fe ions in the spectral range λ ～ 20–800 Å were investigated. In experiments performed at Sandia National Laboratories, spectra of FeXIII-FeXVII ions were observed. A comparison of the measured and calculated spectra shows that the electron plasma temperature in the anode-cathode gap is T _e ～ 200 eV.     

毛状副冠对高山植物喉毛花的适应意义

高山地区生境极端,却拥有许多形态特化的植物,非生物因素在塑造花部性状及其进化过程中发挥着重要作用。该研究选取龙胆科典型高山植物喉毛花(Comastoma pulmonarium)为对象,探究其毛状副冠在多雨、强辐射的极端高山环境中的适应意义及其对植物雌雄繁殖适合度的影响。结果表明:通过比较自然状态和人工去除副冠的花,毛状副冠有效减少了雨水对花粉的冲刷(t=2.61,P0.05),提高了受精比率(t=2.05,P0.05),但是对种子的质量,即种子重量和种子萌发率的影响不显著。另外,花粉浸泡在蒸馏水中后,其萌发率显著低于蔗糖溶液中(t=30.67,P0.001),表明毛状副冠能够有效减小雨水浸泡对花粉活力的影响;同时,与自然状态相比,去除毛状副冠后的花,经太阳暴晒后,其花粉萌发率同样极显著地降低(t=9.89,P0.001),表明毛状副冠有效地避免了太阳辐射对花粉质量产生的不利影响。该研究结果表明喉毛花的毛状副冠结构是应对高山恶劣环境的一种适应策略,对植株的雌性和雄性繁殖成功都具有重要意义,从而进一步证实了非生物因素在植物花部特征演化中的重要作用。     

High-power terahertz optically pumped NH3 laser for plasma diagnostics

The parameter of a terahertz (THz) laser intended for plasma diagnostics in electrodynamic accelerators and tokamaks with a strong magnetic field are discussed. Generation of THz radiation in an ammonia laser under the action of high-power pulsed optical pumping by the radiation of a 10P(32) CO₂ laser is simulated numerically. The main characteristics of the output radiation, such as its spectrum, peak intensity, time dependence, and total energy, are calculated.     

Accelerated electrons and hard X-ray emission from X-pinches

The generation of accelerated electrons in the X-pinch minidiode is studied experimentally. It is well known that the explosion of an X-pinch consisting of two or more wires is accompanied by the formation of a minidiode, in which electrons are accelerated. The subsequent slowing down of electrons in the products of wire explosion causes the generation of hard X-ray (HXR) emission with photon energies higher than 10 keV. In this work, the spatial and temporal characteristics of X-pinch HXR emission are studied, the specific features of HXR generation are discussed, and the capability of applying this radiation to point-projection X-ray imaging of various plasma and biological objects is considered. The parameters of the electron beam produced in the X-pinch are measured using a Faraday cup and X-ray diagnostics. The experiments were performed with the XP generator (550 kA, 100 ns) at Cornell University (United States) and the BIN generator (270 kA, 150 ns) at the Lebedev Physical Institute (Russia).     

Reconnection in photospheric-chromospheric current sheet and coronal heating

It has been observed by various ground and space based solar missions that magnetic reconnection occurs frequently in the photosphere-chromosphere region as well as in the solar corona. The purpose of this article is to examine the process of reconnection in thin current sheet formed between two oppositely directed magnetic flux tubes in photospheric-chromospheric region. Using the data of different atmospheric models for the solar photosphere and chromosphere, we have estimated the rate of magnetic reconnection in terms of Alfvénic Mach number, growth rate of tearing mode, island length scales, and energy dissipation rate necessary to heat the chromospheric plasma. It is found that magnetic Reynolds number for the current sheet in the chromosphere varies from 1.14 × 10³ to 7.14 × 10⁶ which indicates that the field lines in the photosphere and chromosphere reconnect with speed, that is, 0.00034 to 0.0297 times the Alfvén speed. Frequency of the MHD waves generated in the chromosphere reconnection region is of the order of 100 Hz, so these high-frequency waves may be the sources of coronal heating and solar wind acceleration.     

X-ray backlighting of the axial region of a multiwire liner plasma in the angara-5-1 facility

Results are presented from experiments on the X-ray backlighting of the axial region of an imploding high-current multiwire liner. Backlighting was performed with the use of an X-pinch serving as a source of soft X-ray emission, which was recorded by pin diodes. The use of several filters with different passbands in front of the pin diodes allowed the interpretation of the results of measurements in experiments with cascade composite liners. The sensitivity of the diagnostics was ≈125 µg/cm² for a plasma of high-Z elements (W) and ≈220 µg/cm² for a plasma of low-Z elements (C, O, N) at a photon energy of the probing radiation of 1.0–1.5 keV. An advantage of the method is its high time resolution (≈1 ns) and the possibility of the separation in time of the emission bursts from Z-and X-pinches on the liner axis. The method does not impose restrictions on the pulse duration of the backlighting radiation source.     

High-power gas-discharge EUV source

The results from studies aimed at creating a high-power high-repetition-rate gas-discharge EUV source based on xenon Z-pinch are presented. In a liquid-cooled EUV source prototype, an average output power of 10 W for the burst mode (～1 s) and 5 W for continuous operation, emitted into a solid angle of 0.25 sr and 2% bandwidth around 13.5 nm is attained at a repetition rate of ～1 kHz. Operating wavelength of the source corresponds to XeXI 13.5-nm ion emission band. It is experimentally shown that the size of the emitting hot plasma can be decreased to ～2 mm without loss in the average output power. The radiation characteristics were determined by using standard techniques and calibrated metrology tools, which allowed a comparison of the absolute values of the measured parameters with the available data on other EUV sources developed for the next-generation lithography with a resolution of ～50 nm. The attained level of an average EUV power of 10 W at λ=13.5 nm into the 0.25-sr solid angle and 2% bandwidth is one of the highest at the moment.     

The settlement and metamorphosis of the marine bryozoan Bowerbankia gracilis (Ctenostomata: Vesicularioidea)

Summary The settlement and metamorphosis of the marine bryozoan Bowerbankia gracilis has been examined by light and electron microscopy. The period of rapid morphogenesis consists of the following sequence of morphogenetic movements: 1) eversion of the internal sac, 2) retraction of the apical disc, 3) coronal involution and exposure of the pallial epithelium, and 4) closure of the internal coronal cavity. The eversion of the internal sac at the onset of metamorphosis coincides with a sudden reversal of the direction of beat of the coronal cilia. The reversed beating of the coronal cilia wafts the adhesive secreted by the internal sac over the metamorphosing larva, forming the pellicle. The internal sac is subsequently internalized and histolyzed with the corona and the other transitory larval tissues, and the extensive pallial epithelium forms the epidermis of the ancestrular body wall (cystid). Type I mesenchyme cells form an incomplete somatic mesothelium beneath the differentiating cystid epidermis, and Type II mesenchyme cells become mobile phagocytes. The main body cavity develops by the histolytic enlargement of the internal cavity formed during coronal involution. The apical disc degenerates and the polypide develops from rudiments in the oral hemisphere of the larva. The distinctive larval morphology and metamorphosis of vesicularioid ctenostomes are compared with other bryozoans, and possible evolutionary trends are considered.     

Impact of solar ultraviolet-B radiation (290-320 nm) upon marine microalgae

For years scientists and laymen alike have casually noted the impact of solar ultraviolet radiation upon the non-human component of the biosphere. It was not until recently, when human activities were thought to threaten the protective stratospheric ozone shield, that researchers undertook intensive studies into the biological stress caused by the previously neglected short-wavelength edge of the global solar spectrum. Stratospheric ozone functions effectively as an ultraviolet screen by filtering out solar radiation in the 220–320 nm waveband as it penetrates through the atmosphere, thus allowing only small amounts of the longer wavelengths of radiation in this waveband to leak through to the surface of the earth. Although this ultraviolet radiation (UV-B radiation, 290–320 nm) comprises only a small fraction (less than 1%) of the total solar spectrum, it can have a major impact on biological systems due to its actinic nature. Many organic molecules, most notably DNA and proteins, absorb UV-B radiation which can initiate photochemical reactions. It is life's ability, or lack thereof, to cope with enhanced levels of solar UV-B radiation that has generated the concern over the potential depletion of stratospheric ozone. The defense mechanisms that serve to protect both plants and animals from current levels of UV-B radiation are quite varied. Whether these mechanisms will suffice for marine microalgae under conditions of enhanced levels of UV-B radiation is the subject of this review.