Magnetic field configurations extending over macroscopic scale distances are shown to be generated in rarefied collisionless plasmas when non-thermal and spatially inhomogeneous electron distributions in phase space emerge. The analyzed representative case is where, in the presence of a significant spatial gradient of the electron pressure and of a sheared magnetic field configuration, an alternating magnetic field reconnection process can develop associated with the anisotropy of the fluctuating electron temperature. The relevant process is intrinsically different from that known as the "Biermann Battery," which does not involve magnetic reconnection and requires that the unperturbed spatial gradient of the (isotropic) electron temperature be misaligned relative to that of the density gradient.

Basic ideas and definitions are surveyed concerning the theory of magnetic reconnection in plasmas, a phenomenon occurring under rather various and different conditions, both in astrophysical systems and in laboratory experiments. Approaches to the description of this phenomenon are reviewed, discussing in the last part a linearized analysis for collisionless regimes.

New tridimensional plasma structures, that are oscillatory and classified as non-separable ballooning modes, can emerge in inhomogeneous plasmas and undergo resonant mode-particle interactions, e.g. with a minority population, that can lead them to modify their spatial profiles. Thus, unlike the case of previously known ballooning modes their amplitudes are not separable functions of time and space. The relevant resonance conditions are intrinsically different from those of the well-known Landau conditions for (ordinary) plasma waves: they involve the mode geometry and affect different regions of the distribution in momentum space at different positions in configuration space. A process for a transfer of energy among different particle populations is envisioned.

Helical plasma structures have been identified and shown to form in and propagate from the high density plasmas in which Black Hole binaries can be imbedded. These structures are envisioned to extend to very low density and distant plasma regions up to where they can be disrupted by encountering plasma patches where the waves, of which the structures are composed, become dissipated. By now experimental observations and analyses of the morphology of jets have found that they can involve double-helix magnetic topologies in one case and, more recently, a single helix in other cases. Thus, plasma structures originating in the plasmas surrounding binary systems are proposed, instead of particle beams emitted by black holes directly, as a possible explanation of the origin of the highly collimated jets associated with a variety of celestial objects that are currently observed. Theoretically, double-helix structures are found to emerge as non-linearly coupled torsional ion-sound waves which, in the presence of a background magnetic field, in both the formation and terminal plasmas generate helical magnetic field configurations while remaining nearly “electrostatic” in regions where no significant background magnetic field is present. These (helical) structures can propagate independently in either of the two vertical directions. The coupling involves Intrinsic Gravitational Modes originating in the circumbinary disk and Inner Gravitational Fluctuations emerging from the Swept (Toroidal) Regions carved, within the highest density plasma region, by one or both Black Holes.

Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios.

Intrinsic Gravitational Modes (IGM) involving electromagnetic field fluctuations are found that are sustained by the time-dependent tridimensional gravitational field of Black Hole binaries as their collapse is approached. These “disk-rippling” modes, emerging from a plasma disk structure surrounding a binary, have ballooning amplitude profiles in the “vertical” direction (referring to the binary angular momentum vector) and rotate mainly with a frequency of twice the binary rotation frequency in the limit where their phase velocity does not exceed the speed of light. Relevant mode–particle resonances (B. Coppi, Plasma Phys. Rep. 45, 438 (2019)) can provide a means to transfer energy from high to low energy populations (a process evidenced by laboratory experiments) and offer an explanation for the absence of detectable high-energy radiation emission as the observed collapse of Black Hole binaries is approached. When the disk structure is immersed in a (stationary) magnetic field (B. Coppi, Plasma Phys. Reports. 45, 438 (2019)), another class of modes, affected by gravity-sustained disk structures, has to be considered.

plasmas, and magnetic fusion plasmas. The goal of this project was to study in the laboratory, the basic physical processes that occur in dusty plasmas. This report provides a summary of the major scientific products and activities of this award.

An oscillatory mode propagating along and across a confining magnetic field is identified that involves magnetic reconnection in the presence of a significant electron temperature gradient within the reconnection region where the ratio of the longitudinal ( proportional to D-parallel to(e) ) to transverse electron thermal conductivity (proportional to D-perpendicular to(e)) is relatively large. A periodic exchange of reconnected magnetic field energy with electron thermal energy is sustained within a region that remains significant even when the magnetic field configuration from which the mode can emerge involves large scale distances. The mode growth rate depends on the particle density gradient (aligned with the electron temperature gradient) and the relevant particle diffusion coefficient. (C) 2021 Elsevier B.V. All rights reserved.

An endogenous magnetic reconnection process is characterized by a driving factor that lays within the layer where a drastic change of magnetic field topology occurs. This kind of process is shown to take place in the presence of an electron temperature gradient in a well-confined plasma where, referring to quasi-collisionless regimes, the resulting electron temperature fluctuations can be anisotropic. Then a class of (radially) localized reconnecting modes is identified. These involve a transverse generated field (B) over tilde (x) of odd parity (as a function of the radial variable), and have finite (phase) velocities of propagation contrary to commonly considered reconnecting modes. The widths of the relevant reconnection layers remain significant even when large macroscopic distances are considered. Given that there are plasmas in the Universe with considerable electron thermal energy contents, these features can be relied upon in order to produce magnetic field generation, or conversion of magnetic energy into particle energy when the coupling of the localized odd modes to extended even modes can be significant. In any case, the resulting magnetic islands are not symmetric. With their excitation these modes can extract momentum from the main body of the plasma column which should recoil in the opposite direction. The excitation of antisymmetric endogenous modes is shown to be relevant to the electron temperature heating due to the reaction products in a fusion burning plasma as, in this case, the longitudinal thermal conductivity on selected rational magnetic surfaces can be decreased, relative to its collisional value, by the effects of reconnection. This kind of steepening is proposed to have a role in enhancing the growth rate of the instability involved in disruption events of the plasma column. The best agreement between theory and experiments concerning the onset of magnetic reconnection is (probably) represented by the theory of the internal kink mode. The observed accelerated reconnection rate following the onset is suggested as being explained by the formation of a relatively large magnetic island with a local steepening of the electron temperature gradient. A new kind of odd 'thermonuclear heating' mode associated with symmetric reconnection is identified.

A novel process is proposed to create high-energy particle populations in well-organized plasma structures surrounding nonaxisymmetric systems in which one or more components orbit around another. Binaries of black holes or neutron stars and light objects rotating around a massive object are examples of current interest. The relevant tridimensional and time-dependent gravitational potentials are shown to sustain the excitation of vertically localized ballooning modes in a plasma structure imbedded in a vertical magnetic field. These modes are viewed as composed of waves oppositely propagating in the vertical direction and can be excited when their frequency can match that of the orbiting frequency of one object around another. The formation of high-energy particle populations is predicted on the basis of the mode–particle resonance interactions associated with the mode components and the presence or the formation of a high-energy beam is not required. Rather, a vertical oscillatory force acting on the surrounding plasma structure is a necessary factor. High-energy flares associated with composite systems or envisioned precursors to the collapse of binary of compact objects are consistent with the presented theory.

We define an endogenous magnetic reconnection process as the one having a driving factor that lies within the region where a drastic change in magnetic field topology occurs. A process of this kind is shown to take place when an electron temperature gradient is present in a plasma column and when, referring to quasi-collisionless regimes, the evolving electron temperature fluctuations are anisotropic. A two-fluid theory, for weakly collisional plasma regimes and confinement configurations which have sheared magnetic fields, is formulated, and two classes of reconnecting modes are identified. The localized class of modes is characterized by a transverse reconnecting magnetic field B̃x of odd parity, as a function of the radial variable (across the reconnection layer). The width of this remains significant even when large macroscopic distances, such as those of interest to space and astrophysics, are considered. The relevant reconnection can be referred to as antisymmetric. In fact, the (additional and realistic) presence of a finite current density gradient leads to finding modes with mixed B̃x parity which are no longer localized within the reconnection layer. Then, the resulting magnetic islands are not symmetric. In view of the fact that there are plasmas in the Universe with considerable electron thermal energy contents, the features of the novel reconnecting modes can be relied upon in order to produce generation of magnetic fields or conversion of magnetic energy into particle energy (through a sequence of mode-particle resonances).