Ordinary Mode Research Articles

Runaway electron diagnostics for the COMPASS tokamak using EC emission

An electron cyclotron emission (ECE) diagnostic of suprathermal electrons was utilised for runaway electron (RE) experiments purposes in the COMPASS tokamak. Our vertical ECE (V-ECE) system consists of a 16-channel heterodyne radiometer and an E-band horn antenna with a 76.5-88 GHz frequency range front-end. Simulations used for the design of the diagnostic showed a possibility of detecting the emission of low-energy (50-140 keV) runaway electrons. We realized measurements with both extraordinary (X-) and ordinary (O-) mode linear polarizations. The amplitudes of the X-mode and O-mode signals are similar, which can be explained by depolarised reflected radiation. V-ECE measurements in low-density flattop discharges and in discharges with massive gas injections of high-Z elements show correlations with other RE diagnostics. Our results are in the agreement with the principles of the primary runaway generation mechanisms.

On Detecting the Fourth Gyrofrequency Harmonic in Microwave Emission Spectra above Sunspots

Spectral polarization observations of radio sources above sunspots are regularly carried out with the RATAN-600 radio telescope (RATAN is a Russian acronym for the Radio Astronomical Telescope of the Academy of Sciences). The in-depth studies of the spectra reveal new effects. In this paper, we analyze the manifestation of radio emission of the fourth gyrofrequency harmonic in microwave spectra obtained with 1-percent frequency resolution in a range of 3–18 GHz. Registration of the extraordinary mode in the short-wavelength range of the spectrum is compared to the model calculations of the second-to-fifth gyrofrequency harmonics against a background of the thermal bremsstrahlung emission of flocculi, surrounding the spot structure of an active region. The brightening of the extraordinary mode in the short-wavelength spectral range and the kinks in the intensity spectra of emission are analyzed. The interpretation of the RATAN-600 observational data with probable diagnostics of the emission of the fourth gyrofrequency harmonic is considered as examples.

Investigation of Optically Grey Electron Cyclotron Harmonics in Wendelstein 7-X

For a magnetic field of 2.5T, the electron cyclotron harmonics are spectrally well separated in W7-X as it has a large aspect ratio. Because of this advantage from the geometry of W7-X stellarator, it is easier to scan these higher harmonics (70,140,210…..GHz) compared to tokamaks with small aspect ratio. For confinement reasons, W7-X is planned to work at high plasma densities applying O2 electron cyclotron resonance heating (ECRH). For such plasmas, which already have been demonstrated in experimental campaign OP1.2a of W7-X, electron cyclotron emission (ECE) from second harmonic extraordinary mode (X2) is in cutoff. In that case, optically grey higher harmonics provide the only access to ECE signal and hence electron temperature profiles. A Michelson interferometer will be used in the next operational campaign of W7-X for broadband (50-500 GHz) ECE scan and that will be compared to modeling of ECE emission at different plasma parameters from radiation transport calculations (TRAVIS). The strong stray radiation from non-absorbed ECRH is a major concern in scanning these higher harmonics using an interferometer because this stray radiation will dominate the spectra thus masking the ECE signal. For this purpose, a multimode notch filter design based on a multilayer dielectric structure is constructed to attenuate the stray radiation at 140GHz by 50dB.

Mode analysis limitations of ECE-I & ECE measurements at the plasma edge

Interpretation of the Electron Cyclotron Emission (ECE) and ECE Imaging (ECE-I) measurements concerning the measurement position and the radiation temperature (Trad) at the plasma edge is associated with significant uncertainty. Various limitations such as low and high-density limits, relativistic and Doppler shift-broadening, mode overlap were identified in the past. Here, we analyse the influence of density profile variation onto the radiation temperature in H-mode plasmas at ASDEX Upgrade tokamak. We show that, in the region of steep gradients, the variation of the density profile leads to an outward-shift of the measurement position, towards lower Trad. The analysis is extended towards the study of the contribution of the ordinary mode (O-mode) emission to the measured Trad at the plasma edge. With this analysis, we show the qualitative agreement between experimental observations and modeling when taking into account the O-mode contribution to the ECE measurements. All of these effects are assessed via the Electron Cyclotron Radiation transport forward model that is now routinely used to model the response of the ECE-I and ECE systems in different plasma scenarios.

Względna przyczyna odwoławcza związana z błędem w rekonstruowaniu podstawy faktycznej orzeczenia w perspektywie prawnomiędzynarodowej i konstytucyjnej

From the perspective of legal-international and constitutional guarantees of a two-instance procedure one should consider admissible the exclusion of the control of the actual basis in reference to guilt and punishment when such an adjudication constituted the object of a lawsuit-related contract, for the right to instance-based control of adjudications is relinquishable, and the limitations of the challengeability of contractual rulings was regulated in the Polish criminal procedure as not to exclude the right of the parties to bring about control of contractual rulings in a general manner, but only to constrain the catalogue of the admissible appeal-based accusations. However, the complete liquidation of the instance-based control of the establishment of the actual state of affairs contradicts the legal-international and constitutional guarantees, for the reconstruction of the actual state of affairs constitutes a component of the adjudication about someone’s culpability in the trial-related sense, and the control of the solution of this problem is guaranteed at the international level. The abolishment of instance-based control of the establishment of the actual state of affairs, being a manifestation of the pursuit of praxeological economical arrangements, also results in the reduction of the probability of reaching material truth. Moreover, it changes the model of a multi-faceted verification based activities realised within the framework of a typical instance-based course into control which is similar to an analysis and correction peculiar to the extraordinary modes of control-related proceedings.

Enhanced heat transport in ablation plasma under transverse magnetic field by upper hybrid resonance heating

Heat transport properties in a kilotesla transverse magnetic field are compared for the two propagation modes, so-called ordinary (O) and extraordinary (X) modes, of laser using one-dimensional collisional particle-in-cell simulations with ablation-plasma-like settings. The evanescent wave of the X-mode laser is expected to cause an upper hybrid resonance from its dispersion relation, as opposed to the O-mode. Our simulations revealed that significantly hot electrons can be generated by the resonance even if the evanescent wave is initially unreachable to the resonance position, because the radiation pressure steepens the density profile and shortens the cutoff-to-resonance distance. The hot electrons are found to produce a significant amount of heat flux while keeping the transport by the bulk electrons, which results in an enhanced total heat transport.

Rapamycin-inspired macrocycles with new target specificity.

Rapamycin and FK506 are macrocyclic natural products with an extraordinary mode of action—they form binary complexes with FKBP through a shared FKBP-binding domain before forming ternary complexes with their respective targets, mTOR and calcineurin, respectively. Inspired by this, we sought to build a rapamycin-like macromolecule library to target new cellular proteins by replacing the effector domain of rapamycin with a combinatorial library of oligopeptides. We developed a robust macrocyclization method using ring-closing metathesis and synthesized a 45,000-compound library of hybrid macrocycles that are named rapafucins using optimized FKBP-binding domains. Screening of the rapafucin library in human cells led to the discovery of rapadocin, an inhibitor of nucleoside uptake. Rapadocin is a potent, isoform-specific and FKBP-dependent inhibitor of the equilibrative nucleoside transporter 1 and is efficacious in an animal model of kidney ischemia reperfusion injury. Together, these results demonstrate that rapafucins are a new class of chemical probes and drug leads that can expand the repertoire of protein targets well beyond mTOR and calcineurin.

Individuation et affects : les rythmes de l’empathie

Our purpose is to show, from the analysis of interactions between organism and its environment, emotion and affect are the ordinary modes of the process of individuation of the self which makes its environment. To live, a living being needs landmarks, habits, acquired behaviors, which will become innate propensities in the succession of generations, but it needs also to invent, as environment, life, is made of unexpected and unpredictable. The propensity of taking habits is an organizing principle of life but the living must constantly cope with dangers, predators, hazards, climatical variations (like drought) to which economical variations (like unemployment) for human beings are added. These variations require us to take risks, to change course (as we humans all living beings). All these interactions are the habits of a living being are disturbed, disorganized and it has to invent new norms and new habits to survive. The process of individuation, the individual life is rhythmed by emotion, affects, habits, but also by which forces it to derogate from it, to reorganize and reinvent itself: the break in rhythm makes the rhythm.

Validation of the radiation shielding for the Laser Laboratory for Acceleration and Applications

The Laser Laboratory for Acceleration and Applications (L2A2) is a new facility, recently built at the University of Santiago de Compostela in Spain, to investigate laser–plasma acceleration technologies. This facility is equipped with a 50 TW laser system and a radio-protected area where different laser–plasma induced radiation sources are being implemented. In this paper we use Monte Carlo radiation transport simulations based on the code Fluka to validate the radiation shielding installed at L2A2 for proton, neutron and electron sources generated with the present laser system, but also for future possible upgrades increasing the laser power to 100 and 200 TW. Particular attention is paid to the determination of the radiation source term describing the acceleration of electrons, protons and neutrons using over-dense and under-dense plasmas.

Mode-conversion of the extraordinary wave at the upper hybrid resonance in the presence of small-amplitude density fluctuations

In spherical tokamaks, the electron plasma frequency is greater than the electron cyclotron (EC) frequency. Electromagnetic waves in the EC range of frequencies are unsuitable for directly heating such plasmas due to their reduced accessibility. However, mode-conversion of the extraordinary wave to the electron Bernstein wave (X–B mode-conversion) at the upper hybrid resonance makes it possible to efficiently couple externally-launched electromagnetic wave energy into an overdense plasma core. Traditional mode-conversion models describe an X-mode wave propagating in a potential containing two cutoffs that bracket a single wave resonance. Often, however, the mode-conversion region is in the edge, where turbulent fluctuations and blobs can generate abrupt cutoffs and scattering of the incident X-mode wave. We present a new framework for studying the X–B mode-conversion which makes the inclusion of these fluctuations analytically tractable. In the new approach, the high-field cutoff is modeled as an infinite barrier, which manifests as a boundary condition applied to a wave equation involving only one cutoff adjacent to the resonance on the low-field side. The new model reproduces the main features of the previous approach, yet is more suitable for analyzing experimental observations and extrapolating to higher dimensions. We then develop an analytical estimate for the effect of small-amplitude, quasi-monochromatic density fluctuations on the X–B mode-conversion efficiency using perturbation theory. We find that Bragg backscattering of the launched X-mode wave reduces the mode-conversion efficiency significantly when the fluctuation wavenumber is resonant with the wavenumber of the incident X-mode wave. These analytical results are corroborated by numerically integrating the mode-conversion equations.

In-situ frequency calibration of frequency modulated continuous wave reflectometry.

Frequency modulated continuous wave reflectometers have been used to measure the plasma density profiles of the KSTAR tokamak. Three reflectometers are operating in an extraordinary polarization mode in the frequency range of Q band (33-50 GHz), V band (50-75 GHz), and W band (75-110 GHz). Each full frequency band is linearly swept in 20 μs. The accuracy of the density profile measurement is dependent on how precisely the frequency is calibrated. Two new frequency measurement techniques are developed to in situ calibrate the instantaneous frequency during the sweep time of 20 μs. First the intermediate frequency (IF) of the receiver is analyzed based on wavelet transform as applying a fixed frequency signal from a synthesizer to the local oscillator (LO) port. The frequency of the transmitted microwave is simply obtained by adding or subtracting the measured IF to the given LO frequency. Once the group delay of the whole system is known, the frequency can be calibrated by measuring the IF. By measuring the reflectometer output without plasma with delay lines of different lengths and subtracting them, the frequency can be calibrated by eliminating the unknown group delay of the system except the known group delay of the delay line. These two techniques are described in detail, and the calibrated frequencies conducted by the two techniques are compared.

Analysis of the high-energy electron population in surface-wave plasma columns in presence of collisionless resonant absorption

In surface-wave plasmas, the energy can be transferred to the plasma electrons through both ohmic (collisional) and collisionless heating mechanisms. At very low pressure, when the electron–neutral collision frequency is much lower than the wave frequency (collisionless regime), a resonance is excited close to the tube walls where the electron plasma frequency in the radially-inhomogeneous plasma column reaches the wave frequency. In such conditions, the sharp rise of the component of the surface-wave electric field perpendicular to the tube axis can induce transit-time heating. At the resonant point, the long-wavelength electromagnetic surface wave can also be converted into short-wavelength electrostatic Langmuir waves that propagate down the density gradient. In this work, spatially-resolved trace-rare-gases optical emission spectroscopy combined with collisional-radiative modeling is used to analyze the electron energy distribution function (EEDF) and wave–particle interactions in low-pressure argon plasma columns sustained by an electromagnetic surface wave at 600 MHz (over-dense plasma). The EEDF is found to depart from a Maxwellian with the presence of a high-energy tail. The relative population of high-energy electrons increases with the axial distance towards the end of the plasma column where the electron density decreases and the resonance point becomes closer to the discharge axis. Over the range of experimental conditions examined, the high-energy tail increases with the characteristic length of the plasma density gradient at the resonance point; a feature that can be linked to collisionless electron heating by Landau damping of Langmuir waves.

Measurements of electron density profile by frequency modulated continuous wave reflectometer in the T-10 tokamak using high magnetic field side probing and extraordinary mode lower cutoff.

A new, previously unused combination of the high magnetic field side probing and the lower extraordinary mode cutoff was used in the T-10 tokamak for the electron density profile measurements by using a frequency modulation continuous wave reflectometer. This scheme has a significant advantage for large fusion machines where flat electron density profiles and high electron temperatures are expected. The reflectometer design is based on a common scheme with voltage controlled oscillators, active multipliers, and in-phase/quadrature signal detection. Iterative procedures were applied to calibrate a microwave source frequency and compensate the dispersion of probing signals in the conventional rectangular waveguides used as the transmission lines. About 0.2% stability of the beating frequency was reached after the calibration procedure had been finished. An advanced finite-difference scheme was proposed for the reconstruction of the electron density profile to reduce errors and improve the overall performance of the algorithm. Reconstructed electron density profiles demonstrate good agreement with conventional T-10 diagnostic data. Some specific technical and physical aspects of the diagnostic were also discussed on the basis of T-10 operation experience.

Electron Dynamics and Characteristics of Attosecond Electromagnetic Emissions in Relativistic Laser-Plasma Interactions**Supported by the National Natural Science Foundation of China under Grant No 11674146, and the National Basic Research Program of China under Grant No 2013CBA01500.

Generation of attosecond electromagnetic (EM) pulses and the associated electron dynamics are studied using particle-in-cell simulations of relativistic laser pulses interacting with over-dense plasma foil targets. The interaction process is found to be so complicated even in the situation of utilizing driving laser pulses of only one cycle. Two electron bunches closely involved in the laser-driven wavebreaking process contribute to attosecond EM pulses through the coherent synchrotron emission process whose spectra are found to follow an exponential decay rule. Detailed investigations of electron dynamics indicate that the early part of the reflected EM emission is the high-harmonics produced through the relativistic oscillating mirror mechanism. High harmonics are also found to be generated through the Bremsstrahlung radiation by one electron bunch that participates in the wavebreaking process and decelerates when it experiences the local wavebreaking-generated high electrostatic field in the moving direction.

Controlling the ellipticity of attosecond pulses produced by laser irradiation of overdense plasmas

The interaction of high-intensity laser pulses and solid targets provides a promising way to create compact, tunable, and bright XUV attosecond sources that can become a unique tool for a variety of applications. However, it is important to control the polarization state of this XUV radiation and to do so in the most efficient regime of generation. Using the relativistic electronic spring (RES) model and particle-in-cell simulations, we show that the polarization state of the generated attosecond pulses can be tuned in a wide range of parameters by adjusting the polarization and/or the angle of incidence of the laser radiation. In particular, we demonstrate the possibility of producing circularly polarized attosecond pulses in a wide variety of setups.

Particle‐in‐Cell Simulations of the Fast Magnetosonic Mode in a Dipole Magnetic Field: 1‐D Along the Radial Direction

AbstractAn electromagnetic particle‐in‐cell code is used to investigate self‐consistent evolution of the fast magnetosonic mode in a one‐dimensional configuration along the radial direction in a dipole background magnetic field. A previous observation of this wave mode is used to select the simulation parameters. A partial shell velocity distribution of energetic protons with a moderate pitch angle anisotropy is used to excite the waves self‐consistently. Consistent with local linear theory analysis, wave growth occurs only at exact harmonics of the local proton cyclotron frequency, Ωp. However, radial propagation quickly removes the waves from the region where they can grow, leading to a time scale of wave amplification much longer than that predicted by linear theory. In addition, radial propagation from multiple wave sources makes the frequency spectrum measured at a single point much broader. The warm background plasma plays an important role in two ways. First, it increases the phase speed of the fast magnetosonic mode; and second, it causes the breakup of the extraordinary mode dispersion relation in the vicinity of the harmonics, where the broken dispersion curves are connected with multiple ion Bernstein modes. In this case, the waves propagating radially are absorbed at locations where their frequency reaches integer multiples of Ωp and background protons experience perpendicular heating at those locations.

Spatial propagation and damping of ordinary electromagnetic mode

The spatial propagation and damping of the ordinary electromagnetic mode is studied by making use of the Vlasov approach and treating the wave vector as complex while treating the frequency as real. Such a treatment is applicable to situations where an incident electromagnetic wave from outside the spatially confined plasma is absorbed at the plasma surface, or is transmitted into the plasma. This approach of investigating the behavior of plasma wave characteristics shows certain features that are fundamentally different from the analogous wave analysis from the view point of the customary initial value problem in which the wave frequency is treated as complex while regarding the wave vector as real. Both numerical and analytical methods are employed in order to unveil the complicated structure of the hitherto unexplored spatial structure of the ordinary electromagnetic wave as it either propagates in space or suffers spatial attenuation. Possible applications of the present findings are discussed.

Saturation of the low-threshold parametric decay of the O-mode pump in the fundamental harmonic ECRH experiment

The saturation regime of the low-power-threshold ordinary (O) wave parametric decay instability leading to the excitation of a localized upper hybrid (UH) wave and a low-hybrid wave is analysed. The cascade of secondary decays of a daughter UH wave to a localized UH wave and ion Bernstein wave is considered as presumably the most important nonlinear mechanism responsible for the transition to a saturation regime. A set of equations describing this nonlinear frequency down-conversion is derived and then solved both analytically and numerically under the conditions typical of the on-axis fundamental harmonic ordinary mode (O1-mode) electron cyclotron resonance heating experiments at the FTU tokamak.

Turbulence measurements on the high and low magnetic field side of the DIII-D tokamak.

In this paper, we address the challenging question of measuring turbulence levels on the high magnetic field side (HFS) of tokamak plasmas. Although turbulence measurements on the HFS can provide a stringent constraint for the turbulence model validation, to date only low magnetic field side (LFS) measured turbulence has been used in validation studies. To address this issue, an eight channel Correlation Electron Cyclotron Emission (CECE) system at DIII-D was modified to probe both LFS and HFS. In contrast to the second harmonic extraordinary mode electron cyclotron resonance emission that is typically used in CECE, we show that it is possible to probe the HFS using fundamental O-mode electron cyclotron resonance emission. The required hardware modifications for the HFS measurements are presented here, and the potential issues in this measurement are discussed.

Coherent terahertz Smith–Purcell radiation from Dirac semimetals grating with very deep and narrow slits

We demonstrate a physical mechanism of multicolor coherent terahertz (THz) Smith–Purcell radiation from surface plasmon polaritons (SPPs). In Dirac semimetals gratings with very deep and narrow slits, two types of SPP modes, the cavity and ordinary SPP modes, can be excited by fast electrons under different excitation conditions and then diffracted into radiation in specific directions. The radiation intensity is remarkably enhanced when SPPs are excited, and frequencies can be widely tuned by adjusting the parameters of grating and electrons. Our findings could provide a promising way for developing room temperature, coherent, tunable, directional, and intense THz radiation sources.