Electromagnetic energy rotation along plasma-metal interface in cylindrical waveguides initiated by azimuthal surface waves

Energy transfer along finite curvature plasma-metal interfaces in cylindrical metallic waveguides entirely filled by magnetoactive plasma is studied. Angular phase velocity, angular velocity of energy transfer, and angular group velocity are introduced and analyzed as functions of the waveguide parameters: radius, plasma particle density, azimuthal wave number, and external static axial magnetic field

Higher radial modes of azimuthal surface waves above the upper-hybrid frequency in cylindrical waveguides partially filled by plasma

Azimuthal surface waves (ASWs) are known to be eigen waves of cylindrical metal waveguides partially filled by magnetoactive plasma. Zeroth radial modes were under study earlier. Their dispersion properties are known to be significantly influenced by the plasma column properties: its particle density, external axial static magnetic field, geometric dimensions, – rather than properties of the dielectric layer which separates the plasma column from the metal wall. Application of higher order ASWs in the low-frequency range was shown earlier to make it possible to get advantage of exciting ASWs with higher frequency than in the case of zeroth order ASWs without no change in the waveguide design. The present study generalises those investigation for the case of the waves above the upper hybrid frequency.Відомо, що азимутальні поверхневі хвилі (АПХ) є власними хвилями циліндричних металевих хвилеводів, які частково заповнені магнітоактивною плазмою. Нульові радіальні моди АПХ вивчені раніше. Відомо, що на їхні дисперсійні властивості більш значною мірою впливають параметри плазмового стовпа: густина його частинок, зовнішнє аксіальне стале магнітне поле, геометричні розміри, – ніж властивості діелектричного шару, який відокремлює плазмовий стовп від металевої стінки. Раніше було показано, що застосування вищих радіальних мод АПХ в низькочастотному діапазоні дає можливість досягти перевагу при збудженні АПХ у вигляді більш високої частоти, ніж у випадку нульової радіальної моди АПХ, без жодних змін у параметрах хвилеводу. Ця робота узагальнює проведені раніше дослідження на випадок хвиль вище верхньої гібридної частоти.Известно, что азимутальные поверхностные волны (АПВ) являются собственными волнами цилиндрических металлических волноводов, частично заполненных магнитоактивной плазмой. Нулевые радиальные моды АПВ изучены ранее. Известно, что на их дисперсионные свойства заметнее влияют параметры плазменного столба: плотность его частиц, внешнее аксиальное постоянное магнитное поле, геометрические размеры, – чем свойства диэлектрического слоя, который отделяет плазменный столб от металлической стенки. Ранее было показано, что применение высших радиальных мод АПВ в низкочастотном диапазоне позволяет достичь преимущества при возбуждении АПВ в виде более высокой частоты, чем в случае нулевой радиальной моды АПВ, без каких-либо изменений в параметрах волновода. Эта работа обобщает проведенные ранее исследования на случай волн выше верхней гибридной частоты

Excitation of eigen azimthal waves by annular charged particle beam

Investigations of an interaction between charged-particle beams and hybrid waveguide structures are important for radio engineering and plasma electronics. It is the distinctive feature of the interaction between charged particle beams and such structures of finite dimensions that motivated the choice of the subject for our study. Here we investigate the excitation of an extraordinarily polarized electromagnetic azimuthal waves (AW), that are eigen modes of a cylindrical metal waveguide partially filled with a cold magnetized plasma. These modes propagate in azimuthal direction strictly transverse to a constant external axial magnetic field. A two-dimensional self-consistent set of differential equations for interaction between AW and cold low-density charged-particle beam moving above the plasma surface is constructed in the single-mode approximation and is solved numerically. Constructed nonlinear theory can be applied for modeling an operation of short-scale plasma filled devices capable of generating continuously tunable radiation over a broad frequency band (eigenfrequency of the plasma structure can be continuously tuned by varying the plasma density). Influence of nonuniformity of charged particle beam distributions in co-ordinate and phase spaces on evolution of beam-driven instability of the AW are examined.Дослідження взаємодії між потоками заряджених частинок та гібридними хвилеводними структурами є важливим для радіофізики та плазмової електроніки. В даній статті досліджено збудження незвичайно поляризованих електромагнітних азимутальних хвиль, які є власними модами циліндричного металевого хвилеводу, який частково заповнено холодною магнітоактивною плазмою. Двовимірна самоузгоджена система диференціальних рівнянь була виведена для опису нелінійної взаємодії між азимутальними хвилями та потоком заряджених частинок малої густини, який рухається над поверхнею плазми, та досліджена числовими методами в одномодовому наближенні. В роботі досліджено вплив неоднорідності розподілу потоку заряджених частинок в координатному та фазовому просторах на еволюцію пучкової нестійкості азимутальних хвиль.Исследование взаимодействия потока заряженных частиц с гибридными волноводными структурами представляется важным для радиофизики и плазменной электроники. В данной статье исследовано возбуждение необыкновенно поляризованных электромагнитных азимутальных волн, которые являются собственными модами цилиндрического металлического волновода, частично заполненного холодной магнитоактивной плазмой. Двумерная самосогласованная система дифференциальных уравнений была выведена для описания нелинейного взаимодействия между азимутальными волнами и потоком заряженных частиц малой плотности, двигающимся над поверхностью плазмы, и исследована числовыми методами в одномодовом приближении. В работе исследовано влияние неоднородности распределения потока заряженных частиц в координатном и фазовом пространствах на эволюцию пучковой неустойчивости азимутальных волн

BREMSSTRAHLUNG FORMATION IN THE DUAL ENERGY METHOD FOR RADIOGRAPHY OF THE UNAUTHORIZED EMBEDDING

The possibility of an effective method of dual-energy radiography unauthorized inclusions containing heavy elements in cargo containers has been investigated. A method for optimizing the energy performance of the bremsstrahlung radiation: low-energy beam (containing the maximum number of photons in the energy range, which is dominated by Compton effect) and high energy beam (with a maximum number of high-energy photons, electron-positron pairs) has been developed. The influence of the converter thickness and converter material on the spectral characteristics of the beams of photons has been investigated. The variants of treelayers efficient converters have been proposed. On the basis of the Monte Carlo and quasi-analytical method a numerical experiment radiography investments has been completed. It is shown that the use of optimally shaped beams can reliably distinguish embedding from lead to masking the background of steel structures up to 25 c

Lifetime measurements of lowest states in the πg_7/2⊗νh_11/2 rotational band in ¹¹²I

A differential-plunger device was used to measure the lifetimes of the lowest states in the πg7/2 ⊗ νh11/2 rotational band in doubly odd 112I with the 58Ni(58Ni, 3pn) reaction. A differential decay curve method was performed using the fully shifted and degraded γ -ray intensity measurements as a function of target-to-degrader distance. The lifetimes of the lowest three states in the πg7/2 ⊗ νh11/2 band in 112I were measured to be 124(30), 130(25), and 6.5(5) ps, respectively. As the lifetimes of successive excited states in a rotational band are expected to decrease with increasing excitation energy, these measurements suggest that the order of the transitions in the established band in 112I may need revising and that the state tentatively assigned to be (7−) may not belong to the rotational band.peerReviewe

Overview of ASDEX upgrade results in view of ITER and DEMO

Experiments on ASDEX Upgrade (AUG) in 2021 and 2022 have addressed a number of critical issues for ITER and EU DEMO. A major objective of the AUG programme is to shed light on the underlying physics of confinement, stability, and plasma exhaust in order to allow reliable extrapolation of results obtained on present day machines to these reactor-grade devices. Concerning pedestal physics, the mitigation of edge localised modes (ELMs) using resonant magnetic perturbations (RMPs) was found to be consistent with a reduction of the linear peeling-ballooning stability threshold due to the helical deformation of the plasma. Conversely, ELM suppression by RMPs is ascribed to an increased pedestal transport that keeps the plasma away from this boundary. Candidates for this increased transport are locally enhanced turbulence and a locked magnetic island in the pedestal. The enhanced D-alpha (EDA) and quasi-continuous exhaust (QCE) regimes have been established as promising ELM-free scenarios. Here, the pressure gradient at the foot of the H-mode pedestal is reduced by a quasi-coherent mode, consistent with violation of the high-n ballooning mode stability limit there. This is suggestive that the EDA and QCE regimes have a common underlying physics origin. In the area of transport physics, full radius models for both L- and H-modes have been developed. These models predict energy confinement in AUG better than the commonly used global scaling laws, representing a large step towards the goal of predictive capability. A new momentum transport analysis framework has been developed that provides access to the intrinsic torque in the plasma core. In the field of exhaust, the X-Point Radiator (XPR), a cold and dense plasma region on closed flux surfaces close to the X-point, was described by an analytical model that provides an understanding of its formation as well as its stability, i.e., the conditions under which it transitions into a deleterious MARFE with the potential to result in a disruptive termination. With the XPR close to the divertor target, a new detached divertor concept, the compact radiative divertor, was developed. Here, the exhaust power is radiated before reaching the target, allowing close proximity of the X-point to the target. No limitations by the shallow field line angle due to the large flux expansion were observed, and sufficient compression of neutral density was demonstrated. With respect to the pumping of non-recycling impurities, the divertor enrichment was found to mainly depend on the ionisation energy of the impurity under consideration. In the area of MHD physics, analysis of the hot plasma core motion in sawtooth crashes showed good agreement with nonlinear 2-fluid simulations. This indicates that the fast reconnection observed in these events is adequately described including the pressure gradient and the electron inertia in the parallel Ohm’s law. Concerning disruption physics, a shattered pellet injection system was installed in collaboration with the ITER International Organisation. Thanks to the ability to vary the shard size distribution independently of the injection velocity, as well as its impurity admixture, it was possible to tailor the current quench rate, which is an important requirement for future large devices such as ITER. Progress was also made modelling the force reduction of VDEs induced by massive gas injection on AUG. The H-mode density limit was characterised in terms of safe operational space with a newly developed active feedback control method that allowed the stability boundary to be probed several times within a single discharge without inducing a disruptive termination. Regarding integrated operation scenarios, the role of density peaking in the confinement of the ITER baseline scenario (high plasma current) was clarified. The usual energy confinement scaling ITER98(p,y) does not capture this effect, but the more recent H20 scaling does, highlighting again the importance of developing adequate physics based models. Advanced tokamak scenarios, aiming at large non-inductive current fraction due to non-standard profiles of the safety factor in combination with high normalised plasma pressure were studied with a focus on their access conditions. A method to guide the approach of the targeted safety factor profiles was developed, and the conditions for achieving good confinement were clarified. Based on this, two types of advanced scenarios (‘hybrid’ and ‘elevated’ q-profile) were established on AUG and characterised concerning their plasma performance