Interaction Of Fast Particles Research Articles

HALO: A full-orbit model of nonlinear interaction of fast particles with eigenmodes

HALO (HAgis LOcust) solves the initial value Vlasov–Maxwell problem perturbatively for application to certain nonlinear wave-particle problems in tokamak plasmas. It uses the same basic approach as the HAGIS code (Pinches et al., 1998) for wave evolution but is built on the LOCUST-GPU full-orbit code (Akers et al., 2012) for the solution of the Hamiltonian fast particle motion in cylindrical coordinates. The wave amplitude and particle evolution include all finite Larmor radius effects. We describe and benchmark the currently implemented Alfvén eigenmode workflow, demonstrating correct particle motion, linear and nonlinear power transfer. The formulation and numerical scheme are sufficiently general as to allow easy future implementation of different kinds of eigenmodes, such as modes close to the ion-cyclotron frequency. The code can model multiple eigenmodes and multiple fast ion species simultaneously, and supports the general form of the equilibrium distribution in constants of motion.

19th International Summer School on Vacuum, Electron and Ion Technologies (VEIT2015)

The International Summer School on Vacuum, Electron and Ion Technologies (VEIT) has been organized biennially since 1978, when the series of VEIT Schools was launched by the Institute of Electronics, Bulgarian Academy of Sciences with the aim to act as a forum for exchange and dissemination of knowledge and ideas on the latest developments in electron-, ion-, and plasma-assisted technologies. The organizers of the 2015 edition of the event were the Institute of Electronics, Bulgarian Academy of Sciences, Sofia, Bulgaria and the Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands. While the school has initially been providing a meeting place for researchers mainly from Eastern and Central European countries, its importance has grown issue by issue. The school is now a major scientific event and a meeting place for young scientists from Eastern and Western Europe involved in research and development associated with high-tech industries. Many former school participants have gone on to become leading scientists in research establishments and companies throughout the world. Leading international companies, such as High Voltage Engineering, Balzers, Varian, and Hauzer have used the VEIT forum to present their products through oral presentations, poster contributions or exhibits. The School Proceedings have been published in special issues of the international journals Vacuum, Plasma Processes and Polymers, Journal of Physics: Conference Series.The Nineteenth edition of VEIT was held in the Black Sea resort Sozopol, Bulgaria, on 21--25 September 2015. It was attended by 101 participants from 16 countries: Bulgaria, Czech Republic, France, Germany, Greece, The Netherlands, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, Sweden, Turkey, Ukraine and UK.Following the tradition of publishing the VEIT Proceedings, a selection of papers presented at the event are published in this special issue of Journal of Physics: Conference Series, under the originality and quality criteria of acceptance by the journal, including peer reviewing.The school comprised fifteen plenary and three poster sessions. At the plenary sessions, twenty-one invited talks of general interest were presented by highly renowned international experts in the field (5 invited talks and 16 progress reports), as well as ten progress reports by young scientists. In total, 74 contributed papers were presented during the poster sessions. There were several scientific highlights covering fundamentals of interaction of fast particles with solids and challenging practical applications ranging from novel techniques for creating hard coatings, optical/protective layers, biocompatible materials to nanosized structures produced by evaporation, sputtering or external irradiation. Latest results were presented on ion-beam synthesis and modification in both low-energy (deposition and film growth) and high-energy (sputtering, implantation) regimes, and processing of solid materials aiming at patterning the surface or at creating nanophase systems for electronic or tribological/wear resistant applications.Despite the busy scientific program, the atmosphere was relaxed and informal. The early afternoons of most conference days were free to stimulate both scientific and social interaction between participants, which often took place on the beach. The social program included a welcome party, an official dinner, and an outing to a winery in the town of Pomorie.VEIT 2015 owes its success to many people. The International Advisory Committee shaped the scientific program and ensured high-quality plenary presentations by careful selection of invited speakers. The Local Committee bore the brunt of the organization both at the conference site and in dealing with correspondence, abstracts, and manuscripts for these proceedings.We are grateful to our sponsors, the Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands, IUVSTA, and the Ministry of Education and Science of Republic of Bulgaria for there generosity that enabled us to support the attendance of students and provided support to deal with mailing, printing, renting the conference site, etc. We are also grateful to the members of the International Advisory Committee - Th. Czerwiec, M. Dimitrova, G. Dinescu, A. Ehiasarian, N. Guerassimov, V. Guerra, I. Katardjiev, H. Kersten, K. Larsson, D. Mataras, W. Möller, M. Mozetic, R. Panek, I. Petrov, Z. Petrovic, B. Rauschenbach, M.C.M. (Richard) van de Sanden, M. Ürgen, for their continuous concern about the high scientific level and the future of the event, as well as for their contribution to the formation of a new generation of scientists and experts in the field. And, last but not least, we would also like to thank all authors for their valuable contributions to these proceedings and to the school, and all reviewers for their hard and tedious, but very important, work.The next conference in the series will be held in September 2017.M.C.M. van de Sanden, Miglena Dimitrova, Chavdar Ghelev,Guest Editors

Suprathermal electron dynamics and MHD instabilities in a tokamak

The dynamics of suprathermal electrons in the presence of magnetohydrodynamics (MHD) activity and the excitation of MHD modes by suprathermal electrons are studied experimentally to improve the understanding of the interaction of fast particles with MHD instabilities in a tokamak. The study focuses on three different aspects of the internal kink mode with poloidal/toroidal mode number : the sawtooth instability, electron fishbones and coupled bursts alternating with sawtooth crashes (CAS), all located where the safety factor profile approaches or takes the value . New quantitative results on suprathermal electron transport and an investigation of electron acceleration during sawtooth crashes are followed by the characterization of initial electron fishbone observations on the Tokamak à configuration variable (TCV). Finally, bursts associated with the sawtooth cycle, coupled to a persisting mode and alternating with sawtooth crashes, are discussed, in particular in view of the fast electron dynamics and their role in confinement degradation and mode excitation.

A hierarchy of electromagnetic gyrokinetic and fluid hybrid models for the simulation of global modes

The goal of magnetic confinement fusion research is to produce an economically viable power reactor. This will require operation at finite plasma β, where for instance fast particle transport by Alfvén eigenmodes may become important. The density and energy of fast particles originating from heating and fusion will also be higher. Low frequency Alfvénic modes can be destabilised by fast particles, with velocities comparable to the Alfvén velocity, resulting in significant reduction of fast particle confinement. To properly predict and manipulate this behaviour in current and future fusion devices, the numerical simulation of fast particle interaction with Alfvén modes is necessary. Since these simulations are computationally demanding, it is desirable to use the simplest model capable of simulating a given phenomenon. Comparing a case with different physical models also permits the isolation of physics effects responsible for certain phenomena. In this paper we present a hierarchy of such numerical models and investigate their ranges of validity.

13th EU–US Transport Task Force Workshop on transport in fusion plasmas

This report summarizes the contributions presented at the 13th EU–US Transport Task Force Workshop on transport in fusion plasmas, held in Copenhagen, Denmark, 1–4 September 2008. There were sessions on core heat and particle transport; core and edge momentum transport; edge and scrape-off-layer transport and MHD and fast particle interaction with transport.

Requirements for fast particle measurements on ITER and candidate measurement techniques

Recent JET and JT-60U results, have underlined the need to look into the measurement requirements of fast particles diagnostics in ITER. Not only alpha particles but all fast ions (He4,p,D,T,He3) present in the plasma should be diagnosed. Furthermore, the electron diagnostics, monitoring the deviations from a Maxwellian distribution function, play a central role in the electron cyclotron heating and current drive. In the present ITER measurement requirements only alpha particles and He ions are mentioned: space resolution is δr = a/10 (a is the minor radius), time resolution is δτ = 100 ms and accuracy 10–30%. The new proposed measurement requirements for fast particles are spatial resolution ∼a/20 (10 cm on ITER), time resolution (minimum) ∼100 τA (∼100 µs for ITER), density of fast ions: the minority ions could be 4–10% of the plasma density. The candidate diagnostic techniques considered for ITER are amongst others γ-ray spectroscopy, fast ion collective Thomson scattering (CTS) and charge exchange recombination spectroscopy (CXRS). γ-ray spectroscopy detects ions in the energy range 1 < E < 5 MeV and R&D is needed to demonstrate the feasibility of these measurements in the presence of a neutron background. Techniques using ultraviolet spectroscopy of ions such as Krypton are being tested, for the low energy part of spectrum of fast particles. A design study of CTS shows that the requirements are closely met; the system includes a high power gyrotron operating in a region not yet tested in current applications (i.e. using a gyrotron at a frequency below the first ECE harmonic). For CXRS the spatial resolution and accuracy are not achievable for r/a < 0.3 and R&D is needed to assess the minimum figures in terms of accuracy possible for measurements close to the centre. The measurement requirements deduced from the need for detecting the effects of interaction of fast particles with MHD instabilities put forward important new objectives to the candidate diagnostic systems. In particular diagnostics for fast particles in the energy region 200 < E < 1300 keV and diagnostics for escaping fast particles need urgent development.

Quantification of the spreading effect of auroral proton precipitation

A three‐dimensional Monte Carlo model has been developed to study the transverse beam spreading effect of incident energetic auroral protons during their precipitation in the Earth's upper atmosphere. Energetic protons with an isotropic angular distribution are injected at 700 km altitude. Two types of incident energy spectra, a monoenergetic and a Maxwellian distribution, are considered. Interaction of fast particles with a three‐species atmosphere (O, N2, and O2) is included through charge exchange, electron stripping, ionization, excitation, and elastic scattering collisions. A uniform geomagnetic field is assumed in the model. The spreading effect is simulated for both a fine proton beam and a proton arc of longitudinal and latitudinal extent. It is found that the main dispersion region for a fine proton beam is located in the altitude range of around 250–450 km, where the first few charge exchange collisions play a significant role. In the spreading study for a proton arc, we compare the numerical results with previous studies and give a convincing explanation by analyzing atmospheric scale heights and cross‐section data. For the purpose of the model validity check, we make a comparison of the Monte Carlo simulation with observations and the results from other models.

Resonant interaction of fast particles with neoclassical tearing modes

Cherenkov resonance between rotating neoclassical tearing mode (NTM) and energetic ions has been considered. Resonant interaction drives the current, which is in phase quadrature with the magnetic island and thus produces a toroidal torque accelerating island in the direction of the fast ion diamagnetic drift. This torque has been included in the coupled nonlinear first-order differential equations governing evolution of the NTM rotation frequency and amplitude. It has been shown that due to resonant interaction with energetic ions, this autonomous system exhibits Hopf bifurcation from the unstable stationary solution to the stable limit cycle describing nonlinear oscillations of the mode frequency and amplitude. Such behavior resembles the frequency jump events observed during NTM activity in ASDEX Upgrade [S. Guenter et al., Phys. Plasmas 7, 935 (2000)].

Erratum: “Interaction of fast particles with neoclassical tearing modes” [Phys. Plasmas 7, 935 (2000)

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Interaction of fast particles with neoclassical tearing modes

Fast particle driven m=1/n=1 modes in the form of fishbones frequently initiate neoclassical tearing modes (NTMs) on Axisymmetric Divertor Experiment Upgrade [W. Köppendörfer et al., 14th International Conference on Plasma Physics and Controlled Fusion (International Atomic Energy Agency, Vienna, 1993), Vol. I, p. 127] and other neutral-beam-injection heated tokamaks, but disappear after the NTMs have reached a quasistationary state. A burst of other magnetohydrodynamic phenomena, described in this paper, appear instead, similar in repetition rate and time signature of frequency and amplitude. They are associated with the growth of the m=2/n=2 satellite of the m=3/n=2 neoclassical tearing mode, and a transient increase (termed FJ=frequency jump event) in the rotation frequency of the coupled mode system. They lead to a thermal crash, originating at q=3/2, propagating inwards up to the q=1 surface. With a lower repetition rate (more characteristic of sawteeth) similar events occur, where a large 1/1 component also appears and the fast crash propagates to the plasma center frequency jump with sawtooth character (FJST). The analogies to the fishbone case suggest that this phenomenon is caused by the interaction with fast particles, which transiently impress their precession frequency on the pre-existing magnetic perturbation of the NTM.

Diffuse 0.5–1 keV X‐Rays and Nuclear Gamma Rays from Fast Particles in the Local Hot Bubble

We show that interactions of fast particles with the boundary shell of the local hot bubble could make an important contribution to the 0.5-1 keV diffuse X-ray background observed with ROSAT. The bulk of these nonthermal X-rays are due to line emission from fast O ions of energies around 1 MeV/nucleon. This is the typical energy per particle in the ejecta of the supernova which is thought to have energized the bubble. We find that there is sufficient total energy in the ejecta to produce X-rays of the required intensity, subject to the details of the evolution of the fast particle population since the supernova explosion (about 3 10$^5$ years ago based on the age of the Geminga pulsar). The unequivocal signature of lines from deexcitations in fast ions is their large width ($\delta E/E$~0.1 for O lines), which will clearly distinguishes them from X-ray lines produced in a hot plasma. If a small fraction of the total ejecta energy is converted into accelerated particle kinetic energy (>~30 MeV/nucleon), the gamma-ray line emission produced in the boundary shell of the local hot bubble could account for the recently reported COMPTEL observations of nuclear gamma-ray lines from a broad region towards the Galactic center.

Nonlinear interaction of fast particles with Alfvén waves in toroidal plasmas

A numerical algorithm to study the nonlinear, resonant interaction of fast particles with Alfvén waves in tokamak geometry has been developed. When the instability is sufficiently weak, it is known that the wave-particle trapping nonlinearity will lead to mode saturation before wave–wave nonlinearities are appreciable. The spectrum of linear modes can thus be calculated using a magnetohydrodynamic normal-mode code, then nonlinearly evolved in time in an efficient way according to a two-timescale Lagrangian dynamical wave model. The fast particle kinetic equation, including the effect of orbit nonlinearity arising from the mode perturbation, is simultaneously solved for the deviation, δf=f−f0, from an initial analytic distribution f0. High statistical resolution allows linear growth rates, frequency shifts, resonance broadening effects, and nonlinear saturation to be calculated quickly and precisely. The results have been applied to an International Thermonuclear Experimental Reactor [ITER EDA Doc. Series No. 7 (International Atomic Energy Agency, Vienna, 1996), p. V-32] instability scenario. Results show that weakly damped core-localized modes alone cause negligible alpha transport in these reactor-like plasmas—even with growth rates one order of magnitude higher than expected values. However, the possibility of significant transport in reactor-type plasmas due to weakly unstable global modes remains an open question.

Studies of light emission from cathode material in the plasma phase of a glow discharge

Heavy particles bombarding the cathode surface in a glow discharge produce sputtering which liberates cathode material which then appears in the plasma phase in the vicinity of the cathode. The intensity of light emission from fundamental gas atoms depends linearly on the discharge current and this dependence can be explained if it is assumed that these intensities are proportional to the densities of the gas and electron current density. The electron/molecule excitation of sputtered material in the plasma phase is the main source of the light emitted by elements of the cathode. The intensity of light emission from this cathode material in the plasma depends parabolically on the discharge current density. This dependence can be explained if the intensity is assumed to be proportional to the densities of both the electron current and the stream of sputtered particles leaving the cathode surface. The density of the sputtered particles is in turn dependent on the energy of bombarding particles. The excitation of the sputtered material due to fast particle interaction with the cathode bulk seems to be a less important mechanism of light emission.

Deductions from space shuttle glow photographs

It is shown that from the appearance of certain photographs taken from STS‐5, it is possible to make several useful statements about the production mechanism of the visible glow around the shuttle, and presumably other space vehicles. These are: 1) the electronic excitation of particles in the gas phase by either electrons or fast neutrals is probably not important, 2) the interaction of thermal atoms and molecules with the surfaces does not generate the glow, and 3) translational energy accommodation of fast particles is efficient enough that a single surface collision reduces the kinetic energy below the threshold for glow production. There is no glow without the direct interaction of fast particles with the surfaces, and the sum of the contributions of the three above processes does not exceed 14% of the observed surface intensity.

The Interaction of Fast Particles with Frozen Gases in T Tau Nebulae: The Physical Background

The interaction of energetic particles with frozen gas layers plays a relevant role in a variety of astrophysical scenarii and also in T Tau nebulae because of the large fluxes of particles ejected by these stars during their continuous flaring activity and the observed presence of ice grains at least around the very young star KL Tau (Cohen, 1975).

Interaction of Fast Particles with Waves in Cosmic Magnetoactive Plasma

Until recently, the concepts describing cosmic plasma were very simple (see Alfven & Fiilthammar 1963, Pikel'ner 1965), but it is clear now that they were also more or less naive. Plasma was considered to be a state of matter with a large number of charged particles of both signs (in the cosmos, mostly protons and electrons) interacting with each other and with collective and external electric and magnetic fields. Particle collisions were thought to be responsible for the bremsstrahlung radiation in free-free transitions and, with the radiation, to determine the degree of ionization of the cosmic plasma. The temperature of star surfaces and the interstellar medium was inferred from data on the degree of ionization (Pikel'ner 1965, Kaplan & Pikel'ner 1970). In principle, these con­ cepts are not wrong if the plasma is indeed or in thermodynamic equi­ librium. But is the cosmic plasma in such a condition? Astrophysical observa­ tions in recent years give more and more evidence for violent unstationary processes in the cosmic plasma. We mention only some of the well-known phe­ nomena discovered recently. In very distant regions, quasars, galactic nuclei, the wind from galactic nuclei, supernova explosions, and conditions in the plasma surrounding pulsars all demonstrate nonstationarity. In nearer regions, explosive processes in chromospheric flares, solar bursts of different types, and radar probes of the Sun also indicate great instability. Radar probes show irregularities in the reflected signal even in the quiet Sun time, which indicates the develop­ ment of nonstationary processes in the outer layers. The interplanetary media is confined by the nonstationary solar wind, which creates a bow shock near the Earth and causes many nonstationary phenomena in the magnetosphere. Among them are the substorms. The development of substorms due to the solar wind triggers the release of energy confi ned in the magnetosphere. The plasma near the bowshock is always violent. New observations indicate more and more that the cosmic plasma in many conditions is not in a stationary equilibrium state (Kaplan & Tsytovich 1972a). What about the results of laboratory plasma research? Most experiments on

Interaction of fast particles with magneto-hydrodynamical turbulence

The acceleration of fast particles by Alfven and magnetic sound waves of small amplitude is considered. The waves exist against the background of a strong, uniform magnetic field. We take into accunnt the contributions to acceleration from a large scale random field (harmonics withk R−1). The small scale field was considered by perturbation theory, while large scale random field-in an adiabatic approximation. The energy dependence of the diffusion coefficient in momentum space, and the time of acceleration are estimated. The possible anisotropy of angular distribution is taken into account.

Interaction of Fast Particles with Intergalactic Matter

A discussion is given of the relaxation of power-law cosmic-ray spectra in the intergalactic medium. The theoretical time-dependent spectra obtained are used to calculate the nonthermal radiation produced by bremsstrahlung of subcosmic-ray electrons colliding with ambient protons of the intergalactic gas. A comparison is made between the theory and the observations of the diffuse X-ray and gamma-ray background. The calculated cosmic-ray proton spectra are applied to a computation of the heating of the intergalactic medium, and the resulting thermal bremsstrahlung radiation is compared with the suprathermal proton bremsstrahlung flux. We conclude that nonthermal bremsstrahlung is unlikely to be an important contributor to the isotropic X- and gamma-ray background. However, cosmic-ray heating can provide a plausible heat source for maintaining a hot intergalactic gas, especially when evolutionary effects are included in the distribution of cosmic-ray sources.

Cascade interactions of high-energy particles with nuclei

Several tens of thousands of internuclear cascades have been computed at energies up 5 to 30 GeV and the results are given. Comparison with experiment shows that the cascade mechanism of interaction of fast particles with nuclei is predominant at these energies.

C̆erenkov Radiation: its Origin, Properties and Applications

In this account of C̆erenkov radiation, the optical analogue of the 'supersonic bang,' great emphasis is laid on the underlying physical principles of the effect. The historical introduction is followed by a qualitative account of the basic mechanism of the generation of light by the passage of fast charged particles through homogeneous transparent media. After a discussion of the relationship of C̆erenkov radiation to other processes connected with the interaction of fast particles with matter, the article turns to the practical applications of C̆erenkov detectors and counters in the fields of cosmic-ray and high-energy physics. In conclusion, the author describes some interesting experiments carried out by his colleagues and himself on light flashes from the night sky.