Emittance Growth in a Plasma Wakefield Accelerator

The influence of electric fields and neutral particles on the plasma sheath at ITER divertor conditions

The effect of plasma on the transmission properties of electromagnetic waves and its application have always been one of the key research directions of electromagnetic theory and technology and plasma physics. The enhancement effect of collisional plasma on electromagnetic waves is a classic subject of the interaction between electromagnetic waves and plasma. Based on the transmission characteristics of electromagnetic waves in medium, this paper takes plasma as a special medium, and carries out experimental, theoretical and simulation studies on the transmission characteristics of high power microwave (HPM) atmospheric plasma and a certain range of electromagnetic waves under certain experimental conditions. The study found that the plasma formed by the S-band HPM under a vacuum of 50 Pa has a great influence on the electromagnetic wave transmission characteristics of different frequencies, and the electromagnetic wave transmission signal enhancement effect occurs regularly within a certain frequency range. A series of transmission waveforms of continuous electromagnetic waves of different frequencies passing through the HPM plasma area were obtained, and the waveforms were normalized. At 32.4 GHz, the transmission coefficient of continuous electromagnetic waves passing through the plasma area with plasma is about twice as high as that through the area without plasma. A simulation model was established, and the transmission coefficient distribution curve in the range of 31.5−32.5 GHz was obtained. The electromagnetic wave passing through the plasma showed a transmission enhancement effect, and at some frequency points, there was a transmission enhancement of about 1.9 times. The research results provides important technical support for the application of plasma in stealth, emergency communications, and black barrier communications.

Electrical Discharge Machining (EDM) is a well-known machining technique since more than fifty years. Its principle is to use the eroding effect on the electrodes of successive electric spark discharges created in a dielectric liquid. EDM is nowadays widely-used in a large number of industrial areas. Nevertheless, few studies have been done on the discharge itself and on the plasma created during this process. Further improvements of EDM, especially for micro-machining, require a better control and understanding of the discharge and of its interaction with the electrodes. In this work, the different phases of the EDM process and the properties of the EDM plasma have been systematically investigated with electrical measurements, with imaging and with time- and spatially-resolved optical emission spectroscopy. The pre-breakdown phase in water is characterized by the generation of numerous small hydrogen bubbles, created by electrolysis. Since streamers propagate more easily in a gaseous medium, these bubbles can facilitate the breakdown process. In oil, no bubbles are observed. Therefore, the breakdown mechanism in oil could be rather enhanced by particles present in the electrode gap. Fast pulses of current and light are simultaneously measured during the pre-breakdown. These pulses are characteristic of the propagation of streamers in the dielectric liquid. The pre-breakdown duration is not constant for given discharge parameters, but distributed following a Weibull distribution. This shows that the breakdown is of stochastic nature. After the breakdown, the plasma develops very rapidly ( 2·1018 cm-3 during the first microsecond). Then it decreases with time, remaining nevertheless above 1016 cm-3 after 50 μs. During the whole discharge, the density is slightly higher in the plasma center. The EDM plasma has such a high density because it is formed from a liquid, and because it is constantly submitted to the pressure imposed by the surrounding liquid. This extreme density produces spectra with strongly-broadened spectral lines, especially the Hα line, and with an important continuum. During the first microsecond when the density is at its maximum, spectral lines are so broadened that they are all merged into a continuum. The low temperature and the high density of the EDM plasma make it weakly non-ideal. Its typical coupling parameter Γ is indeed around 0.3, reaching 0.45 during the first microsecond. In this plasma, the Coulomb interactions between the charged particles are thus of the same order as the mean thermal energy of the particles, which produces coupling phenomena. Spectroscopic results confirm the non-ideality of the EDM plasma. The strong broadening and shift of the Hα line and its asymmetric shape and complex structure, the absence of the Hβ line, and the merging of spectral lines are typical of nonideal plasmas. The EDM plasma has thus extreme physical properties, and the physics involved is astonishingly complex.

Nuclear fusion, the merging of light nuclei into a heavier one, is an attractive future energy source. It is safe, produces no carbon-dioxide and its resources are practically unlimited. Currently, the most promising concept of nuclear fusion as a commercial energy source is the tokamak. In a tokamak, the hot plasma is confined by a torus shaped magnetic field. However, the plasma gradually diffuses outwards to the so-called scrapeoff layer and is guided to the divertor, the exhaust of a fusion device. In the divertor of ITER, a tokamak experiment under construction that has to demonstrate that fusion is a feasible energy source, an enormous heat flux density of around 10 MW m-2 and particle flux density of around 1024 m-2s-1 are expected. Pilot-PSI and Magnum-PSI, two linear plasma devices at DIFFER, are unique in producing the plasma conditions as expected in the ITER divertor in a well controlled and diagnosed set-up. Therefore, Pilot-PSI and Magnum-PSI are crucial for a successful divertor design for next generation tokamaks. Via computer simulations results of Pilot-PSI and Magnum-PSI can be translated to ITER. The wide ranges of time and length scales of the processes in the divertor make simulations very challenging. For simulation of neutral particles under ITER divertor conditions, a non-linear, kinetic Monte Carlo code is required. Hereto, Eunomia has been developed and coupled to the multi-fluid plasma code B2.5. Eunomia is a welldocumented, modular code with a modern fortran programming style, using objects and dynamic memory allocation. The challenging part of B2.5 simulations of Pilot-PSI and Magnum-PSI is to describe the low temperature, high density plasma beam in suitable boundary conditions. For Monte Carlo simulations of neutral species in a linear device the statistically most challenging region is the plasma region, in particular in front of the target. The aim for B2.5-Eunomia is to simulate both the geometries of linear devices and the scrape-off layer and divertor region of a tokamak and to improve understanding of the important physics in the ITER divertor conditions. Since for a new code validation is essential, Eunomia has been subjected to several test problems, such as Couette flow, to ensure correctness of neutral flow calculations. In addition, performance of several features of Eunomia has been tested, such as the parallel speedup and the algorithms reducing statistical noise. The importance of various collision processes has been studied. As expected, for Pilot-PSI conditions the neutral-neutral collisions and charge exchange collisions with a proton are of great importance. Although typically neglected, because of the small scattering angle, the elastic collisions between a proton and atomic and molecular hydrogen should be included at the relatively high pressure of several Pascals, created by the recycling plasma. The density distributions of excited hydrogen atoms and line-of-sight integrated Balmer emission profiles were calculated with a collisional-radiative model, using Eunomia results as input. Simulation of the vibrational states of the hydrogen molecule as separate species in Eunomia is crucial. The distribution of the molecules over the vibrational states strongly deviates from local thermal equilibrium, due to transport and dissociative processes. This has an impact on the shapes and intensities of the emission profiles. Comparison to spectroscopic measurements in Pilot-PSI showed reasonably good agreement in both the widths and amplitudes of the line integrated emission profiles of Balmer-a. However, the results are sensitive to uncertainties in the association probability of atoms at the vessel wall and the distribution of molecules, produced by this association process, over the vibrational states. B2.5-Eunomia has successfully been coupled and applied to the cylindrically symmetric geometry of Pilot-PSI. The vibrationally excited molecules efficiently recombine the plasma at the edge of the plasma beam, whereas atoms efficiently cool the plasma. Comparison of B2.5-Eunomia simulations to Thomson scattering measurements near the target of Pilot-PSI showed good agreement. B2.5-Eunomia could not reproduce the floating potential and the saturation current to the target quantitatively, however, the amount of biasing required to reach saturation of the total current to the target is reproduced. When the target in Pilot-PSI is floating, so when the total net current is zero, locally strong plasma currents run into and out of the target. B2.5-Eunomia results show current paths from the anode to the target, returning via the center of the plasma to the source. Furthermore, B2.5-Eunomia simulations show that saturation of the total current, as measured experimentally in Pilot-PSI for a biased target, is not a good indicator for obtaining the ion saturation current density over the whole target surface. Locally, at the center of the target, the ion saturation current is only reached when biasing the target 20 V more negative. Only when locally the ion saturation current density has been reached, the sheath potential will increase linearly with the bias potential. Further development of Eunomia, to improve the B2.5-Eunomia code package in the future, and additional benchmarking of B2.5-Eunomia have been discussed. The incorporation of the collisional-radiative model has been initiated. There remain no technical limitations to simulate other linear devices, as well as tokamak divertors, with B2.5-Eunomia.

This thesis describes some of three years'work carried at the Centre Suisse d'Electronique et de Microtechnique (Neuchâtel, Switzerland) under the supervision of Dr. Martha Liley and in collaboration with Prof. Horst Vogel of the Ecole Polytechnique Federale of Lausanne (Switzerland). The goal of this work is to contribute to the development of innovative technologies in the treatment of surfaces, for the lateral organization of various materials on the micrometer and nanometer scale. The aim is therefore to offer a valid alternative to common lithographic techniques that often require expensive capital equipment and infrastructures. In spite of the high-quality and precision of their products, these techniques often have a limit of 70 nm on the resolution of the minimum feature size. In this work, techniques based on the ability of some systems to self-organize were used. In particular, the tendency of immiscible polymer mixtures and of block copolymers to form separate phases was exploited. Films made of different polymer phases formed templates for the organization of various materials, with length scale that varied from some 10 µm to some 10 nm. The materials that were most investigated were particles of the diameter of some nanometer, made of semiconductors (CdSe and ZnS) and of metals (Au, CoPt3 and Co). These nanoparticles have different properties from the corresponding bulk material. This fact is due to two main phenomena: in a nanoparticle the electronic energy levels of electrons are discrete because of their spatial confinement. Also, surface effects arise due to the high surface to volume atom ratio compared to the bulk material. As an example, semiconductor particles of the diameter of some nanometers are fluorescent. Semiconductor nanoparticle fluorescence is usually characterized by long fluorescence lifetimes. This fact promoted the investigation, in the framework of this thesis, of the fluorescence properties of Mn-doped ZnS nanoparticles. These particles turned out to have exceptionally long fluorescence lifetimes compared to the fluorophores commonly used as fluorescent markers in biological techniques. This singular property allowed the construction of a simple and cost effective instrument for time-resolved detection of the nanoparticle fluorescence. This technique allows a remarkable increase of the signal-to-noise ratio compared to conventional detection methods. Two approaches were explored to laterally organize nanoparticles on polymer surfaces. In the first method, the nanoparticles were added into a mixture of immiscible polymers and a film was formed from the solution by spin-coating, typically on silicon or glass slides. Numerical simulations by other authors indicate that if the particles have a higher affinity for one of the two polymers, they will be distributed in the corresponding phase. This behaviour was confirmed by our experiments. The lateral dimensions of the patterns in which the nanoparticles organized could be changed with continuity from some 10 µm to se sub-micrometer range. Their shape was modelled from a stochastic to an ordered type. The second approach explored for the organization of the nanoparticles consisted of the pre-formation of the polymer films and their subsequent decoration with the nanoparticles. Due of the different interactions of the two polymers with the particle-solvent system, different absorption behaviours of the nanoparticles were found on the two polymer phases. This technique allowed nanoparticle organization on homopolymer demixed films in patterns having typical sizes in the micron and in the submicron range. Alternatively, the nanoparticles were organized on block copolymer films in regular patterns having typical periodicities of the order of 100 nm. Nanoparticles organized on thin block copolymer films could be transferred on the hard substrate via removal of the polymer molecules by oxygen plasma etching. This process did not affect the nanoparticle organization. Under particular conditions, an aggregation of 10 nm gold nanoparticles was induced using oxygen plasma. This technique allowed the formation of gold nanowires and nanostructures both on polymer layers and on the hard substrate. Their width varied from about 25 nm to the micrometer, while their length extended for various micrometers. They presented a fingerprint like structure or, alternatively, quasi-parallel nanowires extended for several µm2, the typical periodicities being about 100 nm. The conductivity of these nanowires and nanostructures was demonstrated using SEM.

Band Structure, Alan T. Collins Diamond Morphology, Robert E. Clausing Mechanical Properties of Diamond, Diamond Films, Diamond-Like Carbon, and Like-Diamond Materials, Peter J. Gielisse Surface Properties of Diamond, Mark P. D'Evelyn Thermal Properties Heat Capacity, Conductivity, and the Thermal Coefficient of Expansion, V. I. Nepsha Thermal Measurement Techniques, John E. Graebner Optical Properties, Alexander M. Zaitsev Electrical and Electronic Properties, Alexander G. Gontar Characterization Characterization Methods, Karen McNamara Rutledge and Karen K. Gleason Mined Diamond Natural Diamond, Henry O. A. Meyer and Michael Seal Theory Theory of Diamond Chemical Vapor Deposition, David G. Goodwin and James E. Butler Modeling and Diagnostics of Plasma Reactors Introduction, A. Gicquel Basic Processes in Plasmas Under Conditions Typical for Diamond Deposition, A. Gicquel Basic Processes: Plasma/Surface Interactions, A. Gicquel The Boltzmann Equation, Matt Gordon Flow Modeling for a Plasma Assisted Diamond Deposition Reactor, K. Hassouni, C. D. Scott, and S. Farhat Electromagnetic Field Modeling of Diamond CVD Reactors, Timothy A. Grotjohn Modeling of the Diffusional Transport of an H2 Plasma Obtained Under Diamond Deposition Discharge Conditions, K. Hassouni, C. D. Scott, and S. Farhat Spatially Resolved Spectroscopic Analysis of the Plasma, A. Gicquel, M. Chenevier, and M. Lefebvre Methods of Chemical Vapor Deposition Growth Hot-Filament CVD Methods, Alberto Argoitia, Christopher S. Kovach, and John C. Angus Microwave Plasma Chemical Vapor Deposition of Diamonds, Peter K. Bachmann Diamond CVD Using Radio-Frequency Plasmas, Steven L. Girshick Synthesis of Diamond, Mark A. Cappelli Low Temperature CVD, Akimitsu Hatta and Akio Hiraki Structural Modification of Diamond Nucleation and Epitaxy, S. P. Bozeman, B. R. Stoner, and J. T. Glass Ion Implantation of Diamond and Diamond Films, R. Kalish and S. Prawer Processing, Victor G. Ralchenko and Sergei M. Pimenov Applications of Industrial Diamond Abrasive Applications of Diamond, K. Subramanian and V. R. Shanbhag Active Devices, David L. Dreifus and Bradley A. Fox Applications of Diamond in Computers, Richard C. Eden Diamond Vacuum Electronics, George R. Brandes Special Applications, Naoji Fujimori Cutting and Wear Applications, R. A. Hay and J. M. Galimberti Economics Economics and Commercialization, Adam T. Singer and John V. Busch

In plasma wakefield acceleration, the witness beam's emittance needs to be preserved when it propagates through a plasma stage. The plasma includes density ramps at both the entrance and the exit. Using the Wentzel-Kramers-Brillouin solution of a single particle's motion, analytical expressions for the evolution of the beam emittance and the Twiss parameters in an arbitrary adiabatic plasma profile are provided neglecting the acceleration of the beam inside the plasma. It is shown that the beam emittance can be preserved under the matching condition even when the beam has an initial energy spread. It is also shown that the emittance growth for an unmatched beam is minimized when it is focused to the same vacuum plane for a matched beam. The emittance evolution from 3D QuickPIC simulation results agree well with the theoretical results. In the some of the proposed experiments on nearly completed FACET II facility, the matching condition may not be perfectly satisfied and the wake may not be perfectly symmetric. It is shown that for a given set of beam parameters that are consistent with FACET II capabilities, even when the assumptions of the theory are not satisfied, the emittance growth can still be minimized by choosing the optimal focal plane. Last, another issue that may cause emittance growth in realistic plasmas is also examined. When using a lithium plasma source in FACET II experiments a helium buffer gas is used. The plasma is formed from field ionization which can lead to a nonlinear focusing force when there are nonuniform helium ions due to its high ionization potential. For an initial beam emittance of $20\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$, the helium ionization is found to be small and the witness beam's emittance can be preserved.

Surface plasma H− ion sources for accelerators; design of surface plasma H− ion sources for accelerators; formation of H− ion beams in surface plasma sources for accelerators; surface plasma sources with Penning discharge for microlithography; semiplanotrons; geometric focusing; semiplanotrons for accelerators; semiplanotrons with spherical focusing for continuous operation; compact surface plasma sources for heavy negative ion production; development of surface plasma sources world-wide; large volume surface plasma sources with self-extraction; large volume surface plasma sources for accelerators; large volume surface plasma sources for heavy ion production; surface plasma sources for intense neutral beam production for controlled fusion; RF surface plasma sources for ITER; neutral beam injector with RF SPS development at Novosibirsk; RF surface plasma sources for spallation neutron sources; carbon films in RF surface plasma sources with cesiation; poisoning and recovery of converter surfaces; RF surface plasma sources with external antenna; RF surface plasma sources with solenoidal magnetic field; testing RF surface plasma sources with saddle antenna and magnetic field; estimation of H− ion beam generation efficiency; RF surface plasma source operation in continuous mode; RF surface plasma sources at CERN; surface plasma sources at J-PARC, Japan; surface plasma sources for low-energy neutrals.

The cosmic stories : beginning, evolution, and present days of the universe

The study of the bio-recognition phenomena behind a biological process is nowadays considered a useful tool to deeply understand physiological mechanisms allowing the discovery of novel biological target and the development of new lead candidates. Moreover, understanding this kind of phenomena can be helpful in characterizing absorption, distribution, metabolism, elimination and toxicity properties of a new drug (ADMET parameters). Recent estimations show that about half of all drugs in development fail to make it to the market because of ADMET deficiencies; thus a rapid determination of ADMET parameters in early stages of drug discovery would save money and time, allowing to choose the better compound and to eliminate any losers. The monitoring of drug binding to plasma proteins is becoming essential in the field of drug discovery to characterize the drug distribution in human body. Human serum albumin (HSA) is the most abundant protein in plasma playing a fundamental role in the transport of drugs, metabolites and endogenous factors; so the study of the binding mechanism to HSA has become crucial to the early characterization of the pharmacokinetic profile of new potential leads. Furthermore, most of the distribution experiments carried out in vivo are performed on animals. Hence it is interesting to determine the binding of new compounds to albumins from different species to evaluate the reliability of extrapolating the distribution data obtained in animals to humans. It is clear how the characterization of interactions between proteins and drugs determines a growing need of methodologies to study any specific molecular event. A wide variety of biochemical techniques have been applied to this purpose. High-performance liquid affinity chromatography, circular dichroism and optical biosensor represent three techniques that can be able to elucidate the interaction of a new drug with its target and with others proteins that could interfere with ADMET parameters.

The plasma needle is a novel design of a radio-frequency discharge in helium/air mixtures at atmospheric pressure. The discharge contains neutral, excited and ionized particles, and emits ultraviolet (UV) light. It operates at low electric power and close to ambient temperature; it combines chemical activity with non-destructive character. Therefore it is expected that the plasma needle will be used in future in (micro) surgery, e.g. in wound healing and in controlled tissue removal through cell detachment or apoptosis, avoiding necrosis and in°ammation reactions. Focus of this study is both on optimization of needle design and on assessment of effects of plasma activity on living cells. This work is a pio- neering study of the effects of non-thermal plasma on biological samples. The design of the plasma needle was adjusted in such a way that instead of operating in a closed reactor, now the treatments could be performed in open air. Thus, larger samples could be treated and handling times were reduced. Then, a characterization of the needle was performed using electrical as well as optical diagnostics (Chapter 3). It was found that the needle operated at voltages of 140 Vrms and higher. A model was made to determine the resistance of the plasma and from this an estimation of the electron density could be made. The latter can be regarded as an indirect measure for plasma reactivity. Results from optical emission spectroscopy showed that reactive oxygen species, such as O¢ and OH¢, were produced in the plasma. Furthermore, UV emission was detected. Both the radicals and the UV are known to interact with cells and tissues. For applications, the amount of radicals that reach the sample or that are generated in the sample is important. For this reason, radicals were detected in liquid that was treated with plasma using a chemical technique (Chapter 4). It involved a fluorescent probe: the probe was dissolved in liquid and after reaction with specific radicals it became fluorescent. Radical density in the liquid depended on plasma conditions, treatment time, and amount of liquid used, but it was always in the micromolar range. These concentrations were found to be comparable with physiological concentrations that were stated in literature. Basic cell reactions after plasma treatment were determined by experiments on cultured Chinese hamster ovarian (CHO K1) cells (Chapter 5). One of these reactions was cell detachment: cells detached from their environment but remained alive after treatment. Other reactions included a small percentage of apoptosis and, when high plasma powers were used, necrosis. A comparison with the effect of UV light from UV lamps was made (Chapter 7). The main effect of UV treatment was necrosis, but only above a certain threshold value. For mammalian cells, this threshold was reasonably high. Thus, the ef- fects of plasma treatment could not be explained by the action of the UV light from the plasma. Quantitative experiments were performed on cultured bovine aortic endothelial cells (BAEC) and rat smooth muscle cells (A7r5) (Chapter 6). These two cell types constitute walls of blood vessels. It was shown that treatment times of less than one minute cause detachment of the cells if the layer thickness of the liquid that covered the cells was low (around 0.1 mm). This suggests that at short treatment times, the penetration depth of the plasma into the sample is limited. The percentage of necrotic cells was low after treatment. No difference was found in the detachment behavior of both cell types. Finally, pilot experiments were performed on carotid arteries of C57BL/6 and Swiss mice ex vivo (Chapter 8). They were studied using a two-photon laser scanning microscope (TPLSM). Cell nuclei, elastin bands, and collagen could be visualized. Preliminary results indicate that induced changes are not strongly dependent on applied energy if no heating e®ects are induced. Apparent effects were limited to the adventitia, probably due to a low penetration depth of active plasma species. In conclusion, we can state that the plasma needle is a non-destructive tool that can be ap- plied with precision. It has a superficial action and causes little damage to the tissue. The level of damage can be controlled to achieve a desired therapeutic effect. Both on cultured cells and on ex vivo arteries interesting effects were found that confirm the hypothesis that the plasma needle will have a future in surgery.

A double-beam laser shockwave cleaning (DLSC) process is applied to clean nanoparticles on silicon wafer to eliminate the formation of uncleaned blind zone right under the plasma kernel. The size of the uncleaned blind zone in DLSC is reduced by 95% compared to the single-beam laser shockwave cleaning process. The study of the time-resolved plasma evolution suggests that the formation of multiple plasma kernels makes the nanoparticles in the blind zone exposed to the cleaning-effective zone of the nearby passing plasma. The theoretical calculation of the shockwave force distribution shows that the horizontal drag force from a nearby passing plasma in the DLSC process facilitates the nanoparticle removal in the blind zone.

The brief analytical review of literary data concerning the processes which are a physical basis of vacuum-arc coating deposition technology is presented. The phenomena responsible for formation of films by condensation of substance from plasma of arc discharge in vacuum or in a gaseous ambience of low pressure are described.. Interaction of metal plasma with a gas target, a substrate and other surfaces of working chamber, the processes of nucleation and condensate growth, influence of energetic parameters of a deposition process (kinetic and potential energy of metal ions, activation degree and sort of the gas ) on properties of condensates and near-surface layers of the substrate are described.

This paper briefly discusses the ALICE machine background concerns and the background monitoring system. ALICE RUNNING STRATEGY ALICE (A Large Ion Collider Experiment) [1] is a general purpose detector designed to address the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC. It will allow a comprehensive study of particles produced in Pb–Pb collisions, up to the highest multiplicities anticipated at the LHC. The physics program also includes collisions with lighter ions as well as dedicated proton-nucleus runs. Regular data taking during pp runs will provide reference data for the heavy ion program and address a number of specific pp topics. The pp runs will be in parallel with the other experiments but at a reduced luminosity in IP2. In order to keep the pile-up in the Time Projection Chamber (TPC) and Silicon Drift Detectors (SDD) at an acceptable level, the luminosity during pp runs has to be limited to 3 × 10 cm−2s−1, corresponding to an interaction rate of 200 kHz. At this rate we record on average 20 overlapping events. The optimal detector operation and physics performance with the TPC, i.e. no pile-up, is at 10 cm−2s−1. IMPACT OF MACHINE BACKGROUND General considerations Due to the running at reduced luminosity ALICE has the most unfavorable interaction rate over background rate ratio (at least a factor of 10 less than the high luminosity experiments). Machine background effects are alleviated by the fact that ALICE has been designed to perform tracking for up to 1000 times the pp multiplicity and the trigger reduction factors are relatively small (typically 10). So far the expected effects of the background are mainly of cumulative nature, such as radiation damage (integral dose and neutron fluences). Also the increase of the data volume has obvious negative consequences in terms of data storage and offline computing requirements. To simulate these effects ALICE has so far considered beam gas events in the experimental region IP ±20 m and beam-halo from beam-gas scattering outside the experimental regions. Input for the quartiary background caused by tertiary collimators (TCT) close to the experimental region is not yet available for IP2. In case the collimators are at the nominal settings this contribution could well be the dominant source of machine background. However, since at full beam intensity ALICE will run at high β∗ (10 m), the inner triplet will not limit the aperture of the machine. ALICE requires that for stable beams the TCTs will be put at a position at which they protect the inner triplets against accidental losses but do not produce extra losses for stable beams. Dose in central detectors The radiation environment in the experimental cavern has been simulated for the planned running scenario of the ALICE experiment (Table 1) [2]. Running with p-p, low and high mass ion–ion collisions over a ten year period has been assumed. Beam-beam and beam-gas interactions have been considered as potential radiation sources. The highest doses, up to 2.8 kGy, are expected at the location of the inner tracking system (ITS) (Table 2). The contribution from beam halo [3] amounts to ≈ 20% of the total dose. The contribution from beam-gas collisions within the experimental region has been calculated assuming a very conservative residual gas pressure of 2× 10 molecules/m. Only under these conditions a sizeable contribution of about 10% of the total dose is expected. Charged particle rates on RPCs Among the ALICE detectors, the muon trigger system is one of the most sensitive to the machine induced background. As a matter of fact, the Resistive Plate Chambers (RPC) rate capability (50 − 100 Hz/cm) might be saturated by a too high background level, which might also have an impact on the detector lifetime. The fluxes of secondary charged particles through muon trigger system originating from machine induced background has been simulated [4]. The trigger background consists mainly of electrons from hadronic showers resulting in a hot spot of ≈ 60 Hz/cm located at x = 1.5 m and |y| < 1.5 m. BACKGROUND MONITORING For machine background monitoring during injection ALICE will use the beam condition monitor (BCM) and the V0 forward scintillator detectors at safe photomultiplier settings. Due to the different acceptance of the two detectors an OR of the two signals will be used. With circulating stable beams a combination of signals from BCM, V0, SPD, TPC and forward muon spectrometer will be used to obtain a normalized machine background signal. Beam condition monitors The purpose of the Beam Condition Monitor (BCM) is to detect adverse beam conditions within the ALICE experLHC Workshop on Experimental Conditions and Beam-Induced Detector Backgrounds

In fusion reactors, the walls are exposed to very high particle and energy fluxes. To study the problem of wall erosion and hydrogen retention in these conditions, the Magnum-PSI experiment at the FOM Institute of Plasma Physics is set up. The plasma source for Magnum-PSI is a cascaded arc, where a strong magnetic field is applied to obtain the desired conditions. The focus of this thesis is the development of a numerical model for studying the plasma creation in the source and the consecutive magnetized expansion. To describe the behavior of the different species in the range of conditions in the plasma – from gas to fully ionized, from non-magnetized to strongly magnetized – a multicomponent diffusion description is needed. Numerical techniques are developed to successfully apply multicomponent diffusion to magnetized expanding plasmas. Multi-component diffusion results in a system of coupled continuity equations for all species. In addition this coupled system is subject to mass and charge conservation constraints. To deal with the coupling between the species a new finite volume discretization method is introduced to discretize the system of continuity equations. For numerical stability, mass and charge constraints are not explicitly applied. Instead, all species mass fractions are treated as independent unknowns and mass and charge constraints are a result of the continuity equations, the boundary conditions, the diffusion algorithm and the new discretization scheme. With this method, mass and charge constraints can be satisfied exactly, although they are not explicitly applied. To verify the suitability of the method, simulations of both magnetized and nonmagnetized expansions have been performed. The simulations are able to reproduce important characteristics of magnetic confinement. Results show that in the magnetized case, the plasma production cannot be modeled by considering the source alone, since plasma production extends into the expansion region.