Funciones  objetivo para los casos RP (reasignación

Abstract. In the next generation of fusion reactors, such as DEMO, neutral beam injectors (NBIs) of high energy (0.8-1 MeV) deuterium atoms with high wall-plug efficiency (>50%) will be required to reach burning plasma conditions and to provide a significant amount of current drive. The present NBI system for DEMO assumes that 50 MW is delivered to the plasma by 3 NBIs. In the Siphore NBI concept, negative deuterium ions are extracted from a long, thin ion source 3 m high and 15 cm wide, accelerated and subsequently photo-neutralized. This requires the development of a new generation of negative ion sources. At the Swiss Plasma Center, a novel radio frequency helicon plasma source, based on a resonant network antenna source delivering up to 10 kW at 13.56 MHz, has been developed and is presently under study on the Resonant Antenna Ion Device (RAID). RAID is a linear device (1.9 m total length, 0.4 m diameter) and is equipped with an extensive set of diagnostics for full plasma characterization. In this work, the principles of operation of resonant antennas as helicon sources are introduced. We present absolute spectroscopy, Langmuir probe, and interferometry measurements on helicon plasmas. We characterize the performance of the source in terms of hydrogen/deuterium dissociation and negative ion production as a function of the input power. Furthermore, first results with the helicon birdcage antenna installed on the Cybele negative ion source at CEA-IRFM are presented, as a first step towards the validation of the Siphore concept.

distribution of emitted ions a large fraction of plasma, it goes directly into the RFQ channel. Typically, parameters of RFQ are 100 MHz of operating frequency and input energy of 17 keV/amu. This means that our measures can be used to increasing the charge state inside the plasma and coupling with extraction voltage. Future investigation will be done to characterize the best operation frequency and the best output current beam with coated target. Using low intensity laser, it would be possible to use the coupling of an ion source that uses the coated targets with an Electron Cyclotron Resonance (ECR) that allows to enhance charge state producing ions with charge state up to 30+ and with extraction voltage of about 20-30 kV as performed at INFN-LNS experiments in Catania (Italy). [12]

to expel a significant fraction of the electrons from the high intensity laser region, creating ion channels (see figure 8). With the longer plasma propagation distances associated with longer plasma scalelengths, the laser pulse can be subject to transverse instabilities, resulting in beam filamentation. The filamentation reduces the local laser irradiance and reduces the temperature of accelerated electrons 9 . The drop at electron temperature reduces the

The experiments described in Sect. 2 dealt with phenomena on short time scales, where the ion component could be con- sidered immobile. Similar vortical structures were found nu- merically (Sakanaka, 1972; P´ecseli et al., 1984) and experi- mentally (P´ecseli et al., 1981, 1984) also in ion phase space, where now both electron and ion components participate in the plasma dynamics. In the experiments on ion phase space vortices, the evolution of the ion distribution function, and thereby, the phase space dynamics, could be measured di- rectly by an ion energy analyzer (see also a summary by P´ecseli, 1984). Other experiments later confirmed parts of these observations (e.g. the works by Chan et al., 1984), but investigated only space-time variations of plasma den- sity and potential. Recent and more modern techniques have shown promise in detailed investigations of the ion phase space dynamics associated with the formation of ion holes (Skiff et al., 2001). Recent observations by Nakamura et al. (1999) also point out the formation and propagation of “ion holes”, i.e. ion phase space vortices. These experiments were carried out under conditions similar to those in the studies by P´ecseli et al. (1981) or P´ecseli et al. (1984), but with larger electron to ion temperature ratios. All of these investiga- tions were dealing with externally excited coherent phenom- ena. Evidence for the formation, propagation and subsequent decay of phase space vortices was also obtained in experi- ments carried out in an unmagnetized double-plasma device (Johnsen et al., 1985, 1987), where an ion beam was injected into a background plasma. A conditional sampling method was used for analyzing the space-time variation of the spon- taneously generated fluctuations in plasma density. These studies differ from those previously mentioned by making a statistical analysis of the spontaneously generated fluctua- tions.

In this thesis, we focus on neutron rate measurements during fishbones on MAST. However, other diagnostics on this device have been used in previous work to reinforce the assertion that a loss of confinement is occurring during fishbone events, and that reported drops in neutron rate are an indication of a loss in plasma confinement. For instance, it has been reported that the D-alpha signals (a charge-exchange recombination spectroscopy technique that exploits the large Doppler- shift of Balmer-alpha light from energetic hydrogen atoms to determine fast-ion density [53]), from the edge region spike during the appearance of fishbones [43]. It has been theorised that these transient spikes are generated from the signal bursts of edge neutrals experiencing charge exchange with core-ejected fast ions [43].

evolved (cf., Fig. 4 of Ref. [6]). These results strongly suggest that the source of ICE in those plasmas was the fusion born alpha particles resulting from D - T fusion reactions. Furthermore, in all these large tokamak plasmas, the ICE power spectrum displayed peaks at sequential cyclotron harmonics of alpha particles at the outer mid- plane edge. These characteristics are largely replicated by recent second generation ICE measurements, to which the work reported here is also relevant. ICE is used as a diagnostic for energetic ions lost from D III- D tokamak plasmas due to MHD activity [18]. ICE is observed from ASDEX-Upgrade [19,20] and JT- 60U [21,22] tokamak plasmas, with spectral peaks at edge cyclotron harmonics of ion species that include the energetic products of fusion reactions in pure deuterium, namely, protons, tritons, and helium-3 ions. ICE from sub-Alfvénic beam ions, injected at tens of keV to heat the plasma, was observed from TFTR tokamak plasmas, and is also interpreted in terms of the MCI [23]. ICE that is probably of this kind is also used as a diagnostic of lost fast ions in large stellarator-heliotron plasmas in large helical device (LHD) [24]. Very recently, ICE with spectral peak separation equal to the edge proton cyclotron frequency has been reported from deuterium plasmas in the KSTAR tokamak [25].

Helium ion microscopy (HIM) o ff ers potential as a high spatial resolution technique for imaging insulating samples that are susceptible to charging artifacts. In this study helium and neon ion microscopy are used to image cracking in microindented samples of the non-conductive ceramic silicon nitride. The crack morphology of radial cracks emanating from the microindentations has been characterized for two di ff erent compositions of silicon nitride, with and without conductive coatings. Gold coating enhances crack edge contrast, but masks grain contrast for both He and Ne ion-induced secondary electron (ISE) imaging. Carbon coating enables the crystalline and glassy phases to be distinguished, more clearly with Ne-ISE, and the cracking pathway is found to be primarily intergranular. Zones of < 100 nm diameter depleted ion-induced secondary electron emission along the crack paths are identified, consistent with charging ‘hotspots’.

Abstract. The parametric coupling between large amplitude magnetic field-aligned circularly polarized electromagnetic ion-cyclotron (EMIC) waves and ponderomotively driven ion-acoustic perturbations in magnetized space plasmas is considered. A cubic nonlinear Schr¨odinger equation for the modulated EMIC wave envelope is derived, and then solved analytically. The modulated EMIC waves are found to be stable (unstable) against ion-acoustic density perturbations, in the subsonic (supersonic, respectively) case, and they may propagate as “supersonic bright” (“subsonic dark”, i.e. “black” or “grey”) type envelope solitons, i.e. electric field pulses (holes, voids), associated with (co-propagating) den- sity humps. Explicit bright and dark (black/grey) envelope excitation profiles are presented, and the relevance of our in- vestigation to space plasmas is discussed.

Helium ion microscopy (HIM) o ff ers potential as a high spatial resolution technique for imaging insulating samples that are susceptible to charging artifacts. In this study helium and neon ion microscopy are used to image cracking in microindented samples of the non-conductive ceramic silicon nitride. The crack morphology of radial cracks emanating from the microindentations has been characterized for two di ff erent compositions of silicon nitride, with and without conductive coatings. Gold coating enhances crack edge contrast, but masks grain contrast for both He and Ne ion-induced secondary electron (ISE) imaging. Carbon coating enables the crystalline and glassy phases to be distinguished, more clearly with Ne-ISE, and the cracking pathway is found to be primarily intergranular. Zones of < 100 nm diameter depleted ion-induced secondary electron emission along the crack paths are identi fi ed, consistent with charging ‘hotspots’.

separation and collection of individual, separated isotopes. The plasma ion source is preferably an inductively coupled plasma ion source, and the mass spectrometer is preferably a quadrupole mass spectrometer. The stoichiometry of the deposited or implanted ions can be adjusted by controlling the mass spectrometer to produce an ion beam having a desired composition. Mixtures of different elements can be easily deposited or implanted in any desired stoichiometry by introducing a multielement sample into the plasma ion source and controlling the time the mass spectrometer transmits each element to be deposited or implanted.

small, and the diffusion lines are close to circles in velocity space. Due to the pitch angle diffusion created by waves the initial field-aligned distribution of the pre- cipitating electrons opens like a fan (the origin of the term fan instability for the instability under consideration). This fan instability does not require an electron beam or positive slope in the electron distribution function, but only an asymmetric high-energy tail on one side of the distribution function.

We have consider particle and energy balance for two basic types of discharges: electropositive discharge and electronegative discharge. In electropositive discharges, there are only two species that are normally considered, electrons and positive ion. But in electronegative discharges, there are three species that are normally considered, electrons, one positive ion and one negative ion species. The simulated discharge gas is nitrogen and it is described using 5 chemical species and 16 chemical reactions. The species included in this model are electrons, N, N , N and N . The reactions that are described in this model define the production and loss processes of the different species in the discharge. In our study the following 16 reactions of nitrogen are taken into account.

Before proceeding further, we introduce a convention useful in the present theoretical analysis. Beam probabil- ity P is evaluated by volumetric integration of intensity over a beam segment of some arbitrary selected length. Correspondingly, this defines an inclusive energy E on that beam segment. We use the convention of considering beam segments purely as a convenience in order to pro- ceed with the theoretical analysis using the parameters of probability and energy rather than the associated flux densities of those parameters. Nevertheless, the results of the analysis are fully applicable to the experimentally relevant parameter of the integrated energy flux density, i.e. power, which is proportionate to that inclusive energy E.

The ion beam trajectories of the accelerator column are estimated for the LPIS-1, including an original struc- ture, with the change of slit aperture distance, plasma grid shape, grid gap distance, and voltage ratio between a plasma grid and a gradient grid using the IGUN code [15]. The IGUN numerical simulation has been exten- sively utilized for the design iteration. From the IGUN simulation, divergence information and emittance infor- mation are obtained as well as ion orbits. Ion optics of various geometries were studied theoretically and ex- perimentally by means of an analytic linear optics analy- sis and a numerical simulation using the IGUN program [16,17]. In general, there was a reasonable agreement observed between the theoretical predictions and the ex- perimental measurements. The deviation of the experi- mental divergence angles from the IGUN can be ex- plained by the fact that the multi-aperture system pro- duces other effects that make the beam optics worse. Furthermore, the difference in the optimum beam per- veance (perv  A/V 3/2  10 −6 , A: beam current [A], V:

about 100 times larger than the upstream ion temperature, corresponding to θ = 100. In their Fig. 4, they observed a significant fraction of reflected ions. The upstream, expanding ions had a velocity of 0.1c relative to the laboratory frame, and the shock-reflected beam had a velocity of 0.2c, corresponding to an ion kinetic energy of about 20 MeV relative to the laboratory frame. As a comparison with these studies, show in Figs. 3a–d solutions of Eqs. (12) and (13) in the (u i0 , φ max )-plane for θ = 100 and different values of α. We see in Figs. 3a–d that the system again has

Recently, extended MHD plasmas have been dis- cussed, especially in both theoretical and computational works of plasma physics. In order to test those experimen- tally, we have proposed a new experiment using two non- neutral plasmas, and almost completed constructing a ma- chine to perform it. At the first series of experiments, pure e − and Li + plasmas are not only produced independently but also confined simultaneously on the BX-U machine. No destructive instabilities occur in experiments. After optimizing experimental parameters to precisely control plasma densities, we could apply those two non-neutral plasmas to produce an extended MHD plasma state in lab- oratory experiments, for the first time.

The kinetic processes of magnetic reconnection based on the full kinetic model are drastically different from those based on the MHD and Hall-MHD models. In this paper we first explain how the quadrupole out-of- plane magnetic field, the parallel electric field are pro- duced. Then, we discuss the physical processes that cause the decoupling of the electron and ion dynamics, which lead to the generation of the charge separation and the in- plane electrostatic electric field. The key kinetic physics of driven magnetic reconnection of anti-parallel magnetic fields in collisionless plasmas presented in this paper are obtained by examining the 2-1/2 dimensional particle-in- cell simulation results [1, 2]. We also discuss the similar- ities and di ff erences of the physical mechanisms between the driven reconnection results presented in this paper and the previously published results of undriven (or sponta- neous) reconnection simulations.

below the phase-averaged sheath potential (≈ -350 V), indicating a regime in which this is determined primarily through the high ion-neutral collision frequency. Region II (60 - 180 eV) contains the largest fraction of the IEDF for applied voltage frequencies between 54.24 - 81.36 MHz, this structure becoming visible above 40.68 MHz. This region consists of a single ‘mid-energy’ structure, the magnitude of which increases until approximately 67.80 MHz, and decreases thereafter. The modal energy in this region is inversely proportional to the driving frequency, levelling off at ≈ 80 eV for frequencies above 94.92 MHz.

In the initial study by [2], ion beam dynamics were studied with Boltzmann distributed electrons using the standard reductive pertubation technique [2]. A year later, Misra and Adhikary studied both linear and non linear propagation of large amplitude DIA waves using theoretical and numerical approaches [3]. It was found out that three stable waves, i.e., the “Fast” and “Slow” ion-beam modes and “Ion-acoustic” modes can exist. In all these studies the electrons are Boltzmann distributed. However, several other electron populations follow the Cairns

using a power meter (Ophir Nova). The IR wavelength λ was determined via the OPO signal and idler wavelength using a spectrometer (Ocean Optics HR2000+) and inde- pendently calibrated using a photo acoustic spectroscopy setup. Furthermore, the fast moving ion packet gives rise to a Doppler shift of the counter propagating IR pulse, which accounts for 2 – 5 cm − 1 over the range of the experiment and has been cor- rected for. The Doppler spread due to the axial energy uncertainty of the ion beam is in the range of a few MHz and is therefore much smaller than the bandwidth of the pulsed IR laser system. The laser beam had to undergo reflections from a total of six gold mirrors and cross a CaF vacuum window before counter propagating into the ion beam. The reflectivity for the mirrors (98 ± 0.5%) as well as the transmittance of the CaF window (94 ± 0.5%) can be considered constant over the measured wavelength range, so that the measured laser power multiplied by the photon wavelength is propor- tional to the photon flux in the ion interaction region. A relative photodetachment cross section is then given by