Fast Neutral Particles Research Articles

DC electric field generation and distribution in magnetized plasmas

Very large DC and AC electric fields cannot be sustained between conducting electrodes because of volume gas breakdown and/or surface field emission. However, very large potential fields are now routinely generated in plasma structures, such as laser generated wake in unmagnetized plasmas. In magnetized plasmas, large DC fields can also be sustained and controlled perpendicular to the magnetic field, but the metallic end plates limiting the plasma, terminating the magnetic field lines, and usually providing the voltage drop feed between the field lines impose severe restrictions on the maximum field. However, it is shown that very large radial DC voltage drops can be sustained by injecting waves of predetermined frequencies and wave vectors, traveling along the azimuthal direction of an axially magnetized plasma cylinder, or by injecting fast neutral particles beams along this azimuthal direction. The large conductivity along the magnetic field lines and the small conductivity between the field lines then distribute this voltage drop. The global power balance and control parameters of wave and beam generated large DC electric fields in magnetized plasmas are identified, described, and analyzed.

Installation of a solid state neutral particle analyzer array on mega ampere spherical tokamak upgrade.

A compact solid state neutral particle analyzer (SSNPA) diagnostic, previously installed at NSTX-U, has been moved to MAST-U and successfully operated in the first physics campaign (MU01). The SSNPA operates by detecting the flux of fast neutral particles produced by charge exchange (CX) reactions to diagnose the fast ion distribution. The diagnostic consists of three 16-channel sensors, which provide a radial view of the plasma and have a sightline intersection with the South-South neutral beam line. From this radial geometry, active CX signals from mostly trapped particles are observed. Each channel has a spatial resolution of 3-4cm, a temporal resolution of 200kHz, and an average pitch angle resolution of a few degrees. The three-sensor configuration allows for coarse energy resolution of the CX signals; each sensor sees similar sightlines but different filter thicknesses alter the energy cutoffs by known amounts. Experimental data show that all channels are collecting data as intended. The signal to noise ratio is typically around 15. Preliminary data analysis shows a correlation between the SSNPA signal and magnetohydrodynamic activity in the plasma as expected.

Numerical modelling for beam duct heat loads calculations and application to the new 1 MW neutral beam injector in the COMPASS tokamak

We introduce detailed numerical modelling of the fast neutral particles inside the duct of a new neutral beam injector (NBI) recently installed at the COMPASS tokamak (major radius , vessel midplane minor radius , toroidal field = 0.9–2.1 ). This new NBI system is able to deliver power to the plasma at nominal injection energy of . Collisions with the background neutrals inside the beam duct give birth to fast ions according to the density of the gas and tabulated cross-sections. The ion trajectories are then computed in the complete 3D magnetic field, showing the importance of the stray magnetic field and the magnitude of the field within the gap in between toroidal coils.During the experimental campaign dedicated to the new 1 MW NBI, the beam duct heating was measured by a row of thermocouples located on the top-half of the beam duct. The fast ions collisions with the duct wall cause a local temperature increase with a characteristic pattern. In COMPASS, the location of the fast ions power deposition measured experimentally is in qualitative agreement with modelling of ion losses when following them after the re-ionization process. We trace back the details of the orbits corresponding to deposition at the hot-spot inside the beam duct. Quantitative comparison between the experiment and the simulation shows that a larger than expected amount of neutral gas was inside the duct and this study will guide the design of the future NBI duct in COMPASS Upgrade.

Applications of the Technology of Fast Neutral Particle Beams in Micro- and Nanoelectronics

Applications of the Technology of Fast Neutral Particle Beams in Micro- and Nanoelectronics

Applications of the Technology of Fast Neutral Particle Beams in Micro- and Nanoelectronics

A brief review of the results of the application of fast neutral particle (FNP) beam sources in the field of the production technology of micro- and nanoelectronic devices published in the literature is presented. Processes such as surface cleaning; sputtering and etching of insulators, simiconductors, and metals; layer-by-layer etching; deposition of thin films directly from beams or by sputtering, and neutral-beam-enhanced deposition; oxidation, nitridation, and fluorination of a near-surface layer; production of the elements of micro- and nanoelectromechanical devices; nanostructuring; and modification of self-assembled organic molecular structures are considered. In addition, the results of investigating a decrease in the degree of degradation of the electrophysical properties of materials and electrical characteristics of device structures when passing from ion-beam technologies to FNP beams are discussed.

Cleaning of the dielectric surfaces using a controlled gas-discharge source of fast neutral particles

In the present work is proposed the design of a controlled gas-discharge source of fast neutral particles, allowing to clean surfaces of dielectric and semiconductor materials. Also are shown the results of the research of the source main working characteristics.

The prospects and peculiarities of plasma with hollow cathode using for satellite telecommunications noise stability increase

In this article the main advantages and the peculiarities of artifi cially created plasma environment using are shown with the purpose of compensation of the external plasma membrane for the increase of satellite telecommunications noise stability. The overall pattern of eff ect is set in the plasma hollow cathode for the creation of noise stability environment, which depends on the conditions of energy’s fast electrons creation during their oscillatory motion, positive ions, fast neutral particles, metastable atoms and photons.

Analysis of neutral hydrogenic emission spectra in a tokamak

Balmer-α radiation by the excitation of thermal and fast neutral hydrogenic particles has been investigated in a magnetically confined fusion device, or tokamak, from the Korea Superconducting Tokamak Advanced Research (KSTAR). From the diagnostic point of view, the emission from thermal neutrals is associated with passive spectroscopy and that from energetic neutrals that are usually injected from the outside of the tokamak to the active spectroscopy. The passive spectroscopic measurement for the thermal Balmer-α emission from deuterium and hydrogen estimates the relative concentration of hydrogen in a deuterium-fueled plasma and therefore, makes a useful tool to monitor the vacuum wall condition. The ratio of hydrogen to deuterium obtained from this measurement qualitatively correlates with the energy confinement of the plasma. The Doppler-shifted Balmer-α components from the fast neutrals features the spectrum of the motional Stark effect (MSE) which is an essential principle for the measurement of the magnetic pitch angle profile. Characterization of this active MSE spectra, especially with multiple neutral beam lines crossing along the observation line of sight, has been done for the guideline of the multi-ion-source heating beam operation and for the optimization of the narrow bandpass filters that are required for the polarimeter-based MSE diagnostic system under construction at KSTAR.

The methods of decrease operating pressure of fast neutrals source

The fast neutral particles sources are more and more widely used in technologies of surface processing and coatings deposition, especially in the case of dielectric surfaces processing. However for substantial expansion of the sources applications scope it is necessary to decrease the pressure in the vacuum chamber at which they can operate. This article describes the methods to reduce the operating pressure of the fast neutral particles source with combined ions acceleration and its neutralization regions. This combination provide a total absence of the high-energy ions in the particles beam. The main discussed methods are creation of pressure drop between internal and external volumes of the source and working gas preionization which is provided by combustion of auxiliary gas discharge.

Installation for etching and deposition of thin-film structures by a fast neutral particle beam

An installation for etching and depositing thin-film structures equipped with a Neitral-L original source, which forms a ribbon beam of rapid neutral particles obtained when using various working gases, is developed. A system for the source neutralization and separation ensures hundred-percent beam neutralization. In order to increase the treatment uniformity of the substrates, a system with a programmable controller of the reciprocal motion of the substrate holder relative to the ribbon beam is built-in into the processing chamber of the installation. The technical possibilities of the installation are investigated experimentally. The etching and deposition processes of materials are performed when using various working gases.

Module for dielectric surfaces modification by fast neutral particles beams

In this paper, we describe the module for dielectric and wide-gap semiconductor surfaces modification by fast neutral beam. The module can be used for cleaning, etching or assisting of films deposition. The surface proceeding by neutral beam can prevent an accumulation of surface charge without using current compensation by inserting electrons to the beam or RF power supply. The module beside cathode and anode contains an electrode with floating potential. Insertion of the additional electrode causes electron retention in an electrostatic trap resulting the reducing of the module operating pressure. Moreover, the electrode with floating potential allows increasing the current efficient of the module. An important feature of the module is that neutralization of the ions extracted from the plasma occurs in the cathode potential well. Thereby ions that have not neutralized cannot leave nearcathode region and there are no fast ions in the output beam. Module does not contain sources of the magnetic fields or elements heated by external sources. Module operates with free cooling. Thus, the module does not need water cooling and can be freely moved in the vacuum chamber.

Investigation into the selectivity of etching various materials by fast neutral particle beams

The results of an investigation into the etching rate and selectivity of silicon substrates, as well as SiO2, W, TiN, TiC, and NbN films, with the use of chemically active compounds CF4, C3F6, and SF6 as working gases, which were obtained using a Neutral-110L source of extended fast neutral particle (FNP) beams developed at the Institute of Physics and Technology of the Russian Academy of Sciences (FTIAN), are presented. The possibility of attaining etching selectivity by FNP beams of the mentioned materials relative to SiO2 in a range of 10–16 is shown. The data are compared with the currently published results of investigations into this region.

Direct IR excitation in a fast ion beam: application to NO- photodetachment cross sections

BackgroundOptical access to a travelling ion packet is required in many ion beam experiments that study ion-photon interactions.MethodsAn approach is described for carrying out direct infrared excitation of a fast ion beam that uses an optical-quality reflective beam blocker to illuminate a counter propagating pulsed ion beam in a collinear configuration. This arrangement provides optical access along the axis of ion beam propagation by placing a mirror in the beam path at a 25 degree angle. The ion packet is bumped over the mirror, which is also used to block fast neutral particles produced during ion beam acceleration that also propagate along the beam path.ResultsThe efficiency of this setup is demonstrated in a photodetachment experiment on NO- anions, where a photoinduced depletion of up to 90% of the beam is achieved in a single laser shot. To demonstrate the application of this configuration, the relative photodetachment cross section for NO- has been measured in the range of 2800 – 7200 cm-1. The measured relative cross section shows a set of sharp peaks that are identified as vibrational autodetachment resonances.ConclusionThe new setup paves the way for future experiments where parent anionic species are vibrationally excited via direct infrared excitation first and undergo photodetachment/photodissociation in a subsequent step.PACS33.15.Ry; 33.80.Eh; 33.80.-b

An initial measurement of a fast neutral spectrum for ion cyclotron range of frequency heated plasma using two-channel compact neutral particle analyzers in KSTAR

The accurate measurement of fast neutral particles from high energy ion tails is very important since it is a measure of ion cyclotron range of frequency (ICRF) or neutral beam (NB) ion heating. In KSTAR, fast neutral measurements have been carried out using a compact neutral particle analyzer based on the silicon photo diode since 2010. As a result, the fast neutral spectrum was observed consistent with the ion temperature, diamagnetic energy, and neutron flux in 2011. However, there was fast neutral count beyond the injected neutral beam energy in NB-only heating. Since it is difficult to expect the count unless the temperature is high enough to diffuse the fast ions beyond the beam energy it was required to identify what it is. During the 2012 campaign, the two-channel diode detectors with and without a particle stopper were used to distinguish fast neutral counts and other counts by a hard X-ray or neutrons. As a result, it was confirmed that the high energy component beyond the beam energy originated from a hard X-ray or neutrons. Finally, it was observed that faster neutrals are generated by ICRF heating and enhanced by electron cyclotron heating compared to NB-only heating.

Neutral components in glow-discharge nitriding

It is found that during glow-discharge nitriding, the flow bombarding the surface contains fast neutral particles that play a significant role in realization of the process along with charged particles.

Calculation of the flow capacity of a gas channel in the sources of beams of fast neutral particles by means of the Monte-Carlo method

This paper describes the model based on the Monte-Carlo method and presents the results of the mathematical simulation of the flow capacity of the exit aperture for an ion source with a ribbon-shaped beam and for the same source equipped with the system for ion beam neutralization and the electrostatic deflection system. For the designs mentioned above distributions of the normalized pressure and the collision thickness of gas along the channel axis are given. The results obtained are indicative of the fairly strong effect of these design elements on the flow capacity and, consequently, on the operating conditions of the ion source. The results of simulation can be used for correcting the value of the gas flow rate in the source for the purpose of maintaining invariant conditions of discharge glow, as well as for evaluating the effectiveness of the process of ion charge exchange in the source channel.

Development of a mirror-based endoscope for divertor spectroscopy on JET with the new ITER-like wall (invited)

A new endoscope with optimised divertor view has been developed in order to survey and monitor the emission of specific impurities such as tungsten and the remaining carbon as well as beryllium in the tungsten divertor of JET after the implementation of the ITER-like wall in 2011. The endoscope is a prototype for testing an ITER relevant design concept based on reflective optics only. It may be subject to high neutron fluxes as expected in ITER. The operating wavelength range, from 390 nm to 2500 nm, allows the measurements of the emission of all expected impurities (W I, Be II, C I, C II, C III) with high optical transmittance (≥ 30% in the designed wavelength range) as well as high spatial resolution that is ≤ 2 mm at the object plane and ≤ 3 mm for the full depth of field (± 0.7 m). The new optical design includes options for in situ calibration of the endoscope transmittance during the experimental campaign, which allows the continuous tracing of possible transmittance degradation with time due to impurity deposition and erosion by fast neutral particles. In parallel to the new optical design, a new type of possibly ITER relevant shutter system based on pneumatic techniques has been developed and integrated into the endoscope head. The endoscope is equipped with four digital CCD cameras, each combined with two filter wheels for narrow band interference and neutral density filters. Additionally, two protection cameras in the λ > 0.95 μm range have been integrated in the optical design for the real time wall protection during the plasma operation of JET.

Laser-plasma debris from a rotating cryogenic–solid-Xe target

We investigate the characteristics of laser plasma debris that is responsible for damaging optics. The debris is composed of fast ions, neutral particles, and fragments, and originates from a solid Xe target on a rotating drum that we developed as an extreme ultraviolet (EUV) source. The ice fragments appear to be a problem most notably with solid Xe targets; however, we find that the damage induced by Xe ice fragments can be avoided by simply reducing the laser pulse energy. We find the number of fast neutral particles to be an order of magnitude less than the number of ions, and we clarify that the plasma debris is primarily composed of fast ions. In addition, we find that the number of fast ions having a few dozen keV of energy decreases when using the rotating target compared with the rest target. We attribute this to a gas curtain effect from the Xe gas localized at the rotating target surface. We estimate the sputtering rate of the Mo/Si mirror, which is caused primarily by the fast ions, to be 104 nm/1x10(6) shots at 190 mm from the source plasma and at an 11.25 degree angle from the incident laser beam. Up to the 1x10(6) shots exposure, remarkable degradation of the mirror reflectivity is not observed though the sputtering damages the mirror. Mitigation of the ions by using gas and/or magnetic fields will further improve the mirror lifetime. By comparing with a liquid jet Xe target, we conclude that the sputtering rate per conversion efficiency when using the solid Xe targets on the rotating drum is the same as that when using the liquid Xe targets. The high conversion efficiency of 0.9% in the rotating drum solid Xe target makes this technique useful for developing laser plasma EUV sources.

Practical Calculation of Nuclear Fusion Power for a Toroidal Plasma Device with Magnetic Confinement

An algorithm has been developed and realized as a FORTRAN code to calculate the volume integral power of a magnetic confinement nuclear fusion reactor and the local fusion rate function. It takes the nuclei energy distributions, fusion cross-sections, and magnetic surface geometry as input data. Two fast, simple analytic models of magnetic flux surfaces were used, and the corresponding Jacobian determinants were found. Gaussian kernel empirical probability density estimation has been proposed to reconstruct the ion energy probability density function from experimentally obtained random samples of escaping neutral atom energies. The influence of ion heating and fast ion confinement on high-energy distribution tails, and thus on the neutron yield and fusion power, can be calculated. The code has been applied to obtain radial profiles of the nuclear fusion reaction rate and volume integral power for both Maxwellian and suprathermal D and T particle distributions. A fast neutral particle diagnostic database may serve as a basis for an experimentally confirmed calculation technique for reactor power and ignition criterion.

Numerical estimates of the ITER first wall erosion due to fast neutral particles

Estimates of the ITER first wall steady-state sputtering due to fast atoms are made based on the B2-EIRENE modelling of the scrape-off layer (SOL) plasma. Models with fully diffusive and convective cross-field transport in the SOL are investigated. It is found that strong radial convection in the far-SOL has only a weak effect on the plasma profiles there. Effective yields of the physical sputtering of Be, C, Mo and W as well as their corresponding erosion rates at the first wall are calculated. The results are compared with available published data.