Pellet Charge Research Articles

Features of the Neutralization of Fast Protons in a Hydrocarbon Pellet Cloud

To measure the high-energy part of the energy distribution function of ions in a hot plasma using the pellet charge exchange (PCX) diagnostic, it is necessary to know the energy dependence of the fraction F0(E) of fast ions neutralized when intersecting a pellet cloud. Using experimental and calculated data on the ablation of polystyrene macroparticles (pellets) in the LHD stellarator, the function F0(E) for protons in the hydrocarbon cloud has been calculated in the energy range of 50–1000 keV at pitch angles \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\geqslant {\\kern 1pt} 70^\\circ $$\\end{document}. At energies of 50‒200 keV, it is necessary to take into account the decrease in the flux of neutralized protons multiply intersecting the cloud. Energy losses of protons along the trajectory provide a lower bound E > 100 keV for the possible PCX measurements. The necessity of the control of the charge state composition and structure of the cloud limits the view area of the detector of atoms within ±30 mm from the position of a pellet along the magnetic field. For this reason, the injection axis should be aligned with the observation axis of the neutral particle analyzer for the optimal geometry of PCX measurements with polystyrene pellets.

Purification of Saline Water Using Desalination Pellets

This study establishes that processed zero valent iron can be pelletised and used to desalinate water. The pellets desalinate water using a zero-order reaction, where: product water salinity = −[a][Reaction Time] + Feed Water Salinity. Desalination using the pellets requires no onsite energy, no onsite infrastructure, and produces no reject brine. Potential applications for the pellets, include desalination of saline impoundments, desalination of agricultural water, desalination of irrigation water, desalination of irrigated salinized soils, and aquifer desalination. The examples demonstrate 30% to 60% desalination for saline feed water within the salinity range of 4 to 10 g L−1. The product water has a low outcome variability for a specific pellet charge. The achievable desalination increases as the pellet weight: water volume ratio increases. The pellets can also be used for water purification, wastewater desalination, treatment of domestic wastewater, treatment of industrial wastewater, treatment of livestock feed water, treatment of oil field and mining wastewater, water purification to allow reuse, and the treatment of polluted soils. This study addresses the manufacture of the pellets, their effectiveness in desalinating water, and the outcome variability associated with desalination.

CONFORMITIES TO LAW OF FORMING LAYER FOR POLYDISPERSE PELLET CHARGE ON SINTER BELT

Motion of pellet charge on the loading tray on a sinter belt is accompanied not only by the change of its grain-size composition, but by segregation processes, id est. by the redistribution of charge of different size particles for the most part friable material. The result of this process is formation of local discontinuity with pre-dominance of content for particles of certain factions. The traditional method for analysis of work for loading tray on the basis of factious classification does not allow to educe and analyze appearing heterogeneity in the most part friable material. It results in errors at the calculation for action of the system of the automated control by sintering process and ignoring of notational of the use of segregation of particles of friable material for optimization of technological process. The use of balance method enables to specify and spread understanding of mechanism of processes which take place during motion of pellet charge in relation to the loading tray, and also to form theoretical pre-conditions for the choice of the rational modes of operations of agglomeration separation of sintering plant. It is set that at monotonous increase of angle of slope for loading tray the segregation phenomena increase in a pellet charge, and after achievement of the defined value – go down, id est. have extreme character. Mentioned features of forming of layer for polydisperse material in the conditions of inconstancy of mechanical properties of its separate factions it is possible to take into account at the use of balance of grain-size composition of charge, loaded on a sinter belt, and charge, being on it, when conditional middle diameters of particles of their components must be equal. On the basis of the set conformities to law of forming of friable of structure of layer the method of authentication of grain-size compositions of pellet charge mixture is in theory reasonable in every its horizon taking into account a segregation during loading.

THE p-t RELATIONSHIP BETWEEN BOOSTER PELLET AND MAIN CHARGE UNDER SHOCK WAVE INITIATION

THE p-t RELATIONSHIP BETWEEN BOOSTER PELLET AND MAIN CHARGE UNDER SHOCK WAVE INITIATION

Improved Pellet Charge Exchange Measurements in Large Helical Device

The pellet charge exchange technique (PCX), which is a combination of the compact neutral particle analyzer and an impurity pellet, is a unique method to observe the radial energetic particle distribution. There are not only charge exchange reactions between the hydrogen in the pellet and a proton, but also between the partially ionized carbon in the pellet and the proton. The neutralization factor from energetic ion to neutral particle could be deduced from the electron temperature and the electron density of the pellet cloud. The radial profiles of energetic particle distribution were measured and compared in various ion cyclotron resonance heating (ICH) plasmas. The energetic particle flux significantly increased at the resonance layer created by the ICH. PCX provides more precise information about the resonance layer than conventional neutral particle diagnostics.

An analysis of the influence of impurities on fast particle attenuation and on fast ion spectral shape in LHD

Neutral particle fluxes measured by neutral particle analyzers can provide information about the ion temperature as well as the non-Maxwellian anisotropic ion distribution tails from neutral beam injection and ion cyclotron radio frequency heating. In the case of multidirectional diagnostics employing high resolution atomic energy spectrometers, the neutral atomic flux source is not localized in contrast to pellet charge exchange or diagnostic neutral beam methods. The correct interpretation of such measurements from plasma in a complex toroidally asymmetric geometry, like that of LHD, requires careful numerical modeling of the neutral flux formation. Previously a measured neutral flux calculation scheme was developed and was used for the LHD geometry and a suitable analytic expression for ionization cross sections sigma(s)(z)(E,n(e),T(e),Z(eff)) of impurities was formulated by Janev et al. [Nucl. Fusion 29, 2125 (1989)]. In this paper, the attenuation of fast particles by impurities is incorporated into the neutral flux calculation scheme and the influence of impurities on the calculated neutral flux spectra is shown. Finally, the behavior of the calculated and experimental suprathermal particle distributions is compared for pure hydrogen and for argon impurity seeded plasmas.

Calculation of low-Z impurity pellet induced fluxes of charge exchange neutral particles escaping from magnetically confined toroidal plasmas

Measurements of energy- and time-resolved neutral hydrogen and helium fluxes from an impurity pellet ablation cloud, referred to as pellet charge exchange or PCX experiments, can be used to study local fast ion energy distributions in fusion plasmas. The estimation of the local distribution function f(i)(E) of fast ions entering the cloud requires knowledge of both the fraction F(0)(E) of incident ions exiting the cloud as neutral atoms and the attenuation factor A(E,rho) describing the loss of fast atoms in the plasma. Determination of A(E,rho), in turn, requires the total stopping cross section sigma(loss) of neutral atoms in the plasma and the Jacobian reflecting the measurement geometry and the magnetic surface shape. The obtained functions F(0)(E) and A(E,rho) enter multiplicatively into the probability density for escaping neutral particle kinetic energy. A general calculation scheme has been developed and realized as a FORTRAN code, which is to be applied for the calculation of f(i)(E) from PCX experimental results obtained with low-Z impurity pellets.

Pellet charge exchange helium measurement using neutral particle analyzer in large helical device

It is very important to investigate the confinement of alpha particles, which will be produced by nuclear reactions in ITER and fusion reactors. The pellet charge exchange (PCX) measurement is one of the most powerful methods because it can directly provide the profile of the alpha particle energy spectra in a plasma. In the large helical device, PCX using tracer encapsulated solid pellet (TESPEL) has been tried in many hydrogen and helium plasmas, including helium accelerated by using the cyclotron resonance heating. In the PCX, we use the compact neutral particle analyzer without simultaneous mass separation ability. The helium particle measurement can be achieved by the application of voltage in the condenser plate. The scattering of hydrogen particle is carefully considered during the estimation of the helium amount. The radial helium profiles can also be obtained by comparing four TESPEL injection shots with/without higher harmonic fast wave heating and at applied plate voltages for He or H, respectively.

Simulation of Angle and Energy Resolved Fluxes of Escaping Neutral Particles from Fusion Plasmas with an Isotropic Ion Distribution

Multidirectional diagnostics employing high-resolution atomic energy spectrometers [1, 2] are being used to study the ion component heating mechanisms and fast ion confinement in helical plasmas. Since the natural atomic flux source is not localized in contrast to the pellet charge exchange [3,4] or diagnostic neutral beam methods [5], the correct interpretation of such measurements in a complex toroidally asymmetric geometry requires careful numerical modeling of the neutral flux formation and knowledge of the charge exchange target distributions, relevant cross-sections, and the magnetic surface structure. The measured neutral flux calculation scheme for LHD geometry was given in [6], and the influence of the geometry effect on the interpretation of measured data was shown. The current method was applied for the simulation of the experimental signal of the angular-resolved multi-sightline neutral particle analyzer (ARMS-NPA) [1] along it's 20 sightlines in the LHD geometry configuration. In order to check the influence of the geometry effect on the interpretation of experimental results, calculations were conducted for the isotropic Maxwellian plasma-ion-energy probability density function. The behavior of the calculated and experimental ion spectra from neutral beam injector (NBI) is discussed.

High-energy neutral particle measurements simulating α particle diagnostics in Large Helical Device

It is very important to investigate the confinement of α particles, which is produced by the nuclear reaction in ITER or fusion reactor. In Large Helical Device (LHD), it is possible to perform the simulation experiment of the α particle heating by using the ion cyclotron resonance heating (ICH) because high-energy particles generated by ICH are well confined in the plasma. High-energy particles including α particle are emitted not only by the charge exchange but also by the MHD instability as the Alfven eigen mode. Their particles give damage to the plasma wall in addition to create a poor plasma confinement. Therefore, the suitable method for measuring α particle distribution should be established immediately. For this purpose, the silicon surface barrier detector-type neutral particle analyzer (SD-NPA) and the position sensitive detector are installed in LHD. The neutral particles (mainly hydrogen), which are generated by the charge exchange between the high-energy ion and the background neutrals, can be observed by using them. However, a few neutral helium particles can be observed because α particle (or fully ionized helium) can emit only by double charge exchange process. Therefore, we also introduce the pellet charge exchange system (PCX). The diagnostic pellet is injected to the plasma in order to obtain the charge exchange neutral particle, which is produced by the charge exchange reaction between the ablated pellet cloud and α particle or high-energetic particle. Much hydrogen flux can be obtained around the ion cyclotron resonance region by the PCX. Similar results can be also obtained in SD-NPA. The helium distribution measurement in helium plasma is demonstrated. Here the reliability of PCX as the particle diagnostic and the possibility of α particle (helium) diagnostic are described.

Helium Measurements using the Pellet Charge Exchange in Large Helical Device

Graduate University for Advanced Studies, Hayama, Kanagawa, 240-0193, Japan(Received 3 December 2006 /Accepted 22 March 2007)In Large Helical Device (LHD), it is possible toperformthesimulation experiment of the αparticle heatingby using the ion cyclotron resonance heating (ICH) because high-energy particle generated by ICH is well con-fined in theplasma. Theneutralparticles (mainlyhydrogen), whichare generated bythe charge exchange betweenthe high-energy ion and the background neutrals, can beobserved by using them. However a few neutral heliumparticles can be observed since fully ionized helium like αparticle can emit only by double charge exchangeprocess. Therefore we also introduce the pellet charge exchange system (PCX). The diagnostic pellet is injectedto the plasma in order to obtain the charge exchange neutral particle, which is produced by the charge exchangereaction between the ablated pellet cloud and high-energetic particle. The helium distribution measurement inhelium plasma is also demonstrated.

Local pellet based and line-integrated nonperturbing charge exchange measurements with a compact neutral particle analyzer on Large Helical Device

Experiments on suprathermal ion physics are carried out on the Large Helical Device (LHD) with a 40 channel compact neutral particle analyzer (CNPA). The analyzer is used both in passive nonperturbing chord-integral neutral particle flux measurements and for local probing with an impurity pellet. The analyzer observes trapped particles with ∣v‖∕v∣<0.25 and the pitch angle cosine value v‖∕v changes sign along the diagnostic sight line. The measurable energy range for H0 is 1–170keV. Radially resolved data on local H0 atomic energy spectra have been obtained on LHD by the pellet charge exchange method with CNPA, as well as chord-integral atomic energy distribution data for electron cyclotron heated, neutral beam injected, and high power ion cyclotron heated plasma. The article addresses the diagnostic technical background and the analysis scheme of measurement results taking into account the helical geometry and the species and densities of the charge exchange targets.

Horizontal, vertical, and radial high-energy particle distribution measurement system in Large Helical Device

A horizontal, vertical, and radial high-energy particle distribution measurement system, which consists of the time-of-flight neutral particle analyzer (TOF-NPA), the silicon detector neutral particle analyzer (SD-NPA), and pellet charge exchange (PCX) analyzers, is successfully installed in the Large Helical Device (LHD). In a horizontal scan, it is interesting to measure the pitch angle distribution and to investigate the loss cone feature obtained by it. The pitch angle distribution from 40° to 100° can be obtained by horizontal scanning of the TOF-NPA during a long discharge of over 100 s sustained by the NBI2 (coinjection) at the magnetic axis of 3.6 m. With a vertical scan, the heating deposition profile of the ion cyclotron resonance heating (ICH) has been discussed. The deposition profile can be obtained by the vertical scan of the SD-NPA. The region where the high-energy particle is generated agrees with the location of the resonance layer of the ICH. Similar results can be obtained by the PCX measurement, which gives radial information of the high-energy particle distribution in a short discharge.

Digital processing of solid state detector signals in pellet charge exchange measurements on LHD

Radially resolved measurements of the plasma ion distribution function by detecting charge exchange neutrals from an impurity pellet ablation cloud require a fast operating energy analyzer working at high count rates to build several spectra during the pellet flight. Currently a solid state detector in the pulse height analysis (PHA) mode is used for such measurements on the Large Helical Device. Traditional PHA techniques cannot provide the operating speed required for a good spatial resolution. An algorithm has been proposed based on digital processing of noisy data series containing charge-sensitive preamplifier signals with discontinuities corresponding to incident particles. The algorithm employs the modified Tikhonov regularization and the successive detection–estimation of signal increments at discontinuity points. Such an approach allows one to realize an ultrafast particle energy spectroscopy by taking advantage of detector/preamplifier capabilities without limiting the system throughput by subsequent electronics.

Development and initial operation of the pellet charge exchange diagnostic on LHD heliotron

An active corpuscular diagnostic with an artificially created localized target for the charge-exchange process has been developed and tested on a large helical device. The diagnostic is a combination of an impurity pellet injector and a natural diamond detector-based energy analyzer. High-energy particles neutralized at the pellet ablation cloud are detected while the pellet travels across the plasma column. Time-resolved atomic energy spectra translate into local measurements along the pellet trajectory. Thus, local parameters are obtained in the toroidally non-axis-symmetrical configuration. Physical basis, data interpretation, and the technical description of the diagnostic are given. The requirements to the analyzer geometry, electronics, and data acquisition needed to provide the desired spatial resolution are described. The initial experimental results are presented along with the other diagnostic data. The scope of experiments, possible comparisons with multichord passive charge-exchange measurements and future work on the diagnostic are also discussed.

Neoclassical simulations of fusion alpha particles in pellet charge exchange experiments on the Tokamak Fusion Test Reactor

Neoclassical simulations of alpha particle density profiles in high fusion power plasmas on the Tokamak Fusion Test Reactor [Phys. Plasmas 5, 1577 (1998)] are found to be in good agreement with measurements of the alpha distribution function made with a sensitive active neutral particle diagnostic. The calculations are carried out in Hamiltonian magnetic coordinates with a fast, particle-following Monte Carlo code which includes the neoclassical transport processes, a recent first-principles model for stochastic ripple loss and collisional effects. New calculations show that monotonic shear alpha particles are virtually unaffected by toroidal field ripple. The calculations show that in reversed shear the confinement domain is not empty for trapped alphas at birth and allow an estimate of the actual alpha particle densities measured with the pellet charge exchange diagnostic.

Effective temperatures, sawtooth mixing, and stochastic diffusion ripple loss of fast H+ minority ions driven by ion cyclotron heating in the Tokamak Fusion Test Reactor

This paper presents studies of the H+ minority ions driven by Ion Cyclotron Radio Frequency (ICRF) heating in the Tokamak Fusion Test Reactor (TFTR) [R. J. Hawryluk et al., Phys. Plasmas 5, 1577 (1998)] deuterium plasmas using primarily passive H° flux detection in the energy range of 0.2–1.0 MeV. The measured passive H+ energy spectra are compared with active (Li pellet charge exchange) results. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at an ICRF power of 2 MW to 0.35 MeV at 6 MW. Radial redistribution of ICRF-driven H+ ions was detected when giant sawtooth crashes occurred during the ICRF heating. The redistribution affected ions with energy below 0.7–0.8 MeV. The sawtooth crashes displaces H+ ions outward along the plasma major radius into the stochastic ripple diffusion domain where those ions are lost in ∼10 msec. These observations are consistent with the model of the redistribution of energetic particles developed previously to explain the results of deuterium-tritium (DT) alpha-particle redistribution due to sawtooth oscillations observed in TFTR. The experimental data are also consistent with numerical simulations of H+ stochastic ripple diffusion losses.

Operation of the TFTR pellet charge exchange diagnostic in the pulse counting mode during H+ radio frequency minority heating

The pellet charge exchange technique on TFTR has been used primarily to obtain active charge exchange measurements using a high-energy (0.5–4.0 MeV) neutral particle analyzer (NPA) in conjunction with impurity pellet injection (Li and B) with the scintillator-photomultiplier detector system operated in the current mode. While passive measurements using pulse counting were also obtained using this instrumentation, operation in this mode was very restrictive with pulse counting rates limited to less than ∼10 kHz in the absence of any significant neutron and gamma induced background signal. An upgrade to a specialized pulse counting capability which was developed by the Ioffe Institute was implemented which consisted of CsI(Tl) scintillators having features designed to minimize signals induced by background neutron and gamma rays and 16-channel pulse height analysis electronics on each of the eight NPA energy channels. Passive measurements of rf-driven energetic hydrogen minority ions which served to verify operation of the pulse counting mode are reported. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at a rf power of 2 MW to 0.35 MeV at 6 MW.

Pellet charge exchange measurements of confined alphas in deuterium–tritium plasmas (invited) (abstract)

Alpha particle confinement is essential to achieving ignition in deuterium–tritium plasmas, and measuring the energy and spatial distributions of fusion alphas is one of the most challenging tasks in plasma diagnostics research. Confined trapped-alpha energy spectra and radial density profiles in the Tokamak Fusion Test Reactor (TFTR) have been obtained using the pellet charge exchange (PCX) diagnostic, which measures high energy (Eα=0.5–3.5 MeV), trapped alphas (|v∥/v|=0.048) at a single time slice (Δt∼1 ms) with a spatial resolution of Δr∼5 cm. PCX measures the energy spectrum of energetic helium neutrals resulting from charge exchange interactions of alphas incident on the ablation cloud surrounding small boron and lithium pellets injected radially into TFTR. The success of PCX has led to a number of important results on the behavior of alphas in TFTR. The measured alpha energy spectrum in the plasma core of sawtooth-free discharges is consistent with the alphas being well confined and slowing down classically. Outside the plasma core, the trapped alphas show the effects of stochastic diffusion due to the toroidal magnetic field ripple, with the PCX measured profiles consistent with the functional dependence of the stochastic ripple diffusion on the alpha energy and the q profile. Large sawtooth instabilities result in radial redistribution of the trapped alphas to well outside the q=1 radius and beyond the stochastic ripple loss boundary. Broadening of the radial profiles of trapped alphas is also observed in reversed and reduced shear discharges on TFTR, with potential implications for reactor designs based on optimized shear configurations. Finally, radial redistribution of trapped alpha particles in the presence of core localized Toroidal Alfv́en Eigenmode activity is also observed. Application of PCX measurements to future experiments, including the International Thermonuclear Experimental Reactor will also be discussed.

Modelling of alpha particle slowing down, confinement and redistribution by sawteeth in TFTR using the FPPT code

Results from recent deuterium-tritium (DT) experiments on TFTR to measure the energy spectra and radial profiles of well trapped confined alpha particle distributions using the pellet charge exchange (PCX) diagnostic in quiescent plasmas are compared with a numerical modelling using the Fokker-Planck post-TRANSP (FPPT) processor code and show a classical slowing down behaviour of the alphas (Fisher, R.K., et al., Phys. Rev. Lett. 75 (1995) 846). However, in the presence of sawtooth oscillations PCX experimental data indicate a significant broadening of the trapped alpha radial distributions (Petrov, M.P., et al., Nucl. Fusion 35 (1995) 1437). Conventional models consistent with measured sawtooth effects on passing particles do not provide satisfactory simulations of the trapped particle mixing measured by the PCX diagnostic. A mechanism is proposed for fast particle mixing during the sawtooth crash to explain the trapped alpha particle radial profile broadening after the crash. The model is based on the fast particle orbit averaged toroidal drift in a perturbed helical electric field with an adjustable absolute value (similar to that in Kolesnichenko, Ya.I., et al., Nucl. Fusion 36 (1996) 159). Such a drift of the fast particles results in a change of their energy and a redistribution id phase space. To show the sensitivity of trapped particles to sawteeth, the redistribution in toroidal momentum Pphi (or in minor radius) was calculated in two ways. The first is based on the assumption that Pphi redistribution is stochastic with a large diffusion coefficient and was taken to be flat. The second way is to apply Kolesnichenko's inversion formula (Kolesnichenko, Ya.I., et al., Nucl. Fusion 32 (1992) 449). Both methods are compared with PCX data. The distribution function in a pre-sawtooth plasma and its evolution in a post-sawtooth crash plasma are simulated using the FPPT code. It is shown that FPPT calculated alpha particle distributions are consistent with TRANSP Monte Carlo calculations. Compariso