Ion Loss Rate Research Articles

Reliable transport through a microfabricated X-junction surface-electrode ion trap

We report the design, fabrication and characterization of a microfabricated surface-electrode ion trap that supports controlled transport through the two-dimensional intersection of linear trapping zones arranged in a 90° cross. The trap is fabricated with very large scalable integration techniques which are compatible with scaling to a large quantum information processor. The shape of the radio-frequency electrodes is optimized with a genetic algorithm to reduce axial pseudopotential barriers and minimize ion heating during transport. Seventy-eight independent dc control electrodes enable fine control of the trapping potentials. We demonstrate reliable ion transport between junction legs and determine the rate of ion loss due to transport. Doppler-cooled ions survive more than 105 round-trip transits between junction legs without loss and more than 65 consecutive round trips without laser cooling.

Simulation of Alfvén eigenmode bursts using a hybrid code for nonlinear magnetohydrodynamics and energetic particles

A hybrid simulation code for nonlinear magnetohydrodynamics (MHD) and energetic-particle dynamics has been extended to simulate recurrent bursts of Alfvén eigenmodes by implementing the energetic-particle source, collisions and losses. The Alfvén eigenmode bursts with synchronization of multiple modes and beam ion losses at each burst are successfully simulated with nonlinear MHD effects for the physics condition similar to a reduced simulation for a TFTR experiment (Wong et al 1991 Phys. Rev. Lett. 66 1874, Todo et al 2003 Phys. Plasmas 10 2888). It is demonstrated with a comparison between nonlinear MHD and linear MHD simulation results that the nonlinear MHD effects significantly reduce both the saturation amplitude of the Alfvén eigenmodes and the beam ion losses. Two types of time evolution are found depending on the MHD dissipation coefficients, namely viscosity, resistivity and diffusivity. The Alfvén eigenmode bursts take place for higher dissipation coefficients with roughly 10% drop in stored beam energy and the maximum amplitude of the dominant magnetic fluctuation harmonic δBm/n/B ∼ 5 × 10−3 at the mode peak location inside the plasma. Quadratic dependence of beam ion loss rate on magnetic fluctuation amplitude is found for the bursting evolution in the nonlinear MHD simulation. For lower dissipation coefficients, the amplitude of the Alfvén eigenmodes is at steady levels δBm/n/B ∼ 2 × 10−3 and the beam ion losses take place continuously. The beam ion pressure profiles are similar among the different dissipation coefficients, and the stored beam energy is higher for higher dissipation coefficients.

The orientation of Titan’s dayside ionosphere and its effects on Titan’s plasma interaction

A hybrid particle code has been used to examine how Titan’s interaction with Saturn’s magnetosphere is effected by the orientation of the dayside ionosphere with respect to the incident magnetospheric flow. The hybrid code self-consistently includes a version of Titan’s ionosphere represented by 7 generic ion species, over 40 ionneutral chemical reactions, ion-neutral collisions and Hall and Pederson conductivities. Emphasis is placed on what effects the orientation angle has on the ion loss rates, ion densities, and the electric and magnetic fields. The results are analyzed and regardless of the orientation angle the ionosphere is found to be within photochemical equilibrium below 1200 km altitude. The ion loss rates and field structures also show little dependence on the orientation of the dayside ionosphere. It is found to first order illumination angle does not have a significant effect on these features of the Titan interaction.

Control of ion loss from Mars during solar minimum

A hybrid particle code has been used to examine the interaction of the solar wind with Mars during solar minimum. The results were surprising as they produced ion loss rates from Mars far in excess of what is estimated from MEX. The results are analyzed and found to be consistent with the competition between photochemical rates and advection of the ionosphere. The simulations showed significant erosion of the ionosphere at altitudes between 200 km and 250 km altitudes. Addition of the crustal magnetic fields reduced the erosion and reduced the ion loss rates to a level consistent with the data.

Electron-Catalyzed Mutual Neutralization of Various Anions withAr+: Evidence of a New Plasma Process

The mutual neutralization of anions with Ar+ has been studied by variable electron and neutral density attachment mass spectrometry. Evidence of a previously unobserved plasma loss process, electron-catalyzed mutual neutralization (ECMN), e.g., SF6-+Ar+ + e-→neutrals + e-, is reported. Results for 10 species suggest that ECMN occurs generally and significantly affects the total ion-loss rate in plasmas with electron densities exceeding 10(10) cm-3. ECMN is discussed in the context of other known three-body plasma processes, the mechanisms for which appear insufficient to explain the observed effect. A mechanism for ECMN involving an incident electron facilitating energy transfer to the internal modes of the anion is proposed.

Ionization instability of ion-acoustic waves

Stability of ion-acoustic waves in weakly ionized unmagnetized plasmas is investigated using fluid equations, assuming an arbitrary dependence of ion production and loss rates on electron and ion densities. The linear dispersion relation is derived and the condition for the positive growth rate is identified. Some examples corresponding to different plasma regimes are given to illustrate the application of the obtained results.

Ion transport in Titan's upper atmosphere

Based on a combined Cassini data set including Ion Neutral Mass Spectrometer, Radio Plasma Wave Science, and Magnetometer measurements made during nine close encounters of the Cassini spacecraft with Titan, we investigate the electron (or total ion) distribution in the upper ionosphere of the satellite between 1250 and 1600 km. A comparison of the measured electron distribution with that in diffusive equilibrium suggests global ion escape from Titan with a total ion loss rate of ∼(1.7 ± 0.4) × 1025 s−1. Significant diurnal variation in ion transport is implied by the data, characterized by ion outflow at the dayside and ion inflow at the nightside, especially below ∼1400 km. This is interpreted as a result of day‐to‐night ion transport, with a horizontal transport rate estimated to be ∼(1.4 ± 0.5) × 1024 s−1. Such an ion flow is likely to be an important source for Titan's nightside ionosphere, as proposed in Cui et al. [2009a].

Physical mechanism and mathematical modeling of earthquake ionospheric precursors registered in total electron content

The physical mechanism by which the regions with increased or decreased total electron content, registered by measuring delays of GPS satellite signals before strong earthquakes, originate in the ionosphere has been proposed. Vertical plasma transfer in the ionospheric F2 region under the action of the zonal electric field is the main disturbance formation factor. This field should be eastward, generating the upward compo� nent of plasma electromagnetic drift, in the cases of increased total electron content at midlatitudes and deepened minimum of the F2 layer equatorial anomaly. Upward plasma drift increases electron density due to a decrease in the O + ion loss rate at midlatitudes and decreases this density above the equator due to an enhancement of the fountain effect (plasma discharge into the equatorial anomaly crests). The pattern of the spatial distribution of the seismogenic electric field potential has been proposed. The eastward electric field can exist in the epicentral region only if positive and negative electric charges are located at the western and eastern boundaries of this region, respectively. The effectiveness of the proposed mechanism was studied by modeling the ionospheric response to the action of the electric field generated by such a charge configuration. The results of the numerical computations indicated that the total electron content before strong earthquakes at middle and low latitudes is in good agreement with the observations.

Irradiation damage of uridine molecules with MeV heavy ions

In order to study the mechanism of the nucleotide directly damaged by energetic heavy ions, the residual ratio of uridine molecules after irradiation was measured by means of High Performance Liquid Chromatography (HPLC). The experimental results show that the irradiation damage probability depends on the electronic energy loss rate ( S e ) of incident ions: first it increases quickly with S e , then becomes stable when S e reaches 800 eV/nm. The contribution of the nuclear collisions can be neglected compared with that of the electronic process. This is not only because that the nuclear energy loss rate ( S n ) is much smaller than S e for MeV heavy ions, but also because the energy deposition through the electronic process is more efficient in damaging molecules than through the nuclear process.

On the determination of edge Ti profiles by a supersonic He beam in TJ-II

In the present work, a new diagnostic for the simultaneous measurement of ne, Te and Ti profiles at the edge of a fusion plasma is proposed and tested. First, the propagation of a supersonic He beam is self-consistently simulated from the electron parameter profiles reconstructed from the line ratio method. The radial profile of excited HeII ions, measured simultaneously with the HeI lines, is then compared with the simulated profile and the total effective ion loss rate from the observation volume is deduced, which is function of Ti and the local plasma parameters. The values so obtained are normalized to those from passive CX measurements (NPA). Steeper gradients and lower values are found in the Ti profile compared to those in the Te profiles. The implication of these findings in ion transport at the edge of the TJ-II stellarator is addressed.

Hybrid simulations of the O + ion escape from Venus: Influence of the solar wind density and the IMF x component

As an initial effort to study the evolution of the Venus atmosphere, the influence of the solar wind density and the interplanetary magnetic field (IMF) x component (the x-axis points from Venus towards the Sun) on the O + ion escape rate from Venus is investigated using a three-dimensional quasi-neutral hybrid (HYB-Venus) model. The HYB-Venus model is first applied to a case of the high-density (100 cm −3) solar wind interaction with Venus selected from the Pioneer Venus Orbiter observations to demonstrate its capability for the study. Two sets of simulations with a wide range of solar wind densities and different IMF x components are then performed. It is found that the O + ion escape rate increases with increasing solar wind density. The O + ion escape rate saturates when the solar wind density becomes high (above 100 cm −3). The results also suggest that the IMF x component enhances the O + ion escape rate, given a fixed IMF component perpendicular to the x-axis. Finally, the results imply a higher ion loss rate for early-Venus, when solar conditions were dramatically different.

Observation of Fast Ion Losses Induced by Various MHD Modes Driven by Fast Ions and Bulk Plasma Pressure in the Large Helical Device

Results from a scintillator-based lost-fast ion probe newly installed at the horizontally elongated outboard side of the Large Helical Device are presented. Correlating with bursts of toroidal Alfven eigenmodes (TAEs) and energetic-particle continuum modes (EPMs), recurrent increases in beam ion losses were observed during co-neutral beam injections. Beam ion loss rate was also enhanced, correlating with low-frequency interchange modes driven by the bulk plasma pressure gradient near the plasma edge.

Ion Distribution Function Evaluation Using Escaping Neutral Atom Kinetic Energy Samples

A reliable method to evaluate the probability density function of escaping atom kinetic energies is required for analyzing neutral particle diagnostic data used to study the fast ion distribution function in fusion plasmas. In this paper, digital processing of solid state detector signals is proposed as an improvement of the simple histogram approach. Probability density function of kinetic energies of neutral particles escaping from plasma has been derived in a general form, taking into consideration the plasma ion energy distribution, electron capture and loss rates, superposition along the diagnostic sight line, and the magnetic surface geometry. A pseudorandom number generator has been realized to simulate a sample of escaping neutral particle energies for given plasma parameters and experimental conditions. Empirical probability density estimation code has been developed and tested to reconstruct the probability density function from simulated samples assuming Maxwellian ion energy distribution shapes for different temperatures and classical slowing down distributions with different slowing down times. The application of the developed probability density estimation code to the analysis of experimental data obtained by the novel Angular-Resolved Multi-Sightline Neutral Particle Analyzer has been studied to obtain the suprathermal particle distributions. The optimum bandwidth parameter selection algorithm has also been realized.

Reply to comment by R. M. Thorne and R. B. Horne on Khazanov et al. [2002] and Khazanov et al. [2006

[1] It is well-known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC wave spatialtemporal-spectral distributions and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping and wave propagation/refraction/reflection, along with wave tunneling and mode conversion and particles. Such a self-consistent RC-EMIC wave model is being progressively developed by Khazanov et al. [2002, 2003a, 2006, 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density with explicit inclusion of the ray tracing equations. [2] The theoretical formalism for RC ions and RB electrons is well established and is based on gyroaveraged and bounce-averaged kinetic equations that have been developed over the years and systemized in the book by Khazanov [1979]. The application of this formalism to RC ions was continued by Khazanov and Kozyra at the University of Michigan during 1991–1994 and formed a large part of the Ph.D. dissertation work of Fok [1993] and of Jordanova [1995]. Khazanov et al. also applied this formalism to the study of ionosphere-plasmasphere transport of suprathermal electrons [Khazanov et al., 1992, 1994], and global photo [Khazanov et al., 1996; Khazanov and Liemohn, 2002] and plasma sheet [Khazanov et al., 1998] electron transport. This formalism was also generalized to study relativistic electron transport [Khazanov et al., 1999, 2000], as well as different aspects of RC and RB electron formation using various magnetospheric electric and magnetic field topologies [Khazanov et al., 2003b, 2004b, 2004c]. All these above-mentioned studies are the heritage of our RC-EMIC wave model that was presented by Khazanov et al. [2006]. [3] Thorne and Horne [2007, hereinafter referred to as TH2007] call the Khazanov et al. [2002, 2006] results into question in their Comment. The points in contention can be summarized as follows. TH2007 claim that (1) important damping of waves by thermal heavy ions is treated incorrectly in our model, and Landau damping during resonant interaction with thermal electrons is not included; (2) EMIC wave damping due to RC O is not included in our simulation of the 2–7 May 1998 storm; (3) nonlinear processes limiting EMIC wave amplitude are not included in our model; (4) growth of the background electromagnetic fluctuations to a physically significant amplitude must ‘‘occur during a single transit of the unstable region’’ with subsequent damping in the vicinity of the bi-ion latitude, and consequently the bounce-averagedwave kinetic equation employed in the code is not valid. Our reply will address each of these points as well as other criticisms mentioned in the Comment. [4] TH2007 is focused on two of our papers that are separated by 4 years. Significant progress in the selfconsistent treatment of the RC-EMIC wave system has been achieved during those years. The paper by Khazanov et al. [2006] presents the latest version of our model, and in this Reply we refer mostly to this paper.

Three‐dimensional multifluid simulation of the plasma interaction at Titan

Using a three‐dimensional multifluid simulation, we demonstrate the importance of ion gyroradius and heavy ion effects when characterizing Titan's plasma interaction with the Kronian magnetosphere. Ion gyroradius and heavy ion effects drastically change the mass loading and magnetic field draping at Titan. We find that the large ion gyroradius of picked up ionospheric species results in an extension of the ionosphere and therefore the mass loading and magnetic pileup region on the anti‐Saturn side of Titan. Also, the additional thermal pressure provided by heavy ion cyclotron motion near Titan causes boundary layer currents to form at higher altitudes. The Saturn‐facing side of Titan's ionosphere experiences both magnetic shielding from the incident plasma at lower altitudes and additional heating due to the acceleration of heavy ions in the ionosphere. Finally, we find that well‐confined heavy ion beams form on the anti‐Saturn side of Titan's magnetosphere and extend more than three Titan radii from Titan's main ion tail. The location of this ion beam is dependent on the Kronian field orientation, and we find that during the TA, TB, and T3 encounters, the bulk of the ion beam was located below Titan's equatorial plane. We also find that for a single set of incident conditions, good agreement with Cassini magnetometer data from the TA, TB, and T3 encounters is obtained with the ion loss rate similar to that measured by Cassini during the TA encounter.

Spectroscopic determination of the singly ionized helium density in low electron temperature plasmas mixed with helium in a linear divertor plasma simulator

The spectroscopic method is developed to obtain the He+ ion density nHe+ in low electron temperature, Te=5–20eV, plasmas mixed with He. Plasmas were produced in the PISCES-B linear divertor plasma simulator [R. P. Doerner et al., Phys. Scr. T111, 75 (2004)] where the electron densities are ne=(1−15)×1018m−3 and the ionization degree is ∼1–10%. In the method, the He I line intensity IHeI at λ=447.1nm is used, instead of the He II line intensity in the conventional method. The radial confinement time of He+ ions is requisite, and is measured to be at a level of the Bohm confinement time. The He+ ion concentration, nHe+∕ne, is found to be proportional to IHeI, and to weakly depend on ne and Te. Because of the higher ionization energy of He than other species (D2, Ne, and Ar), the measured nHe+∕ne becomes systematically lower than the He gas pressure fraction, and agrees with data from an omegatron mass spectrometer. The omegatron measurement and estimates of the He+ ion loss rates indicate that the influences of vibrationally excited deuterium molecules on the particle balance of He+ ions are small at Te⩾10eV.

Ion accumulation in an electron plasma confined on magnetic surfaces

Accumulation of ions can alter and may destabilize the equilibrium of an electron plasma confined on magnetic surfaces. An analysis of ion sources and ion content in the Columbia Non-neutral Torus (CNT) [T.S. Pedersen, J.P. Kremer, R.G. Lefrancois, Q. Marksteiner, N. Pomphrey, W. Reiersen, F. Dahlgreen, and X. Sarasola, Fusion Sci. Technol. 50, 372 (2006)] is presented. In CNT ions are created preferentially at locations of high electron temperature, near the outer magnetic surfaces. A volumetric integral of neνiz gives an ion creation rate of 2.8×1011ions∕s. This rate of accumulation would cause neutralization of a plasma with 1011 electrons in about half a second. This is not observed experimentally, however, because currently in CNT ions are lost through recombination on insulated rods. From a steady-state balance between the calculated ion creation and loss rates, the equilibrium ion density in a 2×10−8Torr neutral pressure, 7.5×1011m−3 electron density plasma in CNT is calculated to be ni=6.2×109m−3, or 0.8%. The ion density is experimentally measured through the measurement of the ion saturation current on a large area probe to be about 6.0×109m−3 for these plasmas, which is in good agreement with the predicted value.

Divertor Physics Research on Alcator C-Mod

Many important contributions to the understanding of divertor physics are presented in this review of Alcator C-Mod research. The three regimes of parallel transport, sheath limited, conduction limited, and detached, were identified experimentally, along with their effects on plasma pressure along the magnetic field in the scrape-off layer. The extensive probe and bolometric coverage of the divertor allowed detailed characterization of the physics of detachment. The ability to dissipate ITER-like parallel power densities with extremely high divertor radiation emissivities (>40 MW/m3) was demonstrated under high-recycling and detached divertor conditions. The vertical plate divertor concept, developed and applied first on C-Mod, allowed the effect of divertor geometry to be studied, with the result that the vertical-plate and deep-slot geometries have a lower detachment threshold than the standard, flat-plate divertor. High-density (ne > 1 × 1021 m-3) divertor conditions allowed recombination to be more clearly observed in C-Mod than elsewhere. That, together with the development of spectroscopic techniques, enabled the only quantitative measurements of ion loss rate via recombination (and its role in detachment) as well as the trapping of hydrogenic Lyman alpha radiation. These were both shown to have important roles in detachment physics.

Design, microfabrication, and analysis of micrometer-sized cylindrical ion trap arrays

A description of the design and microfabrication of arrays of micrometer-scale cylindrical ion traps is offered. Electrical characterization and initial ion trapping experiments with a massively parallel array of 5 microm internal radius (r(0)) sized cylindrical ion traps (CITs) are also described. The ion trap, materials, and design are presented and shown to be critical in achieving minimal trapping potential while maintaining minimal power consumption. The ion traps, fabricated with metal electrodes, have inner radii of 1, 2, 5, and 10 microm and range from 5 to 24 microm in height. The electrical characteristics of packaged ion trap arrays were measured with a vector network analyzer. The testing focused on trapping toluene (C(7)H(8)), mass 91, 92, or 93 amu, in the 5 microm sized CITs. Ions were formed via electron impact ionization and were ejected by turning off the rf voltage applied to the ring electrode; a current signal was collected at this time. Optimum ionization and trapping conditions, such as a sufficient pseudopotential well and high ionization to ion loss rate ratio (as determined by simulation), proved to be difficult to establish due to the high device capacitance and the presence of exposed dielectric material in the trapping region. However, evidence was obtained suggesting the trapping of ions in 1%-15% of the traps in the array. These first tests on micrometer-scale CITs indicated the necessary materials and device design modifications for realizing ultrasmall and low power ion traps.

Mass loss of “Hot Jupiters”—Implications for CoRoT discoveries. Part I: The importance of magnetospheric protection of a planet against ion loss caused by coronal mass ejections

Atmospheric erosion due to CME-caused ion pick-up is investigated here for the first time for short periodic gas giants (so-called “Hot Jupiters”) orbiting close to a star. To study the effect of encountering CMEs produced on the magnetospheres and atmospheres of “Hot Jupiters” we model possible interaction of dense CME plasma with the exoplanet HD209458b ( r pl = 1.43 r Jup , M pl = 0.69 M Jup ), which orbits a 4.0–5.0 Gyr old Sun-like star at a distance of about 0.045 AU. A numerical hydrodynamic model is applied for calculation of the upper atmospheric density and the hydrogen wind of HD209458b as a function of planetocentric distance. Taking into account the similarity of HD209458b's host star to our Sun we use for the study of the ion production and loss rate of H + ions the solar CME plasma parameters and apply a numerical test particle model. Tidal-locking of short periodic exoplanets closely located to their host stars should result in weaker intrinsic planetary magnetic moments, as compared to those of the fast rotating Jupiter type planets at much larger orbits. It is shown that in this case the encountering CME plasma can compress the magnetospheric stand-off distance of short periodic “Hot Jupiters” down to the heights at which the ionization and pick-up of the planetary neutral atmosphere by the CME plasma flow take place. Assuming for the host star of HD209458b the same CME occurrence rate as on the Sun, we estimate possible total mass loss rates of HD209458b due to its collisions with CMEs over the planet lifetime. It has been found that under different estimations of the value of a planetary magnetic moment, HD209458b could have lost over its lifetime the mass from 0.2 up to several times of its present mass M pl .