bluuebunny/crossref_metadata_2025 huggingface dataset:
Decisive role of nonlinear temperature advection in El Niño and La Niña amplitude asymmetry
Authors: Duan Wansuo , Xu Hui , Mu Mu
Published: January 2008

The asymmetry of El Niño and La Niña in amplitude is a distinct feature of the observed El Niño–Southern Oscillation (ENSO). In this paper, we investigate the theoretical ENSO asymmetry by applying conditional nonlinear optimal perturbation in a theoretical model and an intermediate ENSO model. It is shown that the nonlinear temperature advection (NTA) plays an important role in ENSO asymmetry. By investigating the different types of nonlinearities in the Zebiak‐Cane model, we identify clearly the origin of ENSO asymmetry and further emphasize the decisive role of the NTA. The NTA enhances the El Niño amplitude but has little effect on La Niña, resulting in the asymmetry of ENSO in amplitude. We also demonstrate that the stronger the El Niño event is, the larger the nonlinear effect related to the NTA is and the more significant the ENSO asymmetry is. This finding may explain why the strong ENSO events after the 1976 climate shift are of significant asymmetry.
Application of pulsed‐excitation fluorescence imager for daylight detection of sparse life in tests in the Atacama Desert
Authors: Weinstein S. , Pane D. , Ernst L. A. , Warren‐Rhodes K. , Dohm J. M. , Hock A. N. , Piatek J. L. , Emani S. , Lanni F. , Wagner M. , Fisher G. W. , Minkley E. , Dansey L. E. , Smith T. , Grin E. A. , Stubbs K. , Thomas G. , Cockell C. S. , Marinangeli L. , Ori G. G. , Heys S. , Teza J. P. , Moersch J. E. , Coppin P. , Diaz G. Chong , Wettergreen D. S. , Cabrol N. A. , Waggoner A. S.
Published: January 2008

A daylight fluorescence imager was deployed on an autonomous rover, Zoë, to detect life on the surface and shallow subsurface in regions of the Atacama Desert in Chile during field tests between 2003 and 2005. In situ fluorescent measurements were acquired from naturally fluorescing biomolecules such as chlorophyll and from specific fluorescent probes sprayed on the samples, targeting each of the four biological macromolecule classes: DNA, protein, lipid, and carbohydrate. RGB context images were also acquired. Preparatory reagents were applied to enhance the dye probe penetration and fluorescence intensity of chlorophyll. Fluorescence imager data sets from 257 samples were returned to the Life in the Atacama science team. A variety of visible life forms, such as lichens, were detected, and several of the dye probes produced signals from nonphotosynthetic microorganisms.
Fractional snow cover in the Colorado and Rio Grande basins, 1995–2002
Authors: Bales R. C. , Dressler K. A. , Imam B. , Fassnacht S. R. , Lampkin D.
Published: January 2008

A cloud‐masked fractional snow‐covered area (SCA) product gridded at 1 km was developed from the advanced very high resolution radiometer for the Colorado River and upper Rio Grande basins for 1995–2002. Cloud cover limited SCA retrievals on any given 1‐km2 pixel to on average once per week. There were sufficient cloud‐free scenes to map SCA over at least part of the basins up to 21 days per month, with 3 months having only two scenes sufficiently cloud free to process. In the upper Colorado and upper Grande, SCA peaked in February–March. Maxima were 1–2 months earlier in the lower Colorado. Averaged over a month, as much as 32% of the upper Colorado and 5.5% of the lower Colorado were snow covered. Snow cover persisted longest at higher elevations for both wet and dry years. Interannual variability in snow cover persistence reflected wet‐dry year differences. Compared with an operational (binary) SCA product produced by the National Operational Hydrologic Remote Sensing Center, the current products classify a lower fraction of pixels as having detectable snow and being cloud covered (5.5% for SCA and 6% for cloud), with greatest differences in January and June in complex, forested terrain. This satellite‐derived subpixel determination of snow cover provides the potential for enhanced hydrologic forecast abilities in areas of complex, snow‐dominated terrain. As an example, we merged the SCA product with interpolated ground‐based snow water equivalent (SWE) to develop a SWE time series. This interpolated, masked SWE peaked in April, after SCA peaked and after some of the lower‐elevation snow cover had melted.
Quantitative tectonic reconstructions of Zealandia based on crustal thickness estimates
Authors: Grobys Jan W. G. , Gohl Karsten , Eagles Graeme
Published: January 2008

Zealandia is a key piece in the plate reconstruction of Gondwana. The positions of its submarine plateaus are major constraints on the best fit and breakup involving New Zealand, Australia, Antarctica, and associated microplates. As the submarine plateaus surrounding New Zealand consist of extended and highly extended continental crust, classic plate tectonic reconstructions assuming rigid plates and narrow plate boundaries fail to reconstruct these areas correctly. However, if the early breakup history shall be reconstructed, it is crucial to consider crustal stretching in a plate‐tectonic reconstruction. We present a reconstruction of the basins around New Zealand (Great South Basin, Bounty Trough, and New Caledonia Basin) based on crustal balancing, an approach that takes into account the rifting and thinning processes affecting continental crust. In a first step, we computed a crustal thickness map of Zealandia using seismic, seismological, and gravity data. The crustal thickness map shows the submarine plateaus to have a uniform crustal thickness of 20–24 km and the basins to have a thickness of 12–16 km. We assumed that a reconstruction of Zealandia should close the basins and lead to a most uniform crustal thickness. We used the standard deviation of the reconstructed crustal thickness as a measure of uniformity. The reconstruction of the Campbell Plateau area shows that the amount of extension in the Bounty Trough and the Great South Basin is far smaller than previously thought. Our results indicate that the extension of the Bounty Trough and Great South Basin occurred simultaneously.
Generation of hyper climate modes
Authors: Dommenget D. , Latif M.
Published: January 2008

It is shown that some important aspects of the space‐time structure of multidecadal sea surface temperature (SST) variability can be explained by local air‐sea interactions. A concept for “Global Hyper Climate Modes” is formulated: surface heat flux variability associated with regional atmospheric variability patterns is integrated by the large heat capacity of the extra‐tropical oceans, leading to a continuous increase of SST variance towards longer timescales. Atmospheric teleconnections spread the extra‐tropical signal to the tropical regions. Once SST anomalies have developed in the Tropics, global atmospheric teleconnections spread the signal around the world creating a global hyper climate mode. A simple model suggests that hyper climate modes can vary on timescales longer than 1,000 years. Ocean dynamics may amplify theses modes and influence the regional expression of the variability, but are not at the heart of the mechanism which produces the hyper modes.
Significant alteration in the hygroscopic properties of urban aerosol particles by the secondary formation of organics
Authors: Mochida Michihiro , Miyakawa Takuma , Takegawa Nobuyuki , Morino Yu , Kawamura Kimitaka , Kondo Yutaka
Published: January 2008

The temporal variation in the hygroscopicity of urban aerosol particles was investigated in Tokyo based on the hygroscopic growth factor (g) measurement in the summer of 2004. For 100 nm particles, sporadic appearance of intermediately hygroscopic (1.11 ≤ g < 1.29) particles was observed when the oxygenated organic mass increased (r = 0.76), suggesting that the formation of secondary organics governs the hygroscopicity of these particles. During a photochemically active period in the daytime, the mode hygroscopicity of 100 nm particles above g = 1.11 rapidly decreased in a few hours. This is explained by the condensation of secondary organics on pre‐existing particles that are highly hygroscopic (g ≥ 1.29) and are transported from outside the Tokyo metropolitan area. The observed rapid change in particle hygroscopicity suggests that the condensation of secondary organics increase the dry particle diameter at rates of 8–17 nm h−1.
Using PFISR measurements and gravity wave dissipative theory to determine the neutral, background thermospheric winds
Authors: Vadas Sharon L. , Nicolls Michael J.
Published: January 2008

Understanding the propagation and dissipation of an atmospheric gravity wave (GW) in the thermosphere requires an accurate dissipative GW dispersion relation, the GW's horizontal wavelength and period, and the background neutral winds and temperatures. Conversely, if the GW's horizontal wavelength, period, and vertically‐varying vertical wavelengths are known instead along with the background temperatures, then the background, horizontal neutral winds along the GW propagation direction can be calculated using GW dissipative theory. Recent daytime observations using the Advanced Modular Incoherent Scatter Radar (AMISR) located in Poker Flat, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), have obtained these latter parameters. Using PFISR data for a GW on December 13, 2006, we calculate the average, background, horizontal neutral winds at z ∼ 160–240 km.
Observed characteristics of upward leaders that are initiated from a windmill and its lightning protection tower
Authors: Wang D. , Takagi N. , Watanabe T. , Sakurano H. , Hashimoto M.
Published: January 2008

We have analyzed the electric field changes of 14 upward leaders that were initiated from a windmill and its lightning protection tower. We found that these upward leaders can be sub‐classified into two types according to whether they are triggered by nearby lightning discharge activity or they are initiated without any nearby preceding discharge activities. We have also obtained evidence of upward aborted leaders that are initiated from high‐grounded objects in response to nearby lightning. All these results suggest that once the electric field which surrounds the high‐grounded object is large enough, an upward leader can be initiated no matter whether the electric field is built up slowly or created rapidly by a nearby lightning discharge, although the later appears to be more efficient in triggering the leader. In addition, we found that without the assistance of a rising electric field produced by a nearby lightning discharge, compared to a stationary windmill and a tower with a similar height, a rotating windmill tends to have a bigger chance of initiating an upward leader.
Evidence for collisionless magnetic reconnection at Mars
Authors: Eastwood J. P. , Brain D. A. , Halekas J. S. , Drake J. F. , Phan T. D. , Øieroset M. , Mitchell D. L. , Lin R. P. , Acuña M.
Published: January 2008

Using data from Mars Global Surveyor (MGS) in combination with Particle‐In‐Cell (PIC) simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion – the Hall magnetic field – that uniquely indicate the reconnection process. These are the first such in‐situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars' recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.
Cascade of whistler turbulence: Particle‐in‐cell simulations
Authors: Gary S. Peter , Saito Shinji , Li Hui
Published: January 2008

A two‐dimensional electromagnetic particle‐in‐cell simulation in a magnetized, homogeneous, collisionless plasma of electrons and protons has been carried out, demonstrating a forward cascade of whistler turbulence. Enhanced magnetic fluctuation spectra are initially imposed with −0.2 < k∥c/ωe < 0.2 and −0.2 < k⊥c/ωe < 0.2 where the directional subscripts denote directions relative to the background magnetic field Bo and c/ωe is the electron inertial length. The late‐time evolution of the simulation shows a cascade of magnetic fluctuation energy to shorter wavelengths; furthermore, the spectrum is anisotropic with more fluctuation energy at a given wavenumber perpendicular to Bo than at the same wavenumber parallel to the background field. The late‐time electron velocity distribution shows a magnetic‐field aligned signature due to the Landau resonance of the obliquely propagating whistlers.
Double‐diffusive layers in the Adriatic Sea
Authors: Carniel Sandro , Sclavo Mauro , Kantha Lakshmi , Prandke Hartmut
Published: January 2008

A microstructure profiler was deployed to make turbulence measurements in the upper layers of the southern Adriatic Sea in the Mediterranean during the Naval Research Laboratory (NRL) DART06A (Dynamics of the Adriatic in Real Time) winter cruise in March 2006. Measurements in the Po river plume along the Italian coast near the Gargano promontory displayed classic double‐diffusive layers and staircase structures resulting from the relatively colder and fresher wintertime Po river outflow water masses overlying warmer and more saline water masses from the Adriatic Sea. We report here on the water mass and turbulence structure measurements made both in the double‐diffusive interfaces and the adjoining mixed layers in the water columns undergoing double‐diffusive convection (DDC). This dataset augments the relatively sparse observations available hitherto on the diffusive layer type of DDC. Measured turbulence diffusivities are consistent with those from earlier theoretical and experimental formulations, suggesting that the wintertime Po river plume is a convenient and easily accessible place to study double diffusive convective processes of importance to mixing in the interior of many regions of the global oceans.
Upwelling off the west coast of Hainan Island in summer: Its detection and mechanisms
Authors: Lü Xingang , Qiao Fangli , Wang Guansuo , Xia Changshui , Yuan Yeli
Published: January 2008

The summertime upwelling off the west coast of Hainan Island is newly detected by satellite remote sensing sea surface temperature, and confirmed by both historical field observations and numerical modeling. Furthermore, numerical experiments are conducted to gain understanding of the upwelling mechanisms. A tidal mixing front (TMF) is identified as the vital factor triggering the formation of the upwelling. The baroclinic pressure gradient force, which stems from the intense density difference across the TMF, causes a frontal‐scale circulation at the TMF. As a result, upwelling appears as a branch of this circulation. The southwest monsoon induces downwelling, which competes with the front‐induced upwelling. Climatologically, the upwelling dominates and can reach about 5 m below the sea surface above the slope bottom. In calm weather with no or weak winds, it is expected that the upwelling can reach all the way to the sea surface.
Inverse solution for pentadal variability in the North Atlantic
Authors: Sidorenko D. , Danilov S. , Schröter J.
Published: January 2008

Seven pentads (1960–1964 to 1990–1994) of the North Atlantic climatology by Lozier et al. (1995) are analyzed with the help of an inverse finite‐element ocean circulation model. The model solves for temperature and salinity fields that are close to observations and respect stationary dynamical balances, and produces estimates of the circulation. The first two EOF's of transport streamfunction variability (39% and 26% of the explained variance) are found to have a high correlation with the North Atlantic Oscillation (NAO) index averaged over pentads and lagged negatively by three years (first EOF) and between zero and one years (second EOF). The spatial pattern of the first EOF corresponds to an anticyclonic anomaly (in the positive NAO phase) located between 20 and 45°N with the largest variability between 30 and 45°N, and much weaker cyclonic anomalies in the subpolar gyre. The second EOF shows a sharp anticyclonic anomaly along the Gulf Stream and its extension and a wide cyclonic cell over most of subtropical gyre. The anomaly in the meridional overturning streamfunction is characterized by a single positive cell which poorly correlates with the NAO index.
Geomagnetically induced currents during intense storms driven by coronal mass ejections and corotating interacting regions
Authors: Kataoka Ryuho , Pulkkinen Antti
Published: January 2008

Geomagnetically induced currents (GIC) flowing in ground‐based conductor systems during large geomagnetic storms are one of the most significant space weather phenomena that affect our ground‐based technological systems. Here we show that GIC activity in subauroral latitudes depends on the storm phase and on the interplanetary drivers, such as coronal mass ejections (CMEs) and corotating interacting regions (CIRs). For example, it is shown that GIC amplitudes are relatively small during CIR storms in comparison to CME storms. However, Pc3‐5 pulsation activity during CIR storms drives long‐lasting GIC in the local prenoon sector. Despite of the differences between CME and CIR storms, the relationship between GIC and the time derivative of the horizontal ground magnetic field is always the same. A novel power law equation is derived to accurately characterize the relation.
Flux enhancement of the outer radiation belt electrons after the arrival of stream interaction regions
Authors: Miyoshi Yoshizumi , Kataoka Ryuho
Published: January 2008

The Earth's outer radiation belt electrons increase when the magnetosphere is surrounded by the high‐speed solar wind stream, while the southward interplanetary magnetic field (IMF) is also known as an important factor for the flux enhancement. In order to distinguish the two different kinds of solar wind parameter dependence statistically, we investigate the response of the outer belt to stream interaction regions (SIRs). A total of 179 SIR events are identified for the time period from 1994 to 2005. We classify the SIR events into two groups according to the so‐called “spring‐toward fall‐away” rule: IMF sector polarity after the stream interface is toward in spring or away in fall (group A) and vice versa (group B). According to the Russell‐McPherron effect, groups A and B have a significant negative and positive offset of the IMF Bz after the stream interface, respectively. Comparing groups A and B by superposing about the stream interface, only IMF Bz dependence can be obtained because the other solar wind parameters change in the same manner. As a result, the greatest flux enhancement is found in the highest‐speed streams with a southward offset of the IMF Bz, indicating that only the solar wind speed by itself is not a sufficient condition for the large flux enhancement. It is also found that the large flux enhancement tends to be associated with weak geomagnetic activities with minimum Dst of about −50 nT on average, implying that the existence of intense magnetic storms is not essential for the flux enhancement.
Effects of the induction electric field on ionospheric current systems driven by field‐aligned currents of magnetospheric origin
Authors: Takeda Masahiko
Published: January 2008

The effects of induction electric field on ionospheric current systems driven by field‐aligned currents of magnetospheric origin were studied, and a new method for estimating the equivalent current function representing the system was developed. It was found that a current system with a period of less than 4 min is significantly affected by the induction field and tends to be symmetric with noon, probably because the field overcomes the electrostatic field that creates the asymmetry. This result is consistent with the observed result for the preliminary impulse of storm commencement in which the local time variation of its appearance is symmetric with noon.
Long‐term memory in 1000‐year simulated temperature records
Authors: Rybski Diego , Bunde Armin , von Storch Hans
Published: January 2008

We study the appearance of long‐term persistence in temperature records, obtained from the global coupled general circulation model ECHO‐G for two runs, using detrended fluctuation analysis. The first run is a historical simulation for the years 1000–1990 (with greenhouse gas, solar, and volcanic forcing), while the second run is a 1000‐year “control run” with constant external forcings. We consider daily data of all grid points as well as their biannual averages in order to suppress 2‐year oscillations appearing in the model records for some sites near the equator. Our results substantially confirm earlier studies of (considerably shorter) instrumental data and extend their results from decades to centuries. In the case of the historical simulation we find that most continental sites have correlation exponents γ between 0.8 and 0.6. For the ocean sites the long‐term correlations seem to vanish at the equator and become nonstationary at the Arctic and Antarctic circles. In the control run the long‐term correlations are less pronounced. Compared with the historical run, the correlation exponents are increased, and show a more pronounced latitude dependence, visible also at continental sites. When analyzing biannual averages, we find stronger long‐term correlations in the historical run at continental sites and a less pronounced latitude dependence. In all cases, the exponent γ does not depend on the continentality of the sites.
Experiments on the non‐Boussinesq flow of self‐igniting suspension currents on a steep open slope
Authors: Turnbull B. , McElwaine J. N.
Published: January 2008

Pyroclastic flows from volcanoes, dust storms in the desert, and submarine turbidity currents are all gravity currents of particles in suspension occurring in nature. Powder snow avalanches are one such flow where the density difference between the suspended particles and the interstitial air is high and the particles carry a significant proportion of the flow's momentum. This means that the Boussinesq approximation, where density differences are considered negligible in inertia terms, is not valid. Aspects of such flows, such as their internal structure and the transition from a dense flow to a suspension current are not well understood. Repeatable laboratory experiments are necessary for a better understanding of the underlying physics. Up to now, an experiment has not been designed with the correct similarity criteria for modeling powder snow avalanches. We have addressed this by designing and analyzing the results from a new experimental model of powder snow avalanches that had three distinctive features. Fine, dry snow was used to form suspension currents in air. The high density ratio of powder snow avalanches was preserved so that the currents are non‐Boussinesq. Our experiments started with a dense current that then self‐ignited, undergoing the transition to a suspension current. The shape and position of the current was tracked with two video cameras, and the air flow measured with a high‐frequency response pressure transducer mounted in the base. We show how the air pressure data closely match theory and reveal whether a current is primarily dense or suspended.
Multisensor historical climatology of satellite‐derived global land surface moisture
Authors: Owe Manfred , de Jeu Richard , Holmes Thomas
Published: January 2008

A historical climatology of continuous satellite‐derived global land surface soil moisture is being developed. The data consist of surface soil moisture retrievals derived from all available historical and active satellite microwave sensors, including Nimbus‐7 Scanning Multichannel Microwave Radiometer, Defense Meteorological Satellites Program Special Sensor Microwave Imager, Tropical Rainfall Measuring Mission Microwave Imager, and Aqua Advanced Microwave Scanning Radiometer for EOS, and span the period from November 1978 through the end of 2007. This new data set is a global product and is consistent in its retrieval approach for the entire period of data record. The moisture retrievals are made with a radiative transfer‐based land parameter retrieval model. The various sensors have different technical specifications, including primary wavelength, spatial resolution, and temporal frequency of coverage. These sensor specifications and their effect on the data retrievals are discussed. The model is described in detail, and the quality of the data with respect to the different sensors is discussed as well. Examples of the different sensor retrievals illustrating global patterns are presented. Additional validation studies were performed with large‐scale observational soil moisture data sets and are also presented. The data will be made available for use by the general science community.
Interannual variability of surface energy exchange depends on stand age in a boreal forest fire chronosequence
Authors: Liu Heping , Randerson James T.
Published: January 2008

Understanding how changes in the boreal fire regime will affect high latitude climate requires knowledge of the sensitivity of the surface energy budget to shifts in vegetation cover. We measured components of the surface energy budget in three ecosystems that were part of a fire chronosequence in interior Alaska for 3 years. Our sites were within the perimeter of stand‐replacing fires that occurred in 1999, 1987, and ∼1920 (hereafter referred to as the 1999‐burn, the 1987‐burn, and the control). Vegetation cover consisted primarily of sparse short grasses at the 1999‐burn, aspen and willow (deciduous trees and shrubs) at the 1987‐burn, and black spruce (evergreen conifer trees) at the control. Averaged over the 3 years of our study, annual net radiation decreased by approximately 25% at the 1999‐burn and 30% at the 1987‐burn, relative to the control. Sensible heat decreased by an even larger amount, by approximately 57% for the 1999‐burn and 44% for the 1987‐burn as compared with the control. Climate during spring and summer varied considerably among the 3 years. The three stands responded differently to this climate variability with consequences for surface energy exchange. As a result of earlier snow cover loss in 2003 and 2004, net radiation during spring increased substantially in the recently disturbed stands, but not in the control. In response to a sustained summer drought in 2004, latent heat decreased more in the 1987‐burn during August than in the control. Our results imply that a shift in plant functional types expected to accompany increases in boreal fire activity may amplify interannual climate variability during both spring and summer.
Meridional reorganizations of marine and terrestrial productivity during Heinrich events
Authors: Menviel L. , Timmermann A. , Mouchet A. , Timm O.
Published: January 2008

To study the response of the global carbon cycle to a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a series of freshwater perturbation experiments is conducted both under preindustrial and glacial conditions using the earth system model of intermediate complexity LOVECLIM. A shutdown of the AMOC leads to substantial cooling of the North Atlantic, a weak warming of the Southern Hemisphere, intensification of the northeasterly trade winds, and a southward shift of the Intertropical Convergence Zone (ITCZ). Trade wind anomalies change upwelling in the tropical oceans and hence marine productivity. Furthermore, hydrological changes associated with a southward displacement of the ITCZ lead to a reduction of terrestrial carbon stocks mainly in northern Africa and northern South America in agreement with paleoproxy data. In the freshwater perturbation experiments the ocean acts as a sink of CO2, primarily through increased solubility. The net atmospheric CO2 anomaly induced by a shutdown of the AMOC amounts to about +15 ppmv and −10 ppmv for preindustrial and glacial conditions, respectively. This background state dependence can be explained by the fact that the glacial climate is drier and the terrestrial vegetation therefore releases a smaller amount of carbon to the atmosphere. This study demonstrates that the net CO2 response to large‐scale ocean circulation changes has significant contributions both from the terrestrial and marine carbon cycle.
Temporal moments for transport with mass transfer described by an arbitrary memory function in heterogeneous media
Authors: Luo Jian , Cirpka Olaf A. , Dentz Marco , Carrera Jesus
Published: January 2008

Temporal moment equations are generalized for transport under linear mass transfer, which has been used to model a broad range of small‐scale processes: kinetic sorption, diffusion into immobile regions, and transport through heterogeneous aquifers. Solving the moment equations, which are formally identical to steady state transport equations, is computationally more efficient than evaluating the temporal moments by integrating the transient flux concentrations. We derive recursive relations for the moments of the flux concentration, which involve the moments of the memory function but do not dependent on its shape. It turns out that two mass transfer models have the same kth temporal moment if the moments of order lower than k are equal. Particularly, the mean retention time, i.e., the first moment of the retention probability density function (pdf) in the immobile domain, decides the second temporal moment of concentration. A mass transfer model with two first‐order rate coefficients can match up to the fourth temporal moment described by a multirate model with a predescribed pdf of the mass transfer rate coefficient. The kth temporal moment is finite when the (k‐1)th moment of the memory function exists.
Time-of-flight analyzer system to detect reflected particles from a solid surface following low-energy particle injection
Authors: Yamaoka H. , Tanaka N. , Tsumori K. , Nishiura M. , Kenmotsu T. , Hirouchi T. , Kisaki M. , Shinto K. , Sasao M. , Matsumoto Y. , Wada M.
Published: January 2008

We have developed a time-of-flight analyzer to measure energy distributions of reflected particles from solid surfaces bombarded by low-energy (1–2keV) ions. The analyzer yields energy distributions of neutrals which can be compared with the energy distributions of charged particles measured by a magnetic deflection-type momentum analyzer. We have tested the system to measure the angular dependence of energy and intensity for neutrals reflected from a polycrystalline W target. The energies of the reflected neutrals are much smaller than the incident ion energies, suggesting multiple scattering in the target. No angular dependence is observed under the condition that the sum of the incident and reflected angles is constant. The intensity of the reflected neutrals takes the maximum around the mirror angle. We compare these characteristics of neutral particle reflections with those of reflected ions.
An ion thruster internal discharge chamber electrostatic probe diagnostic technique using a high-speed probe positioning system
Authors: Herman Daniel A. , Gallimore Alec D.
Published: January 2008

Extensive resources have been allocated to diagnose and minimize lifetime-limiting factors in gridded ion thrusters. While most of this effort has focused on grid erosion, results from wear tests indicate that discharge cathode erosion may also play an important role in limiting the lifetime of ring-cusp ion thrusters proposed for future large flagship missions. The detailed characterization of the near-cathode discharge plasma is essential for mitigating discharge cathode erosion. However, severe difficulty is encountered when attempting to measure internal discharge plasma parameters during thruster operation with conventional probing techniques. These difficulties stem from the high-voltage, high-density discharge cathode plume, which is a hostile environment for probes. A method for interrogating the discharge chamber plasma of a working ion thruster over a two-dimensional grid is demonstrated. The high-speed axial reciprocating probe positioning system is used to minimize thruster perturbation during probe insertion and to reduce heating of the probe. Electrostatic probe measurements from a symmetric double Langmuir probe are presented over a two-dimensional spatial array in the near-discharge cathode assembly region of a 30-cm-diameter ring-cusp ion thruster. Electron temperatures, 2–5eV, and number density contours, with a maximum of 8×1012cm−3 on centerline, are measured. These data provide detailed electron temperature and number density contours which, when combined with plasma potential measurements, may shed light on discharge cathode erosion processes and the effect of thruster operating conditions on erosion rates.
Hyperthermal neutral beam sources for material processing (invited)
Authors: Yoo S. J. , Kim D. C. , Joung M. , Kim J. S. , Lee B. J. , Oh K. S. , Kim K. U. , Kim Y. H. , Kim Y. W. , Choi S. W. , Son H. J. , Park Y. C. , Jang J.-N. , Hong M. P.
Published: January 2008

Hyperthermal neutral beams have a great potential for material processes, especially for etching and thin film deposition for semiconductor and display fabrication as well as deposition for various thin film applications. Plasma-induced damage during plasma etching is a serious problem for manufacturing deep submicron semiconductor devices and is expected to be a problem for future nanoscale devices. Thermal and plasma-induced damage is also problematic for thin film depositions such as transparent conductive oxide films on organic light emitting diodes or flexible displays due to high temperature processes in plasma environments. These problems can be overcome by damage-free and low-temperature processes with hyperthermal neutral beams. We will present the status of the hyperthermal neutral beam development and the applications, especially, in semiconductor and display fabrication and introduce potential applications of thin film growing for optoelectronic devices such as light emitting diodes.
A radio frequency driven H− source for Linac4
Authors: Küchler D. , Meinschad Th. , Peters J. , Scrivens R.
Published: January 2008

Future requirements on higher beam intensity and brightness will need an upgrade of the present CERN accelerator chain. Linac4 will be an essential part of the upgrade of the proton accelerator facility. The source for this H− linac will be based on a copy of the DESY rf driven H− source. New possible radio frequency quadrupole alternatives (with different injection energies) and a pressing linac schedule made it necessary to develop a flexible two-source design.
Helicon plasma generator-assisted surface conversion ion source for the production of H− ion beams at the Los Alamos Neutron Science Center
Authors: Tarvainen O. , Rouleau G. , Keller R. , Geros E. , Stelzer J. , Ferris J.
Published: January 2008

The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H− ion beams in a filament-driven discharge. In this kind of an ion source the extracted H− beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H− converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H− ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H− ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H− production (main discharge) in order to further improve the brightness of extracted H− ion beams.
Status of the electron cyclotron resonance charge breeder for the Cf252 fission source project at ATLAS
Authors: Vondrasek R. C. , Scott R. , Carr J. , Pardo R. C.
Published: January 2008

The construction of the Californium Rare Ion Breeder Upgrade, a new radioactive beam facility for the Argonne tandem linac accelerator system (ATLAS), is in progress. The facility will use fission fragments from a 1 Ci Cf252 source, thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams, the existing ATLAS ECR1 ion source has been redesigned to function as a charge breeder source. The design features, initial results, and status of this charge breeder configuration are presented.
Effect of energy relaxation of H atoms at the wall on the production profile of H− ions in large negative ion sources
Authors: Takado N. , Matsushita D. , Fujino I. , Hatayama A. , Tobari H. , Inoue T.
Published: January 2008

Production and transport processes of the H0 atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code is applied to the large JAEA 10 ampere negative ion source under a Cs-seeded condition to obtain a spatial distribution of surface-produced H− ions. In this analysis, we focus on the effect of the energy relaxation of the H0 atoms at the wall on the H− ion production from the H0 atoms. The result indicates that, by considering the energy relaxation of the H0 atoms at the wall, the production profile of the surface-produced H− ion is well reflected in the production profile of the H0 atom production.
Long pulse beam extraction with a prototype ion source for the KSTAR neutral beam system
Authors: Oh Byung-Hoon , Chang Doo-Hee , Jeong Seung Ho , Lee Kwang-Won , In Sang-Ryul , Yoon Byung-Joo , Seo Min-Seok , Jin Jung-Tae , Kim Bum-Ryul , Chang Dae-Sik , Jung Ki-Sok , Kim Jinchoon , Kim Tae-Seong , Bae Young Soon
Published: January 2008

Long pulse operational characteristics of the high current ion source for the KSTAR neutral beam system are described. The beam pulse length of 300s was successfully operated at a beam power of 1.6MW with a beam energy of 70keV. Beam energy, beam current, beam divergence, arc power, and several other operational parameters were measured during a pulse to analyze the long pulse properties. The increase of the cooling water temperature of the accelerator grids and plasma generator components were measured by water flow calorimetric system using thermocouples. The temperature rises of the filament electrodes of the ion source and the G1 grids (plasma grids) of the accelerator turned out to be the critical factors of the long pulse operation in the current system.
Ion source for neutral beam injection meant for plasma and magnetic field diagnostics
Authors: Vainionpaa Jaakko Hannes , Leung Ka Ngo , Gough Richard A. , Kwan Joe W. , Levinton Fred
Published: January 2008

At the Lawrence Berkeley National Laboratory a diagnostic neutral beam injection system for measuring plasma parameters, flow velocity, and local magnetic field is being developed. The system is designed to have a 90% proton fraction and small divergence with beam current at 5–6A and a pulse length of ∼1s occurring once every 1–2min. The ion source needs to generate uniform plasma over a large (8×5cm2) extraction area. For this application, we have compared rf driven multicusp ion sources operating with either an external or an internal antenna in similar ion source geometry. The ion beam will be made of an array of six sheet-shaped beamlets. The design is optimized using computer simulation programs.
Experimental comparison of time-of-flight mass analysis with magnetic mass analysis
Authors: Gushenets V. I. , Bugaev A. S. , Oks E. M. , Kulevoy T. V. , Hershcovitch A. , Brown I. G.
Published: January 2008

A series of experiments was carried out in which both a magnetic analyzer (mass separator) and a time-of-flight (TOF) spectrometer were used for ion charge/mass spectral analysis of the ion beam formed by a dc Bernas ion source made for semiconductor implantation. The TOF analyzer was a detachable device that provides rapid analysis of charge-to-mass composition of moderate energy ion beams. The magnetic analyzer was a massive device using a 90°-sector bending magnet with radius of the central orbit of 35cm. Comparison of these two methods for measuring ion beam composition shows good agreement.
Microcalorimeters May Provide a Solution to the Big Problem of Small Contaminants
Authors: Ladbury Ray
Published: January 2008

As microelectronic devices continue to shrink, submicrometer-sized contaminants pose a serious threat to semiconductor yields and performance—and thereby to the profits of the nearly $200 billion a year industry. Chemical analysis of these tiny particles can suggest remedies for avoiding contamination by helping to pinpoint its sources. One of the most successful microchemical analysis tools combines electron microscopy with spectroscopic analysis of x rays excited in the target impurity by the microscope's electron beam. Unfortunately, the choice of x-ray detector has traditionally involved a trade-off between energy resolution and speed. So the semiconductor industry—where time equals a lot of money—has often had to supplement spectrometry with educated guesswork. Now, John Martinis, Kent Irwin, Gene Hilton and David Wollman, working at the National Institute of Standards and Technology facility in Boulder, Colorado, have developed an x-ray detector that they hope will remove some of that guesswork.
Theoretical characterization of titanyl phthalocyanine as a p-type organic semiconductor: Short intermolecular π-π interactions yield large electronic couplings and hole transport bandwidths
Authors: Norton Joseph E. , Brédas Jean-Luc
Published: January 2008

The charge-transport properties of the triclinic phase II crystal of titanyl phthalocyanine (α-TiOPc) are explored within both a hopping and bandlike regime. Electronic coupling elements in convex- and concave-type dimers are calculated using density functional theory, and the relationship between molecular structure and crystal packing structure in model dimer configurations is considered. Hole transport bandwidths derived from crystal structure dimers are compared to those obtained from electronic band structure calculations; very good agreement between the two approaches is found. The calculations predict large hole bandwidths, on the order of 0.4eV, and correspondingly very low hole reorganization energies.
LEP is Now Making Pairs of W Bosons
Authors: Schwarzschild Bertram
Published: January 2008

Shortly after noon on 9 July, an important new experimental regime of high-energy physics was inaugurated with the first observation of a W+W− pair at CERN's Large Electron-Positron (LEP) collider. The charged W's and their neutral cousin, the Z0, are the three spin-1 bosons that mediate the weak interactions. Because they are almost 100 times heavier than the proton, these “intermediate vector bosons” present a particular challenge to accelerator builders and experimenters. Though their existence and their masses were predicted by the Glashow-Salam-Wemberg unification of the electromagnetic and weak forces in the late 1960s, they could not be observed until the 540-GeV CERN proton-antiproton collider was completed in the early 1980s. (See PHYSICS TODAY, November 1983, page 17).
Characterization of cyclic and linear C3H− and C3H via anion photoelectron spectroscopy
Authors: Sheehan Sean M. , Parsons Bradley F. , Zhou Jia , Garand Etienne , Yen Terry A. , Moore David T. , Neumark Daniel M.
Published: January 2008

Anion photoelectron spectroscopy of C3H− and C3D− is performed using both field-free time-of-flight and slow electron velocity-map imaging. We observe and assign transitions originating from linear/bent (l-C3H) and cyclic (c-C3H) anionic isomers to the corresponding neutral ground states and low-lying excited states. Transitions within the cyclic and linear manifolds are distinguished by their photoelectron angular distributions and their intensity dependence on the neutral precursor. Using calculated values for the energetics of the neutral isomers [Ochsenfeld et al., J. Chem. Phys. 106, 4141 (1997)], which predict c-C3H to lie 74meV lower than l-C3H, the experimental results establish c-C3H− as the anionic ground state and place it 229meV below l-C3H−. Electron affinities of 1.999±0.003 and 1.997±0.005eV are determined for C3H and C3D from the X̃B22←X̃A11 photodetachment transition of c-C3H. Term energies for several low-lying states of c-C3H and l-C3H are also determined. Franck-Condon simulations are used to make vibrational assignments for the bands involving c-C3H. Simulations of the l-C3H bands were more complicated owing to large amplitude bending motion and, in the case of the neutral ÃΠ2 state, strong Renner-Teller coupling.
Preliminary results of the ion extraction simulations applied to the MONO1000 and SUPERSHyPIE electron cyclotron resonance ion sources
Authors: Pierret C. , Maunoury L. , Biri S. , Pacquet J. Y. , Tuske O. , Delferriere O.
Published: January 2008

The goal of this article is to present simulations on the extraction from an electron cyclotron resonance ion source (ECRIS). The aim of this work is to find out an extraction system, which allows one to reduce the emittances and to increase the current of the extracted ion beam at the focal point of the analyzing dipole. But first, we should locate the correct software which is able to reproduce the specific physics of an ion beam. To perform the simulations, the following softwares have been tested: SIMION 3D, AXCEL, CPO 3D, and especially, for the magnetic field calculation, MATHEMATICA coupled with the RADIA module. Emittance calculations have been done with two types of ECRIS: one with a hexapole and one without a hexapole, and the difference will be discussed.
Solvation effect on conformations of 1,2:dimethoxyethane: Charge-dependent nonlinear response in implicit solvent models
Authors: Jha Abhishek K. , Freed Karl F.
Published: January 2008

The physical content of and, in particular, the nonlinear contributions from the Langevin-Debye model are illustrated using two applications. First, we provide an improvement in the Langevin-Debye model currently used in some implicit solvent models for computer simulations of solvation free energies of small organic molecules, as well as of biomolecular folding and binding. The analysis is based on the implementation of a charge-dependent Langevin-Debye (qLD) model that is modified by subsequent corrections due to Onsager and Kirkwood. Second, the physical content of the model is elucidated by discussing the general treatment within the LD model of the self-energy of a charge submerged in a dielectric medium for three different limiting conditions and by considering the nonlinear response of the medium. The modified qLD model is used to refine an implicit solvent model (previously applied to protein dynamics). The predictions of the modified implicit solvent model are compared with those from explicit solvent molecular dynamics simulations for the equilibrium conformational populations of 1,2-dimethoxyethane (DME), which is the shortest ether molecule to reproduce the local conformational properties of polyethylene oxide, a polymer with tremendous technological importance and a wide variety of applications. Because the conformational population preferences of DME change dramatically upon solvation, DME is a good test case to validate our modified qLD model. The present analysis of the modified qLD model provides the motivation and tools for studying a wide variety of other interesting systems with heterogeneous dielectric properties and spatial anisotropy.