Ion Debris Research Articles

Asymmetry of hemispheric climate during MIS 16 versus MIS 12

Marine isotope stage (MIS) 16 (676-621 ka) and MIS 12 (478-424 ka) stand out as two significant glacial periods during the late Quaternary, demonstrating consistent continental ice volume or sea level, as discerned from benthic δ18O records. Intriguingly, the average sea surface temperature (SST) during MIS 16 surpasses that of MIS 12 by approximately 0.54–0.79 °C, while the atmospheric CO2 concentration during MIS 16 is approximately 16 ppmv lower than that of MIS 12. The underlying mechanism driving these discrepancies remains enigmatic. In this study, we present new high-resolution X-ray fluorescence (XRF) and grain size records covering the interval from 700 to 400 ka from Ocean Drilling Program (ODP) Site 1090 in the South Atlantic Ocean. We also integrated benthic δ13C, ice-rafted debris (IRD) and carbonate ion concentration ([CO32−]) records globally, to elucidate the distinct climate evolution during the MIS 16 versus MIS 12. Our findings suggest that MIS 12 is distinguished by a more substantial Antarctic ice-sheet, coupled with a weakened and/or equatorward displacement of southern westerly winds, and expansion of southern source water (SSW) alongside contractive northern source water (NSW). Conversely, the opposite climate state can be observed in MIS 16. The elevated atmospheric CO2 in MIS 12 and diminished atmospheric CO2 in MIS 16 may be attributed to reconfigurations in the ocean carbon reservoir regulated by the reorganization of deep-water masses and meridional ocean circulation, as a result of the divergent evolution of bipolar ice-sheets. Our study underscores the critical role of the interplay between the two polar regions in modulating deep-sea carbon storage on the orbital timescale and atmospheric CO2. This interplay is essential for a comprehensive understanding of past and future carbon cycle adjustments in response to climate change.

Acceleration mechanisms of energetic ion debris in laser-driven tin plasma EUV sources

Laser-driven tin plasmas are driving new-generation nanolithography as sources of extreme ultraviolet (EUV) radiation centered at 13.5 nm. A major challenge facing industrial EUV source development is predicting energetic ion debris produced during the plasma expansion that may damage the sensitive EUV channeling multilayer optics. Gaining a detailed understanding of the plasma dynamics and ion acceleration mechanisms in these sources could provide critical insights for designing debris mitigation strategies in future high-power EUV sources. We develop a fully kinetic model of tin-EUV sources using one-dimensional particle-in-cell simulations to study ion debris acceleration, which will be valuable for cross-validation of radiation-hydrodynamic simulations. An inverse-bremsstrahlung heating operator is used to model the interaction of a tin target with an Nd:YAG laser, and thermal conduction is included through a Monte Carlo Coulomb collision operator. While the large-scale evolution is in reasonable agreement with analogous hydrodynamic simulations, the significant timescale for collisional equilibration between electrons and ions allows for the development of prominent two-temperature features. A collimated flow of energetic ions is produced with a spectrum that is significantly enhanced at high energies compared to fluid simulations. The dominant acceleration mechanism is found to be a large-scale electric field supported mainly by the electron pressure gradient, which is enhanced in the kinetic simulations due to the increased electron temperature. We discuss the implications of these results for future modeling of tin-EUV sources and the development of debris mitigation schemes.

Effect of angular mismatch on tribocorrosion at taper-trunnion junction using a finite element model considering mechanical and chemical wear

Wear debris and metal ions arising from tribocorrosion at the taper-trunnion junction have been associated with early complications after total hip replacement. Wear and electrochemical phenomena occur simultaneously in this tribo-system, however, chemical wear has been usually neglected in previous computational studies on the interface damage. In this study, we developed a finite element model incorporating both the mechanical and chemical wear processes, and then investigated the effect of taper mismatch on the tribocorrosion at a CoCr/Ti6Al4V taper interface. This model was initially verified through a ball-on-disk wear testing and then applied to the study of degradation mechanism at the taper-trunnion junction. It was found that material loss at the taper-trunnion junction was linearly related to the number of gait cycles and chemical wear was evident, contributing up to 26 % to total material loss. A taper mismatch as small as possible was not necessarily beneficial to minimize the material loss. Instead, a larger positive taper mismatch helped reduce total wear volume but maximized the contribution of chemical wear. The model with a negative taper mismatch performed better than the ones with a positive taper mismatch in terms of corrosion resistance. These findings would benefit preoperative planning and the design of implant with reduced risk of tribocorrosion and failure.

Experimental study of dynamics and soft X-ray emission of laser produced plasma from low-density foam Ti targets

Low-density foam targets are expected to be good candidates for efficient laser produced plasma (LPP) and soft X-ray (SXR) sources due to the less energetic debris compared with solid targets. Three Ti targets with different densities were irradiated by a pulsed Nd:YAG laser in vacuum. The average ion energy and the time-of-flight (TOF) peak voltage decreased as the Ti target density decreased. Furthermore, the differences among the three Ti targets increased with increasing laser intensity. The average ion energy of low-density foam Ti targets had a slightly weaker angular dependence compared with solid Ti targets. The plasma plume optical images illustrated that solid Ti plasma expanded faster in the direction of laser incidence with stronger anisotropy compared to foam Ti plasma. In addition, the optical radiation intensity integrated from a wavelength region of 200–850 nm of plasma plume increased with decreasing initial target density, which indicated that more absorbed laser energy was converted to plasma optical radiation energy (internal energy) instead of ion kinetic energy for targets with lower initial densities. The SXR radiation had no significant difference among the three Ti targets. These results demonstrate that appropriately reducing the initial target density can significantly reduce kinetic energy of ion debris without affecting the SXR radiation output.

High repetition rate mapping of the interaction between a laser plasma and magnetized background plasma via laser induced fluorescence

The laminar coupling of energy between a laser-produced plasma and a background magnetized plasma was investigated via planar laser induced fluorescence diagnostic and magnetic flux probes. Experiments performed on the Large Plasma Device at the University of California, Los Angeles, mapped out the two-dimensional spatiotemporal evolution of the laser-plasma (debris) ion velocity distribution function (VDF) to assess debris-background coupling in a sub-Alfvénic regime. The acquisition of these data necessitates high repetition rate (1 Hz) as each dataset is the accumulation of thousands of laser shots, which would not be feasible in single-shot experiments. Fully kinetic, three-dimensional particle-in-cell simulations are compared to the measured VDFs to provide a framework in which we can understand the coupling of a sub-Alfvénic plasma flow through a preformed, magnetized plasma. The simulations display the same departure from the expected gyromotion of the debris plasma as observed in the experimental data, and in conjunction with the measured magnetic field traces, have led to the direct observation of the collisionless coupling via laminar fields.

Metallosis following hip arthroplasty: two case\xa0reports

BackgroundThere has been increasing recognition of local and systemic adverse events associated with the release of metal ions and nanoparticles from hip arthroplasty components. Adverse local tissue reactions to metal ion debris can include periprosthetic solid and cystic masses known as pseudotumors. These masses can result in pain, swelling, extensive destruction to surrounding hip soft-tissues, and compression syndromes on neurovascular, gastrointestinal, and genitourinary structures. As reports of pseudotumors requiring multidisciplinary excision are limited, we present two pseudotumor cases that were excised through a combined approach.Case presentationsThe first case involves a 60-year-old Caucasian female with a large pseudotumor with intrapelvic and vascular involvement associated with a metal-on-polyethylene total hip arthroplasty, excised with contributions from general surgery, vascular surgery, and orthopedic surgery. Pseudotumor excision was followed by a revision total hip reconstruction in addition to an abductor mechanism reconstruction with tendo-Achilles allograft. The second case is that of a 64-year-old Caucasian female with a pseudotumor in close relationship to the femoral vessels following a metal-on-metal hip resurfacing, excised with a combination of vascular surgery and orthopedic surgery, with subsequent revision total hip reconstruction.ConclusionsThere remains a lack of literature to support the extensiveness of pseudotumor excision required in complex cases with significant intrapelvic or vascular involvement. Given the potential for significant adverse effects of large masses, the authors’ preference is to involve a multidisciplinary team to achieve a more comprehensive excision while minimizing the risk of potential complications.

Effect of plasma properties on magnetic bubbles

In this work, a three-dimensional hybrid simulation program is used to investigate the process of the explosion and expansion of a large number of thermal debris ions in a low density background plasma. By quantitatively calculating the variation of the magnetic bubble and the bubble constraint in the motion of the debris cloud, studied are the influences of the background plasma charge density, the background ion atomic weight, and the charge-mass ratio of the fragment ion on the magnetic bubble. The results show that the background charge density has an important effect on the motion of the bubble and debris cloud. In the early stage of the debris cloud expansion, the background ion atomic weight has little effect on the bubble expansion, but it affects the movement of debris cloud at a later time. When the charge-mass ratio of the debris ion is small, the radius of the ion gyration is larger than the bubble radius, and the bubble radius is small so that it cannot restrain the debris cloud. When the charge-mass ratio of the debris ion is large, the radius of the ion gyration is smaller than the bubble radius. If the background charge density is low in this condition, the early expansion of the bubble and the debris cloud are slightly affected by the charge-mass ratio of the fragment ions, and only the subsequent evolution of the system is influenced. If the background charge density is large in this condition, the charge-mass ratio of the fragment ion has a prominent influence on the motion of the bubble and the debris cloud.

High-altitude nuclear explosion energy accumulation law in atmosphere

An accumulation model of X-ray and debris in a high altitude nuclear explosion is built in this work. Using the established model, we simulate the energy accumulations of four large scale experiments (i.e. the Checkmate, Starfish, K3 and K4) conducted by the United States and the Soviet Union. The dynamics of the kinetic accumulation at 100–200 km altitude is analyzed. Our simulation results show that the kinetic patch spreads a relatively small spatial region and has a large energy density compared with the X-ray patch. The accumulation of the debris ions can be finished within around 0.5 s, and two absorption peaks (hence two kinetic patches) can be observed at an altitude of about 115 km and the burst point. The shape of the kinetic region projected onto the horizontal plane is roughly elliptical, the eccentricity will be smaller at higher latitudes, and the area will be larger at higher altitudes. Away from the bursting point, the maximum energy density of the kinetic patch is near the magnetic field line that crosses the bursting point. Within the magnetic bubble, the maximum energy density of the kinetic patch occurs near the bursting point.

A systematic review of metal ion concentrations following instrumented spinal fusion.

Metallic spinal implants undergo wear and corrosion which liberates ionic or particulate metal debris. The purpose of this study was to identify and review studies that report the concentration of metal ions following multi-level spinal fusion and to evaluate the impact on clinical outcomes. Databases (PubMed, EBSCO MEDLINE) were searched up to August 2019 for studies in English-language assessing metal ion levels [chromium (Cr), titanium (Ti), nickel (Ni)] in whole blood, serum, or plasma after spinal fusion using a specific search string. Study, patient, and implant characteristics, method of analysis, metal ion concentration, as well as clinical and radiographic results was extracted. The systematic search yielded 18 studies encompassing 653 patients. 9 studies reported Ti ions, eight reported Cr, and six reported Ni. Ti levels were elevated compared to controls/reference range/preoperative baseline in seven studies with the other two reporting no difference. Cr levels were elevated compared to controls/reference range in seven studies with one reporting no difference. Ni levels showed no difference from controls/reference range in four studies with one reporting above normal and another elevated compared to controls. Radiographic evidence of corrosion, implant failure, pseudarthrosis, revision surgery and adverse reaction reporting was highly variable. Metal ions are elevated after instrumented spinal fusion; notably Cr levels from stainless steel implants and Ti from titanium implants. The association between clinical and radiographic outcomes remain uncertain but is concerning. Further research with standardized reporting over longer follow-up periods is indicated to evaluate the clinical impact and minimizing risk.

In vitro fretting crevice corrosion damage of CoCrMo alloys in phosphate buffered saline: Debris generation, chemistry and distribution

Fretting crevice corrosion in modular tapers of total hip replacements has become a major concern in orthopedic medical devices. Solid and ionic debris arising from fretting crevice corrosion have been implicated in device failure and revision surgery. This study aims to use a 2D pin-on-disk fretting corrosion test system to visualize damage progression and debris generation during fretting corrosion of CoCrMo alloys in phosphate buffered saline (PBS). The results provide direct evidence of rapid debris generation during fretting corrosion (after only 12 min of testing). Debris was generated and either extruded from the contact region or impacted into adjacent crevice sites as long as fretting continued. After testing, the fretting region consisted of a damaged and plastically deformed contact region surrounded by a halo of fretting debris consisting entirely of oxides and phosphates within the crevice region. Evidence of pitting corrosion and grain boundary corrosion was observed. Solid debris consisted of chromium (Cr), phosphate (P) and oxygen (O). X-ray photoelectron spectroscopy analysis of the near-fretted metal surface area showed a thicker oxygen (O1s) containing film with the depth profile of O1s above 10% penetrating up to 5.75 nm while the O1s concentration on the unfretted area fell to below 10% after 1 nm depth. Ion concentration in the PBS, measured using inductively coupled mass spectrometry, showed cobalt (Co) ions were most prevalent (1.46 ppm) compared to chromium (Cr) (0.07 ppm) and molybdenum (Mo) (0.05 ppm) (p <0.05). All of these results are consistent with the analysis of in vivo modular taper corrosion processes. Statement of SignificanceCoCrMo alloys has been widely used as a metallic biomaterial for implant devices and can lose their durability and reliability due to wear, corrosion and tribocorrosion. Debris, as one of the major products of these reactions, is associated with implant device failure. In the first time, we developed a fretting corrosion testing system to visualize the debris generation process in real-time between CoCrMo alloy pin and disk samples. Debris was generated rapidly during fretting corrosion and some of the debris egressed from the crevice site while also accumulating within the crevice area as fretting continued. Our study opens a new method for future studies to advance understanding of debris generation processes during wear and tribocorrosion phenomenon.

Erratum: “Equation-of-state, critical constants, and thermodynamic properties of lithium at high energy density” [Phys. Plasmas 26, 122702 (2019)

High-density lithium plasmas are expected to be generated in the Inertial Confinement Fusion (ICF) reactor chamber due to energy deposition of the prompt X-rays and ion debris in the first wall. These dense plasmas are encountered in many other applications as well. The design and optimization of such lithium-based applications requires information about the thermodynamic properties of Li fluid over a wide range of parameters including the high-energy-density regime. A model that takes into account all essential features of strongly-coupled plasmas of metal vapors is developed and used to predict the equation-of-state (EOS), critical constants, thermodynamic functions, and principal shock Hugoniot of hot dense lithium fluid. Predictions and computational results from the present model are analyzed and presented and are available in electronic form suitable for use to interested researchers and scientists.

Equation-of-state, critical constants, and thermodynamic properties of lithium at high energy density

High-density lithium plasmas are expected to be generated in the Inertial Confinement Fusion reactor chamber due to energy deposition of the prompt X-rays and ion debris in the first wall. These dense plasmas are encountered in many other applications as well. The design and optimization of such lithium-based applications require information about the thermodynamic properties of Li fluid over a wide range of parameters including the high-energy-density regime. A model that takes into account all essential features of strongly coupled plasmas of metal vapors is developed and used to predict the equation-of-state, critical constants, thermodynamic functions, and principal shock Hugoniot of hot dense lithium fluid. Predictions and computational results from the present model are analyzed and presented and are available in electronic form suitable for use to interested researchers and scientists.

Automated Data Cleanup for Mass Cytometry.

Mass cytometry is an emerging technology capable of 40 or more correlated measurements on a single cell. The complexity and volume of data generated by this platform have accelerated the creation of novel methods for high-dimensional data analysis and visualization. A key step in any high-level data analysis is the removal of unwanted events, a process often referred to as data cleanup. Data cleanup as applied to mass cytometry typically focuses on elimination of dead cells, debris, normalization beads, true aggregates, and coincident ion clouds from raw data. We describe a probability state modeling (PSM) method that automatically identifies and removes these elements, resulting in FCS files that contain mostly live and intact events. This approach not only leverages QC measurements such as DNA, live/dead, and event length but also four additional pulse-processing parameters that are available on Fluidigm Helios™ and CyTOF® (Fluidigm, Markham, Canada) 2 instruments with software versions of 6.3 or higher. These extra Gaussian-derived parameters are valuable for detecting well-formed pulses and eliminating coincident positive ion clouds. The automated nature of this new routine avoids the subjectivity of other gating methods and results in unbiased elimination of unwanted events. © 2019 International Society for Advancement of Cytometry.

Local Biological Reactions and Pseudotumor-Like Tissue Formation in relation to Metal Wear in a Murine In Vivo Model.

Metal wear debris and released ions (CoCrMo), which are widely generated in metal-on-metal bearings of hip implants, are also found in patients with metal-on-polyethylene bearings due to the mechanically assisted crevice corrosion of modular taper junctions, including head-neck and neck-stem taper interfaces. The resulting adverse reactions to metal debris and metal ions frequently lead to early arthroplasty revision surgery. National guidelines have since been published where the blood metal ion concentration of patients must consistently be monitored after joint replacement to prevent serious complications from developing after surgery. However, to date, the effect of metal particles and metal ions on local biological reactions is complex and still not understood in detail; the present study sought to elucidate the complex mechanism of metal wear-associated inflammation reactions. The knee joints in 4 groups each consisting of 10 female BALB/c mice received injections with cobalt chrome ions, cobalt chrome particles, and ultra-high-molecular-weight polyethylene (UHMWPE) particles or PBS (control). Seven days after injection, the synovial microcirculation and knee joint diameter were assessed via intravital fluorescence microscopy followed by histological evaluation of the synovial layer. Enlarged knee diameter, enhanced leukocyte to endothelial cell interactions, and an increase in functional capillary density within cobalt chrome particle-treated animals were significantly greater than those in the other treatment groups. Subsequently, pseudotumor-like tissue formations were observed only in the synovial tissue layer of the cobalt chrome particle-treated animals. Therefore, these findings strongly suggest that the cobalt chrome particles and not metal ions are the cause for in vivo postsurgery implantation inflammation.

Characterization of radiative and kinetic properties of laser produced plasmas for efficient extreme ultraviolet nanolithography sources

Increasing extreme ultraviolet (EUV) photon power in laser-produced plasma (LPP) sources is critically important for efficient future nanolithography devices. Enhancing the lifetime of the optical collector system in these devices is another important challenge for reliable and economically feasible devices. In this work, various mechanisms affecting ion acceleration in LPP were investigated to predict the maximum ion energies and flux arriving at the collecting mirror surfaces. Plasma evolution produced by an Nd:YAG laser from Sn targets was studied in detail to predict the dynamics of EUV producing ions and their contribution to the EUV power. The multiphysics fully 3D integrated HEIGHTS computer package was used in this analysis. HEIGHTS simulations of detail plasma evolution and ion kinetic energies were compared with various worldwide experimental data. Excellent agreement was shown regarding the range of ion kinetic energies and their angular distribution as well as recombination processes and their effect on the temporal output of EUV photons. Spatial and charge distributions were predicted for EUV producing ions and ionic debris. The analysis showed that mainly two Sn ions, i.e., Sn XII and Sn XIII, determine the EUV source intensity and spatial location. It was also shown that reducing the laser spot size and increasing the pulse duration allow a significant reduction in ion kinetic energies that is important for a longer lifetime of the optical collection system.

Correlated ion stopping in dense plasmas

Correlated ion stopping arising from an intense cluster ion beam (CIB) interacting with an ultradense plasma target of relevance to inertial confinement fusion (ICF) is first investigated in a two-body approximation in an arbitrarily degenerate electron fluid target. The specific advantages of CIB-driven ICF are first demonstrated through 1D simulations, highlighting the very fine focusing of the ion beam on the target pellet. Then, the N-body configurations of ion debris resulting from the impact of heavy cluster ions are determined in terms of their specific topology. The validities of the usual assumptions of equal ion fragment charge and negligible coupling between stopping and Coulomb explosion are assessed.

Techniques of Insertion and Early Clinical Impressions with a Short Curved Tissue Sparing Implant for Total Hip Arthroplasty (The French Experience)

Background: Total hip arthroplasty (THA) is one of the most effective orthopedic procedures, providing consistently high success rates across all population segments as measured by pain relief, improved function, and patient satisfaction. However clinical outcomes have been less favorable in young active patients, that lead to the re-development of metal on metal hip resurfacing (HR), with the most successful being the Birmingham Hip Replacement (BHR) introduced in 1997. Evolving complications due to increased metal ion debris has lead to a great reduction of use for all metal on metal (MOM) HR designs, leading many surgeons and patients to look for an alternative surgical selection. This search has focused on the development and use of short stems for THA. One such style of short stems is curved neck preserving designs. This paper will review our French experience with one of those designs.Materials and Methods: This is a retrospective review of four surgeons series of a short curved tissue sparing cementless femoral implant (TSI™ Hip Stem, Signature Orthopaedics) for THA. The femoral component was used with two different cementless acetabular styles (Mathys RM Pressfit, and Zimmer Biomet Allofit®). Results on the cups will not be revived in this paper. 150 TSI™ Stems by four surgeons at the same institution utilizing the posterior surgical approach since September 2016. 40% women, average age 66 years with extremes of 27 to 78 years. 10 cases of dysplastic hips, 6 cases of aseptic osteonecrosis, 1 fracture, 1 rheumatoid coxitis, and the rest primary coxathosis, with 7 patients operated on both hips at the same time. 23.3 % have been Dorr type A canal shape.Results: There has been no aseptic loosing, three femoral components have been explanted due to postoperative infection. There was one intra-operative femoral distal fracture in a Dorr type A bone profile during stem insertion. One posterior dislocation; there has been two patients with thigh pain with pathological bone scan, and one with low back pain and no leg length discrepancies greater than plus or minus 5 mm.Conclusion: This short curved tissue sparing implant has demonstrated excellent initial short-term results, with excellent implant stability, excellent medial calcar bone remodeling with one dislocated stem, two thigh pain and one patient with low back pain. One distal intra-operative fracture in a Dorr type A bone. This has now been addressed with the use of distal sizing gauges and the use of flexible reamers to open the distal canal prior to stem insertion. Removal of the infected stems demonstrated implant stability with early bone attachment in the proximal porous surface. The high neck resection allows for ease of revision and conversion implanting a new primary conventional length cementless stem design.There is a short but definitive learning curve in fitting the implant to the femoral neck versus the standard metaphyseal and diaphyseal conventional style stems.

Water-window soft X-ray source using cryogenic Ar laser plasma

A water-window soft X-ray source using laser plasma from a cryogenic solid Ar target has demonstrated an average output power of 0.5 W with continuously repeated pulses at 3.3 Hz. A higher output power of up to 1 W at 10 Hz can be achieved by simply improving the target system. The characteristics of the Ar ion debris from the plasma were also studied and the kinetic energies of the main ions were found to be less than 2 keV. Using the measured ion spectrum, the erosion damage sputtered by Ar ions on the silicon nitride membrane was studied and the results indicated that the damage should cause no problems in the application of a contact soft X-ray microscope. Our laser plasma X-ray source will provide a compact and convenient source suitable for the soft X-ray microscopy in place of conventional synchrotron facilities.

Chromium and Nickel Concentrations in Subjects with a Stainless Steel Metal-on-Metal Cervical Disc Arthroplasty: Results from a Prospective Longitudinal Study with 7 Years Follow-Up.

Cervical disc arthroplasty (CDA) has emerged as an alternative to anterior cervical discectomy and fusion for degenerative cervical disc disease. The artificial discs provide intervertebral motion using multicomponent articulation and thus tend to generate particulate debris and soluble metal ions. Limited information is available on the long-term metal concentrations and associated systemic adverse events observed in metal-on-metal CDA. Serum chromium (Cr) and nickel (Ni) concentrations were assessed in patients implanted with ball-in-trough stainless steel-based cervical disc through 7 years. A prospective, nonrandomized longitudinal study was conducted that included 25 patients following rigorous exclusion criteria that included no previous permanent metal implants and no professional exposure to metal particles. Blood serum Cr and Ni concentrations were assayed preoperatively and at 3, 6, 12, 24, 36, 60, and 84 months postoperatively using high-resolution inductively coupled plasma-mass spectrometry. Longitudinal statistical comparisons were made using the Friedman test with statistical significance at P < .05. Median serum concentrations determined preoperatively and at 3, 6, 12, 24, 36, 60, and 84 months postoperatively were 0.074, 0.106, 0.132, 0.170, 0.172, 0.274, 0.192, and 0.203 ng/mL for Cr and 0.085, 0.178, 0.222, 0.175, 0.205, 0.284, 0.181, and 0.194 ng/mL for Ni. The serum Cr concentrations were statistically higher for all postoperative time periods compared to preoperative concentration (Friedman P <.01), whereas serum Ni concentration was statistically higher at the 84-month postoperative time period than the preoperative concentration (Friedman P <.01) and then the concentration at 3, 12, 24, and 60 months postoperatively (Friedman P < .03). The Cr concentrations detected at all postoperative times were statistically higher than preoperative concentrations, whereas Ni concentration was statistically higher than the preoperative concentration only at 84 months.

Observations of a field-aligned ion/ion-beam instability in a magnetized laboratory plasma

Collisionless coupling between super Alfvénic ions and an ambient plasma parallel to a background magnetic field is mediated by a set of electromagnetic ion/ion-beam instabilities including the resonant right hand instability (RHI). To study this coupling and its role in parallel shock formation, a new experimental configuration at the University of California, Los Angeles utilizes high-energy and high-repetition-rate lasers to create a super-Alfvénic field-aligned debris plasma within an ambient plasma in the Large Plasma Device. We used a time-resolved fluorescence monochromator and an array of Langmuir probes to characterize the laser plasma velocity distribution and density. The debris ions were observed to be sufficiently super-Alfvénic and dense to excite the RHI. Measurements with magnetic flux probes exhibited a right-hand circularly polarized frequency chirp consistent with the excitation of the RHI near the laser target. We compared measurements to 2D hybrid simulations of the experiment.