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A G G M Tielens - One of the best experts on this subject based on the ideXlab platform.
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charge exchange emission from solar wind Helium Ions
The Astrophysical Journal, 2006Co-Authors: D Bodewits, Ronnie Hoekstra, B Seredyuk, R W Mccullough, G H Jones, A G G M TielensAbstract:Charge exchange X-ray and far-ultraviolet (FUV) aurorae can provide detailed insight into the interaction between solar system plasmas. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy, we have studied state-selective charge exchange in collisIons between fully ionized Helium and target gasses characteristic of cometary and planetary atmospheres (H2O, CO2, CO, and CH4). The experiments were performed at velocities typical for the solar wind (200-1500 km s-1). Data sets are produced that can be used for modeling the interaction of solar wind alpha particles with cometary and planetary atmospheres. These data sets are used to demonstrate the diagnostic potential of Helium line emission. Existing Extreme Ultraviolet Explorer (EUVE) observatIons of comets Hyakutake and Hale-Bopp are analyzed in terms of solar wind and coma characteristics. The case of Hale-Bopp illustrates well the dependence of the Helium line emission to the collision velocity. For Hale-Bopp, our model requires low velocities in the interaction zone. We interpret this as the effect of severe post-bow shock cooling in this extraordinary large comet.
Zhenghua Huang - One of the best experts on this subject based on the ideXlab platform.
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Helium abundance and speed difference between Helium Ions and protons in the solar wind from coronal holes active regIons and quiet sun
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: M S Madjarska, Lidong Xia, Zhenghua HuangAbstract:Two main models have been developed to explain the mechanisms of release, heating and acceleration of the nascent solar wind, the wave-turbulence-driven (WTD) models and reconnection-loop-opening (RLO) models, in which the plasma release processes are fundamentally different. Given that the statistical observational properties of Helium Ions produced in magnetically diverse solar regIons could provide valuable information for the solar wind modelling, we examine the statistical properties of the Helium abundance (A_He) and the speed difference between Helium Ions and protons (v_alpha,p) for coronal holes (CHs), active regIons (ARs) and the quiet Sun (QS). We find bimodal distributIons in the space of A_He and v_alpha,p/v_A (where v_A is the local Alfven speed)for the solar wind as a whole. The CH wind measurements are concentrated at higher A_He and v_alpha,p/v_A values with a smaller A_He distribution range, while the AR and QS wind is associated with lower A_He and v_alpha,p/v_A, and a larger A_He distribution range. The magnetic diversity of the source regIons and the physical processes related to it are possibly responsible for the different properties of A_He and v_alpha,p/v_A. The statistical results suggest that the two solar wind generation mechanisms, WTD and RLO, work in parallel in all solar wind source regIons. In CH regIons WTD plays a major role, whereas the RLO mechanism is more important in AR and QS.
D Bodewits - One of the best experts on this subject based on the ideXlab platform.
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charge exchange emission from solar wind Helium Ions
The Astrophysical Journal, 2006Co-Authors: D Bodewits, Ronnie Hoekstra, B Seredyuk, R W Mccullough, G H Jones, A G G M TielensAbstract:Charge exchange X-ray and far-ultraviolet (FUV) aurorae can provide detailed insight into the interaction between solar system plasmas. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy, we have studied state-selective charge exchange in collisIons between fully ionized Helium and target gasses characteristic of cometary and planetary atmospheres (H2O, CO2, CO, and CH4). The experiments were performed at velocities typical for the solar wind (200-1500 km s-1). Data sets are produced that can be used for modeling the interaction of solar wind alpha particles with cometary and planetary atmospheres. These data sets are used to demonstrate the diagnostic potential of Helium line emission. Existing Extreme Ultraviolet Explorer (EUVE) observatIons of comets Hyakutake and Hale-Bopp are analyzed in terms of solar wind and coma characteristics. The case of Hale-Bopp illustrates well the dependence of the Helium line emission to the collision velocity. For Hale-Bopp, our model requires low velocities in the interaction zone. We interpret this as the effect of severe post-bow shock cooling in this extraordinary large comet.
Dietmar Georg - One of the best experts on this subject based on the ideXlab platform.
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implementation of spot scanning dose optimization and dose calculation for Helium Ions in hyperion
Medical Physics, 2015Co-Authors: H Fuchs, M Alber, T Schreiner, Dietmar GeorgAbstract:Purpose: Helium Ions (4He) may supplement current particle beam therapy strategies as they possess advantages in physical dose distribution over protons. To assess potential clinical advantages, a dose calculation module accounting for relative biological effectiveness (RBE) was developed and integrated into the treatment planning system Hyperion. Methods: Current knowledge on RBE of 4He together with linear energy transfer consideratIons motivated an empirical depth-dependent “zonal” RBE model. In the plateau region, a RBE of 1.0 was assumed, followed by an increasing RBE up to 2.8 at the Bragg-peak region, which was then kept constant over the fragmentation tail. To account for a variable proton RBE, the same model concept was also applied to protons with a maximum RBE of 1.6. Both RBE models were added to a previously developed pencil beam algorithm for physical dose calculation and included into the treatment planning system Hyperion. The implementation was validated against Monte Carlo simulatIons within a water phantom using γ-index evaluation. The potential benefits of 4He based treatment plans were explored in a preliminary treatment planning comparison (against protons) for four treatment sites, i.e., a prostate, a base-of-skull, a pediatric, and a head-and-neck tumor case. Separate treatment plans taking into account physical dose calculation only or using biological modeling were created for protons and 4He. Results: Comparison of Monte Carlo and Hyperion calculated doses resulted in a γ mean of 0.3, with 3.4% of the values above 1 and γ 1% of 1.5 and better. Treatment plan evaluation showed comparable planning target volume coverage for both particles, with slightly increased coverage for 4He. Organ at risk (OAR) doses were generally reduced using 4He, some by more than to 30%. Improvements of 4He over protons were more pronounced for treatment plans taking biological effects into account. All OAR doses were within tolerances specified in the QUANTEC report. ConclusIons: The biological 4He model proposed above is a first approach matching biological data published so far. The advantage of 4He seems to lie in the reduction of dose to surrounding tissue and to OARs. Nevertheless, additional biological experiments and treatment planning studies with larger patient numbers and more tumor indicatIons are necessary to study the possible benefits of Helium ion beam therapy in detail.
G De Temmerman - One of the best experts on this subject based on the ideXlab platform.
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surface modificatIons induced by high fluxes of low energy Helium Ions
Scientific Reports, 2015Co-Authors: Irem Tanyeli, L Marot, Mauritius C M Van De Sanden, Daniel Mathys, G De TemmermanAbstract:Several metal surfaces, such as titanium, aluminum and copper, were exposed to high fluxes (in the range of 1023 m−2s−1) of low energy (<100 eV) Helium (He) Ions. The surfaces were analyzed by scanning electron microscopy and to get a better understanding on morphology changes both top view and cross sectional images were taken. Different surface modificatIons, such as voids and nano pillars, are observed on these metals. The differences and similarities in the development of surface morphologies are discussed in terms of the material properties and compared with the results of similar experimental studies. The results show that He Ions induced void growth and physical sputtering play a significant role in surface modification using high fluxes of low energy He Ions.
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nanostructuring of iron surfaces by low energy Helium Ions
ACS Applied Materials & Interfaces, 2014Co-Authors: Irem Tanyeli, L Marot, Mauritius C M Van De Sanden, G De TemmermanAbstract:The behavior of iron surfaces under Helium plasma exposure is investigated as a function of surface temperature, plasma exposure time, and He ion flux. Different surface morphologies are observed for a large process parameter range and discussed in terms of temperature-related surface mechanisms. Surface modification is observed under low-He ion flux (in the range of 1020 m–2 s–1) irradiation, whereas fiberlike iron nanostructures are formed by exposing the surface to a high flux (in the range of 1023 m–2 s–1) of low-energy He Ions at surface temperatures of 450–700 °C. The effects of surface temperature and plasma exposure time on nanostructures are studied. The results show that surface processing by high-flux low-energy He ion bombardment provides a size-controlled nanostructuring on iron surfaces.
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nanostructuring of molybdenum and tungsten surfaces by low energy Helium Ions
Journal of Vacuum Science and Technology, 2012Co-Authors: G De Temmerman, K Bystrov, J Jakub J Zielinski, M Balden, G Matern, C Arnas, L MarotAbstract:The formation of metallic nanostructures by exposure of molybdenum and tungsten surfaces to high fluxes of low energy Helium Ions is studied as a function of the ion energy, plasma exposure time, and surface temperature. Helium plasma exposure leads to the formation of nanoscopic filaments on the surface of both metals. The size of the Helium-induced nanostructure increases with increasing surface temperature while the thickness of the modified layer increases with time. In addition, the growth rate of the nanostructured layer also depends on the surface temperature. The size of the nanostructure appears linked with the size of the near-surface voids induced by the low energy Ions. The results presented here thus demonstrate that surface processing by low-energy Helium Ions provides an efficient route for the formation of porous metallic nanostructures.