This statistical work studies the abundances and the charge states of the carbon, oxygen, and iron ions in 281 interplanetary coronal mass ejections (ICMEs) measured at 1 au by ACE spacecraft from 1998 to 2011. The Gaussian distribution test is applied, and the analysis of variance is used to quantify the similarity between two distributions of ionic charge states and abundances. The correlation coefficient is calculated to reveal the dependence of the abundances and the mean charge of heavy ions on the solar activity. The results show that the mean charge, the abundance, and the speed at 1 au are highly related to the sunspot number (SN). The O7+/O6+ shows statistical difference between the high speed and the low speed groups of ICMEs. Different from the cold materials inside ICMEs, the mean charge of carbon ions shows a positive relation to that of oxygen ions. The Mg/O in the studied ICMEs are much higher than that in the solar wind. Three types of charge distribution of C, O, and Fe ions are summarized. The fraction of each of the three types is related to the solar minimum or the solar maximum. The mean charge and the flux of oxygen ions show quasi-linear relations to the SN during solar minimum, and show fluctuations during maximum. The results reveal that the solar activity, which represents the solar magnetic field status by nature, controls the composition of heavy ions in ICMEs.
Context. Coronal mass ejections (CMEs) are extremely dynamical, large-scale events in which plasma – but not only the coronal plasma – is ejected into interplanetary space. If a CME is detected in situ by a spacecraft located in the interplanetary medium, it is then called an interplanetary coronal mass ejection (ICME). This solar activity has been studied widely since coronagraphs were first flown into space in the early 1970s. Aims. Charge states of heavy ions reflect important information about the coronal temperature profile due to the freeze-in effect and it is estimated that iron ions freeze in at heights of ∼5 solar radii. However, the measured charge-state distribution of iron ions cannot be composed of only one single group of plasma. To identify the different populations of iron charge-state composition of ICMEs and determine their sources, we developed a model that independently uses two, three, and four populations of iron ions to fit the measured charge-state distribution in ICMEs detected by the Advanced Composition Explorer (ACE) at 1 AU. Methods. Three parameters are used to identify a certain population, namely freeze-in temperature, relative abundance, and kappa value (κ), which together describe the potential non-Maxwellian kappa distributions of coronal electrons. Our method chooses the reduced chi-squared to describe the goodness of fit of the model to the observations. The parameters of our model are optimized with the covariance-matrix-adaptation evolution strategy (CMA-ES). Results. Two major types of ICMEs are identified according to the existence of hot material, and both, that is, the cool type and the hot type, have two main subtypes. Different populations in those types have their own features related to freeze-in temperature and κ. The electron velocity distribution function usually contains a significant hot tail in typical coronal material and hot material, while the Maxwellian distribution appears more frequently in mid-temperature material. Our model is also suitable for all types of solar wind and the existence of hot populations as well as the change of temperatures of individual populations may indicate boundaries between ICMEs and individual solar wind streams.
Plasma based ion implantation for a planar target was simulated using the particle-in-cell model. The plasma sheath evolution and the ion implantation details (the incident ion flux, the ion impact angle and the ion impact energy) were studied for targets with different sizes, with an aim to investigate the dependence of dose uniformity on target size. The effect of plasma density and pulse width on dose distribution was studied as a plus. The simulation results show that a larger target leads to a faster and less cylindrical sheath expansion. By increasing the target size, a more uniform distribution of incident ion flux can be obtained and the normal impact effect can be improved, while the distribution of impact energy is slightly influenced. As a result, the ion implantation dose presents a better uniformity on a larger target. By increasing plasma density or pulse width, we get a higher ion implantation dose but worse dose uniformity.
<p>Coronal Mass Ejections~(CMEs) are extremely dynamical large scale events in which plasma-not only the coronal plasma-is ejected into the interplanetary space. Their interplanetary counterparts measured in-situ are Interplanetary Coronal Mass Ejections (ICMEs), which is also an important part of space weather.</p> <p>Even though the kinetic properties of the&#160;plasma might change because of dynamic effects occurring during the expansion of the CME, the heavy ion characteristics&#160;remain unchanged after it leaves the low corona. Charge states of heavy ions reflect important information about the coronal&#160;temperature profile due to the freeze-in effect, while elemental abundances indicate potential source regions of the plasma.</p> <p>With the help of the Pulse Height Analysis (PHA) data from the Solar Wind Ion Composition Spectromet (SWICS) on board the Advanced Composition Explorer (ACE), combined with a newly developed multi-population model, we are able to conduct a high time resolution (12 minutes) case study on a complex ejecta detected by ACE in May 2005. This case lasted more than 80 hours and caused a strong geomagnetic response, with a Dst index at -247.</p> <p>Multiple discontinuous&#160;periods with highly charged heavy ions are identified, elemental abundances also differ during those &#8221;hot&#8221;&#160;periods. Heavy ion characteristics provide us an unique opportunity to see the boundaries of different parts of an ICME.</p>
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