Context. The solar wind originating from coronal holes is comparatively well-understood and is characterized by lower densities and average charge states compared to the so-called slow solar wind. Except for wave perturbations, the average properties of the coronal-hole solar wind are passably constant. Aims. In this case study, we focus on observations of the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) of individual streams of coronal-hole solar wind that illustrate that although the O and C charge states are low in coronal-hole wind, the Fe charge distribution is more variable. In particular, we illustrate that the Fe charge states in coronal-hole solar wind are frequently as high as in slow solar wind. Methods. We selected individual coronal-hole solar wind streams based on their collisional age as well as their respective O and C charge states and analyzed their Fe charge-state distributions. Additionally, with a combination of simple ballistic back-mapping and the potential field source surface model, transitions between streams with high and low Fe charge states were mapped back to the photosphere. The relative frequency of high and low Fe charge-state streams is compared for the years 2004 and 2006. Results. We found several otherwise typical coronal-hole streams that include Fe charge states either as high as or lower than in slow solar wind. Eight such transitions in 2006 were mapped back to equatorial coronal holes that were either isolated or connected to the northern coronal-hole. Attempts to identify coronal structures associated with the transitions were so far inconclusive.

Context. He+ pickup ions are either born from the ionization of interstellar neutral helium inside our heliosphere, the so-called interstellar pickup ions, or through the interaction of solar wind ions with small dust particles, the so-called inner source of pickup ions. Until now, most observations of pickup ions were limited to reduced 1D velocity spectra, which are insufficient to study certain characteristics of the He + velocity distribution function (VDF). Aims. It is generally assumed that rapid pitch-angle scattering of freshly created pickup ions quickly leads to a fully isotropic He + VDF. In light of recent observations, this assumption has found to be oversimplified and needs to be reinvestigated. Methods. Using He+ pickup ion data from the PLASTIC instrument on board the STEREO A spacecraft, we reconstruct a reduced form of the He + VDF in two dimensions. This allows us to study relative changes of the 2D He + VDF as a function of the configuration of the heliospheric magnetic field. Results. Our observations show that the He + VDF is highly anisotropic and even indicates that, at least for certain configurations of B, it is not fully gyrotropic. Our results further suggest, that the observed velocity and pitch angle of He + depends strongly on the local solar magnetic field vector, B, the ecliptic longitude, λ, the solar wind speed, v sw , and the global distribution of B. Conclusions. We found two distinct signatures that systematically change as a function of the alignment of B: (1) a ring beam distribution that is most pronounced at w sw > 0.5 and likely attributed to interstellar He + ; (2) a beam signature aligned parallel to B that is most pronounced at w sw < 0.5 and attributed to inner-source He + . The strong anisotropy and the aforementioned dependencies of the He + VDF also imply that observations of 1D velocity spectra of He + pickup ions are potentially deceiving.

Most electron cyclotron resonance ion sources use hexapolar magnetic fields for the radial confinement of the plasma. The geometry of this magnetic structure is then--induced by charged particles--mapped onto the inner side of the plasma electrode via sputtering and deposition. The resulting structures usually show two different patterns: a sharp triangular one in the central region which in some cases is even sputtered deep into the material (referred to as thin groove or sharp structure), and a blurred but still triangular-like one in the surroundings (referred to as broad halo). Therefore, both patterns seem to have different sources. To investigate their origins we replaced the standard plasma electrode by a custom-built plasma electrode acting as a planar, multi-segment current-detector. For different biased disc voltages, detector positions, and source biases (referred to the detector) we measured the electrical current density distributions in the plane of the plasma electrode. The results show a strong and sharply confined electron population with triangular shape surrounded by less intense and spatially less confined ions. Observed sputter- and deposition marks are related to the analysis of the results. Our measurements suggest that the two different patterns (thin and broad) indeed originate from different particle populations. The thin structures seem to be caused by the hot electron population while the broad marks seem to stem from the medium to highly charged ions. In this paper we present our measurements together with theoretical considerations and substantiate the conclusions drawn above. The validity of these results is also discussed.

Context. During the last decades great progress has been achieved in understanding the properties and the origin of the solar wind. While the sources for the fast solar wind are well understood, the sources for the slow solar wind remain elusive. Aims. The upcoming Solar Orbiter mission aims to improve our understanding of the sources of the solar wind by establishing the link between in situ and remote sensing observations. In this paper we aim to address the problem of linking in situ and remote observations in general and in particular with respect to ESA's Solar Orbiter mission. Methods. We have used a combination of ballistic back mapping and a potential field source surface model to identify the solar wind source regions at the Sun. As an input we use in situ measurements from the Advanced Composition Explorer and magnetograms obtained from the Michelson Doppler Interferometer on board the Solar Heliospheric Observatory. For the first time we have accounted for the travel time of the solar wind above and also below the source surface. Results. We find that a prediction scheme for the pointing of any remote sensing instrumentation is required to capture a source region not only in space but also in time. An ideal remote-sensing instrument would cover up to ≈50% of all source regions at the right time. In the case of the Spectral Imaging of the Coronal Environment instrument on Solar Orbiter we find that ≈25% of all source regions would be covered. Conclusions. To successfully establish a link between in situ and remote observations the effects of the travel time of the solar wind as well as the magnetic displacement inside the corona cannot be neglected. The predictions needed cannot be based solely on a model, nor on observations alone, only the combination of both is sufficient.

In this paper we present our measurements of charge-state and current-density distributions performed in very close vicinity (15 mm) of the extraction of our hexapole geometry electron cyclotron resonance ion source. We achieved a relatively high spatial resolution reducing the aperture of our 3D-movable extraction (puller) electrode to a diameter of only 0.5 mm. Thus, we are able to limit the source of the extracted ion beam to a very small region of the plasma electrode's hole (Ø = 4 mm) and therefore to a very small region of the neutral plasma sheath. The information about the charge-state distribution and the current density in the plane of the plasma electrode at each particular position is conserved in the ion beam. We determined the total current density distribution at a fixed coaxial distance of only 15 mm to the plasma electrode by remotely moving the small-aperture puller electrode which contained a dedicated Faraday cup (FC) across the aperture of the plasma electrode. In a second measurement we removed the FC and recorded m/q-spectra for the different positions using a sector magnet. From our results we can deduce that different ion charge-states can be grouped into bloated triangles of different sizes and same orientation at the extraction with the current density peaking at centre. This confirms observations from other groups based on simulations and emittance measurements. We present our measurements in detail and discuss possible systematic errors.