3.10 Spacecraft SEP observations
3.10.1 Parker Solar Probe (PSP)
Parker Solar Probe (PSP) was launched on12August2018from Cape Canaveral, USA, with a Delta IV-Heavy launch vehicle. At its closest approach to the Sun, the PSP will fly within9RJ of the photosphere, at approximately692 000kmh−1, facing temperatures in excess of1400◦C.
It has three main scientific objectives, i) to trace the flow of energy that heats and accelerates the solar corona and solar wind, ii) to determine the structure and dynamics of the plasma and magnetic fields at the SWSS, and iii) to explore mechanisms that accelerate and transport energetic particles. In order to do so, the PSP has four main instruments.
The FIELDS instrument is designed to measure the magnetic and electric fields in the solar corona, including the fast and slow solar wind streams [Bale et al., 2016]. It measures turbu- lence with a high cadence to better understand the B~ and E~ fields associated with shocks,
40 3.10. SPACECRAFT SEP OBSERVATIONS waves, and magnetic reconnection. The instrument has five2m antennas, four of which are outside the protective barrier of the heat shield in order to observe electric fields bothin-situ and remotely. The fifth antenna is perpendicular to the other, and behind the heat shield, in order to provide a three-dimensional picture of the electric fields. The magnetic fields are de- tected by the three magnetometers. These instruments observe changes in voltages when the magnetic fields change. A fluxgate magnetometer is used to analyse the magnetic fields further away from the Sun with a slower observing rate. The search coil magnetometer (SCM) is used to analyse the magnetic fields close to the Sun where the magnetic fields change very quickly, hence the sampling rate of2×106Hz.
The Wide-Field Imager (WISPR) is the only imaging instrument on the PSP and has a field of view from13◦ to108◦ away from the Sun [Vourlidas et al., 2016]. This instrument is designed to image coronal structures from far away before flying through it, providing both remote and in-situobservations of CMEs, plumes, coronal streamers, and solar flares. WISPR images the Sun in a coronagraph-style, using the heat shield to block most of the Sun’s light in order to observe the fainter corona.
The Solar Wind Electrons Alphas and Protons (SWEAP) instrument counts electrons, protons, and helium ions and measure their properties such as velocity, density, and temperature to gain better understanding of the SW and coronal plasma [Kasper et al., 2016]. These measurements are done with a Faraday cup, called the Solar Probe Cub (SPC) on-board the PSP. Variable voltage is used to sort the particles according to charge, and also aids in identifying the back- ground noise such as CRs and photoionised electrons which could have a negative influence on the data.
The Integrated Science Investigation of the Sun (ISJ
IS) instrument, pronounced“ee-sis”, mea- sures electrons, protons and ions, in order to understand these particles’ life-cycle, e.g. their origin, how these particles were accelerated and how they propagate from the Sun through the heliosphere [McComas et al., 2016]. EPI-Lo (Energetic Particle Instrument Lo) and EPI-Hi are the two energetic particle instruments on ISJ
IS. EPI-Lo measures, among other elements, the two helium isotopes, namely3He and4He. As discussed in Chapter2, knowing these ra- tios very close to the Sun will significantly help to deconvolve the acceleration mechanisms of these particles. EPI-Hi measures the energy of particles higher than what can be measured by EPI-Lo. The higher energy particles are able to penetrate the instrument much deeper and this characteristic is exploited to identify them, as well as ionization, detecting how many electrons the particles strip away from atoms inside the detector. EPI-Hi has a high cadence and is able to detect particles at a frequency of100 000Hz when close to the Sun.
Figure 3.10 shows the first light data of the different instruments on the PSP. Figure 3.10a is the first light image taken by the WISPR instrument; the left panel is from the outer telescope (58◦ field of view) and the right panel from the inner telescope (40◦ field of view). The left panel shows the large scale structure of the Milky Way galaxy, while Jupiter can be seen in the right panel (bright object slightly right from the centre of the image). These images were taken in early September2018to test the instrument before the spacecraft made its first approach to the Sun. The background CR radiation was picked up once EPI-Lo (part of ISJ
IS) was switched on, shown in figure 3.10b. Strong signals of both hydrogen and helium were detected
(a)
(b) (c)
(d) (e)
Figure 3.10: First light data from Parker Solar Probe (PSP) instrument suite. Details are in the text. (a) Credit: NASA/Naval Research Laboratory/Parker Solar Probe. (b) and (c) Credit:
NASA/Princeton University/Parker Solar Probe. (d) Credit: NASA/UC Berkeley/Parker So- lar Probe. (e) Credit: NASA/University of Michigan/Parker Solar Probe.
42 3.10. SPACECRAFT SEP OBSERVATIONS
Figure 3.11: First radio burst observed by the FIELDS instrument on-board the PSP. Credit:
NASA/UC Berkeley/Parker Solar Probe/Wind.
when EPI-Hi was switched on, shown in figure 3.10c. Figure 3.10d shows the three components (Bx,By,Bz) magnetic field changes during the antenna boom deployment. The first section of the data shows the magnetic field of the spacecraft itself, and then it drops significantly after the boom were extended away from the spacecraft. This clearly illustrates why it is critically important for the antennas to be as far away from the spacecraft as possible. The SPC observed a sudden and intense gust of solar wind particles after it was switched on, shown as the red streak in figure 3.10e. The blue regions of the graph show the background noise. The first ob- servation of a radio burst associated with a solar flare was observed by the FILEDS instrument in6September2018and shown in figure 3.11. The top panel shows the radio burst observed by the WIND spacecraft, and the bottom panel shows the burst observed by the FIELDS instru- ment. The first light data from the PSP had limited scientific value, but it showed that all the instruments are working and ready to capture solar data when close to the Sun.