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The Solar Wind Analyser(SWA) on board Solar

Orbiter

The Solar Wind Analyser(SWA) on board Solar

Orbiter

Raffaella D’AmicisINAF‐Istituto di Astrofisica e Planetologia Spaziali

On behalf of the SWA team

2016 Meeting of the Italian SOlar and HEliospheric community

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Solar Orbiter will be the first spacecraft since Helios to sample the innerheliosphere at distances as close to the Sun as 60 RS. The main goal is to study thelink between solar sources and in situ measurements. To do that:

It will be equipped with in‐situ instruments significantly more capable thanthose flown on Helios, as well as with remote‐sensing instruments for theobservation of the corona and photosphere.

Its orbital design allows the spacecraft to achieve approximate co‐rotation withthe Sun for periods of several days, measuring the solar wind plasma andmagnetic field in‐situ while simultaneously observing their source regions onthe Sun.

Increasing inclination up to more than 30° with respect to the solar equatorallows out‐of‐ecliptic measurements.

Solar Orbiter’s novelties respect to previous missions


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SolO’s orbit


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Objective 1: What drives the solar wind and where does the heliospheric magnetic field originate?

1.1 What are the source regions of the solar wind and heliospheric magnetic field?1.2 What mechanisms heat and accelerate the solar wind?1.3 What are the sources of solar wind turbulence and how does it evolve?

Solar Orbiter detailed science objectives

Objective 2: How do solar transients drive heliospheric variability?2.1 How do CMEs evolve through the corona and inner heliosphere?2.2 How do CMEs contribute to solar magnetic flux and helicity balance?2.3 How and where do shocks form in the corona?

Objective 3: How do solar eruptions produce energetic particle radiation that fills the heliosphere?

3.1 How and where are energetic particles accelerated at the Sun?3.2 How are energetic particles released from their sources and distributed in space and time?3.3 What are the seed populations for energetic particles?

Objective 4: How does the solar dynamo work and drive connections between the Sun and the heliosphere?

4.1 How is magnetic flux transported to and re‐processed at high solar latitudes?4.2 What are the properties of the magnetic field at high solar latitudes?4.3 Are there separate dynamo processes acting in the Sun?

Solar Orbiter in situ instrumentsSolar Orbiter in situ instruments


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Solar Wind Analyser (SWA), PI Chris Owen (UK)

Magnetometer (MAG), PI Tim Horbury (UK) vector magnetic field up to 64 Hz

Radio Plasma Waves (RPW), PI Milan Maksimovic (France)magnetic and electric fields at high time resolution, electromagnetic and electrostatic waves in the solar wind up to 20 MHz

Energetic Particle Detector (EPD), PI Javier R.‐Pacheco (Spain) composition and distribution functions of suprathermal and energetic particles (8 keV/n – 200 MeV/n ions; 20‐ 700 keV electrons); sources, acceleration mechanisms, and transport processes of these particles.

SWA Plasma SuiteSWA Plasma Suite

The Solar Wind Plasma Analyzer (SWA) consists of a suite of 3 sensors: • the Electron Analyser System (EAS), • the Proton‐Alpha Sensor (PAS) and • the Heavy Ion Sensor (HIS), together with a common DPU.

Stefano Livi(SwRI/USA), Co‐PI

Philippe Louarn(CESR/France), Co‐PI

Chris Owen (MSSL/UK),PI of SWA and responsible for EAS

Roberto Bruno (INAF‐IAPS/Italy), Co‐PIResponsible for the common DPU


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Consortium structureConsortium structure

EASPAS

HIS

DPU


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SWA Science – At the core of Solar Orbiter scientific goals

“The overarching objective of SWA is to provide the comprehensive in situ measurements of the solar wind which are critical to establish the fundamental physical links between the Sun’s highly dynamic magnetised atmosphere and the solar wind in all its quiet and disturbed states.” [Scientific and Technical Plan]

First suite of coordinated in situ measurements made inside 1 AU, which include mass composition as well as high resolution 3‐D velocity distributions (ions and electrons).


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Electron Analyser System (EAS)

• Energy range from ~1 eV to ~5 keV with ΔE/E ~10% • FoV: elevation ±45° = 5.625°, azimuth 360°

= 11.25°

High temporal resolution• Full 3D VDF sampled at 1 sec (NM)• Moments (number density, bulk speed, pressure

tensor and heat flux) of the electron distribution at 4s (NM)

• 2‐D pitch angle distributions at 8Hz (BM)

Scientific objectives kinetic evolution of solar wind electrons

with distance from the Sun; magnetic connectivity of solar wind

regions

Electrons Velocity Distribution Functions

Helios data

The electron distribution consists of a dense thermal core (T ~ 10 eV), which contains ~ 95% of the total electron density component, and more tenuous suprathermal population. The suprathermal population consists of two energetic components: (i) a halo that can be approximated by Maxwellian distribution with hotter temperature incomparison with the core distribution and (ii) an anisotropic component, so called strahl anti‐sunward moving electrons with narrow pitch angle distribution which carries most of the heat flux along B.

(Pilipp et al, 1987)

fast slow


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Suprathermal populations

The relative number of halo electrons is increasing while the relative number of strahlelectrons is decreasing with distance from the sun thus providing evidence that the heliospheric electron halo population consists partly of electrons that have been scattered out of the strahl.

Linking the Solar Wind and the Sun

http://genesis.lanl.gov/plots/gem_phi/description.html

At times, the supra‐thermal electrons exhibit peak flux both parallel and anti‐parallel to the interplanetary magnetic field, often referred as ‘bi‐directional electron streaming’ along magnetic loops formed by CME and connected to the sun.


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time

s/c spin angle

Typical unidirectional suprathermal (above 100 eV) electron flux peaked along the local field direction (not the same flux in all directions).


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Proton and Alpha Sensor (PAS)

• Energy range from 0.2 – 20 keV/q, with ΔE/E ~7.5%• FoV: elevation ±22.5° = 5 °, azimuth ‐24° ÷ 42°

= 6°

High temporal resolution• Full 3D VDF sampled at 1 sec (NM)• Moments (number density, bulk speed, pressure

tensor) of the proton distribution at 4s (NM) • Reduced 3‐D distributions up to 14 Hz (BM)

Scientific objectives kinetic and fluid properties of the bulk solar wind

plasma and dominant physical processes (e.g.: wave‐particle interactions, origin and dissipation of turbulence, etc);

dynamics and evolution of stream interactions, shocks and CMEs

Typical VDF and heating

Slow wind Fast wind

0.3 AU

1.0 AU

(Marsch et al, 1982)


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0,2 0,4 0,6 0,8 1,00,0

0,1

0,2

0,3

0,4

0,5

0,6

p=Tperp/B

p [10

5 °K/n

T]

r[AU]

First adiabatic invariant in fast wind

Fast wind does not expand adiabaticallyPreferencial heating perpendicular to local B direction

Helios 2 observations

Thermal anisotropies hide kineticprocesses not fully understood

Wave‐particle interactions are the key to understand ion kinetics in the corona and solar wind

• Vp increases with VSW • Vp increases approaching the sun • No radial dependence for slow wind • Vp is of the order of VA

Helios observations

Kinetic aspects

Alfvénic fluctuations might play an important role in determining the speed of minor ions.

(Marsch et al, 1982)

slow

fast


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Shaping of the proton VDF by ion‐cyclotron resonance caused by Alfvén‐cyclotron waves

(Marsch and Tu, 2001)

ions in resonance with transverse ion‐cyclotron waves, propagating parallel to the magnetic field, undergo merely pitch‐angle diffusion which shapes the VDF

Solar wind turbulence

500 103LVR

Reynolds number

10-7 10-6 1x10-5 1x10-4 10-3 10-2 10-1 100 101

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

pow

er d

ensi

ty [

2 /Hz]

frequency [Hz]

Ωp / 2� π

ν� -2.91

ν� -1.67

fc

f-5/3

InjectionInertial Range

IMF power spectrum at 1 AULow freq. from Bruno el al, 1985; high freq. Tail from Leamon et al, 1999

Dissipation

(Matthaeus et al 2005)

z

2Pz z

tz 2

Navier‐Stokes equations

4πbvz

Elsässer variables

If z+ and z‐ are both present, an energy cascade takes place.

]Bksign[- 0


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The shift of the spectral break in fast wind suggests the presence of non‐linear interactions between “in” and “out” Alfvénic modes (Tu, 1984)

Fast wind populated by inward and outward Alfvén modes (Z+, Z‐)

buz

zz

0

The solar wind as a fluid


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(Bruno & Carbone, 2013)


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Radial evolution of the ‘kinetic’ break

Magnetic field spectral densities relative to measurements recorded by Messenger (at 0.42 and 0.56 AU), Helios 2 (at 0.29, 0.65 and 0.89 AU), Wind at the Lagrangian point L1, and Ulysses at 1.4 AU within high‐speed streams observed in the ecliptic.

(Telloni et al, ApJ 2015)

PAS will offer the possibility to study turbulence up to the proton cyclotron frequency for the first time so close to the Sun.


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Studying turbulence with PAS

Solar wind turbulence is mainly made of two ‘ingredients’(Mariani et al., 1973; Thieme et al., 1988, 1989; Tu et al., 1989, 1997; Tu and Marsch, 1990, 1993; Bieber and Matthaeus, 1996; Crooker et al., 1996; Bruno et al., 2001, 2003, 2004; Chang and Wu, 2002; Chang, 2003; Chang et al., 2004; Tu and Marsch, 1992, Chang et al., 2002, Borovsky, 2006, 2009, Li, 2007, 2008, Tu and Marsch, 1991; Bruno and Bavassano, 1991, Bieber et al, 1996; see more refs. in Bruno and Carbone, 2013)

• Alfvénic fluctuations which progate

• Structures advected by the wind or locally generated

(Tu and Marsch, 1995)Alfvénic fluctuations would cluster within adjacent flux‐tubes along the local magnetic field direction


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(Bruno et al, 2001 )


Structures advected by the wind

A height-time plot of small-scale structures in the solar wind, as measured by the Heliospheric Imager on STEREO. At the perihelia of Solar Orbiter (yellow) the advected structure of the wind is clearly visible.

0.28AU

Going close to the sun and sampling for long enough time intervals will allow to go through the advected structure of the wind

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(Courtesy J. Davies, Rutherford Appleton Laboratory, UK)


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Heavy Ion Sensor (HIS)

• mass in the range 2‐56 amu/q• energy in the range 0.5 – 100 keV/q• FoV: elevation ±18°, azimuth ‐30°÷+66°

• Heavy ion charge state ratios, elemental abundances, charge state distributions and 3D velocity distribution functions

• Full 3D distribution measurements at 30s in NM and reduced 3D at 4s in BM

Scientific objectives 3D VDF of minor ions for the first time in the inner

heliosphere (temperature anisotropy and differential heatingmechanism);

ion composition as a key to link the Sun and the Heliosphere; origin and acceleration of solar wind; seed population of SEP

Some of the main features of heavy ions

Courtesy of S, Livi


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Charge states of heavy ions are established deep in the solar corona and do not change afterwards.

Heavy ions are a minor component of the solar wind: they act as tracers.

Chemical composition is different in the solar wind and in the energetic particles. Suprathermals are the link in between.

Courtesy of S, Livi

Energetic ions might be accelerated directly out of the solar wind suprathermal tail by a stochastic process associated with the shock wave disturbance.

Comparison between SWA suprathermal composition near the shock and that of energetic particle will shed light on the role of shocks in generating SEP’s.


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HIS measures ion composition and energy distribution extending from the solar wind into the suprathermal domain and covering the energy range of SEP seed particles injected to shock acceleration.

Suprathermal ions

The transition between fast and slow wind is sharply detected by elemental and charge composition which remains unchanged during wind expansion.

Small scale properties of coronal hole boundaries can be detected

Slow wind has higher oxygen freeze‐in temperatureSlow wind has higher FIP effect (enrichment of Mg/O, Mg has a lower FIP with respect to O)


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Origin of the solar wind

SWA measurements of• electron pitch angle distribution, • alpha/proton ratio, • freeze‐in temperature (e.g. Fe), • O and Fe charge state ratios will establish firm links between coronal sources of CME’s and their in‐situ counterparts.

Heavy ions will help to identifythe source regions of CME’sHeavy ions will help to identifythe source regions of CME’s


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Schedule Delivery Dates

EAS PAS HIS DPU SUITE (Hardwareready)

STM to MSSL Completed Completed Completed Testing In progress – No delivery expected.

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STM to ESA ‐ Completed Completed ‐ ‐

EM to MSSL Completed Completed Completed Completed ‐

EM to ESA ‐ ‐ ‐ ‐ June 2016

Qualification ProgrammeComplete

July 2016 25 March 2016

March 2016 28 March 2016 ‐

PFM to MSSL 4 October 2016 1 November 2016

October 2016 30 September 2016

PFM to ESA ‐ ‐ ‐ ‐ December 2016

The SWA team is embarking on an AIT Plan B involving testing with flight‐like EM units until PFM units become available.


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SolO is a discovery mission, never been a mission like this in the inner heliosphere (remote & in situ packages @ 0.28 AU, corotation, high latitude)

SolO will answer fundamental questions relevant to both solar and stellar physics

SWA will investigate kinetic and fluid properties of the bulk solar wind plasma and dominant physical processes (e.g. wave‐particle interactions, origin and dissipation of turbulence, particles acceleration, etc.)

Launch in 2018… 44 years after Helios!

Conclusion

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