1. The Sun as a Particle Accelerator S.A. Matthews 1, D.R. Williams 1, L.M. Green 1, L. Fletcher 2, E. Kontar 2, I. Hannah 2, A.L. MacKinnon 2, V. Nakariakov 3, D. Tsiklauri 4, V.V. Zharkova 5, P. Browning 6, R.A. Harrison 7, M. Mathioudakis 8, C. Parnell 9 1 UCL Mullard Space Science Laboratory 2 University of Glasgow 3 University of Warwick 4 Queen Mary University 5 University of Bradford 6 University of Manchester 7 STFC Rutherford Appleton Laboratory 8 Queen’s University Belfast 9 St Andrews University

2. Øleroset et al. 2001 Fundamental process for energising plasma in a host of cosmic settings: –F–Flares in main-sequence stars –s–solar wind –a–accretion disks –T–T Tauri stars (star formation) –m–magnetosphere –+–+... Gap in our knowledge: –W–We have empirical evidence about e - acceleration, but... –w–we still know almost nothing about ion acceleration! –L–Lacking crucial data in windows yet to be opened up. Acceleration through Collisionless Reconnection

3. Hurford et al. 2006 γ-rays (protons, ions) X-rays (electrons) 3 We know magnetic fields play a role,... But, how and where is acceleration triggered? Why is acceleration so efficient? Are ions always accelerated? –A–Are they accelerated in different places than e - ? –O–Or are they just accelerated differently? Can we trace them from cradle to grave? Magnetic structures reorganise Energetic particles hit Particle Acceleration

4. 4 Huge amounts of energy are carried by particles, often at ultra-relativistic velocities. What is the nature of the acceleration process? –Stochastic acceleration (waves, turbulence) ; –Direct electric fields (e.g. reconnection Ē) ; –Fermi acceleration at shocks (first- and second-order)? –ion vs electron vs positron acceleration And what carries the energy? –how much is carried by ions, electrons,...neutrals; –π 0, π ± decay gives clues to ions’ high energy cut-off By understanding how and where this energy is deposited on our closest star, we can build a solid foundation for a physical understanding of astrophysical plasmas.

5. 5 Kaufmann et al. (2004) Particle-heated chromosphere is also expected to radiate in THz range –feedback between non-thermal particles, thermal populations and, magnetic fluctuations and structures is poorly understood Recent sub-THz observations give tantalising clues to e - / e + acceleration –Gyrosynchrotron emission? –Shape of the spectrum into the THz domain is key to discriminating the mechanism(s) responsible for this acceleration. ? Our atmosphere is opaque!

6. 6 Tracing the process Thermal continuum emission from the chromosphere when particles hit Achieve upper limits on the initial accelerated particle energies –First measurements of solar flares in THz (35 and 150 μm... and beyond) from space. Probe the very highest energy particles (protons and ions) that are produced by the Sun –HXR/gamma-ray spectrometry at highest energies attained with a solar instrument (10 keV – 600 MeV). Look for the sources and sinks of energetic particles –At thermal and non-thermal energies –Which field lines do the particles stream down? –Direct HXR imaging up to ~70 keV (focussing optics). –High resolution (0.1”) SXR imaging up to 20 keV Find where the particles end up in the chromosphere. –What are the magnetic structures, low down, associated with these sites? –How do they guide particles and determine the coronal magnetic field? –High resolution chromospheric imaging and magnetic field information

7. Concept – Baseline Payload Instrument Comparison ε min or λ max ε max or λ min ΔΕ or ΔλΔsΔt 1. THz Imager (sub-mm) 0.9 Thz (350 µm) 8.5 THz (35 µm) multiple bands50”100 ms No comparison! 2. High-ε Spectrometer10 keV600 MeV2 keV (662 keV) 32 ms – 1 s RHESSI3 keV30 MeV1 – 10 keV2.3” to 36” < 10 ms to 4 s 3. Focusing X-ray Imager (Direct Imaging) ~3 keV70 keV~1 keV15”~0.1 s Solar Orbiter/STIX4 keV150 keV1 – 15 keV7”1 – 5 s 4. Hi-Res X-ray Imager (smart X-ray optics) ~1 keV20 keV0.5 keV0.1”0.1 s Hinode/XRT0.06 keV6.2 keVmultiple bands2”~60 s 5. Lyman α imager1216 Å1”0.2 – 20 s Solar Orbiter/EUI1216 Åequivalent 0.3”<1 – 100 s

8. 8 0.1 10 100 ε timescales 1keV101001MeV101001GeV 1 High-ε Spectrometer Smart Imager RHESSI Focussing Imager

9. 9 0.1 10 100 ε spatial scales 1keV101001MeV101001GeV 1 High-ε Spectrometer Smart Imager RHESSI Focussing Imager

10. 10 Platform Requirements OrbitSun synchronous (e.g., TRACE, RHESSI, Hinode) PointingAccuracy: 1 – 5”Stability: better than 0.1” Telemetry~ 50 Gb day -1

11. 11 Scientific Base of Interest (UK) UK: UCL Mullard Space Science Laboratory University of Glasgow University of Warwick Queen Mary University University of Bradford University of Manchester STFC Rutherford Appleton Laboratory Queen’s University Belfast University of Central Lancashire University of St Andrews +... Europe Observatoire de Paris à Meudon +... This is a proto-consortium, and we welcome new involvement! Key UK academic institutes have been involved in developing this concept

12. In a nutshell Novel science with direct application to particle acceleration across physics. Strong support from a large cross-section of the community, in UK and in Europe Builds directly on key UK science strengths, technology development and heritage.