1. Plasma Physics – the ubiquitous environment Hugh Potts, Craig Stark, Craig MacLachlan and Declan Diver Make a surface from the data and allow ‘floating’ tracking particles to be randomly nudged by the granulation ‘bumps’ Balltrack – efficient flow measurement Take MDI continuum images of the photosphere Filter to extract granulation signal V(x i,y i, t) : smoothed velocity  : spatial smoothing radius  t: time smoothing interval r n,t : distance from (x i,y i ) to ball Average the velocities of trackers over space and time to obtain macroscopic flow field How accurate can you be? The errors are dominated by the random walk of the granules, inherent in the fluid motion, so results are nearly as good as you can get! Small scale magnetic reconnection on the sun The surface flows advect small magnetic elements of both polarities into the sink points of the convective cells. At these points of convergence small scale energy release is observed as soft X-ray bright points. Comparison of soft X-ray images of bright points from Yohkoh with regions of high convergence of flow driven magnetic elements. The black lines are the lanes between the convection cells. The area is 4x5.5 armin, roughly at disk centre. Use BALLTRACK to get high resolution flow field from MDI continuum data Process flow field as described above, to get the convection cell structure (black lines, RH figure) Track the smallest magnetic elements from MDI high resolution magnetogram data (red/blue, RH figure) Find the areas where large amounts of field of bopth polarities are beiong advected to the same place (green circles, RH figure) Compare with the bright points observed in soft X-ray data from Yohkoh-SXT (black circles, LH figure) Alfvén Ionization and FIP Dust growth in plasmas Neutral flux impinges on charge-balanced magnetised plasma - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + Neutral-ion collisions eject ions, leaving strongly magnetised electrons in place Pocket of charge imbalance Neutral flow encounters magnetised plasma Neutral – ion impact results in some ions being ejected Electrons transport strongly constrained by magnetic field Pocket of unbalanced charge is created, persisting until impeded electron transport can neutralise Resultant electric field grows until resists further ejection of ions Electrons are excited to new potential by local field. If then ionisation occurs Voltage steady over large discharge current range, then sudden increase at critical Voltage V c – total ionisation V c different for each element ! Critical voltage scales with magnetic field – shows that critical speed – E/B drift – is being selected At the photosphere of the sun large scale convective flows interact with the motions of the smallest magnetic structures, tangling them and making them unstable, leading to the release of energy The chemical composition of the solar Atmosphere is different from that of solar surface. Low first ionisation potential (FIP) elements are more abundant in the atmosphere by factors ranging from 4-11. How does this happen? neutrals Magnetised plasma Magnetic field + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - Grains of dust in a plasma accumulate negative charge. The electric field produced by this charge accelerates ions to the surface of the grain. Asymmetries in the shape of the grain affect the shape of the electric field, and hence the subsequent growth of the grain. Proposed Mechanism: Alfvén ionisation Alfvén in the Lab: Rotating plasma Reactor Note the anomalies: Observed bias for large FIP elements….. Low FIP can’t be the only factor for bias Electronegative Plasmas Alfvén ionization fits the data better than existing models: Elements sorted by first ionisation energy. Shaded rows indicate elements where FIP bias has been observed in the upper solar atmosphere or wind Elements sorted by Alfvén critical speed. electron density high:  p >  Electric Field excluded Electron energy drops: formation of negative ions Negative species now less mobile:  p <  Electric Field penetrates negative ions broken up by electric field Periodic (kHz) optical emission from plasma: flashing instability Numerical simulations show periodic electronegative ion formation and destruction, after transients MacLachlan et al, 2005 Corr, Steen & Graham PSST 12 265 2003 Electronegative plasmas are unstable to formation of negative ions, resulting in up to 40% in modulated light output. We have a fundamental explanation of the instability. Potts, Barrett, & Diver: 2004, A & A, 424 253-262 Potts, Barrett & Diver: 2003, Solar Physics, 217 69-78 Diver, Fletcher & Potts: 2005 Solar Physics, 228, 207 We will build a rotating plasma reactor for laboratory and astrophysical plasma experiments elliptical dust grain uniform electron-ion plasma. mobility of the electrons ensures grain negatively charged sheath forms, with non-radial electric field ion transport to grain surface affected by distorted field - a spherical shell of ions follow nearly radial paths until close to the elliptical surface, where the local inhomogeneous field will deflect their trajectories and distort the mass deposition. Contour and surface plot of grain potential arc length around ellipse is given by the incomplete elliptic integral of the second kind - ratio of the two arc lengths in the first quadrant created by the intersection of the ellipse and the 45 0 parabola is As the eccentricity tends to zero, material at infinity is uniformly deposited over the surface since hence RESULTS critical parameter: optimal grain size for elliptical growth - grains of a:b less than 3:1 do not grow elliptically Stark et al, 2005