3D reconnection and flow dynamics in Swarthmore Spheromak Experiment (SSX)

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3D reconnection and flow dynamics in Swarthmore
Spheromak Experiment (SSX)
Michael Brown Swarthmore College, NSF Center
for Magnetic Self-Organization Chris Cothran,
David Cohen, Jason Horwitz 07, Vernon Chaplin
07, Nick Murphy (UW) M. J. Schaffer E. V.
Belova Research supported by US DOE and NSF
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The SSX Laboratory
10kV/100kA Pulsed power
Cylindrical flux conservers and vacuum chamber
(?0.40m, L0.65m)
Coaxial magnetized plasma guns on each end (1 mWb)
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SSX parameters
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2D MHD simulation
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Tangled 3D magnetic lines (lab and solar)
5 earth diameters tall
one foot tall
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Reconnection geometry
Separatrix
Current flow (out) Electron flow (in)
Inflow (slow)
Electron Diffusion Region
Outflow (fast, Alfvenic)
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Simulation results 3D resistive MHD (E. Belova,
PPPL)
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Local 3D probe measurements
Right-handed Spheromak
Left-handed spheromak
Reconnected poloidal flux
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SSX device (distributed probe array)

• Opposing magnetized plasma guns
• Close fitting copper flux conserver
• Midplane IDS access for flow studies

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• Goals of SSX research program
• understand simple, compact magnetic structures
• underlying 3D physics (magnetics, flow)
• inform astrophysical/solar physics concepts
• motivate/train undergraduate scientists

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• Reconnection and flow dynamics in SSX
• Ion Doppler spectroscopy (jets, heating)
• local flow (Mach probes)
• electron heating (soft x-rays, vacuum
  ultraviolet)
• 3D reconnection structure

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Bi-directional outflows in SSX High resolution
ion Doppler spectroscopy (Cothran, et al, PRL to
be submitted J. Fung thesis 06)
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Ion Doppler Spectroscopy (1.33m)
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Ion Doppler Spectroscopy (1.33m)
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Ion Doppler spectrometer layout
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IDS line shapes (high resolution)
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Observation of bi-directional outflow
Data is effectively f(v_r) one pixel is 10 km/s
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Stills from IDS movie
Dynamics of the flow (bursts, turbulence) encoded
in the lineshape
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Bi-directional outflows on the sun D. Innes
(SOHO SUMER chromosphere) Innes, Nature,
1997 Innes, Solar Physics, 1997
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Location of SUMER slit on solar disk
SiIV light dispersed along slit
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Velocity resolution 10 km/s
Spatial resolution 1000 km
Spatially localized events
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Local flow measurement Mach probes (Jason
Horwitz 07)
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Mach probe schematic idea
Mach number K ln(Iup/Idown) Calibrate with edge
array of mag probes
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Mach II probe mounted (r gt ri)
U Wisc MST flange
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Mach II probe during assembly
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Mach I probe in Helium plasma
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Small Mach I probe (r lt ri)
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Mach II probe flip test (single spheromak)
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Large inflow from plasma gun
M 2, v 100 km/s
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Mean azimuthal flow during merging
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Mean axial flow during merging
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Hot ions in SSX Cothran, et al (SSX) (low
density discharges, after glow discharge
conditioning, short gas delay)
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Hot ions in SSX (merging)
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IDS hot ion temperature measurement
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IDS hot ion flow measurement
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Scaling of Ti with density
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Scaling of Ti with density (single sph)
Dipole-trapped, Gaussian fit, early in formation
(30-40 ms)
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Hot ions in the extended corona Cranmer, Space
Science Rev, 2002 (UVCS)
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UVCS line of sight
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Solar wind parameters
SSX density
SSX magnetic field
SSX Alfven speed
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Greater than mass ratio ion temperatures
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Collier (1996)
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Hot electrons in SSX Vernon Chaplin 06 and
David Cohen (VUV spectrometer and soft x-ray
array)
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Typical calculated spectra
12 eV case
28 eV case
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Soft x-ray diode response
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SXR responsivities with spectrum
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Sample SXR signals
Anomalously strong signal in high energy bins
electron tail?
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Soft x-ray array assembly
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Soft x-ray array in SSX plasma
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Vacuum ultraviolet monochrometer (50-250 nm)
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Te from CIII (97.7 nm) to CIV (155 nm) ratio
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Te from CIII (97.7 nm) to CIV (155 nm) ratio
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Te from SXR array fitting
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Mean azimuthal flow during merging
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IDS hot ion temperature measurement
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Quadrupole measurement in themagnetopause Mozer,
et al, PRL, 2002 (Polar)
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RECONNECTION
Reconnection is the process that occurs when
magnetized plasmas flow into each other. It
produces a. Change of topology b. Particle
acceleration Reconnection occurs at the
magnetopause, on the sun, on all scales in
astrophysics (accretion disks, etc.) and in
laboratory plasmas.
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Reconnection at the magnetopause
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Cluster Encounter with the Diffusion Region in
the Magnetotail on 2003-09-19
Quadrupolar magnetic field
Bipolar electric field

• Clear detection of Hall electromagnetic fields
• - Large electric fields in density minima in the
  vicinity of separatrices

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Borg et al, GRL, 2005

• Context
• Reconnection jet (Vx) reversal
• Normal magnetic field (Bz) reversal
• Clear evidence for Hall electric field

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Trajectory of POLAR spacecraft
Polar trajectory
Mozer, et al, PRL (2002)
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POLAR SUB-SOLAR OBSERVATION OF THE ION SCALE
distance in ion inertial lengths
Mozer, et al, PRL (2002)
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SYMMETRIC, 2-D MODEL OF MAGNETIC FIELD
RECONNECTION
Separatrix
Electron Diffusion Region

• COMMENTS
• Two scale sizes
• In the real world, this geometry occupies a
  volume having a measure of zero.
• Two classes of electron diffusion regions.

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Quadrupole measurement in SSX Mattheaus, et al,
GRL (2005) Landreman, (2003) Cothran, et al, GRL
(2003)
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Driven magnetic reconnection experiments
Large slots cut into FC rear walls define the
reconnection region 3D magnetic
structure Energetic particles
RGEAs
Magnetic probe array
Cothran et al GRL 30, 1213 (2003) Brown et al
ApJL 577, 63 (2002) Brown et al Phys. Plasmas 9,
2077 (2002) Brown et al Phys. Plasmas 6, 1717
(1999) Kornack et al Phys. Rev. E 58, R36 (1998)
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3D magnetic probe array
600 coils, 5?5?8 array 2 cm spacing 25 three
channel 81 multiplexer/integrator boards 10
eight channel 8-bit CAMAC digitizers Full probe
readout every 0.8 ?s
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Flux conservers for partial merging
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Flux conservers for partial merging
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3D probe measurements in SSX
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3D probe measurements in SSX
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3D probe measurements in SSX
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Magnetic reconnection in three dimensions
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In-plane-field
Ion inertial scale 2 cm
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Quadrupole out-of-plane field
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Quadrupole out-of-plane field
Ion inertial scale 2 cm
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Trajectory of Polar spacecraft
Path of tiny Polar
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POLAR SUB-SOLAR OBSERVATION OF THE ION SCALE
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Summary (1)
Bi-directional sub-Alfvenic outflow first
measured with ion Doppler spectroscopy on SSX
Hot ions and warm electrons also observed in the
laboratory
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Summary (2)
Mach probe measurements corroborate IDS flow
results during merging events
Electron heating observed during merging events
less heating for single spheromak
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Summary (3)
3D structure measured at the ion inertial scale
in SSX merging experiments
First laboratory measurement of out of plane
quadrupole field observed on length scale similar
to Polar observations at the magnetopause
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Oblate FRCs in SSX Summer 2007 (in
collaboration with Mike Schaffer GA)
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Trapezoidal flux conserver in SSX
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2D merging simulation (N. Murphy)
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FRC equilibrium with trapezoidal FC
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FRC equilibrium with trapezoidal FC
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Equilibrium with trapezoidal FC
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Coming up (summer 2007) Search for hot ions (O,
N, ) will need amplifiers (32 ch) and/or
doping
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New high resolution mag probe(will need
amplifiers 48 channels)
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Trapezoidal flux conserver in SSX