Presentation given at Max Planck Institute for Plasma Physics (Garching) on 13th July 2018.

1. Tiziano Fulceri 1Garching, 13th July 2018
Max-Planck-Institut
für Plasmaphysik
Measurement of the Spatiotemporal
Development of a Plasma Profile during
Magnetic Reconnection
T. Fulceri
Supervisors: U. Stroth (TUM), O. Grulke (IPP Greifswald)
Special Thanks to: A. v. Stechow (IPP Greifswald)

2. Tiziano Fulceri 2Garching, 13th July 2018
Outline
 Magnetic Reconnection
 Vineta II
 Diagnostics
 Plasma Profiles
 Summary and Outlook

3. Tiziano Fulceri 3Garching, 13th July 2018
Magnetic Reconnection - Introduction
 M.R. is a topological
rearrangement of
magnetic field lines
 Efficient transfer of
magnetic to kinetic
and thermal energy
 Sweet-Parker model
 Ideal non-resistive
MHD…
 …except in
current sheet Yamada, Rev. Mod. Phys. Vol. 82, Jan-Mar 2010
Magnetic energy conversion:

4. Tiziano Fulceri 4Garching, 13th July 2018
Magnetic Reconnection – Non-Collisional Plasmas
 Magnetic Reconnection in non-
collisional plasmas is not modeled
by Sweet-Parker
 In astrophysics: driven by matter
flows (CMEs, Earth Magnetosphere)
 In the lab: externally driven with
axial guide field
 Need: Fast, Reliable, Precise system
for the recording of plasma profiles
current sheet structure and evolution
→ Vineta II + diagnostics for:
Top Left: NASA/Yohkoh solar observatory; Bottom Left: MMS Mission NASA Website

5. Tiziano Fulceri 5Garching, 13th July 2018
VINETA II - Overview
 Linear device
 Guide field along axial
direction
 Highly-reproducible
electron-gun plasma
discharges at z = -0,36 m
 Drives X-point magnetic
field geometry
 Drives magnetic
reconnection (not active yet)
 Plasma profiles on a cross-
sectional plane at z = 0
Parameter Value
Length 1,5 m
Diameter 1 m
Axial Guide Field (B//) 15 mT
Gas Used Argon
guide field
coils
Reconnection-Drive
1m
E-gun
position
X-Drive

6. Tiziano Fulceri 6Garching, 13th July 2018
VINETA II – Guide Field Geometry
● X-Drive generates different
guide field geometries
● 3D magnetic field lines can
be calculated
● Plasma profiles shape can
be predicted

7. Tiziano Fulceri 7Garching, 13th July 2018
VINETA II - Diagnostics
● Two movable diagnostics available on the measurement plane:
• B-dot probe (magnetic field in (x,y,z) directions)
• Langmuir probe (temperature, electron density, plasma potential)
Langmuir probe
B-dot probe

8. Tiziano Fulceri 8Garching, 13th July 2018
B-dot Probe - Principle
 Set of 3 mutually perpendicular coils in (x,y,z) directions
 Faraday’s Law → induced EMF’s give B-vector as time integral
A. v. Stechow, PhD Thesis, 2014

9. Tiziano Fulceri 9Garching, 13th July 2018
Langmuir Probe - Principle
 Small metallic electrode inserted into
a plasma
 Probe is biased to various voltages
(in our case: -80 V to + 80 V)
 Current is collected by the probe
 An IV-characteristic is recorded
 From 3-parameter fit of region (A,B)
plasma parameters can be
extracted:
• Electron Temperature (Te)
• Electron Density (ne)
• Plasma Potential (Vp)
(A) (B) (C)

10. Tiziano Fulceri 10Garching, 13th July 2018
Langmuir Probe – Fast Sweeps
 Plasma profile evolution
timescale: 300 µs → several 10’s
of kHz needed for time evolution
→ 50 kHz (fast sweep)
 Inductance/capacitance in the
measuring circuit introduce
hysteresis
• Measurement circuit optimized
for fast measurements:
• fast high-current amplifier
(BW = 120 kHz, Ipeak = 10 A)
• low inductance (contactless current
monitor instead of shunt resistor),
• floating circuit (ground loop
mitigation)

11. Tiziano Fulceri 11Garching, 13th July 2018
Langmuir Probe – Sample Evaluation
 24 IV-characteristics during
rising voltage
 24 IV-characteristics during
falling voltage
24 x
Voltage Cycles
Identification
&
Signal Splitting
 Time trace of Bias
Voltage
 Time trace of
Collected Current
 48 non-linear fits for every plasma discharge…
 …giving time evolution of Te, ne, Vp at an (x,y) position

12. Tiziano Fulceri 12Garching, 13th July 2018
Plasma Profiles - Te and ne, X-Drive OFF

13. Tiziano Fulceri 13Garching, 13th July 2018
Plasma Profiles - Te and ne, X-Drive at 1,4 kA

14. Tiziano Fulceri 14Garching, 13th July 2018
Plasma Profiles - Te and ne, X-Drive at 2,8 kA

15. Tiziano Fulceri 15Garching, 13th July 2018
Plasma Profiles - p, (Ex,Ey), and Vp, X-Drive OFF

16. Tiziano Fulceri 16Garching, 13th July 2018
Plasma Profiles - p, (Ex,Ey), and Vp, X-Drive at 1,4 kA

17. Tiziano Fulceri 17Garching, 13th July 2018
Plasma Profiles - p, (Ex,Ey), and Vp, X-Drive at 2,8 kA

18. Tiziano Fulceri 18Garching, 13th July 2018
Plasma Profiles - p, (Ex,Ey), X-Drive OFF

19. Tiziano Fulceri 19Garching, 13th July 2018
Plasma Profiles - p, (Ex,Ey), X-Drive at 1,4 kA

20. Tiziano Fulceri 20Garching, 13th July 2018
Plasma Profiles - p, (Ex,Ey), X-Drive at 2,8 kA

21. Tiziano Fulceri 21Garching, 13th July 2018
Summary and Outlook
 Summary:
• Magnetic reconnection needs laboratory investigation
• Vineta II can produce suitable guide-field geometry
• Plasma profiles can be measured
 Conclusions:
• Data extraction procedure is reliable
• Reconstructed profiles shapes compare well with expected field
geometry
 Next Steps:
• MHD force balance analysis → ?
• Include magnetic diagnostic data
• Introduce ECRH-driven background plasma
• Introduce Reconnection Drive

22. Tiziano Fulceri 22Garching, 13th July 2018
Max-Planck-Institut
für Plasmaphysik
Thank You!