This document summarizes work using a fast-swept Langmuir probe to observe the evolution of plasma parameters during magnetic reconnection experiments on the VINETA.II device. The probe measures electron temperature, density, and potential with 10 microsecond temporal and 1 cm spatial resolution. Profiles reconstructed from a transient plasma generated by electron guns show consistency with the expected magnetic field topology. An localized warmer and denser region is observed, corresponding to a current-carrying sheath. The in-plane electric field points away from this sheath and provides information on electron dynamics relevant to the reconnection rate. Further refinement of the data analysis is underway.

1. *Corresponding author: tiziano.fulceri@ipp.mpg.de
DPG Spring Meeting
Munich – Germany, 17 – 22 March 2019
Max-Planck-Institut für Plasmaphysik
This work has been carried out within the framework of the EUROfusion Consortium and has received funding
from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement number
633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
Acknowledgement to the Max Planck Princeton Center for Plasma Physics
Langmuir Probe Data Processing
● Langmuir probe voltage (V) and current (I) signals
associated with a transient E-gun discharge are acquired.
● The signals are splitted cycle-wise.
● At 100 kHz frequency there is hysteresis, coming from the
measurement circuit and from the plasma itself.
● Plasma potential (Vplasma) is taken as a root of Ipoly’’(V)
● Electron temperature and density are estimated through
the phenomenological model
where:
 I0 is a current offset
 a models the current sheath expansion [1]
 b is a function of electron saturation current, plasma
potential and electron temperature [2]
 c is the inverse of electron temperature
From which:
Conclusions and Outlook
● The profiles of plasma parameters have been estimated with
a spatiotemporal resolution high enough to observe M.R..
● The geometry of the profiles is consistent with the
reconnection topology.
● Development of a more precise data analysis procedure is
underway
Abstract
VINETA.II is an experimental device suitable for the
investigation of magnetic reconnection in laboratory
plasmas. A fast-swept (100 kHz) Langmuir probe is used
to reconstruct electron temperature, electron density,
and plasma potential profiles with ~10 µs temporal
resolution and ~ 1 cm spatial resolution. The evolution of
both a transient plasma generated by an array of
electron guns can be observed within a 300 µs
timeframe. Reconstructed profiles are interpreted taking
into account the expected magnetic field topology and in
relation to their effect on the magnetic reconnection rate.
[1]Plasma Diagnostic Techniques. Edited by R. H. Huddlestone
and S. L. Leonard. Academic Press, 1965 – Ch. 4 “Electric
Probes” F. Chen
[2] American Journal of Physics 75, 1078 (2007)
Observation of plasma profiles evolution
relevant for magnetic reconnection at VINETA.II
T. Fulceri1*, A. von Stechow1, O. Grulke1,2 1Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany; 2Technical University of Denmark, 2800 Kgs, Lyngby, Denmark
Motivation
● Magnetic Reconnection (M.R.) is the change of
topology of magnetic field lines in a plasma, associated
with the release of thermal and/or kinetic energy.
● Some aspects of the M.R. phenomenon are not
completely understood.
● Investigation in controlled laboratory conditions is
necessary in order to individuate key parameters and
mechanisms associated with M.R. events.
Data Interpretation
● All the data shown corresponds to the same time
instant (t = 181.4 µs) within a 300 µs discharge.
● All the profiles show a consistency with the magnetic
field X-topology produced by the axial conductors.
● Temperature, density, and current density profiles
clearly show the cross-section of a localized, current-
carrying, relatively denser and warmer region
(current sheath).
● The reconstructed in-plane E-field (~ 1 kV/m) points
away from the current sheath and gives information on
the electron dynamics, which is expected to affect the
reconnection rate.
x5 Int.
VINETA.II device Vacuum system:
• Reconnection module
(D = 0.97 m, L = 1.60 m)
• Auxiliary module
(D = 0.40 m, L = 1.12 m)
Axial magnetic field:
• Rec. module coils (B = 50 mT)
Current drives:
• X-drive (I ~ 2 kA)
• Reconnection-drive (I ~ 1.5 kA)
Plasma sources:
• ECRH 1 kW-Magnetron
(stationary, ne ~ 1016 m-3)
(expected)
• Electron-gun array
(transient, ne ~ 1019 m-3)
x5 Int.
Diagnostics
Spatial resolution: Δx = Δy = 10 mm
Langmuir probe
• direct: Te, ne, Vplasma
• indirect: pe, Exy
• temporal resolution: Δt = 10 µs
B-dot probe
• direct: B-field
• indirect: Ez,ind, jz
• temporal resolution: Δt < 1 µs
2D E-Gun plasma profiles in reconnection topology
Electron Gun Array (cut)
E-Gun
Array
position
ECRH
Magnetron
position
Reconnection-
DriveX-Drive
●Two sets of values of Te, ne, Vplasma are extracted for each time
point (rising and falling voltage respectively) and averaged.