Magnetic Field and Current Profile Diagnostics for the VINETA ...Magnetic reconnection is the...
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Introduction Collisional vs Collisionless Reconnection Magnetic Field and Current Profile Diagnostics for the VINETA II (V.II) Magnetic Reconnection Experiment MPI for Plasma Physics, EURATOM Association, Greifswald H. Bohlin, F. Braunmueller, O. Grulke, T. Klinger Magnetic Field Diagnostics Sweet-Parker Reconnection Asumptions: Steady state The plasma is an incompressible fluid Mass is conserved Uniform pressure Problems: Observed reconnection rate much faster than predicted Model does not explain collisionless reconnection ? ? ? ? ? Field lines and plasma expelled at velocity V =V out a ? ? Experiment Sweet-Parker Reconnection Rate: Lundquist Number: , B-probe array: ? ? 2D reconstruction of reconnecting magnetic field Inductive coils 1.6m 1m Comparison of Sweet-Parker Model with Experiment [M. Yamada, "Review of Controlled Laboratory Experiments on Physics of Magnetic Reconnection," Journal of Geophysical Research 104 14,529 (1999)] 10 1 10 2 10 3 10 -4 10 -2 10 0 10 2 10 4 f [kHz] U [V] U probe U pickup Capacitive pickup 10 1 10 2 10 3 10 2 10 3 10 4 10 5 f [kHz] Sensitivity [V/T] Sensitivity of Single Probe Reconnection in Space [W. Baumjohann and R. A. Treumann, Basic Space Plasma Physics, Imperial College Press, 1997] [http://upload.wikimedia.org/wikipedia/commons/a/aa/Polarlicht_2.jpg] [http://www.nasa.gov/vision/universe/solarsystem/solar_cycle_graphics_prt.htm] v in v out v in B B 2L 2ä V in V in V = out V A A R I Measurement of Electromagnetic Fluctuations During Fast Reconection Magnetic reconnection is the topological rearrangement of magnetic fields through the breaking and reconnection of magnetic field lines. It plays an important role in many space plasmas, such as solar flares, as well as in some laboratory processes. A review of the planned upgrade of the linearly magnetized plasma device VINETA is given. The setup of VINETA has been modified by adding a new module, whose larger dimensions will allow for the study of the plasma dynamics of driven magnetic reconnection. Furthermore, diagnostic tools for magnetic field and current measurements are presented. An array of induction coils will be used for determening the spatio-temporal evolution of the magnetic field. Current profile measurements will be done using a Rogowski coil. Reconnection Drive Working Gas Argon Guide Field B < 0.1 T z Pressure -3 p= 10 Pa Electron Temperature T =6eV e Density 16 -3 n=10 m Lundquist Number 3 S= (1.2-4.9)*10 Driving Current I =3kA D Drive Time ô =10ìs D gas anode cathode Biased plate +200V Plasma Gun Rogowski Coil on XY-Positioning System 10cm -10 -5 0 5 10 -10 -5 0 5 10 x [mm] y [mm] 0 0.2 0.4 0.6 0.8 1 Magnetic field coils To pump 4m Helical antenna 0 20 40 60 80 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Voltage [V] Time [us] Current Monitor Rogowski Coil 0 20 40 60 80 -50 0 50 100 150 200 250 300 350 Current [A] Time [us] Current Diagnostics N~470 R=7.5mm Induction Equation: [http://sprg.ssl.berkeley.edu] ? Current produced by resonant LC circuit ? Parallel conductors produce in-plane magnetic field In-Plane Reconnection Magnetic Field y [m] -0.4 -0.2 0 0.2 0.4 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 x [m] -20 -15 -10 -5 0 5 10 15 20 V in V in V out V out B [mT] Configuration for Measurement of Alfvén Waves Magnetic Field of Single Wire Current Density Profile of Single Wire Magnetic Field of Alfvén Wave Current Density Profile of Alfvén Wave Setup for Measuring Current Profile of Plasma Gun Discharge Current Density Profile of Plasma Gun Discharge Rogowski Coil for Determination of Current Profile j [I/A] Induced Voltage of Rogowski Coil [H. Ji et al., ,Phys.l Rev. Lett. 92, 115001 (2004)] [F. Braunmueller, ”Fluktuationsdiagnostik zur Messung dynamischer Magnetfelder in Plasmen, Diploma thesis, Heidelberg University, (2011) Setup for the Princeton Magnetic Reconnection Experiment Calculated Current
Transcript of Magnetic Field and Current Profile Diagnostics for the VINETA ...Magnetic reconnection is the...
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Magnetic reconnection is the topological rearrangement of magnetic fields through the breaking and reconnection of magnetic field lines. It plays an important role in many space plasmas, such as solar flares, as well as in some laboratory processes. Though extensive theoretical and experimental research has been carried out on magnetic reconnection, the mechanism behind the process is still not fully understood.
A review of the planned upgrade to the linearly magnetized plasma device VINETA is presented. The current setup will be modified by adding a new module, whose larger dimensions will allow for the study of the plasma dynamics of driven magnetic reconnection. A guide field will be used to confine the plasma and the reconnection will be driven by passing a current through two parallel conductors placed inside the new module.
Besides the standard Langmuir probes, the main diagnostics will consist of a B-dot probe array for reconstructing the magnetic field and Laser Induced Fluorescence (LIF) for determining the ion energy distribution function near the X-point. The role of axial boundaries is discussed in detail.
Introduction
Collisional vs Collisionless Reconnection
Magnetic Field and Current Profile Diagnostics for the VINETA II (V.II) Magnetic Reconnection Experiment
MPI for Plasma Physics, EURATOM Association, Greifswald
H. Bohlin, F. Braunmueller, O. Grulke, T. Klinger
Magnetic Field Diagnostics
Reconnection Parameters
Sweet-Parker Reconnection
Asumptions:Steady stateThe plasma is an incompressible fluidMass is conservedUniform pressure
Problems:Observed reconnection rate much faster than predictedModel does not explain collisionless reconnection
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?Field lines and plasma expelled at velocity V =Vout a
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Experiment
Sweet-Parker Reconnection Rate:
Lundquist Number: ,
Characteristic Length scale:
Diffusion time:
Lundquist number:
Resistive layer width: Spitzer resistivity:
Sweet-Parker rate:
L
Electron gyroradius/Plasma size:
Electron gyroradius/Plasma size:
Te16 -310 m
Electron temperature:
Plasma density: n3 eV 3 eV 6 eV
19 -310 m 16 -310 m 16 -310 m
3 eV 3 eV 6 eV19 -310 m 16 -310 m
0.1m 0.1m 0.1m
-45.8*10 -45.8*10 -48.4*10
-24.1*10 -24.1*10 -24.1*10
-26.1*10 m -25.2*10 m -23.8*10 m
31.2*10 81 34.9*10
-22.3*10 0.1 -21.4*10
-55.4*10 s
-42.3*10 Ùm
-57.4*10 s -41.4*10 s
-41.7*10 Ùm -40.9*10 Ùm
Magnetic guide field: Working gas:Bg
