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MRX Research in the Context of Princeton Max-Planck Collaboration MRX research in the context of Princeton Max-Planck collaboration Masaaki Yamada Princeton Plasma Physics laboratory Princeton University January 14, 2013 With MRX Staff: H. Ji, R. Kulsrud, E. Lawrence, T. Tharp + Graduate students Magnetic Reconnection • Topological rearrangement of magnetic field lines! • Magnetic energy => Kinetic energy! • Key to stellar flares, coronal heating, particle acceleration, star formation, energy loss in lab plasmas! Before reconnection After reconnection Outline! !Magnetic reconnection! – Leading issue in space, astro- and fusion plasma physics" –! A major question was: Why does it occur so fast?" –! New question: How does energy flow from magnetic field to plasmas?" •! Generation of a reconnection layer on MRX => Local analysis" •! Two fluid physics analysis! Recent Emphasis:! •! Energy conversion processes from B2 to ions and electrons! •! A new series of experimental campaign and the recent results! –! Plasma jog experiment: Addresses heating and acceleration of ions and electrons" –! Guide field effects on two-fluid reconnection" –! Reconnection in partially ionized plasmas" –! Solar flare relevant plasma arcs" Plans for Princeton-MPPC collaboration! Magnetic Reconnection Experiment Primary objectives of MRX is to create a proto-typical reconnection layer and study it experimentally with cross- validation with numerical simulations Experimentally measured flux evolution! 13 -3 ne= 1-10 x10 cm , ! Te~5-15 eV, ! B~100-500 G, ! S < 1000! Reconnection layer Profile changes with Collisionality: Experimentally measured field line features in MRX •! Manifestation of Hall effects •! Electrons would pull magnetic field lines with their flow Two-fluid physics dictates reconnection layer dynamics (a) (b) R •! Out of plane magnetic field is generated during reconnection. •! Electron acceleration and heating with mirror- Plasma Electron Outflow trapped electrons. Current •! Parallel electron y conduction determines Z PlasmaPlasma potential profile! InflowInflow Sheath width ~ c/ωpi In-plane Potential Profile Karimabadi et al, 2007 Wygant et al. 2005 MRX, 2012 •! A large bipolar electrostatic field (BEF) exists in the reconnection layer due to two-fluid effects. •! It can accelerate ions generating a pair of counter-streaming ion beams in the diffusion layer. Ion Acceleration (Mach probe) •! Clear ion acceleration by the in-plane electric field. •! Asymmetry in the ion inflow is caused by asymmetry in the upstream density. Both flows and temperature of electron and ion measured by plasma jogging %# 9:$+5/67 9:!;+5/67 %$ !# )9 8 !$ 400 Z=0 (cm) Z=14 (cm) # 350 300 250 $ 200 !!"# !! !$"# $ $"# ! !"# Intensity (A.U.) &'()'*+(),-'./0+-1+/2330.-+,400-+/0.-03+5/67 150 100 50 468.45 468.5 468.55 468.6 468.65 468.7 Wavelength (nm) J. Yoo, 2012 Ion acceleration data and simulation results Goldman et al., 2012 Wygant JGR 2005 Drake et al., 2009 Downstream Ion Heating3 Φ (V) J ⋅E (W/cm3) (a) p (b) i (a) (b) 60 40 20 T 25 (R,Z) = (37.5,0) i 42 42 V 50 30 80 (R,Z) = (37.5,15) 15 V 15 iZ iz (km/s) 40 40 20 10 5 40 (eV) i 38 38 10 T 30 60 5 −5 R (cm) R (cm) 0 36 36 20 0 −15 −10 0 5 10 15 34 34 Z (cm) 10 −20 40 (c) 20 25 32 32 0 −30 V Number of photons 15 15 0 5 10 15 0 5 10 15 iz Z (cm) Z (cm) (km/s) 20 10 5 (eV) i T 5 −5 FIG. 3. (a) In-plane ion flow vector measured by Mach probes 0 0 −15 468.55 468.6 468.65 30 35 40 45 together along with contours of Φp and Ψ.Theflowvectors λ (nm) R(cm) are measured every 1 cm along R and every 3 cm along Z. The maximum ion velocity is 16 km/s. As ions flow across • Ions are heated downstream. FIG. 4. (a) Spectra of He 4686 Aat(˚ R, Z)=(37.5, 0) (black) the separatrices, they are accelerated by Ein and turn into • Classical viscous heating under the assumption of unmagnetized ions and at (R, Z)=(37.5, 15) (green). Solid lines are from fitting the outflow direction. (b) Work done by the electric field on the spectra cannot explain into the the sum observed of 13 Gaussianion heating. functions. Both ion ions. It is dominated by the strong Hall field. heating• Downstream and acceleration ion thermalization are observed is due at (toR, re-magnetization Z)=(37.5, 15). (b) Axial (NumericalTi and V simulations)iZ profiles at R =37.5cm.ForZ>9 cm, the ion temperature rises significantly while ViZ begins the above equation at Z = 0 leads to to saturate. (c) Radial Ti and ViZ profiles at Z =15cm (downstream). The ion temperature profile is peaked at the ∗ ER (VeY V )BZ , (2) center of the layer while the outflow profile is broader. ≈− − eY ∗ where VeY = (1/eneBZ )∂pe/∂R is the electron diamag- netic drift velocity.− The diamagnetic drift term is not negligible due to strong electron heating near the cur- V/m). Furthermore, its spatial scale is smaller than the rent sheet that cannot be explained by classical Ohmic ion skin depth δi = c/ωpi ( 9cm).Thus,assoonasthe ∼ heating [27]. The radial electric field reverses sign at the ions see the strong Ein, they are accelerated toward the X point where the sign of BZ also reverses. This indi- outflow direction. Figure 3-(a) shows the ion flow vector cates that the bipolar radial electric field is the result of profile measured by Mach probes along with contours of electron force balance [28]. Since VeY contains the dia- Φp. Considerable changes in the ion flow occur near the magnetic component, Eqn. (2) implies that the electron boundary. The corresponding large difference between diamagnetic drift does not contribute to ER; only pure the ion and electron in-plane flow profiles produces the acceleration by EY plays a role [29]. By integrating the well-known quadrupole out-of-plane magnetic field [30]. right-hand side of Eqn. (2) along R, the radial potential It is worth noting that the stagnation point of the ion profile can be estimated. The electron drift velocity is flow is shifted to the inboard side (R<37.5), which is obtained by Ve = J/ene + Vi = B/µ0ene + Vi. caused by the upstream density asymmetry [31]; the out- As shown in Fig. 2-(b),− the estimates−∇ × by Eqn. (2) (the board side (R>37.5) has about 2–3 times larger density blue line) agree with the measured values (red asterisks). than the inboard side due to radial symmetry-breaking Similarly, the electron momentum equation along the processes in the earlier phases of the discharge [32]. outflow direction at R =37.5 cm yields Figure 3-(b) shows the profile of the work done by ∗∗ the electric field on the ions per unit volume and unit EZ (VeY VeY )BR, (3) ≈ − time, Ji E. The in-plane electric field is calculated by ∗∗ E · where V = (1/eneBR)∂pe/∂Z is the electron dia- in = Φp and the out-of-plane reconnection electric eY − −∇ magnetic drift from the pressure gradient along Z.As field is estimated by EY =(∂Ψ/∂t)/2πR.Theworkdone electrons flow out of the EDR with high VeY ,theycreate by EY is fairly uniform over the measurement region, 3 a further potential decrease along the outflow direction which is inside of the IDR, with values of 2–8 W/cm . Z. The amount of the further potential decrease can be On the other hand, the work done by Ein is localized 3 estimated by integrating Eqn. (3) along Z, which agrees downstream with higher values of 20–50 W/cm . This with the measured values as shown in Fig. 2-(c). Due to means that ions gain energy mostly from the Hall electric the high mobility of electrons, the potential drop around field, which agrees with recent simulation results [22, 33]. the EDR is conveyed along magnetic field lines, creating In addition to ion acceleration, we also observe ion astrongEin near the separatices as shown in Fig. 2-(a). heating downstream. Figure 4-(a) shows measured He The strong Hall electric field ballistically accelerates 4686 A˚ spectra at the X point [(R, Z)=(37.5, 0), blue] ions near the separatrices where the ions are unmagne- and downstream [(R, Z)=(37.5, 15), red]. Clear broad- tized. The magnitude of Ein near the boundary can ex- ening (heating) and shifting (acceleration) exist in the ceed 700 V/m, which is much larger than EY ( 200 spectrum at Z = 15 cm. Figure 4-(b) shows the axial ∼ Electron Heating • Strong increase near the electron diffusion region. • Inboard side has higher electron temperature. A jog experiment on MRX (2011)! NASA MMS Satellite to be launched in 2014 In collaboration with UNH, MMS, UC-Berkeley. Hall Effects on Guide Field Reconnection in MRX Effects of Guide Fields on Collision-less Reconnection ' ,!1233'-4563780 "#!$ ,!1233'-79:63780 ,!)*+ "#! ,(-%)*+'./0 "#"$ " ' !! !"#$ " "#$ ! %&'('%)*+ Modified Quadrupole Field There isn’t a simple analytic model for this, but measurements qualitatively match two-fluid simulations <BT>=<BT>=−15 <BT>=−15 <BT>=−15 −<BT>=15 −15 <BT>=<BT>=−101<BT>=−101<BT>=−101 −<BT>=101 −101 <BT>=<BT>=−141<BT>=−141<BT>=−141 −<BT>=141 −141 <BT>=<BT>=−212<BT>=−212<BT>=−212 −<BT>=212 −212 <BT>=<BT>=−287<BT>=−287<BT>=−287 −<BT>=287 −287 −80 −80 −80 −80 −80 −120 −160 −160 −160 −160 −160 45 45 45 45 45 0 0 0 0 0 −120 −120 −120 −120 −100 −180 −180 −180 −180 −180 −260 −260 −260 −260 −260 −100 −100 −100 −100 −140 40 40 40 40 40 −20 −20 −20 −20 −20 −140 −140 −140 −140 −200 −200 −200 −200 −200 −280 −120 −280 −280 −280 −280 R (cm) −120 −120 R (cm) −120 R (cm) −120 R (cm) 35 35 35 35 R (cm) 35 −40 −40 −160 −160 −160 −160 −160 −40 −40 −40 −220 −220 −220 −220 −220 −300 −300 −300 −300 −300 −140 −140 −140 −140 −140 30 30 30 30 30 −60 −180 −180 −180 −180 −180 −240 −240 −60 − 60 −60 −60 − 240 −240 −240 −10Z−10 (cm)Z− 10(cm) +10Z− 10(cm) +10Z −(cm)10 +10 Z +10(cm) − +1010Z−10 (cm)Z− 10(cm) +10Z− 10(cm) +10Z −(cm)10 +10 Z +10(cm) − +1010Z−10 (cm)Z− 10(cm) +10Z− 10(cm) +10Z −(cm)10 +10 Z +10(cm) − +1010Z−10 (cm)Z− 10(cm) +10Z− 10(cm) +10Z −(cm)10 +10 Z +10(cm) − +1010Z−10 (cm)Z− 10(cm) +10Z− 10(cm) +10Z −(cm)10 +10 Z +10(cm) +10 GF=0 GF~BR +di 0 -di Simulations performed by A.
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