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<p class="MsoNormal">Please take note of Colloquium taking place today, Tuesday, February 17, 2015 at 4:00 PM in The Robert Smith Seminar Room. There will be a reception in the Atrium at 3:45PM. Details concerning the talk are as follows:
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<p class="MsoNormal">Speaker: Cary Forest (University of Wisconsin-Madison)<o:p></o:p></p>
<p class="MsoNormal">Date: Tuesday, February 17, 2015<o:p></o:p></p>
<p class="MsoNormal">Time: 4:00 PM<o:p></o:p></p>
<p class="MsoNormal">Place: 1080 Physics Research Building, The Robert Smith Seminar Room<o:p></o:p></p>
<p class="MsoNormal"><b>Title: </b><span lang="EN">Chasing Fast Dynamos in the Plasma Lab<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN" style="font-size:10.0pt;font-family:"Arial",sans-serif">Abstract:</span><span lang="EN"> Most astrophysical plasmas are often characterized by turbulent, flowing plasma in which the flow energy is continuously transformed
into magnetic energy through the dynamo process. Understanding this energy transformation and predicting what form the magnetic field might take, be it small-scale turbulent magnetic fields or large scale magnetic flux is the dynamo problem. In this review,
I will give an overview of the taxonomy of magnetic fields observed in nature, including those of stars, disks, galaxies and clusters of galaxies. Then, I will give an overview of the theory of dynamos based upon the relative values of the magnetic Reynolds
number $Rm =VL / \eta$, the fluid Reynolds number $Rm =VL / \nu$ (or their ratio $Pm=Rm/Re$), and the scales at which magnetic energy grow. Both limits of $Pm$ are relevant in astrophysics: diffuse plasmas (eg. the interstellar medium of the galaxy) have
$Pm\gg 1$ whereas dense plasmas (like stellar plasmas) have $Pm \ll 1 $. We also distinguish between fast and slow dynamos. Fast dynamos amplify magnetic field at a rate independent of magnetic diffusivity eta and probably require magnetic reconnection, while
slow dynamos require resistive diffusion. Dynamos can be classified as small-scale or large-scale. Small-scale dynamos tend to generate magnetic energy but little net magnetic flux, whereas large-scale dynamos generate both net flux and energy. While the mechanism
by which magnetic energy at small-scales is generated is now well understood, how a large scale field self-organizes from small-scale magnetic fluctuations clusters is a grand challenge for plasma astrophysics. Theoretical dynamos studies are now focused on
understanding how subcritical transitions make some dynamos essentially non-linear and also how dynamos in nearly collisionless plasmas may differ from MHD dynamos.
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<p class="MsoNormal"><span lang="EN">I will finish by reviewing how dynamo experiments have and may inform us about astrophysical dynamos. In particular, the Madison Plasma Dynamo eXperiment is now exploring a hitherto unexplored part of plasma parameter space
where dynamos operate in Nature. For understanding astrophysical magnetic fields, the most important issue to be resolved is the fast large scale dynamo problem, namely "How does a highly conducting turbulent plasma self-generate magnetic energy at small-scales
that ultimately self-organizes into large scale field?" MPDX has the potential to study dynamos, including fast dynamos, and related processes experimentally.</span><span lang="EN" style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal">The website for the colloquium is <a href="https://physics.osu.edu/physics-colloquium-schedule">
<span style="color:windowtext">https://physics.osu.edu/physics-colloquium-schedule</span></a><span style="color:#1F497D">.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Segoe Script",sans-serif;color:blue">Robin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#0070C0"><img border="0" width="224" height="45" id="Picture_x0020_1" src="cid:image001.png@01D04A90.43CD52E0" alt="The Ohio State University"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<b><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:#BB0000;background:white">Robin Patterson</span></b><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:#333333"><br>
Undergraduate Program, Colloquium and Seminar Coordinator<br>
</span><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:#BB0000;background:white">Department of Physics</span><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:#333333">
<br>
1040K Physics Research Building, 191 W. Woodruff Avenue, Columbus, OH 43210<br>
(614) 292-8523 Office (614) 292-7557 Fax<br>
</span><u><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:blue;background:white"><a href="mailto:patterson.716@osu.edu">patterson.716@osu.edu</a></span></u><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:#333333">
<a href="http://osu.edu/"><span style="color:blue;background:white">osu.edu</span></a>
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