1 / 14

The Maxwell Demon and its Instabilities

The Maxwell Demon and its Instabilities. Chi- Shung Yip Noah Hershkowitz JP Sheehan Umair Suddiqui University of Wisconsin – Madison Greg Severn University of San Diego. What is a Maxwell demon?.

elisha
Download Presentation

The Maxwell Demon and its Instabilities

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Maxwell Demon and its Instabilities Chi-Shung Yip Noah Hershkowitz JP Sheehan UmairSuddiqui University of Wisconsin – Madison Greg Severn University of San Diego

  2. What is a Maxwell demon? Maxwell imagined a being that could measure atomic speeds and let the fast ones pass and block the slow ones….. MacKenzie (‘71) implemented a plasma `demon’ using a positively biased grid immersed in a DC hot filament discharge…..Te rises of course, but instabilities limited this effect…..

  3. We implemented a Grid-type Demon to understand the instabilities. Ceramic insulated stainless steel shaft We measure Te and Plasma potentials In the usual way with Langmuir probes and Emissive probes…….. 0.025mm Tungsten wires nicely lined up (Dutifully made in sweat factories run by Chinese grad students.)

  4. The Demon turns Bi-Maxwellians into single Maxwellian distributions by absorbing cold electrons NO GRID BIAS VARIOUS GRID BIASES Cold + hot Hot part Cold part is determined by subtracting the hot extrapolated into plasma potential from the Cold + Hot part.

  5. The Demon efficiently raises Te, but also gives rise to global instabilities

  6. Maxwell demon creates anode spots, in some cases, they can be unstable: Anode Spot *Gracefully photoshopped to show epic visual effects

  7. A small plate gives similar effect, but makes stable anode spots.

  8. Anode Spot:The Baalrud theory The Baalrud theory of anode spots: • Anode spots occurs when number of ions born from ionizations in a Debye cube in an electron sheath matches the number of total electrons within the Debye cube • Ion density from ionizations would be given by • For no better approximations, we assume electron density to be bulk density and ion exit velocity to be cs. [2] S. D. Baalrud, B. Longmier, and N. Hershkowitz, Plasma Sources Science & Technology 18 (2009).

  9. We measured plasma parameters in an unstable plasmas using the `slow sweep’ method Probe fixed at this voltage Time Lapsed • We fix the voltage, record current trace over time and then change voltage.

  10. Major change within a cycle: Plasma Potential and Density Argon 1.7mTorr Plasma current 0.75mA Argon 1.7mTorr Plasma current 0.65mA

  11. Global loss-production balance as a mechanism of the relaxation time (A) (neB) (neC) • A crude model can be formulated solving the production-loss equation: e • Solving the rate equation results in: • Resolving the equation both when the anode spot turns on and off : ne,2 ne,1

  12. The model gets the qualitative features of instability right, however, improvements are needed

  13. Conclusion • The Maxwell demon has been revisited and found to be having identical functions as a small plate, except with a higher resistance to forming anode spots. • Demon instability as MacKenzie et al. has discovered was investigated and (at least partially) its nature established • We need to know more about how anode spots are formed and extinguished

  14. Acknowledgements: The authors would like to thank Dr. YevgenyRaitses and Dr. Igor Kanganovich of the Princeton Plasma Physics Laboratory for their advices on this work. This work was supported by U.S. Department of Energy Grants No. DE-FG02-97ER54437 and No. DE FG02- 03ER54728, National Science Foundation Grants No. CBET-0903832, and No. CBET-0903783

More Related