"Chasing Dynamos with Confined and Unmagnetized Flowing Plasma"
Event details
| Date | 29.01.2015 |
| Hour | 15:00 › 16:00 |
| Speaker | Prof. Cary Forest (Univ. of Wisconsin, Madison, USA) |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
The Madison Plasma Dynamo Experiment (the MPDX) a 3 meter diameter spherical vacuum vessel that uses an array of 3000 4 kG samarium cobalt permanent magnets in a 36 ring ring cusp arrangement, and ~200kWs of LaB6 hot cathode power to ionize and heat plasma; this is now generating a steady-state, hot (20eV) plasma with densities of 1018m-3. The cathodes also can stir the unmagnetized core plasma at speeds of up to 12km/s through J´B torque at the magnetized edge of He plasmas. Laminar counter-rotating two-vortex flows, are predicted to have a critical threshold of spontaneous creation of magnetic field that depends upon the magnetic Reynoµlds number Rm=m0sLV, a dimensionless triple product that must exceed 250 for self-excitation. Hence the electron confinement plays a critical role in governing the dynamo onset. Two dimensional VPIC simulations of density, temperature and wall losses to the dipole magnet rings are compared directly to measurements of 2D plasma profiles and measured confinement times. The fluid Reynolds number, depends largely upon density, the ion temperature and the effective charge, scaling ReµL V Z4 n/Ti5/2; hence ion heating and confinement are also important. To study the hydrodynamic turbulence requires high density and low ion temperature (and/or multiply charged ions). So far, MPDX has achieved Rm»300 and Re»200 which is nearly optimal for observing a laminar dynamo. Fast turbulent dynamos seem feasible give the confinement scaling projections based upon the experimental parameters.
Practical information
- Informed public
- Free
Organizer
- Prof. P. Ricci
Contact
- Prof. P. Ricci