Events at Physics |
Events on Monday, December 2nd, 2024
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Tearing-mediated reconnection in magnetohydrodynamic poorly ionized plasmas
- Time: 12:05 pm - 1:00 pm
- Place: 1610 Engineering Hall
- Speaker: Elizabeth Tolman, Flatiron Institute
- Abstract: Many plasma environments, such as star-forming molecular clouds, the solar chromosphere, and the diffuse interstellar medium, are poorly ionized and threaded by dynamically important magnetic fields. We use theory and computation to study tearing-mediated reconnection in such poorly ionized systems. In this work, we focus on the onset and linear evolution of this process. In poorly ionized plasmas, magnetic nulls on scales below vA,n0/𝜈 ni0, with vA,n0 the neutral Alfvén speed and 𝜈 ni0 the neutral–ion collision frequency, will self-sharpen via ambipolar diffusion. This sharpening occurs at an increasing rate, inhibiting the onset of reconnection. Once the current sheet becomes thin enough, however, ions decouple from neutrals and the thinning of the CS slows, allowing the onset of tearing in a time of order 𝜈 ni0 . We find that the wavelength and growth rate of the mode that first disrupts the forming sheet can be predicted from a poorly ionized tearing dispersion relation; as the plasma recombination rate increases and ionization fraction decreases, the growth rate becomes an increasing multiple of 𝜈 ni0 and the wavelength becomes a decreasing fraction of vA,n0/𝜈 ni0. After reconnection onsets in a current sheet, the system enters a nonlinear phase characterized by a stochastic plasmoid chain, but the characteristics of this chain differ from those of a stochastic plasmoid chain in fully ionized plasma. The plasma in the plasmoids is characterized by an ionization fraction which is much larger than that of the background plasma. Our results could have significant implications for understanding of several important astrophysical processes, including the transport of cosmic rays in the interstellar medium.
- Host: Vladimir Zhdankin, John Sarff
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Advanced Fuel Oscillating Fusion Reactor
- Time: 4:00 pm - 5:00 pm
- Place: 106 Engineering Research Building (access via Materials Science Building)
- Speaker: Richard Nebel, Tibbar Plasma Technologies, Inc
- Abstract: A new type of fusion reactor is presented. This device produces fusion by the collision of two oscillating plasma rings. This is a linear device similar in shape to a magnetic mirror with direct energy converters on its ends. Analysis shows that this system can create net energy gain, even with an advanced fuel like p-11B. This advanced fuel eliminates neutrons and thus eliminates radioactive byproducts. It is compact and can provide terrestrial power and power for space propulsion.
- Host: John Sarff