Lower Hybrid Drift Waves and Associated Electron Heating during Guide field Reconnection
| Lower Hybrid Drift Waves and Associated Electron Heating during Guide field Reconnection | |
|---|---|
| Principal Investigator | Masaaki Yamada |
| Institution | Princeton |
| Project Status | Active |
Introduction
This project tests the basic eruption processes that occur on the Sun by using a laboratory experiments aided by numerical simulations. Solar eruptions are known to be related to magnetic reconnection which lead to global reconfiguration of the magnetic field. These global reconnection phenomena almost always occur unsteadily or impulsively. In laboratory fusion plasmas, reconnection is seen to occur suddenly with very fast semi-Alfvenic speed after a long flux build up phase. In solar flares, reconnection sites are often identified with hard X-ray emissions near the top of solar flare arcades during Coronal Mass Ejections or near the top of a half-dome shape shape magnetic configuration (such as in a coronal hole). The reconnection speed was almost always measured to be very fast. Coronal X-ray jets are a subclass of the solar eruptions that can occur when a small bipolar magnetic arcade, a miniature active region, emerges in the feet of a high-reaching unipolar field, such as the ambient field in a coronal hole or in one leg of a large-scale coronal loop. The Hinode satellite reported the ubiquitous presence of chromospheric jets with inverted Y-shaped exhausts outside sunspots. If the eruption makes the ejected plasma hot enough to be seen in coronal X-ray movies such as from Hinode XRay Telescope (XRT), the eruption is observed as an X-ray jet [Shibata et al., 1992]. Shibata dubbed these dome-shaped structures ’anemones’ because of the fan shape of the magnetic field, similar to that of a sea anemone. This magnetic configuration is similar enough to the spheromak which is one of the well explored fusion configurations [Bellan, 2000], which, in the low plasma pressure limit, is basically a simply connected force-free magnetic field configuration.
Experimental Method
The laboratory experiments will be carried out at the Magnetic Reconnection Experiment (MRX) [Yamada et al., 1997], which was built in 1995 to study the fundamental physics of magnetic reconnection. Magnetic profiles of spheromak are formed in MRX by producing a plasma discharge between two coaxial gun electrodes that are mounted on the one end of MRX. Prior to initiating the discharge, a static magnetic field is generated by currents that are driven in up to three sets of independently controlled magnetic field coils. In order to enforce the requisite magnetic field line-tying in the electrode plane (i.e., the photosphere), magnetic field lines are connected to gun electrodes. Primarily an inductive spheromak gun constructed for the present experimental goals are used. Once the static background magnetic field has been generated, a small amount of neutral gas is injected. Typically, hydrogen or helium will be used due to their low mass and corresponding high degree of magnetization. In order to initiate the discharge, the capacitor bank that is connected across the electrodes is fired and the plasma breaks down along the magnetic field lines that intersect the electrodes. The current in the inductive gun rises quasi-statically to satisfy slow build-up of the magnetic energy of a forming spheromak plasma.
A typical discharge lasts for less than a millisecond. The dynamic timescale of the plasma (i.e., the Alfv´en transit time) is 2 microseconds, while the driving timescale over which the plasma current is injected is 75–300 microseconds. The peak plasma current ranges from 10–15 kA, depending on the voltage applied by the driving capacitor bank. This amount of current is sufficient to produce non-potential magnetic fields of 100–300 G. Fields of this strength are capable of modifying the applied potential field configuration.
A number of measurement devices are used to characterize the plasma,
- magnetic probes
- visible light camera to visualize discharges
- electrostatic probes
- interferometry, CO2 laser interferometer that provides non-perturbative line-integrated plasma density measurements
Results
Funding
- Funded by HTIDS20, proposal id is 20-HTIDS20-0017. This is a follow-on study to a previous proposal.
Presentations and Publications
Presentations
- M. Yamada, Plenary talk at International Congress of Plasma Physics, Nov.28-Dec.1, 2022,Korea
- M. Yamada, US-Japan Workshop on Magnetic Reconnection, Monterey, May 17-21, 2022
- M. Yamada and E. Belova; Numerical Study of X-Ray Jets in Coronal Hole Theoretical Seminar at PPPP, Princeton U. February 2021.
Publications None
Patents
- M. Yamada and H. Gota: “Spheromak Gun for Inductive flux Injection” Princeton University and Tri-Alpha Energy", Feb. 2022