Researchers Report Period Doubling Route to Chaos with Magnetic Field Strength

A magnet placed on one’s refrigerator might keep a calendar in place, but Indian Researchers from Saha Institute of Nuclear Physics discovered that when a magnet is placed outside a plasma chamber it creates a localized, fireball-like structure. The study may provide an insight into plasma dynamics under these dipolar or north-south magnetic fields. The results of the study are described in the journal Physics of Plasmas, from AIP Publishing.

Localized glow region, the complex space charge configuration, near cathode surface with application of ~28G magnetic field (Credit: Shaw et al/AIP Publishing)

The Researchers discovered that a localized glow appeared close to the cathode surface when exposed to the magnetic dipole field generated by a bar magnet. As described in their paper, this localization is the result of enhanced degree of ionization due to confinement of electrons in the magnetic field close to the surface of negatively charged cathode. The Researchers also observed that the glow region’s intensity increased when they increased the strength of the magnetic field.  

Work in this field is traditionally performed by keeping a permanent magnet within a plasma chamber which means there is no other means to change the field line structure or field strength. The Authors of this paper could change the magnet’s position and alter the strength of the magnetic field by placing the bar magnet on the outside of the plasma chamber.

Though bar magnets have been used in plasma experiments, the focus was mainly on the measurement of plasma equilibrium parameters like density, potential and other fluctuation measurements. In our opinion, this is the first effort to investigate nonlinear dynamical phenomena of the fluctuations under dipolar magnetic field.

Pankaj Kumar Shaw, Lead Author

In the studies carried out earlier, the plasma fluctuation would go from order to chaos when a magnetic field is introduced to plasma. By keeping the bar magnet outside the plasma chamber, Shaw and his colleagues observed that when the strength of the magnetic field is increased, a transition from order to chaos occurs through a process of a period doubling bifurcation

“Following a particular sequence from order to chaos via [a] period-doubling route was unexpected,” said Shaw. He also added that while the emergence of chaos and turbulence caused by a magnetic field was reported in previous experiments, this was the first experiment to reveal a doubling route to chaos with magnetic field strength.

Changing position of the bar magnet varied the strength of magnetic field over 1-10G. This observation in such a low range of magnetic field was surprising.

Pankaj Kumar Shaw, Lead Author

Shaw informed that his team is planning to develop a new plasma experiment in the future. This experiment would involve integrating more bar magnets and exploring their effects on plasma dynamics.

He also added that the results of this study could play a major role in space plasma research. It could particularly help Scientists to gain an insight on the effects such as magnetic anomalies seen on solar wind-lunar surface interactions. It could also prove significant in other fields of plasma applications such as plasma processing of materials where magnetic fields are widely used.

Knowledge about the,“Root cause of plasma instabilities is important for applications of plasma-surface interactions,” Shaw said. Moreover, he believes this could help educate future generation of Physicists, “This simple experiment can be used to teach various aspects of plasma physics, nonlinear dynamics, and time series analysis to high school students.”

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