Researchers have made a major advance in solar physics by capturing the first direct evidence of small-scale torsional Alfvén waves in the Sun’s outer atmosphere, known as the corona.

About Alfvén Waves
Alfvén wavesare low-frequency, transverse electromagnetic waves that propagate along magnetic field lines within a plasma (an ionized gas or conducting fluid). They were first predicted in 1942 by Nobel Prize-winning physicist Hannes Alfvén, the founder of magnetohydrodynamics (MHD). 
Key Characteristics

• Nature: They are a type of magnetohydrodynamic (MHD) wave, where both the magnetic field and the plasma particles oscillate.
• Propagation: They travel in the direction of the background magnetic field lines.
• Motion: The oscillations of the ions and the perturbations of the magnetic field are transverse (perpendicular) to the direction the wave is traveling, similar to "wiggles" on a stretched string.
• Restoring Force: The tension in the magnetic field lines provides the restoring force for the oscillation, while the ion mass density provides the inertia.
• Energy Transport: Alfvén waves effectively transport energy and momentum through magnetized plasmas.
• Dispersionless: Basic Alfvén waves can maintain their shape over extended distances without spreading out. 

Occurrence and Significance
Alfvén waves occur wherever magnetic fields interact with plasma, which is the most common state of matter in the universe. They are observed in: 

• The Sun: They are crucial for explaining the mystery of why the Sun's outer atmosphere (corona) is millions of degrees hotter than its surface, by transporting energy from the solar surface into the corona.
• Space: They are found in the solar wind, the Earth's magnetosphere, and the magnetotail. They help accelerate charged particles, contributing to phenomena like auroras.
• Astrophysical Environments: They are present in stellar interiors, black hole accretion disks, and galaxy clusters.
• Laboratory Settings: They are studied in fusion devices like tokamaks to understand plasma stability and confinement, which is vital for achieving sustained nuclear fusion. 

Variants
A variant, the kinetic Alfvén wave, can have a parallel electric field, enabling it to exchange energy directly with plasma particles and accelerate them to high speeds. This process is important in space weather and particle energization in various regions of space. 

Download Pdf