Unraveling the nature of 'whistlers' from space in the lab

August 14, 2018

WASHINGTON, D.C., August 14, 2018 -- Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets of radio waves that race along magnetic field lines. This first-of-its-kind study, appearing in the Physics of Plasmas, from AIP Publishing, provides new insights into the nature of whistlers and space plasmas -- regions of energized particles trapped by Earth's magnetic fields. These studies could one day aid in the development of practical plasma technologies with magnetic fields, including spacecraft thrusters that use charged particles as fuel.

"We have discovered new effects of these so-called whistler waves," said Reiner Stenzel, an author on the paper. "These new laboratory studies will help expand our knowledge on this intriguing electromagnetic phenomenon and suggest new applications and possible inventions."

Whistler waves were first detected in the early 1900s. They were found to come from lightning interacting with Earth's magnetic fields. As they traveled through Earth's ionosphere and magnetosphere, whistlers with low tones propagate more slowly than the higher frequency whistlers. As a result, simple radio receivers were used to listen to the radio waves, and the falling pitch sounded like a whistle.

Stenzel and his co-author, Manuel Urrutia, studied the growth, propagation and decay of whistler waves in nonuniform magnetic fields in their laboratory. They discovered that these waves behaved differently than predicted by an 80-year-old theory.

These laboratory studies involved creating whistler waves with magnetic antennas inside a plasma-filled chamber. The researchers then studied the behavior and propagation of these waves in 3D space with a movable probe. This enabled the team to study how these waves propagate through 3D space as a function of time. They could also study the waves under a variety of conditions, including how they behave when exposed to both straight and circular magnetic field lines and magnetic null points -- regions where there was no field at all.

"Our laboratory experiments reveal three-dimensional wave properties in ways that simply cannot be obtained from observations in space," said Stenzel. "This enabled us to study continuous waves as well as the growth and decay of waves with amazing detail. This produced unexpected discoveries of wave reflections and of cylindrical whistler modes."

Whistler waves are considered a form of helicon waves, or low-frequency electromagnetic waves that travel in a corkscrewlike, or helixlike, pattern. When helicons interact with plasmas, they exert a pressure and torque on the electrons.

The researchers believe that better understanding these properties could someday lead to the design of plasma thrusters for space vehicles. These thrusters use electricity to propel plasma to extremely high speeds, faster than a chemical rocket.
The article, "Whistler modes in highly nonuniform magnetic fields. I. Propagation in two-dimensions," is authored by Reiner Stenzel and Manuel Urrutia. The article appeared Physics of Plasmas August 14, 2018, (DOI: 10.1063/1.5030703) and can be accessed at http://aip.scitation.org/doi/full/10.1063/1.5030703.


Physics of Plasmas is devoted to the publication of original experimental and theoretical work in plasma physics, from basic plasma phenomena to astrophysical and dusty plasmas. See http://pop.aip.org.

American Institute of Physics

Related Magnetic Fields Articles from Brightsurf:

Physicists circumvent centuries-old theory to cancel magnetic fields
A team of scientists including two physicists at the University of Sussex has found a way to circumvent a 178-year old theory which means they can effectively cancel magnetic fields at a distance.

Magnetic fields on the moon are the remnant of an ancient core dynamo
An international simulation study by scientists from the US, Australia, and Germany, shows that alternative explanatory models such as asteroid impacts do not generate sufficiently large magnetic fields.

Modelling extreme magnetic fields and temperature variation on distant stars
New research is helping to explain one of the big questions that has perplexed astrophysicists for the past 30 years - what causes the changing brightness of distant stars called magnetars.

Could megatesla magnetic fields be realized on Earth?
A team of researchers led by Osaka University discovered a novel mechanism called a ''microtube implosion,'' demonstrating the generation of megatesla-order magnetic fields, which is three orders of magnitude higher than those ever experimentally achieved.

Superconductors are super resilient to magnetic fields
A Professor at the University of Tsukuba provides a new theoretical mechanism that explains the ability of superconductive materials to bounce back from being exposed to a magnetic field.

A tiny instrument to measure the faintest magnetic fields
Physicists at the University of Basel have developed a minuscule instrument able to detect extremely faint magnetic fields.

Graphene sensors find subtleties in magnetic fields
Cornell researchers used an ultrathin graphene ''sandwich'' to create a tiny magnetic field sensor that can operate over a greater temperature range than previous sensors, while also detecting miniscule changes in magnetic fields that might otherwise get lost within a larger magnetic background.

Twisting magnetic fields for extreme plasma compression
A new spin on the magnetic compression of plasmas could improve materials science, nuclear fusion research, X-ray generation and laboratory astrophysics, research led by the University of Michigan suggests.

How magnetic fields and 3D printers will create the pills of tomorrow
Doctors could soon be administering an entire course of treatment for life-threatening conditions with a 3D printed capsule controlled by magnetic fields thanks to advances made by University of Sussex researchers.

Researchers develop ultra-sensitive device for detecting magnetic fields
The new magnetic sensor is inexpensive to make, works on minimal power and is 20 times more sensitive than many traditional sensors.

Read More: Magnetic Fields News and Magnetic Fields Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.