Center for Magnetic Self Organization
in Laboratory and Astrophysical Plasmas
The SSX device at Swarthmore College features a 1-meter long, high vacuum chamber in which we form and merge hot plasma plumes at 100 km/s and up to one-million degrees. The SSX experiment aims to perform studies that inform and are motivated by processes we observe in space, for example on the solar surface and in the solar wind. We have studied the 3D magnetic structure of the merging process using large probe arrays. A process called magnetic reconnection heats the plasma. We have studied ion and electron heating due to reconnection using high resolution spectroscopy. Finally, the result of the merging process generates self-organized, twisted, magnetically relaxed structures (see figure).
MST is a toroidal (donut-shaped) magnetic confinement device used for research on magnetic fusion and basic plasma science. MST plasmas exhibit a full range of magnetic self organization processes associated with magnetic reconnection, particle heating and acceleration, dynamo and momentum transport, and magnetic turbulence. These processes are closely intertwined, since all depend on magnetic reconnection caused by variations in the current flowing in the plasma. For magnetic fusion, the reversed field pinch configuration studied in MST has possible advantages associated with reduced magnetic field requirements and simple ohmic plasma heating to temperatures hotter than the Sun.
Energetic ion creation in MST
Magnetic fields can store large amounts of energy. Some of this energy is released when the structure of the magnetic field is rearranged in a process called magnetic reconnection. The energy released during magnetic reconnection accelerates, or heats, the ions (charged particles) in a plasma. New measurements of plasma in the Madison Symmetric Torus have shown that many particles are accelerated to high energies during magnetic reconnection. This is similar to what happens in many astrophysical plasmas, so this laboratory experiment may help us understand the details of a particle acceleration process that occurs in many parts of the universe.
Experimental Observation of Magnetic Turbulence in the Madison Symmetric Torus
Plasmas almost always exhibit some form of turbulence, i.e., irregularity or randomness in properties like the plasma's density or temperature. In MST, we have discovered that the plasma causes turbulence in the magnetic field. There are two types of magnetic fields in MST. One is a well-ordered component that confines the plasma and keeps it insulated from the cold surroundings. The other component is turbulent. Recent measurements show that this turbulent component is not uniformly distributed in space, rather it has a preference to align perpendicular to the direction of the well-orderded magnetic field. This is exciting because theories based on magnetohydrodynamics predict this behavior, which is also measured in astrophysical plasmas like the solar wind.
Experimental detection of relaxation to a helical state
The typical result of the turbulent mixing of two fluids is more chaotic turbulence. However, in some cases, turbulence can lead to organized, swirling structures. One example is the organization of wind patterns in the Atlantic to form hurricanes. Another example from the SSX experiment at Swarthmore College is the observation of magnetic turbulence evolving into a self-organized helical structure. Two turbulent plumes of magnetized plasma are merged in the experiment, and after a brief chaotic phase, the plasma relaxes to a beautiful helical structure.
What is Plasma?
A plasma is a like a gas, except that it contains charged particles that can conduct electricity and respond to magnetic fields.
As gas heats up, electrons can escape gas molecules or atoms in a process called ionization. A plasma is a hot gas that contains a collection of electrons moving freely among the atoms they left behind (called ions).
Plasma is the most common state of matter in the Universe, making up over 99% of visible matter!
What are some examples of plasma?
On Earth, plasma can be found in fluorescent bulbs, neon signs, lightning, aurora, and laboratory experiments. Almost everything that we see in space is made of plasma, including stars (the Sun) and nebulae.
What is Nuclear Fusion?
In a basic fusion reaction, two energetic hydrogen nuclei combine to form a heavier helium nucleus, releasing enormous amounts of energy in the process.
Three things must happen for fusion to occur: hydrogen nuclei must be packed together very closely (high density), they must be held together for a long enough time to collide (high confinement time), and they must be moving very fast (high temperature).
Fusion occurs in stars because plasma is compressed and heated by the force of gravity. On Earth, fusion can be created by using magnetic fields as a bucket to confine and heat plasma to temperatures even hotter than the Sun!
If we could produce fusion energy on Earth, we would have a clean, cheap energy source to power the world for millions of years!
What is a Light Year?
Even though it’s called a “light year” , this is actually a unit used to measure distances in outer space.
A light year is the distance that light would travel in one year. For example, you would have to travel at the speed of light for one year to travel a distance of 1 light year, or 6 trillion miles!
Our Sun’s nearest neighboring star, Proxima Centauri, is 4.2 light years away. Our own galaxy, the Milky Way, is about 100,000 light-years across. The closest galaxy, Andromeda, is approximately 2.5 million light years away.
How fast is light?
According to theory, nothing can travel faster than the speed of light, which is about 671 million miles per hour. It takes light about 8 minutes to travel from the Sun to the Earth, and about 5.3 hours to get to Pluto.
What is a Nebula?
A nebula is a cloud of gas, dust, and plasma in outer space. Nebulae contain the elements that make up all of the stars and planets. They are some of the most beautiful objects in the universe, glowing with many different colors and detailed structures, and can be hundreds of light years across.
Nebulae in which star formation occurs are often called stellar nurseries and are created when gas and dust in outer space clumps together through the force of gravity. Other nebula can form in the final life stages of Sun-like stars (planetary nebula), or from the supernova remnants created when a high-mass star explodes.