| What
spheromaks are: Spheromaks are
plasmas with very large internal currents and internal
magnetic fields that are aligned so as to be in a nearly
force-free equilibrium, i.e., the currents are very
nearly parallel to the magnetic fields. The spheromak
equilibrium is a `natural' state since magnetic
turbulence tends to drive magnetically dominated plasmas
towards the spheromak state.
|
| Planar spheromak gun on 1.4
m diameter vacuum tank |
 |
|
Spheromak
technology: Laboratory
spheromaks involve very large currents, typically 100's
of kiloamperes and high voltages, typically kilovolts.
These currents and voltages are obtained using high
energy capacitor banks which are switched in
microseconds. The formation geometry is arranged such
that magnetic flux cuts across the electrodes connected
to the capacitor bank. This configurations generates
helicity (twistedness) in the flux tube going from one
electrode to the other. With enough helicity a spheromak
is formed. |
| Why
spheromaks are interesting:
Spheromaks are inherently
three-dimensional and involve the concept of magnetic
helicity which is a measure of the twistedness of a
magnetic flux tube. Spheromaks have been proposed as the
basis of magnetic fusion confinement schemes and as a
means for refueling tokamaks. The physics of spheromaks is closely
related to the physics of astrophysical jets. |
What we are
doing: We are
interested in learning more about the topology of
spheromaks as they form. To do this we are using an
ultra-fast camera (10 ns shutter speed) to photograph the
various stages of a spheromak as it forms. We have
observed very distinctive and reproducible twisted flux
tubes. We are measuring the internal magnetic fields in
these flux tubes. Publications Home
Page
Spheromak
formation movies
Links
to related activities elsewhere
|
Making spheromaks:
Making spheromaks is analogous to blowing bubbles: the
component of the magnetic stress tensor parallel to the
magnetic field acts like the surface tension in the soap
film while the perpendicular component acts like the air
pressure inflating the bubble. When the destabilizing
stress due to the perpendicular component overwhelms the
stabilizing stress due to the parallel component, a
detached spheromak breaks off. |