Pinch (plasma physics)

A pinch (or: Bennett pinch (after Willard Harrison Bennett), electromagnetic pinch, magnetic pinch, pinch effect, or plasma pinch.) is the compression of an electrically conducting filament by magnetic forces, or a device that does such. The conductor is usually a plasma, but could also be a solid or liquid metal. Pinches were the first type of device used for experiments in controlled nuclear fusion power. Pinches occur naturally in electrical discharges such as lightning bolts, planetary auroras, current sheets, and solar flares. Pinches exist in nature and in laboratories. Pinches differ in their geometry and operating forces. These include: Uncontrolled – Any time an electric current moves in large amounts (e.g., lightning, arcs, sparks, discharges) a magnetic force can pull together plasma. This can be insufficient for fusion. Sheet pinch – An astrophysical effect, this arises from vast sheets of charged particles. Z-pinch – The current runs down the axis, or walls, of a cylinder while the magnetic field is azimuthal Theta pinch – The magnetic field runs down the axis of a cylinder, while the electric field is in the azimuthal direction (also called a thetatron) Screw pinch – A combination of a Z-pinch and theta pinch (also called a stabilized Z-pinch, or θ-Z pinch) Reversed field pinch or toroidal pinch – This is a Z-pinch arranged in the shape of a torus. The plasma has an internal magnetic field. As distance increases from the center of this ring, the magnetic field reverses direction. Inverse pinch – An early fusion concept, this device consisted of a rod surrounded by plasma. Current traveled through the plasma and returned along the center rod. This geometry was slightly different than a z-pinch in that the conductor was in the center, not the sides. Cylindrical pinch Orthogonal pinch effect Ware pinch – A pinch that occurs inside a Tokamak plasma, when particles inside the banana orbit condense together.