page_title: Magnetic mirror
section_title: Biconic cusps
hierarchical_section_title: Magnetic mirror / Biconic cusps
caption_attribution_description: English: This image shows how a biconic cusp is generated, by placing two coils of wire close together. These are electromagnets, and are arranged so that the poles face one another. In the center is a null point of zero magnetic field. Particles moving far away from the null point experience a stable motion, while particles close to the null point are more erratic. Other information This image shows how a biconic cusp is generated, by placing two coils of wire close together. These are electromagnets, and are arranged so that the poles face one another. In the center is a null point of zero magnetic field. Particles moving far away from the null point experience a stable motion, while particles close to the null point are more erratic.
context_page_description: A magnetic mirror, known as a magnetic trap in Russia and briefly as a pyrotron in the US, is a type of magnetic confinement device used in fusion power to trap high temperature plasma using magnetic fields. The mirror was one of the earliest major approaches to fusion power, along with the stellarator and z-pinch machines.
  In a magnetic mirror, a configuration of electromagnets is used to create an area with an increasing density of magnetic field lines at either end of the confinement area. Particles approaching the ends experience an increasing force that eventually causes them to reverse direction and return to the confinement area. This mirror effect will only occur for particles within a limited range of velocities and angles of approach, those outside the limits will escape, making mirrors inherently "leaky".
  An analysis of early fusion devices by Edward Teller pointed out that the basic mirror concept is inherently unstable. In 1960, Soviet researchers introduced a new "minimum-B" configuration to address this, which was then modified by UK researchers into the "baseball coil" and by the US to "yin-yang magnet" layout.
context_section_description: If one of the poles in the magnetic bottle is reversed, it becomes a biconic cusp, which can also hold charged particles. Biconic cusps were first studied by Harold Grad at the Courant Institute, studies reveal the presence of different types of particles inside a biconic cusp.
caption: A biconic cusp
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