On steady flows in smooth-walled magnetrons: Fundamental modes and no-cutoff flows in planar geometry

Journal Article · Tue Nov 15 00:00:00 EST 2005 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2122427· OSTI ID:20782359

Goedecke, G H; Davis, Brian T; Chiping, Chen; Baker, C Vincent ^[1]

---

1. Physics Department, New Mexico State University, Las Cruces, New Mexico 88003 (United States)and Raytheon Missile Systems, 1151 E. Hermans Road, Tucson, Arizona 85706 (United States)

The Maxwell equations coupled with the ideal fluid equations for a warm isothermal non-neutral plasma are applied without approximation to predict three modes of time-independent electron flow in smooth-walled planar magnetrons, at any temperature. For all three modes, the equations predict that the fluid flow velocity tangent to the cathode is the Brillouin velocity. One of the modes is the well-known magnetic insulation mode, in which the magnetic field is larger than the Hull cutoff field [Phys. Rev. 18, 31 (1921)], the anode current is essentially zero, and virtually all the electrons reside in a sheath near the cathode. The other two modes exhibit fairly large anode currents. One of these modes is the well-known Child-Langmuir flow [Phys. Rev. 32, 492 (1911); ibid. 21, 419 (1923)], in which the magnetic field is smaller than the Hull cutoff field. The other high-current mode, in which the magnetic field is larger than the Hull cutoff field, has not been discussed previously; in this paper, it is called the 'no-cutoff' (NC) mode. Experiments using a thin smooth-walled magnetron were conducted, during which large anode currents were observed even for magnetic fields much larger than the Hull cutoff field. It is shown that NC mode parameters can be adjusted to produce a complete agreement with the experimental results, but that this requires the transverse flow velocity near the cathode to be superthermal and even mildly relativistic for the larger magnetic fields. Matching the experimental values also predicts a number density that is larger near the anode than near the cathode, but is small enough that space-charge effects are negligible in most cases.

• OSTI ID: 20782359
• Journal Information: Physics of Plasmas, Vol. 12, Issue 11; Other Information: DOI: 10.1063/1.2122427; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ANODES
APPROXIMATIONS
CATHODES
CHARGED-PARTICLE TRANSPORT
ELECTRIC CURRENTS
ELECTRON TEMPERATURE
ELECTRONS
GEOMETRY
IDEAL FLOW
ION TEMPERATURE
MAGNETIC FIELDS
MAGNETIC INSULATION
MAGNETRONS
MAXWELL EQUATIONS
PLASMA DENSITY
PLASMA INSTABILITY
PLASMA SHEATH
RELATIVISTIC PLASMA
RELATIVISTIC RANGE
SPACE CHARGE