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Browse Prior Art Database

Improving Field Linearity in MMD Magnet

IP.com Disclosure Number: IPCOM000123171D
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 59K

Publishing Venue

IBM

Related People

Ross, J: AUTHOR [+2]

Abstract

The magnet in a magnetic matrix display (MMD) is used to collimate the modulated electron beams. The major effect sought is to retain the electrons in a tight beam as they are accelerated from the cathode region to the front of the magnet where the deflection anodes perform the beam shaping. Thereafter, the beam is more rapidly accelerated to the phosphor screen/final anode. Each aperture may be thought of as a small magnetic lens.

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Improving Field Linearity in MMD Magnet

   The magnet in a magnetic matrix display (MMD) is used to
collimate the modulated electron beams.  The major effect sought is
to retain the electrons in a tight beam as they are accelerated from
the cathode region to the front of the magnet where the deflection
anodes perform the beam shaping.  Thereafter, the beam is more
rapidly accelerated to the phosphor screen/final anode.  Each
aperture may be thought of as a small magnetic lens.

   The complete magnet also behaves as a large lens with all of
the small magnetic lenses across its surface being contained within
this large lens.  Although the majority of the magnetic field is
contained within a region close to the magnet, there is a residual
field further away from the magnet and flux lines close around the
edge of the magnet.  In each magnet aperture the field is
predominately in the same direction as the motion of the electron
beam.  Outside the aperture, the field has a larger component
orthogonal to the direction of motion of the electron beam.  This,
in conjunction with the accelerating voltage in the different
regions of the display (cathode, aperture and anode regions) gives
rise to a force on the electrons in the beam, given by F = q(E + v x
B) where F is the force, q is the charge on the electron, v is the
velocity of the electron and E and B are the electric and magnetic
fields respectively.  Note that v x B is a vector cross product and
therefore the force acts at right angles to both v and B.

   This residual field causes the electron beams to deviat...