Electron Beam Source Temescal SFIH – 270 – 2 March 2014 Fernando Lloret Vieira

Electron Beam Source

Temescal SFIH – 270 – 2

March 2014

Fernando Lloret Vieira

Electron beam source

Index

• Electron beam gun

• Temescal SFIH – 270 – 2

• Heat diffusion

• Emitter

• Coils and magnetic fields

• In the MBE system

Electron beam gun

A cathode is placed a high potential and electron are leaked in a stream to the anode.

Cathode: It is operate at high negative potential.

Tungsten filament: It is heated to a bright glow for thermionic emission.

Anode: At ground potential, the anode accelerates the electrons in a vacuum environment as an electrostatic field.

E-beam gun EmitterHeat diffusion

SFIH - 270 - 2

Coil magnetic

field

System

Electron beam gun


SFIH - 270 - 2

Coil magnetic

field

System


Filament is inside of a cavity and both (filament and cavity) are at the same negative potential. This cavity generates the electrostatic field which forms the beam.

Electrons are directed to the ground potential of the material in the crucible.

The electromagnetic coils direct the beam, and the surrounding magnetic fields guide and focus the beam on the target.


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

The emision of electrons is carried out by the filament. These electrons are accelerated by the electrostatic field generated by the cavity. A beam is formed by carriers in movement so the cavity (as it is the generator of the electrostatic field) forms the beam.


The design of the Temescal e-beam use a 270º geometry

The crucible must be water cooled

5000-20000V

Powers as high as 300kW

Geometry of the emitter can reduce contamination of the electron source and electron beam scanning range can be expanded


SFIH - 270 - 2

Coil magnetic

field

System

Heat diffusion

The energy of the beam is so intensely concentrated on the surface of the evaporant that it forms a pool of molten evaporant.

In the evaporation from a water-cooled crucible, high boiling point materials remain in a solid “skull” at the interface with the crucible.

Cold-hearth containment

The heat diffusion mechanism is a combination of conduction and convection.

The magnitude of heat flow is proportional to the first power of temperature


SFIH - 270 - 2

Coil magnetic

field

System

Emitter

Formed by an anode, a cathode and a filament inside a cavity, the emitter generates the beam by thermionic emission.

Emission voltage: 4 to 10kVFilament voltage: 12V maximumFilament current: 50A maximum


SFIH - 270 - 2

Coil magnetic

field

System

Emitter

Filament clamps & screws

Filament Anode


SFIH - 270 - 2

Coil magnetic

field

System

Coils and magnetic fields

Magnet Magnetic coils

Coil extensions


SFIH - 270 - 2

Coil magnetic

field

System


Basic view of the SFIH – 270.


SFIH - 270 - 2

Coil magnetic

field

System


The field of the permanent magnet is used to maintain the beam on the hearth area

Magnet


SFIH - 270 - 2

Coil magnetic

field

System


Magnet

Magnetic coils

The deflection coil is used to accomplish X-Y beam sweep


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

A beam is charges in movement, so it can be modify by electromagnetic fields. Magnetic coils are coils with the shapes shown in the figure. In this way we can generate two perpendicular magnetic fields (magnetic lines are perpendicular to the wires of the coils). Modifying the intensity through the coils modifies the intensity of the magnetic field. This is the way to deflect the beam.


Magnet

Magnetic coils

Magnetic suppressor


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

To avoid unwanted changes in the beam due the magnetic fields. The beam is oriented before come to the crucible.


Magnet

Magnetic coils

Magnetic suppressor

Pole extension

The pole extension pieces serve to defocus the beam and enlarge the size of the spot.


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

By magnetic fields modifies the shape of the spot (see right lower corner figure).


Magnet

Magnetic coils

Magnetic suppressor

Pole extension

Coil shield


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

To protect the magnetic coils and its connexions


Magnet

Magnetic coils

Magnetic suppressor

Pole extension

Coil shield

Pole piece

The lateral pole pieces supply the field to bend the beam toward the crucible.


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

No, they are different. However, pole pieces, pole extension pieces and permanent magnet (the magnet in slide 10) guide and focus the beam on the target.


Pole piece

Coil shield

Crucible

Pole extension

Emitter Electro magnetic coil assembly


SFIH - 270 - 2

Coil magnetic

field

System

FLloret

I don't know what brazement means. Crucible marks the place for the crucible (the target).

In the MBE system


SFIH - 270 - 2

Coil magnetic

field

System

In the MBE system

Carbon e-gun

Silicone-gun


SFIH - 270 - 2

Coil magnetic

field

System

Documents

Electron Beam Source Temescal SFIH – 270 – 2 March 2014 Fernando Lloret Vieira