Electron Gun

Electron Guns have been used since the late 1940s in cathode ray tube (CRT) televisions and monitors.

Electron guns consist of a cathode (filament) that is heated to the point of thermionic emission via joule heating. The emitted electrons from the filament then accelerate towards an anode. As the collimated spread of electrons passes through the anode, the beam of electron is then focused through a series of cylindrical apertures which manipulates the beam using an electric field without changing the energy of the beam known as an Enzil lens. The beam eventually passes through two sets of deflection parallel plates in the Y-Z direction before it is detected with either a phosphorous screen (illumination as the electron impinges on the screen) or measured with a Faraday cup.

Team Members

Irvin Lim
Aliki Sofia Rotelli
Tan Chuan Jie (A0154805E)
Lai Tian Hao (A0236351l)

Idea

There are two parts to this project. The first would be to create the electron source which seems to be done with the use of a Lenard/Crookes tube [1]. Secondly, we would want to focus this electron beam into a spot with the use of a homemade magnetic lens (probably a solenoid of some form). We could perhaps perform a measurement of the focal length with respect to the magnetic field strength of the lens.

Concepts

Thermionic Emission

Published by Richardson in 1901, Richardson's emission law proposed that current from a heated wire depends exponentially on the temperature of the wire with the mathematical form:

$J=A_{G}T^{2}e^{-W/kT}$

where J is the emission current density, T is the temperature of the metal, W is the work function of the metal, k is the Boltzmann constant, and $A_{G}$ id definded as:
$A_{G}=\lambda _{R}A_{0}$
where $\lambda _{R}$ is a material-specific correction factor that is typically of order 0.5, and $A_{0}$ is a universal constant given by:

$A_{0}={\frac {4\pi mk^{2}q_{e}}{h^{3}}}=1.20173$ x $10^{6}Am^{-2}K^{-2}$

where m and $-q_{e}$ are the mass and charge of an electron, respectively, and h is Planck's constant.

Based on

Equipments & Components

High Vacuum (HV) Components

• Roughing Pump
  
• Turbo-Molecular Pump
  
• KF-25 Stainless Steel vacuum bellow (1 meter)
  
• CF-40 Stainless Steel Tee
  
• CF-40 Stainless Steel Cross
  
• CF-40 Stainless Steel Viewport
  
• CF-40 Stainless Steel High-voltage Dual Port Feedthroughs (x2)
  
• CF-40 Stainless Steel Multi-Pin Feedthrough, Double-Ended
  
• CF-40 to KF-25 Stainless Steel Flange Adapter
• CF-40 Straight Connector (x2)

Electrical Components

• High Voltage Power Supply Unit (PSU) (up to 5kV)
  
• Current Controlled PSU

Beam Focusing Components

• Enzil Lens
  
• Pair parallel plates (x2)

Measurement Components

• RBD's 9103 USB Picoammeter, (Alternative: Multimeter)
  
• High Vacuum Digital Gauge, with range $(10^{-3}$ ~ $10^{-7})$ mbars
  
• Thermocouple

Other Components

• Filament (Possible Choice)
  
  • Tungsten (W)
  • Lanthanum Hexaboride(LaB6)
  • Cerium Hexaboride(CeB6)
• Phoshors
  • Zinc sulfide(ZnS) (Copper/Silver Activated)
• CF-40 Copper Gaskets