Design, Fabrication & Testof Thermionic Electron
Beam Emitter Assemblies
Munawar Iqbal
Associate Professor, PhD.
Centre for High Energy Physics, University of thePunjab, Lahore-Pakistan
Presented at:
High Energy Accelerator Research Organization (KEK), 1-1OHO,Tsukuba, Ibaraki, Japan
October 11, 2016

OutlineØ Preliminaries
Ø Thermionic DC Electron Guns
1.
2.
3.

Line Source/Sheet Beam EG
Hairpin Source/Point Beam EG
Strip Source/Sheet Beam EG

Ø Conclusions
Ø References

132 of 73 are public
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private universi3es
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ComputaGonal Physics, 25 Master in High EnergyPhysics, 10 PhD in High Energy Physics
o Experimental High Energy Physics (BESIII) CollaboraGono TheoreGcal High Energy Physics
o Accelerator Technology & Material ScienceIntroduction
Ø A device that generates, accelerate and to someextent focuses the beam of electrons.
Ø Thermionic, photo and field emissions are much
popular ways for electron generation.
Ø Further, these emissions are temperature & spacecharge limited.

Applications
Electron beam gun is a basic part of many types of applied &fundamental Research.
Ø Joining, welding ,cutting, machining and modifications of refractory metals in thefield of engineering sciences.
Ø Evaporation & coating in the field of nano- technology.
Ø In Electron Devices (SEM,TEM) for characterization purposes.
Ø In Experimental HEP, in studying electron-positron physics, e-gun is the basic
component of the Accelerator and also of Klystron.

Thermionic DC
Electron Beam
Emitter Assemblies

Design Considerations of Electron Gun
For electron beam design, three parameters should carefully betaken into the considerations.
ü Firstly, a cathode should supply an adequate emission over apredetermined length of the surface with good thermal efficiency.
ü Secondly, the beam should have a homogenous emission across alength of several centimeters to enable large area processing of thebeam.
ü Thirdly, a uniform magnetic field is essential to provide theuniform energy density to the beam by making the trajectories
parallel to each other in the field-free region to achieve a common
crossover at the target.

1.

Line Source/Sheet Beam Electron Gun

A sheet beamelectron gun with electromagnetic
focusing using EGUN and CST-PS was simulated. The gun
was tested up to 50 kW at 5A and10 kV, achieves power
density of 33 kW/cm^2 at the target. The cathode temperature
was uniform over a length of 120 mm of the cathode surface.
The beam density profile strongly relates to the temperature
distribution along the cathode. The gun is immersed in auniform external magnetic field to give guidance and extra
focusing to the electrons in the post-anode region. The test andsimulations results are in agreement. The gun has a remarkableapplications in heat treatment of large surface area and to coatlarge substrate surfaces at much faster evaporation and scanrates of refractory metals. Moreover, it is a potential
candidate for Klystron application.

Design of the e-gun

Gun Specifications
Component

Material

Dimension

Quantity

Filament

Tungsten

0.98φ×140L (120 exposed)

1

16.2w×140L×1t

Focusing
Tantalum
electrodes

2
Filament Dist. H=3.75,V= 7Vertical section 9h×120L×1w
Horizontal section

Vertical electrodes

Tantalum26w×120L×1t
Filament dist. H=3Casing

Filament clamps

Stainless steel

40w×40h×330L

1Upper: 20w×3h×10L

2Lower: 20w×3h×40L

2

Molybdenum

Insulators

Alumina

6φ×20L

2

Insulator holder

Aluminum

7.5φ×8.5L×2t

2hearthCopper

230w×80h×350L

1

Key: Units millimeter (mm), φ = diameter, L= length, w = width, t = thickness, h =height, H = horizontal distance, V = vertical distanceGun optimization

Optimization Parameters
ParametersOptimized values

Cathode-anode distance (mm)6Anode slit spacing (mm)2.5

Focusing electrode spacing (mm)4.3

Anode-focusing electrodes distance (mm)3Cathode-focusing electrodes distance3(mm)Acceleration potential (kV)10

2-D EPLOT of gun with beam trajectories

Electromagnetic coils and the generated field

Coil turns

1049

Coil Current(A)13.75

Sheet Beam in Electromagnetic Field

Test of the Assembly•! K)A,,A56&1L"9"17$9,A,31,&Beam profile of the electron gun
at the SS target

Specifications of the Sheet Beam
Electron GunParametersGun type
CathodeFilament heating power
Acceleration potential
Beam current
Emission current density
Output power
Power density
Perveance
Pressure

Characteristics
Thermionic diode gun
Tungsten wire of
140 mm length
600 W
10 kV
5A
10 A/cm2
50 kW
33 kW/cm2
5 µA/V3/2
5 × 10-5 Torr

Thermal Analysis of the Gun

Thermal Analysis

ML$9)"2&"6"2D,A,&Summary of thermal analysis
Contents

Temperature Co

Heat Flux W/mm2

Minimum

Maximum

Maximum

Electron Gun

603052.823.851

Focusing electrode1703.42959.88.9687

Anode313.71

330.220.3133

Casing405.65427

1.404

Alumina

426

2204.57.6572

Alumina Holder

358.294500.38761

Molybdenum blockand Clamp

1367.23048.620.235

Alumina insulation
strip on tight clamp

694.582712.31.0862

2.

Hairpin Source/Point Beam Electron Gun(a) Two dimensional schematic view of the gun with electromagnetic coiland target, and (b) Three dimensional model of the gun.

Parameters for beam optimization
Parameters

ValuesCathode potential (V)0Focusing electrode potential (V)0Anode (kV)

10

Cathode- anode spacing (mm)5.1Cathode - focusing electrode spacing (mm)1.0

Anode hole diameter (mm)3.1

Focusing electrode hole diameter (mm)3.2

Magnetic field (Gauss)

630

EGUN Simulation of the Gun

Beam trajectories in the Magnetic Field

Two dimensional (2-D) Plot of beam trajectories.

Three dimensional (3-D) schematic of thegun and its convergence with the coil.

Emission Characteristics of the AssemblyTest Results of Hairpin source EG• Emission Characteristics

Beam profile at SS and joining of metals

Results
Parameters

Simulated values
EGUNCST

Measured values

Beam diameter (mm)0.85

0.96

0.90

Beam convergence distance (mm)606060Beam current (mA)

41.5

41.5

42Current density (A/cm2)

5.86

5.60

5.35

Power density (W/cm2)

5.86×104

5.6×104

5.35×104

Specifications of Hairpin Source
Electron Gun
Parameters
Gun type
CathodeCharacteristics
Thermionic hairpin
Tungsten wire of 0.7 mm
diameterAcceleration potential
Beam current
Emission current density

10 kV
42 mA
32.96 A/cm2

Power density

5x 105 W/cm2

Beam emittance
Perveance

1.1 Pi mm-mRad
10-5 A/V3/2

3C&Parameters fixed for beam optimizationParameters
Cathode to focusing electrode distance(mm)
Cathode to anode distance (mm)Focusing electrode to anode distance(mm)

Optimized gun
configuration
6.1
8.5
2.4

Focusing electrode slit spacing (mm)13.35Anode hole diameter (mm)13.4

Acceleration potential (kV)10

Designing and simulation of the gunElectromagnetic focusing of the BeamK)A,,A56&O"9")$7$9,&5H&7L$&P+6&

Emission parameters of focusing results withexperimental results.
Parameters

Electrostatic focusingresults

Experimental results

Electromagnetic focusingresults

Magnetic Field(Gauss)--

350

Beam Focusing Distancefrom Anode (mm)15.9

15.968Beam Waist diameter atbeam focusing distance
(mm)

3.04

3.15

4.0

1.12

1.12

1.12

1.15

1.02

5.04

1.15×104

1.02×104

5.04×104

208.8

-

162.3

41.5

-

31.72

Beam Current(Ampere)Average Current Density(A/cm2)
Power Density (A/cm2)
Total Emittance(π mm mRad)
Normalized Emittance(π mm mRad)Test Results of the AssemblyExperimental validation

Conclusions
Ø The guns are without any biasing and have flat geometry ofthe electrodes. Thermionic electron gun is economical, easyand simple to produce electron beams.
Ø EGUN & CST soft wares are comprehensive and user friendly
software to optimize the electron beam trajectories both forelectrostatic & magnetic fields.
Ø ANSYS software is good for modeling and then thermal
analysis of E-gun to keep each gun component under
permissible temperature limit for long duty cycle.

ReferencesThanks for yourPatience