BARIUM OXIDE (BaO) CATHODES
LOW LIGHT THERMIONIC EMITTERSFEATURES / OPTIONSOXIDE PLANAR CATHODE
LOW LIGHT / LOW TEMPERATURE
GOOD STABILITY
LOW ENERGY SPREAD
ACCURATELY PRE-ALIGNEDINTERNATIONAL STANDARD AEI BASE
NON-STANDARD MOUNTING AVAILABLE

Barium Oxide-Coated Disc Cathodemounted on a standard AEI ceramic base
The Kimball Physics Barium Oxide Cathode is a low-light,
low-temperature thermionic emitter. The cathode structure of theES-015, ES-064, and ES-066 consists of a barium oxide (BaO) coateddisc substrate that is heated by conduction from a tungsten hairpin andmounted on an industry-standard ceramic AEI base or on a compact
Kimball Physics ceramic base. Other bases are available on a custombasis. When ordering a spare cathode or firing unit for use in a Kimball
Physics electron gun, simply specify the gun model and options (forexample, EFG-7, standard energy, BaO) as this will determine theparticular cathode configuration.
The BaO cathode has a lower cathode heating current range and alower operating temperature than a standard, un-coated, refractory
metal cathode, because BaO has a lower work function. With the lowertemperatures, there is less light emitted which is an advantage insituations where light could interfere with viewing the target. The BaOcathode gives a smaller energy spread than a standard cathode, andhas a longer lifetime due to the lower heating current. However, theBaO coating is susceptible to degradation from water vapor, so it isrecommended that the barium oxide (BaO) cathode be operated in a
vacuum of 10-7 torr or better. In addition, the cathode should be storedin vacuum or in a dry environment.

ES-015, ES-064 and ES-066
BaO-coated Disc Cathodes
The BaO disc cathode structure is available mounted on anindustry-standard ceramic AEI base, or on a Kimball Physics ceramicbase (CB-104 or CB-105), as well as on custom or nonstandard bases.
Base options include two or four pins, pins made of molybdenum orKovar, various pin lengths and positions, as well as different mounting
heights of the cathode surface from the ceramic base. Some
combinations of various options may not be possible due to design
considerations.
To protect the coating on the emission surface during storage andshipping, the cathode is sent in a non-activated (carbonate) form andneeds a one-time activation by the user. If the BaO cathode is part ofan electron gun system, it will have already have been activated during
the gun testing in the laboratory. The activation process involves theconversion of carbonate to oxide, the release of barium to the themetal-barium oxide interface, and the diffusion of the free barium.
Once the cathode has been activated, care should be taken not toexpose the cathode to air unnecessarily. Exposure to moisture in theair allows the oxide to form hydrates, which can cause flaking of thebarium oxide. If the cathode needs to be exposed to air, the cathodeshould be restored to a vacuum environment as soon as possible, orbe placed in a clean, dry environment (such as in a tightly sealed
plastic box with desiccant). All cathodes are shipped vacuum clean.

The performance of all coated cathodes will degrade as coating isdepleted through use, lost due to mechanical shock, or sputtered away
by ion bombardment. The lifetime of a BaO-coated cathode is basedon the evaporation rate or degradation of the coating materials andheater wire, which are dependent on the temperature at which thecathode is run and the vacuum. The work function of the cathode also
affects its lifetime; contamination of the cathode surface can increase
the work function, increasing the filament current needed to produce
the same beam current.
There are several factors to consider in choosing a cathode size. A
larger disc has a larger emission area, and thus more total current fora given current density. The current density of course is amonotonically increasing function of temperature. However, a larger
disc loses more power to radiation, and thus more heating power isrequired. A smaller disc tends to have a more uniform temperature
distribution, which results in a more uniform emission. Larger discs
with larger legs tend to have a longer lifetime.

Barium Oxide-Coated Disc Cathodemounted on a CB-104 ceramic baseKimball Physics has determined several combinations of cathodedimensions that have proved to work well in the Kimball Physics
electron guns. The model ES-015 utilizes a 0.033 inch (0.84 mm)diameter refractory metal disc coated with barium oxide, attached to a
0.003 inch (0.08 mm) diameter tungsten 3% rhenium heater wire. Thehigher current models, ES-064 and ES-066 have larger discs andthicker heater wires (see specifications table). Custom BaO cathodes
are available with different disc sizes, and various heater designs.
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It is not necessarily possible to achieve all maximum specifications
simultaneously. Specifications Subject to Change Without Notice.

ELECTRON GUNSBARIUM OXIDE (BaO) CATHODES

ES-064 BaO disc on CB-105 baseES-066 BaO disc on CB-105 base

CATHODE MATERIALDISC SIZEHEATER WIRE SIZELEG LENGTHHEIGHT ABOVECERAMIC BASE
EMISSION AREA
EMISSION CURRENTHEATING CURRENTPOWER SUPPLYCAPABILITYCATHODE LOADINGWORK FUNCTION
OPERATING TEMPENERGY SPREAD
LIFETIMEVACUUM LEVELSTORAGE

ES-064ES-066

Barium oxide (BaO)
0.033 in dia. x .004 in thick
0.048 in dia. x .004 in thick
0.062 in dia. x .004 in thick(0.84 mm dia. x 0.1 mm thick)(1.22 mm dia.x 0.1 mm thick)(1.57 mm dia. x 0.1 mm thick)
0.003 in dia. (0.08 mm dia.)0.004 in dia. (0.1 mm dia.)0.005 in dia. (0.13 mm dia.)approx. 0.11 in (2.8 mm)
approx. 0.12 in (3.0 mm)
approx. 0.15 in (3.8 mm)
on CB-104 base: 0.14 in (3.5 mm)
on CB-105 base: 0.25 in (6.4 mm)
on CB-105 base: 0.27 in (6.9 mm)
on AEI base: 0.256 in (6.5 mm)
on AEI base: 0.256 in (6.5 mm)
on AEI base: 0.256 in (6.5 mm)
5.52x10-3 cm2
11.7x10-3 cm2
19.5x10-3 cm2500 μA typical
1 mA typical
2 mA typical
1.0 A to 1.1 A
2.1 A to 2.3 A
3.0 A to 3.3 A
Voltage regulated power supply
Voltage regulated power supply
Voltage regulated power supply
recommended, 2 V, 2 A
recommended, 2 V, 3 A
recommended, 2 V, 4 A
0.1 A/cm2 recommended, typical; High loadings result in reduced lifetime
1.0 eV to 1.8 eV, depending on experimental method
1150 K typicalapprox. 0.3 eVThousands of hours with medium currents and proper handling
10-7 torr or better, recommended
Dry environment (vacuum or desiccant)

2.0 X

DETECTORS

2.0 X

EMITTERS

ES-015ION GUNS

ES-015 BaO disc on a standard AEI ceramic baseES-015 Barium Oxide Disc Cathodemounted on a CB-104 ceramic baseES-064 Barium Oxide Disc Cathodemounted on a high current CB-105 ceramic base

2.0 X

COMPONENTS

2.0 X

ES-015 Barium Oxide Disc Cathode mounted on an AEI ceramic baseES-064 and ES-066 also available on AEI bases
Toll Free: 1 888 KIM-PHYS (1 888 546-7497) e-mail: info@kimphys.com
Tel. 1 603 878-1616 Fax: 1 603 878-3700

ALL DIMENSIONS ARE IN INCHES(MILLIMETERS IN PARENTHESES)

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INDEX / INFORMATION

ES-066 Barium Oxide Disc Cathodemounted on a high current CB-105 ceramic base