Why we use thoriated tungsten cathodes?

COST 529

Eindhoven, 2006.March.31.

I.Gaal, L.Bartha

Electron emission micrographs of thoriated tungsten wire

Fig.1: As drawn, fibrous state. All others: Recrystallised state

All pictures are made at the same surface location. Time sequence: 6-8 sec between each part

Transport of W in halogen lamp

• 220V/650W halogen studio lamp labelled with W185 isotope

• Autoradiogram of filament sections after 10 hours of burning

..

• 220V/1000W halogen lamp labelled with Ta182 annealed

• 1.) 180V, 2 hours • Deposition on

surface• 2.) 220V, 8 hours• Diffusion into the

coil• 3.)Co 60 annealed 220V• Co deposition at the

central part, onto the inner side of the coil

0

0.5

1

1.5

2

2.5

3

0 500 1000 1500 2000

Time (min)

Rat

io o

f T

h t

o W

1400 K1500 K1600 K1700 K

IDC = 2.5 A --->>2.35 A A homérséklet végig állandó maradt. Csak az elektron áramsuruség értékében történt változás.