<s>
A	O
thermionic	B-Algorithm
converter	I-Algorithm
consists	O
of	O
a	O
hot	O
electrode	O
which	O
thermionically	O
emits	O
electrons	O
over	O
a	O
potential	O
energy	O
barrier	O
to	O
a	O
cooler	O
electrode	O
,	O
producing	O
a	O
useful	O
electric	O
power	O
output	O
.	O
</s>
<s>
Caesium	O
vapor	O
is	O
used	O
to	O
optimize	O
the	O
electrode	O
work	O
functions	O
and	O
provide	O
an	O
ion	O
supply	O
(	O
by	O
surface	B-Algorithm
ionization	I-Algorithm
or	O
electron	O
impact	O
ionization	O
in	O
a	O
plasma	O
)	O
to	O
neutralize	O
the	O
electron	O
space	O
charge	O
.	O
</s>
<s>
A	O
thermionic	B-Algorithm
converter	I-Algorithm
consists	O
of	O
a	O
hot	O
emitter	O
electrode	O
from	O
which	O
electrons	O
are	O
vaporized	O
by	O
thermionic	O
emission	O
and	O
a	O
colder	O
collector	O
electrode	O
into	O
which	O
they	O
are	O
condensed	O
after	O
conduction	O
through	O
the	O
inter-electrode	O
plasma	O
.	O
</s>
<s>
The	O
resulting	O
current	O
,	O
typically	O
several	O
amperes	B-General_Concept
per	O
square	O
centimeter	O
of	O
emitter	O
surface	O
,	O
delivers	O
electrical	O
power	O
to	O
a	O
load	O
at	O
a	O
typical	O
potential	O
difference	O
of	O
0.51	O
volt	O
and	O
thermal	O
efficiency	O
of	O
520%	O
,	O
depending	O
on	O
the	O
emitter	O
temperature	O
(	O
15002000	O
K	O
)	O
and	O
mode	O
of	O
operation	O
.	O
</s>
<s>
After	O
the	O
first	O
demonstration	O
of	O
the	O
practical	O
arc-mode	O
caesium	O
vapor	O
thermionic	B-Algorithm
converter	I-Algorithm
by	O
V	O
.	O
Wilson	O
in	O
1957	O
,	O
several	O
applications	O
of	O
it	O
were	O
demonstrated	O
in	O
the	O
following	O
decade	O
,	O
including	O
its	O
use	O
with	O
solar	O
,	O
combustion	B-Application
,	O
radioisotope	O
,	O
and	O
nuclear	O
reactor	O
heat	O
sources	O
.	O
</s>
<s>
The	O
exceptionally	O
high	O
operating	O
temperature	O
of	O
thermionic	B-Algorithm
converters	I-Algorithm
,	O
which	O
makes	O
their	O
practical	O
use	O
difficult	O
in	O
other	O
applications	O
,	O
gives	O
the	O
thermionic	B-Algorithm
converter	I-Algorithm
decisive	O
advantages	O
over	O
competing	O
energy	O
conversion	O
technologies	O
in	O
the	O
space	O
power	O
application	O
where	O
radiant	O
heat	O
rejection	O
is	O
required	O
.	O
</s>
<s>
Prototype	O
combustion-heated	O
thermionic	O
systems	O
for	O
domestic	O
heat	O
and	O
electric	O
power	O
cogeneration	O
,	O
and	O
for	O
rectification	B-Algorithm
,	O
have	O
been	O
developed	O
.	O
</s>
<s>
All	O
practical	O
thermionic	B-Algorithm
converters	I-Algorithm
to	O
date	O
employ	O
caesium	O
vapor	O
between	O
the	O
electrodes	O
,	O
which	O
determines	O
both	O
the	O
surface	O
and	O
plasma	O
properties	O
.	O
</s>
<s>
The	O
properties	O
of	O
the	O
interelectrode	O
plasma	O
are	O
determined	O
by	O
the	O
mode	O
of	O
operation	O
of	O
the	O
thermionic	B-Algorithm
converter	I-Algorithm
.	O
</s>
<s>
All	O
the	O
applications	O
cited	O
above	O
have	O
employed	O
technology	O
in	O
which	O
the	O
basic	O
physical	O
understanding	O
and	O
performance	O
of	O
the	O
thermionic	B-Algorithm
converter	I-Algorithm
were	O
essentially	O
the	O
same	O
as	O
those	O
achieved	O
before	O
1970	O
.	O
</s>
<s>
During	O
the	O
period	O
from	O
1973	O
to	O
1983	O
,	O
however	O
,	O
significant	O
research	O
on	O
advanced	O
low-temperature	O
thermionic	B-Algorithm
converter	I-Algorithm
technology	O
for	O
fossil-fueled	O
industrial	O
and	O
commercial	O
electric	O
power	O
production	O
was	O
conducted	O
in	O
the	O
US	O
,	O
and	O
continued	O
until	O
1995	O
for	O
possible	O
space	O
reactor	O
and	O
naval	O
reactor	O
applications	O
.	O
</s>
<s>
Similarly	O
,	O
improvements	O
via	O
use	O
of	O
oxygen-containing	O
electrodes	O
have	O
been	O
demonstrated	O
in	O
Russia	O
along	O
with	O
design	O
studies	O
of	O
systems	O
employing	O
the	O
advanced	O
thermionic	B-Algorithm
converter	I-Algorithm
performance	O
.	O
</s>
<s>
Recent	O
studies	O
have	O
shown	O
that	O
excited	O
Cs-atoms	O
in	O
thermionic	B-Algorithm
converters	I-Algorithm
form	O
clusters	O
of	O
Cs-Rydberg	O
matter	O
which	O
yield	O
a	O
decrease	O
of	O
collector	O
emitting	O
work	O
function	O
from	O
1.5	O
eV	O
to	O
1.0	O
–	O
0.7	O
eV	O
.	O
</s>
