Page 220 - Fundamentals of Magnetic Thermonuclear Reactor Design

202 Fundamentals of Magnetic Thermonuclear Reactor Design

TABLE 6.5 Average Characteristics of Surface-Action Pumps
Pumping
Operating specific Max sorption Max heat
Gas temperature speed capacity load
2
2
3
3
2
Pump type removed (K) (m /(s·m )) (m ·Pa/m ) (W/m )
Condensate D–T 2–4 70–100 4 × 10 4 10 3
Cryosorption D–T 15–30 70–100 4 × 10 4 10 4
(microporous
adsorbents)
Cryosorption D–T 10–30 40–70 4 × 10 4 10 4
(condensed
gases)
Sorption D–T 300–700 5–100 (7–13) × 10 3 –
(non-
dispersible
getters)
Cryosorption He 4 15–40 5000 10 3
(microporous 20 1.0–1.5 4–6 10 4
adsorbents)

Hydrogen cryosorption pumping can be performed at 10–30 K using micro-
porous adsorbents, such as coals and zeolites, or gas condensate layers as
cryosorbents.
Cryosorption pumps outperform condensate pumps in terms of resistivity to
heat flows and sensitivity to temperature changes, but have weaknesses, such as
structural and operating complexity and a less stable performance when dealing
with large flows.
Non-dispersible metal getters prove effective for removing hydrogen. Their
key strength is the relatively high operating temperature. They may be placed
close to potentially high-temperature components of the vacuum pumping duct.
The getters are a little sensitive to radiant energy and particle flows [16].
He condensation is undesirable due to the high energy consumption. The
only way to remove it is through cryosorption pumping. For example, a cryo-
2
3
sorption pump using charcoal removes He at a rate of up to 40 m /(s·m ), and
2
4
3
has a sorption capacity of up to 10 m Pa/m . The sorbent regeneration requires
a heating at 35 K. A cryosorption pumping of a D–T–He mixture (zeolite; 4 K)
−3
is only possible at pressures lower than 7 × 10 Pa. At a higher pressure, the
cryopanel system gets blocked by H isotopes, and He removal stops. It is there-
fore necessary to use separate He absorbing panels in reactor-scale cryopumps
to absorb He and H isotopes. A stable He pumping is possible at up to 0.1 Pa;
3
whereas a He flow removed from a fusion reactor is close to 1 m Pa/s.