Page 47 - Fundamentals of Magnetic Thermonuclear Reactor Design

Facilities With Magnetic Plasma Confinement Chapter | 2 29

TABLE 2.7 Key Parameters of Largest Stellarators [21–23]
Parameter W7-X (Germany, 2015) LHD (Japan, 1998)
Plasma major radius (m) 5.5 3.9
Plasma minor radius (m) 0.53 0.6
Maximum diameter (m) 16 13.5
Facility height (m) 4.5 9.1
Facility mass (t) 725 1500
Total cold mass at 4 K 450 822
Superconductor type NbTi NbTi
3
Plasma column volume (m ) 30 30
Periods in the poloidal/toroidal –/5 2/10
directions
Rotational transfer 5/4–5/6 1/2–3/2
Toroidal magnetic field (T)
on plasma axis 3.0 3–4
on coil surface 6.7 9.2
Superconducting coil current (kA) 17.2 17.3
Plasma toroidal beta (%) 5.0 a 5.0
Plasma energy confinement time (s) 2.1 a 0.36
Plasma mean temperature (keV) 20 a 12
−3
20
Plasma mean density (10 m ) 1.5 a 1.4
Maximum criterion value 0.56 a 0.44
−3
20
(10 keV·s·m )
Additional heating power (MW) 30 a >30
Stored magnetic energy (MJ) 660 a 800 b
Operating cycle time (min) Up to 30 a 54 b
a Design parameters and predictions.
b Highest value ever attained.

However, the implementation of such configurations is a technical challenge.
Modular stellarators have a magnetic field with a non-planar axis. This gives
rise to complex induced eddy current configurations and appreciable electro-
magnetic loads during fast discharge/current quench. The latter, however, are
much less than those caused by plasma current disruptions in tokamaks. Be-
sides, modular stellarators are easier to assemble and dismantle due to the ab-
sence of closed toroidal or helical coils [22].
The only stellarator currently in operation in Russia is the L-2M (launched
in 1972 and re-launched in 1993 after modernisation) has a UHF heating system
3
that enables the introduction of up to 5 MW/m into the plasma.
The Uragan-3 machine, run by the Kharkov Physical and Technical Institute
since 1981, uses a divertor with a ‘natural’ configuration: its plates are located