Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

the last fifteen years. small device testing demonstrated that helium cooling can be as effective
as water when handling several tens of kilowatts. other disadvantages for helium and the brayton
cycle include the nature of a compressible gas working fluid that requires higher pumping or
blower power and larger supply and return piping compared to liquids, and the safety issues surrounding
the large amount of stored energy in high-pressure systems.
Us research efforts on helium-cooled heat sink applications began in 1993 on copper devices.
small businesses fabricated helium-cooled heat sinks with various enhancement techniques including
microfins, jet impingement, plasma-sprayed, sintered or brazed porous media, and metal
foams. several of these devices exhibited record heat flux handling capabilities with heat transfer
coefficients close to 30,000 W/m 2 k as shown in Figure 1. Refractory heat sink development started
in 1998 on pure tungsten and continues today with lanthanated tungsten, tungsten-rhenium
alloys and molybdenum (youchison 2001, diegele 2003).
40000
35000
30000
2 25000 K)
20000
15000
h (W/m
10000
5000
Progress in helium cooling
Cu microchannels Cu dual channel pellets
Cu single channel pellets Tungsten foam
Tungsten pellets water
0
1993 1995 1997 1999 2001 2003 2005 2007 2009
year
Figure 1. Helium now rivals the cooling capability of water on small devices.
consider pure tungsten as an example. tungsten heat sinks require inlet temperatures greater
than 600 o c (dbtt) and must operate at the highest outlet temperatures possible (~1000 o c) for
higher efficiency, but stay below the recrystallization temperature (~1100 o c). Gas cooling studies,
including thermomechanical modeling and high heat flux testing, and substantial upgrades to
test facilities, are necessary to evaluate these components. The production of reliable high-performance
heat sinks for demo PFcs will require further refractory materials development, innovative
fabrication techniques and clever thermal engineering coupled with power-relevant testing.
Us industry was instrumental in developing low-cost, near-net-shape fabrication techniques for
our small, present-day helium heat sink mock-ups for first wall, divertor and ic applications. The
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