John,JohnP wrote:Whatever else he's saying, this is an interesting point. Am I to assume that the magnets are getting a high pressure stream of LN2 to keep them cool while they're getting roasted with neutrons (in D-D)? I also assume that with p-B11 the helium nuclei will tend to fly off around the magnetic field lines and not at the magnets directly?- 20 MW of fusion power is dumped as heat into the ring magnets when reaction products including neutrons hit them.
First off the problem is not neutrons when running pBj. It is alphas. In fact neutrons would be better since if they are high energy they will not react much with the materials inside the reactor. This may be balanced by the greater number of neutrons produced.
Second taking out the major portion of the heat with LN2 is not going to work.
I expect to use 3 coolants.
H2O at around 120 to 350 deg C (I haven't run the numbers so this is not very exact).
LN2 at 77K
LHe at 10 to 30 deg K
It will be interesting trying to balance all the delta Ts and flows and required pressures to get the heat flows to balance at useful temperatures.