3 ms·

Again: I used the term "full sized prototype" in the first comment. Which is not exactly what Asimov wrote. The remaining possible show stoppers are less plasma

Again: I used the term "full sized prototype" in the first comment. Which is not exactly what Asimov wrote. The remaining possible show stoppers are less plasma physics and more mechanical, which is certainly better than what Asimov predicted. (I wrote repeatedly that the main thing missing from the planned prototype to be a prototype power plant is a heat exchanger, like most every other power plant that heats a medium. It boggles incredibility to assume you failed reading that.) Your link is from 2009, when they were new to building experimental hardware. Hardly an authoritative reference. Edit: A simulation of the vortex. It was hard to find, took me 3 minutes with Google: http://www.cs.ubc.ca/~jgregson/images/JamesGregsonMAScThesis.pdf http://www.cs.ubc.ca/~jgregson/images/JamesGregsonMAScThesis... Edit 2: The old papers, before much experiments: http://www.generalfusion.com/wp-content/uploads/2013/08/GF_Scientific_References_list.pdf http://www.generalfusion.com/wp-content/uploads/2013/08/GF_S... Edit 3: The recent TED talk is (claimed) to be up today, but the ted.com site is down as I write.

BugBrother 12y ago
Addendum: The TED talk was on Youtube (and ted.com is up now). It was for a non-technical audience, the message is that the GF target is to make economical power plants. A commercial venture, as I wrote. The only real news is that the plasma injectors are probably done now, over the last month.
dalke 12y ago
Thank you for the find for #1. I am pleased and surprised to see that my back-of-the-envelope calculation on the speed is correct. I am still gob-smacked to think of that much lead spinning a 2km/sec. I don't have the knowledge of supersonic fluid flows to be able to evaluate that. The paper itself points out various difficulties, including delamination, decavitation, jet formation with speeds up to 6km/sec, and: > practically generating shocks mechanically at Mach numbers greater than 1.5 without destroying the machine that creates them (as is the focus of this work) seems challenging. For example, a steel piston impacting liquid lead to produce an approximately Mach 1.1 shock would see a compressive stress of approximately 2 GPa, well above the yield stress of most steels. The paper talks about pressures up to 400 GPa. Another back-of-the-envelope calculation suggests 20 GPa of centrifugal force at the equator, which of course means the pumps need all the more force. This is well beyond a regime where I can make any mechanical estimates. At this point I suggest that the biggest problem is the engineering to bring the lead up to speed, keeping the sphere in shape with that much force on it, generating a plasma collapse through all of that, and connecting everything to the heat exchanger. That will be a huge challenge in its own right, and must be solved before I would call it an experimental power plant. BTW, this vortex simulation is from 2008, ... "hardly an authoritative reference" by your own criterion. ;) Indeed, I note that the simulation says 100 kg pistons impacting at 100 m/s, while this 2012 PDF http://fire.pppl.gov/FPA12_Richardson_GF.pdf http://fire.pppl.gov/FPA12_Richardson_GF.pdf says the target impact velocity is 50 m/s, which is 1/4th the total amount of energy. Link #2 directs me to http://generalfusion.com/downloads/ICC2008_MGL.pdf http://generalfusion.com/downloads/ICC2008_MGL.pdf, which shows that in 2008 they indeed planned on a 100 m/s impact, so parameters from 2008 are obviously no longer valid for 2014.
- BugBrother 12y ago
  >> I am still gob-smacked to think of that much lead spinning a 2km/sec. That is NOT the value for the spin speed. The paper says: "The collapse of the cavity is accelerated by geometric focusing, resulting in cavity wall velocities over 2 km/s at the end stages of collapse" The spin speed -- think centrifuge, as in a washing machine or in a chemical lab. Lead is high density, but you'd hardly need 2 km/s (around 12K RPMs!!). That is ridiculous. (I do think I've seen articles on that the demands on the pistons might be smaller than the first calculations, after experiments. The self reinforcing shock wave might be involved.) Edit: If you really need to estimate the spin speed, this should work? Consider how many G you'd need at the inner part of the evacuated tube. Then check that on some online calculation (there is a simple formula) to get the RPM (and hence speed) instead of trying the "back of the envelope" thing... :-) Edit 2: I googled a page with the G formula for RPMs. 0.2 meter empty in the middle at 1000 RPMs gives 112 G which should be <cough> more than ample. :-) The formula use (RPM/1000)², so 12,000 RPMs... I don't even want to think about > 1400 G on tons of lead!! http://clinfield.com/2012/07/how-to-convert-centrifuge-rpm-to-rcf-or-g-force/ http://clinfield.com/2012/07/how-to-convert-centrifuge-rpm-t...
  - dalke 12y ago
    That is the value for the spin speed. Quoting from the paper, 4 paragraphs after the 2km/s you referenced: > Probably the most signicant feature of the flow in the concept reactor is that it involves a compressible liquid. With flow velocities exceeding 2 km/s and pressures reaching 400 GPa, compressibility is unavoidable. "Flow" refers to the spin speed, not the collapse. Like I said earlier, I used the equation for a liquid mirror telescope -- h = 1/(2g) * (omega * r) ^ 2 -- for my '"back of the envelope" thing.' See http://en.wikipedia.org/wiki/Liquid_mirror_telescope http://en.wikipedia.org/wiki/Liquid_mirror_telescope for the full derivation. Using h = 2.7 m, g = 9.8m/s, and r = 0.20m gives 40 Hz (or 2,400 rpm). Note though that this gives 20 cm at the top, and 0cm at the bottom. It's a paraboloid, so the center is probably 14-15 cm across. Thus, 40 Hz is a lower bound. Using 40 Hz in (2 * pi * 1.5m) * 40/s implies a minimum equatorial speed of 380m/s, which is Mach 1. The equatorial pumps of course must be providing fluid at an even higher speed. The g-forces at the equator, 1.5 meters away, are even larger than the g-forces at the surface 20 cm away. a = r * omega^2 = 1.5m * 1600/s/s = 2500 G. To get a more uniform evacuated center requires higher speeds still, but the formula I used (first discovered by Newton, btw), no longer holds. It will likely need to be several times faster. Flow speeds of 2km/s require only 6 times faster than the minimum possible speed, which sounds reasonable. Even if 2km/s doesn't sound reasonable. I don't think General Fusion has done the engineering testing to show that they can actually construct one of these, much less use it to provide power. Feel free to correct my calculations.

BugBrother 12y ago

Addendum: The TED talk was on Youtube (and ted.com is up now). It was for a non-technical audience, the message is that the GF target is to make economical power plants. A commercial venture, as I wrote. The only real news is that the plasma injectors are probably done now, over the last month.

dalke 12y ago

Thank you for the find for #1. I am pleased and surprised to see that my back-of-the-envelope calculation on the speed is correct. I am still gob-smacked to think of that much lead spinning a 2km/sec. I don't have the knowledge of supersonic fluid flows to be able to evaluate that. The paper itself points out various difficulties, including delamination, decavitation, jet formation with speeds up to 6km/sec, and: > practically generating shocks mechanically at Mach numbers greater than 1.5 without destroying the machine that creates them (as is the focus of this work) seems challenging. For example, a steel piston impacting liquid lead to produce an approximately Mach 1.1 shock would see a compressive stress of approximately 2 GPa, well above the yield stress of most steels. The paper talks about pressures up to 400 GPa. Another back-of-the-envelope calculation suggests 20 GPa of centrifugal force at the equator, which of course means the pumps need all the more force. This is well beyond a regime where I can make any mechanical estimates. At this point I suggest that the biggest problem is the engineering to bring the lead up to speed, keeping the sphere in shape with that much force on it, generating a plasma collapse through all of that, and connecting everything to the heat exchanger. That will be a huge challenge in its own right, and must be solved before I would call it an experimental power plant. BTW, this vortex simulation is from 2008, ... "hardly an authoritative reference" by your own criterion. ;) Indeed, I note that the simulation says 100 kg pistons impacting at 100 m/s, while this 2012 PDF http://fire.pppl.gov/FPA12_Richardson_GF.pdf http://fire.pppl.gov/FPA12_Richardson_GF.pdf says the target impact velocity is 50 m/s, which is 1/4th the total amount of energy. Link #2 directs me to http://generalfusion.com/downloads/ICC2008_MGL.pdf http://generalfusion.com/downloads/ICC2008_MGL.pdf, which shows that in 2008 they indeed planned on a 100 m/s impact, so parameters from 2008 are obviously no longer valid for 2014.

BugBrother 12y ago
>> I am still gob-smacked to think of that much lead spinning a 2km/sec. That is NOT the value for the spin speed. The paper says: "The collapse of the cavity is accelerated by geometric focusing, resulting in cavity wall velocities over 2 km/s at the end stages of collapse" The spin speed -- think centrifuge, as in a washing machine or in a chemical lab. Lead is high density, but you'd hardly need 2 km/s (around 12K RPMs!!). That is ridiculous. (I do think I've seen articles on that the demands on the pistons might be smaller than the first calculations, after experiments. The self reinforcing shock wave might be involved.) Edit: If you really need to estimate the spin speed, this should work? Consider how many G you'd need at the inner part of the evacuated tube. Then check that on some online calculation (there is a simple formula) to get the RPM (and hence speed) instead of trying the "back of the envelope" thing... :-) Edit 2: I googled a page with the G formula for RPMs. 0.2 meter empty in the middle at 1000 RPMs gives 112 G which should be <cough> more than ample. :-) The formula use (RPM/1000)², so 12,000 RPMs... I don't even want to think about > 1400 G on tons of lead!! http://clinfield.com/2012/07/how-to-convert-centrifuge-rpm-to-rcf-or-g-force/ http://clinfield.com/2012/07/how-to-convert-centrifuge-rpm-t...
- dalke 12y ago
  That is the value for the spin speed. Quoting from the paper, 4 paragraphs after the 2km/s you referenced: > Probably the most signicant feature of the flow in the concept reactor is that it involves a compressible liquid. With flow velocities exceeding 2 km/s and pressures reaching 400 GPa, compressibility is unavoidable. "Flow" refers to the spin speed, not the collapse. Like I said earlier, I used the equation for a liquid mirror telescope -- h = 1/(2g) * (omega * r) ^ 2 -- for my '"back of the envelope" thing.' See http://en.wikipedia.org/wiki/Liquid_mirror_telescope http://en.wikipedia.org/wiki/Liquid_mirror_telescope for the full derivation. Using h = 2.7 m, g = 9.8m/s, and r = 0.20m gives 40 Hz (or 2,400 rpm). Note though that this gives 20 cm at the top, and 0cm at the bottom. It's a paraboloid, so the center is probably 14-15 cm across. Thus, 40 Hz is a lower bound. Using 40 Hz in (2 * pi * 1.5m) * 40/s implies a minimum equatorial speed of 380m/s, which is Mach 1. The equatorial pumps of course must be providing fluid at an even higher speed. The g-forces at the equator, 1.5 meters away, are even larger than the g-forces at the surface 20 cm away. a = r * omega^2 = 1.5m * 1600/s/s = 2500 G. To get a more uniform evacuated center requires higher speeds still, but the formula I used (first discovered by Newton, btw), no longer holds. It will likely need to be several times faster. Flow speeds of 2km/s require only 6 times faster than the minimum possible speed, which sounds reasonable. Even if 2km/s doesn't sound reasonable. I don't think General Fusion has done the engineering testing to show that they can actually construct one of these, much less use it to provide power. Feel free to correct my calculations.