3 ms·

Reading between the lines it seems the failure to replicate results is down to a lack of precision engineering capability. Is anyone who understands the experim

Reading between the lines it seems the failure to replicate results is down to a lack of precision engineering capability. Is anyone who understands the experiment in detail able to comment? Sounds like what goes on at the focal point of the laser requires nanometers of accuracy in design, position and orientation. Perhaps part of the problem is that we abandoned physical engineering and manufacture in the west in favour of outsourcing it all?

sandworm101 4y ago
Focal point isn't the problem. It is more about timing, getting all the lasers to hit at the same time. And no, this has nothing to do with outsourcing. There are no outside experts in this field.
- nonrandomstring 4y ago
  I see. A similar problem to aligning the detonation wave in the early plutonium bomb designs then, only with the speed of light as a constraint. Tricky.
doctorwho42 4y ago
This is a facility that is critical to US stockpile stewardship. None of the tech or engineering or manufacturing has been offshores/outsourced. The engineering and fabrication side is just that precise. In this facility they indirectly drive the target with the lasers. So instead of uniformly heating a sphere with lasers, they heat the inside of both ends of a gold tube (holhraum). This causes a bath of x-rays to uniformly heat a glass sphere that contains your fusion fuel. That glass sphere needs to be suspended in the center of the tube, but any inconsistency can cause huge knock on effects on yield. So they hold it between two <1um thick sheets of plastic. But if you can imagine, part of the sphere will be in contact with this plastic and part will not. That adds some reduction in how uniformly you heat the glass sphere. But let's back up, how do they even make this perfect sphere of glass that is hollow? And how big is it? Well the sphere can be anywhere from 420um to 800+ um in diameter. From what I recall, the only way to make these is to drop small amounts of glass from a tall tower into water. Then do metrology on it, and toss away >90% of them right off the bat. Another issue is that some of the fuel leaks out of this hollow glass sphere over time. So timing from when you load the target from storage to actually firing the lasers can have non-zero effects on the yield. Long story short. It's really hard to convey how close to the edge of precision ICF research is to the edge of micro fabrication. Now add the fact that some of these targets need to survive going from atmosphere to ultrahigh vacuum, and not break or tear... Remember that 1um thick plastic? So yeah, no one is outsourcing this stuff. It's not being negatively effected by brain drain or lack of funding. It's just absurdly difficult to build to the designed tolerances the physics demands. Fun fact, this is why a lot of physicists got behind the ITER project. The bigger you make something, the less important the minor fluctuations are to the overall yield. :D

sandworm101 4y ago

Focal point isn't the problem. It is more about timing, getting all the lasers to hit at the same time. And no, this has nothing to do with outsourcing. There are no outside experts in this field.

nonrandomstring 4y ago
I see. A similar problem to aligning the detonation wave in the early plutonium bomb designs then, only with the speed of light as a constraint. Tricky.

doctorwho42 4y ago

This is a facility that is critical to US stockpile stewardship. None of the tech or engineering or manufacturing has been offshores/outsourced. The engineering and fabrication side is just that precise. In this facility they indirectly drive the target with the lasers. So instead of uniformly heating a sphere with lasers, they heat the inside of both ends of a gold tube (holhraum). This causes a bath of x-rays to uniformly heat a glass sphere that contains your fusion fuel. That glass sphere needs to be suspended in the center of the tube, but any inconsistency can cause huge knock on effects on yield. So they hold it between two <1um thick sheets of plastic. But if you can imagine, part of the sphere will be in contact with this plastic and part will not. That adds some reduction in how uniformly you heat the glass sphere. But let's back up, how do they even make this perfect sphere of glass that is hollow? And how big is it? Well the sphere can be anywhere from 420um to 800+ um in diameter. From what I recall, the only way to make these is to drop small amounts of glass from a tall tower into water. Then do metrology on it, and toss away >90% of them right off the bat. Another issue is that some of the fuel leaks out of this hollow glass sphere over time. So timing from when you load the target from storage to actually firing the lasers can have non-zero effects on the yield. Long story short. It's really hard to convey how close to the edge of precision ICF research is to the edge of micro fabrication. Now add the fact that some of these targets need to survive going from atmosphere to ultrahigh vacuum, and not break or tear... Remember that 1um thick plastic? So yeah, no one is outsourcing this stuff. It's not being negatively effected by brain drain or lack of funding. It's just absurdly difficult to build to the designed tolerances the physics demands. Fun fact, this is why a lot of physicists got behind the ITER project. The bigger you make something, the less important the minor fluctuations are to the overall yield. :D