My mind is open on the original issue of fusion in metal lattices, Pd in particular. I see no fundamental reason why it couldn't work, the only real problem is the endless hype over possible applications. For example, I don't ever see it becoming a way of generating significant power, because you still have the fundamental problem of turning low level heat into mechanical work.
That low-level energy inputs can be concentrated to produce localised keV energies is now well-established. Two of my favourite recent Nature papers involve making neutrons by gently heating a pyroelectric crystal, and X-rays from sellotape:
"Observation of nuclear fusion driven by a pyroelectric crystal"
B. Naranjo, J.K. Gimzewski and S. Putterman
Nature 434, 1115-1117 (2005)
"Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape"
C.G. Camara, J.V. Escobar, J.R. Hird and S. Putterman
Nature 455 1089-1092 (2008)
Haha. Sorry. Left off the k in the keV. 100,000,000 K. That should be better. And its just order of magnitude - 11,000 K/eV, even though the real conversion is 11,604 K/eV. But what's a couple hundred degrees amongst friends.
Originally Posted by alanrockwood
Fusion does not occur at 8.6 eV. Trust me on that one. Hydrogen ionizes at 13.6 eV. It's not going to start fusing at a lower energy.
I've attached a graph of fusion cross sections for DD, DT, and DHe3. Sorry its a pdf. DT is the reaction of choice because it peaks at such a lower temperature. Fusion projects shoot for 20-40 keV.
I'm sure there's something interesting going on in cold fusion experiments. Like I said, maybe even fusion. But as an energy source, you'd have to dump a lot of energy in to get a lot of energy out. Fusion doesn't spontaneously happen on a large scale, unlike fission.
Last edited by Tim Gray; 04-24-2009 at 09:55 AM. Click to view previous post history.
I think that's the sticking point for me. It needs to be more than localized for power applications. We've been generating fusion neutrons for years, but it needs to be large scale to get to the point where it can be stuck in a power plant.
Originally Posted by Struan Gray
Shouldn't this topic be in the lounge?
The neutron generators in nuclear weapons utilize D-D and D-T reactions. The acceleration potential used to be on the order of 50KV, and a lot of neutrons were produced.
Is there an asymptotic formula that does a good job of correlating and extrapolating the data in the chart to low collision energies? Ideally this would be based on some kind of theoretical considerations, and not just an engineering correlation.
As I think about this in terms of a collision problem (from a kind of hybrid view, but largely as a problem in gas-phase kinetics, with a smattering of over-simplified quantum theory thrown in) I see at least several significant factors. They are inter-related, but could be considered somewhat separately. 1) What energy is required to climb the coulomb hill. 2) How long do the nuclei spend near the turning point - probably significantly less than one vibrational period of a "conventional" diatomic vibration, so a vibrational period could be taken as a very conservative upper limit. 3) What is the probability of fusion as a function of internuclear distance - probably determined largely by tunneling. 4) What mechanisms are available for stabilizing the newly formed Helium nucleus, which will be in a highly excited state. 5) What selection rules and/or rates would govern stabilization. 6) What role does angular momentum play, since a direct head-on hit will be a low probability event.
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I don't know of what's out there for low collision energies.
Just to give you an idea of the quantities involved, for thermonuclear fusion of DT, either magnetic or inertial, a triple product is used as a formula to estimate when you will have ignition, which is the goal. At this point, the energetic helium ash can deposit enough energy in the plasma to maintain continued fusion reactions. Anyway, the triple product is basically density * temperature * time. You need to keep enough particles together for long enough that are hot enough to fuse. You can reach ignition from different approaches. Inertial fusion jacks up the density at the expense of the time the atoms are held close together (confinement time). Densities are 1000 times solid densities, confinement times are extremely short (ns-us, not exactly sure). Magnetic fusion goes the opposite way, long confinement times (seconds) and lower densities (10^20 particles / m^3). Temperatures are roughly the same - 10's of keV.
I just did a quick search ('low energy fusion cross section') and saw a couple papers out there which talk about the cross section down to about 4 keV. I didn't see anything much lower than that.
nworth: I assume you have some experience with this stuff, noting your location
Lol! - I wonder what company Mr OldGeek works for? Do a google: he has spammed this all over the 'net...
Originally Posted by oldgeek64
Interesting titles they use in that company - "Chief Visionary Officer", anyone?
But the CVO is no anyone - he's Dr. Irving Dardik, MD!
-- Ole Tjugen, Luddite Elitist
Sandia's Z-Pinch Program
The Z-Pinch inertial confinement method being researched at Sandia promises a long-term road map to a functioning fusion power plant.
Here's a link to a lengthy PDF of the program overview.
Here's Wikipedia's overview of the Z-Pinch Sandia machine.
True, but there are some interesting applications for a tunable benchtop neutron source, and that's before you get into the wilder power-source-on-a-chip dreams of the nano-technologists.
Originally Posted by Tim Gray
Lund is in the final stages of bidding and raising funding for both a new synchrotron lab and the European Spallation Source. If funded they will be built all over one of my favourite lunchtime photo-hunting areas. If I can persuade the powers that be that all we really need is a Bunsen burner and a roll of sellotape I'll be happy :-)