Small update from Lawrenceville Plasma Physics

[D Tibbets]

I hadn't considered that. Nitrogen and/ or oxygen would be good substitutes for more difficult to handle boron for plasma studies and Bremsstrung studies. Possibly even a tangent for testing the machine as a high energy X-ray source , or testing their direct X-ray conversion scheme.

Dan Tibbets

[Axil]

Ivy Matt: LPP is currently using only deuterium as the FF-1 fill gas. No tritium

But in Deuterium-Deuterium fusion, two reactions occur with about equal probability.

D + D = T (tritium 1.01 MeV) + P (3.02MeV)
D + D = He3 (.82 MeV) + N (2.45 MeV)

So the neutron flux of N indicates a production of N atoms of tritium.

Consider, Vermont is shutting down Vermont Yankee for failure of its tritium containment.

This is a big and expensive step for Vermont where the fear of this radiation source is acute. For example, a recent audit report on the state auditor's decommissioning trust fund found decommissioning costs for this reactor could hit $990 million in 2006 dollars, or more than $1 billion in current figures.

A $billion in decommissioning costs shows significant fear. This is on top of the closing of a plant that has a construction cost of many $billions to build in the first place. Is tritium that fearful a thing?

First off, tritium is an isotope of hydrogen, which is very difficult to contain. Tritium binds to hydroxyl radicals to form tritiated water (HTO), and that it can bind with carbon atoms readily (C-T). The HTO and the carbon-tritium compounds are easily ingested by breathing, by drinking, or by eating organic or water-containing foodstuffs. Since tritium is not a very active beta emitter, it is not dangerous externally, but it is a radiation hazard when inhaled, ingested via food, water, or absorbed through the skin.

On the plus side, once tritium enters the body, it disperses quickly and is uniformly distributed throughout the body. Tritium is excreted through the urine within a month or so after ingestion. This reduces the total effects of single-incident ingestion and precludes long-term bioaccumulation of HTO from the environment.

However, organically bound tritium (tritium that is incorporated in organic compounds) can remain in the body for a longer period.

Since tritium is perceived to be a very dangerous radiation danger the question remains… do 10e14 tritium atoms per FF-1 shot pose a danger to the researchers and/or the surrounding neighborhood?

[D Tibbets]

The answer to 10^14 tritium atoms being a danger is easily answered, if you know the Curies this represents, and the dispersion, and the half life. With a 12 yr half life, that would be ~ 60sec/min * 60 min/hr * 24 hr/Day*365 day per year*12 yr=~ 360,000,000 sec/half life. Divide the number of tritiums by this by the half life in seconds gives ~ 10^8 beta particles per second. This would be ~ 0.01 Curie.

http://en.wikipedia.org/wiki/Curie

Not highly dangerous levels compared to medical radiation sources, but you probably wouldn't want to wrap your lips around the vacuum pump exhaust. Venting to the outside would quickly disperse and dillute this tritium to extremely smaller densities.
Perhaps, with a few more orders of magnitude fusion output they would need to consider the local dilution effect and ensure adequate dispersion was obtained. A trap might also be an option (something that absorbs hydrogen and or chemically binds it- then you would need to consider disposal of low level radioactive waste- much like medical materials that are used for radiation treatments).

Dan Tibbets

[D Tibbets]

All strength to them.

But let's just check the reality; let's given them the benefit of the doubt and hit their upper ranges;

a) temp: In our best shot, on September 29, we calculate the average ion energy at between 160 and 220 keV

b) density: LPP physicists were able to calculate that the density of the plasma in the plasmoids is between 1 and 4X1020/cc

c) [from graph] tau: 300e-9s

Triple product reported; [22e4]x[4e26]x[3e-7] = 3e25 keVs/m^3

Lawson requirement for {>Q=1} >= 1e21 keVs/m^3

So the thing that worries me now is that with 4 orders of magnitude over the Lawson criterion, why is the thing still putting out only mJ outputs for kJ inputs? If that triple product were right, what's going wrong that it is still several oom below Q=1?


hmmmm.....

Again, I wonder about the validity of these numbers, even if they are accurate.

http://en.wikipedia.org/wiki/Lawson_criterion

Essentially the Lawson criterion says that the power in cannot exceed the power out if you wish to maintain a certain temperature.
[EDIT- Err... perhaps I should say that the total power leaving the system cannot be exceeded by the input power if breakeven is desired.]

Lets see. In the DPF experiments, they had ~ 200 KeV temperatures generated, and with their densities and current, this resulted in ~ 10^10 fusions in a ~ 100 nanosecond interval.

10^10 D-D fusions represents in ~ 10 Joules of energy.
They put in ~ 30 Kv at ~ 1 million Amps for a short interval, that was still much longer than the lifetime of the plasmoid. Lets say it was for a few microseconds. I think that would represent ~ 30*10^9 W/ 10^-6 sec, or ~ 30,000 Joules. Then you have to consider the energy wasted in forming the plasmoid (is it 1 % efficient, 10%?). If my calculations are correct, these tests resulted in Q's of ~ 1/3000.
[EDIT- actually I think I am erroring on the Joules input by quite a bit. The Q may be closer to 1/ 100,000 as they speak of ~ 1 megajoule inputs.]

Finally , the Lawson criteria says almost nothing about fusion (I think), only the energy input/ output balance. This could be met if you had only a few fusions, if you were confining and heating only a few atoms for very long times with very good insulation. Alternately, you could be confining a lot of atoms for short times and with poor insulation.

I know this argument is vague, but what I think I'm saying, is that you are considering the confined energy, density and time, but ignoring the excess energy (due to various inefficiencies and losses) necessary to establish those conditions. During the 'steady state' period of ~ 100 NS, the numbers might apply, but the time and excess energy flows needed to establish this brief steady state condition is not accounted for.

In another way my interpretation of the lawson criterion is analogous to how much heat you need to keep a house warm. This ignores how much heat it needs to initially warm the house. This is the difference between true steady state conditions, and pulsed systems, especially when the brief plateau steady state phase is relatively short. If you keep a house at the same temperature for a year, the initial warming may be trivial. But if you only keep the house warm for an hour, the initial warming cost is much more significant.

Dan Tibbets

[Skipjack]

Seems like LPP has released a few more interesting updates:
Head over to Next Big Future for that and a bunch of other fusion related news. Lots of stuff going on lately.

Confinement of over 100 billion degrees will be published in a peer reviewed journal:
http://nextbigfuture.com/2011/01/confin ... llion.html

LPP December 2010 report:
http://nextbigfuture.com/2011/01/lawren ... ember.html

[Brian H]

http://focusfusion.org/index.php/site/a ... -_summary/

Lots of additional links, like http://focusfusion.org/index.php/site/a ... se_plasma/
and
http://focusfusion.org/index.php/site/a ... apacitors/

[Henning]

Seems like Springer's "Journal of Fusion Energy" has accepted their paper "Theory and experimental program for p-B11 Fusion with the Dense Plasma Focus". Not yet published, though.

http://lawrencevilleplasmaphysics.com/i ... &Itemid=90

[MSimon]

The Poly works better the larger you build it.

Actually it works better the smaller you can make it. If size = S then Polywell output is a function of 1/S discounting losses which are at this time unknown (we have general equations but limited practical experience).

The limiting factor re: size is the size of the magnets needed for a given field strength. There may also be others.

[D Tibbets]

The Poly works better the larger you build it.

Actually it works better the smaller you can make it. If size = S then Polywell output is a function of 1/S discounting losses which are at this time unknown (we have general equations but limited practical experience).

The limiting factor re: size is the size of the magnets needed for a given field strength. There may also be others.

Where did that come from? The scaling laws is B^4 r^3 for output and perhaps B^0.25 r^2 for input. r^3 / r^2 implies gain with increasing size. This of course assumes B strength keeps pace.

Perhaps you are referring to confluence/ central focus. As the central focus is improved the core shrinks. As the core shrinks the reactive volume also shrinks at 1/r^3, but the density increases the same amount d^3 and the fusion rate scales as the square of the density, so the reaction rate and yields both increase. Also, keeping the radius the same and increasing the B field will produce similar results.

Even presuming that my reasoning is accurate, I'm not sure that it really makes much difference. If the Polywell works near the predicted scaling laws I suspect engineering concerns will set the minimal practical size. This is why I wonder if better confluence/ POPS is practical. If the thermal heat loads and magnet cooling limits the minimal size at a given output power, then improving reaction rates per unit size may be counterproductive.

Dan Tibbets

[MSimon]

Even presuming that my reasoning is accurate, I'm not sure that it really makes much difference. If the Polywell works near the predicted scaling laws I suspect engineering concerns will set the minimal practical size. This is why I wonder if better confluence/ POPS is practical. If the thermal heat loads and magnet cooling limits the minimal size at a given output power, then improving reaction rates per unit size may be counterproductive.

Because of magnetic shielding at high levels of magnetic field strength thermal loads are not a significant concern. Yea!!!!!!!!!!

This was discussed around these parts some time back. As was the increasing output for reduced size.

OTOH your point about engineering concerns is quite true. But who knows? We may some day see a 100 MW Polywell a meter or two across (total enclosed volume) vs the 20 or 30 m size currently postulated.

Today I'd settle for a working Polywell and let the engineering improvements follow.

[KitemanSA]

Today I'd settle for a working Polywell and let the engineering improvements follow.

o!a

Sorry, that is the best I can do for a "thumbs up".

[DeltaV]

Meanwhile, Corvette owners and space hopper designers remain hopeful and observant.

[D Tibbets]

Even presuming that my reasoning is accurate, I'm not sure that it really makes much difference. If the Polywell works near the predicted scaling laws I suspect engineering concerns will set the minimal practical size. This is why I wonder if better confluence/ POPS is practical. If the thermal heat loads and magnet cooling limits the minimal size at a given output power, then improving reaction rates per unit size may be counterproductive.

Because of magnetic shielding at high levels of magnetic field strength thermal loads are not a significant concern. Yea!!!!!!!!!!

This was discussed around these parts some time back. As was the increasing output for reduced size.

OTOH your point about engineering concerns is quite true. But who knows? We may some day see a 100 MW Polywell a meter or two across (total enclosed volume) vs the 20 or 30 m size currently postulated.

Today I'd settle for a working Polywell and let the engineering improvements follow.

Assuming P-B11 fusion, the heating by direct bombardment of fusion products (ions) is significantly less (ideally almost zero) than that due to neutron bombardment from D-D fusion, but the bremsstrulung radiation will be considerably more, and the cross field transport of energetic fuel ions will still occur. Presumably this leakage is proportionatly low.

Has anyone roughly figured the relative thermal load on the magrid between D-D and P-B11 fuels? Assume superconductors, so there is no Ohmic resistance heating concerns. Also assume that the D-D reactor is operating at ~ 80 KeV, while the P-B11 reactor is operating t ~ 200 KeV, and the ratio of P to B11 is 10:1.

Dan Tibbets

[Betruger]

Today I'd settle for a working Polywell and let the engineering improvements follow.

Vahid,
Now that you have your fusor up and running, are you looking to improve it, seems like you could "polish" it up a bit and get more neutrons out of it. Thoughts/Plans?

ladajo,
We intend to improve it by adding ion sources, titanium coating and cooling system. We will appriciate your useful ideas about that.
.

They could use some of your insights, it sounds like.

[ladajo]

Anyone who wants to jump in...Dan? Tom? M?