[jamesr]

Brian H wrote: It occurs to me that starting up an FF generator in a remote location or carried on/powering a vehicle (distant from either other (operating) generators or the grid) will take some arranging. The capacitors have to be charged up to initiate the self-sustaining sequence, and that would have to be from either the grid, a small auxilliary generator, or batteries, I suppose. The capacitors couldn’t be counted on to hold charge for any useful period of time after a shutdown, either.

Is this likely to be much of a concern or problem?

I don’t see a problem with charging the capacitors?? The capacitors only need to hold enough energy for one pulse to start. With a bit of margin say 100kJ, ie to charge them you could supply for example 200W for 500s. A small solar panel on the roof could do that, or for that matter a person with an crank handle winding a dynamo for a few minutes.

The main startup power would be the vacuum system, since it needs to have pumped down the chamber, preheated it etc. The cooling system (helium & water pumps) could be ramped up as you increase the pulse rate. So you could have for example all the excess power output for the first few minutes of operation is used purely to get all the pumping systems & flow rates up to speed as you increase the pulse rate to its normal output rate, then you can sync up to the grid and start supplying power when everything is ready.

[jamesr]

MTd2 wrote: What is the angular distribution of x-rays around the plasmoid?

It will be isotropic. So any part of the device, such as the base of the electrodes, pump inlets, rogowski coil etc. which covers area the onion could be gathering energy from will also detract from the overall efficiency.

[jamesr]

vansig wrote:
. o Oh! you mean flux as the peak intensity. that makes much more sense.

this really is new territory

Yep – I assumed although you get some soft xrays during the few microseconds of each pulse as the plasma heats up & filaments, the bulk will come out in a very short flash of ~50ns while the plasmoid it at the 50-500keV temperature.

The flux levels are not unheard of – it is just that getting the energy out as a usable current will not be trivial. I doubt early prototypes would get anything like the efficiency needed for a working power generator.

This is the kind of research which really could be done alongside the main focus fusion experimental program. There are plenty of x-ray sources around the world that could be used to test and play with different laminations of material.

[jamesr]

Rezwan wrote:

How about a scene of the future… a vast green forest (of young trees) with a gleaming city poking out of the horizon.

There’s a clearing with a camp fire in the middle. An old geezer and his grandson are camping. He’s saying ….

“Of course, when I was a lad, all this was oil derricks and desert… until they built the fusion desalination plant.”

Fusion. Energy to spare for the necessities.

Yes! We need an image of the gleaming city. Anyone have an original gleaming image?

How about this?

[jamesr]

I’ve always liked the idea of breaking away from the steam era

tcg wrote: The Plasma Focus, along with solar, has the further distinction of not even having any moving parts, if I understand the mechanism correctly.

But we’ll still have lots of vacuum pumps, cooling pumps. Also I think most large scale solar would be mirrors heating a pumped liquid not photovoltaics – at least until they can break away from silicon to some cheaper & more efficient fabrication method.

[jamesr]

The group is set “Public, Closed” ie. anyone can view the group, but to add papers to it you need an invite to join. I have send messages to a few who I have email addresses for, but if anyone else want to contribute send me a message and I’ll add you.

[jamesr]

vansig wrote: Would a wide band gap semiconductor do, for this purpose? such as
Aluminium gallium indium nitride (AlGaInN) ?

I just checked up the various methods for normal diagnostic X-ray detectors, such as in X-Ray Data Booklet. They use different materials are used for different energy ranges an fluxes. We are operating in a completely different regeme to these detectors, as the flux of x-rays will be much larger (and harder). Although the premise is the same – to produce a current from the energy deposited by the x-rays as efficiently as possible. It is just that in our case the total current should be substantial.

A rough calculation of 15kJ of X-rays at average of 50keV emitted over 50ns onto a 50cm radius sphere puts the flux at ~10^21 photons/cm^2/s. Which is many orders of magnitude greater than a normal detector would saturate at.

Googling for recent papers I found one using a different wide band gap semiconductor (Fast High-Flux Response of CdZnTe X-Ray Detectors by Optical Manipulation of Deep Level Defect Occupations), quoted as high flux levels a figure of 10^9photons/cm^2/s on a 2mm thick slice.

So unlike detectors which are built to be as sensitive as possible and absorb as many x-ray photons in a small volume as they can. We need a material that as it saturates the rest of the photons pass through to the next layer & so on. Rather than one which absorbs more than it can cope with, and the excess ending up wasted as heat.

So if we have a flux of 10^21photons/cm^2/s and an onion with 1000 layers, (ignoring the fact that the outer layers have a larger area), then each layer has to cope with absorbing 10^18 photons/cm^2/s – still 9 orders of magnitude higher that their wide band-gap semiconductor can cope with.

Of course this assumes the materials don’t exhibit some weird non-linear response at such high fluxes & short pulse duration. I guess the only way to really find out is by experiment (or very detailed modeling).

[jamesr]

vansig wrote:

By the way, where does FoFu fall on the 2nd chart?

wasn’t 70 keV ion temperature reported this spring? that places Focus fusion just a few ticks from the right-hand edge, within the yellow zone.

The shaded ignition area, and green ‘burning’ line are for D-T fusion. For pB11 the curves would be further to the right so the bottom of the curves lie at around 550keV

[jamesr]

Indeed – reminds me of a T-shirt I’ve got with a quote from Einstein…. “If we knew what we were doing it wouldn’t be called research, would it?”

[jamesr]

I’ve had a quick skim through the list of devices given, most are little more than historical curiosities now, on the road of how magnetic, and inertial confinement machines have developed over the years.

Most designs were build to investigate a particular regieme of plasma behaviour, and were never thought as serious energy producing canidates.

The only mention of Dense Plasma Focus devices is a one line entry in the table under the Z and theta pinch section with a date range of 1965-1970, with a reference to a book published in 1981. Given this article was written in 2005 when there were plently of DPF research machines around the world highlights the fact that DPFs are not well known in the mainstream fusion community.

An interesting part of the overview is the graphs of funding, which increase steadily upto 1983, then as the oil price was so cheap then the funding level dropped off again. We can now see over the past few years since the oil prices have gone up again a renewed interest in fusion. If only the policy makers could have been a little more longsighted and realised it was a long term investment and that to make progress they should have kept up the funding levels for the past 30 years.

[jamesr]

They quote a plasma beta (the ratio of pressure over magnetic pressure) as >7 which is very good, and is a measure of how strong (ie big & expensive) a magnet you need to confine the plasma. This compares to 0.02 for some tokamaks & upto 0.5 for spherical tokamaks respectively. This is encouraging as you can confine the plasma at a much higher density in a cheaper machine.

Also, although the temperature they achieve is only 0.5keV, the electron temperature is 1/4.5 of the ion temperature, which is also promising.

After the two ‘smoke rings’ or compact toroids (CT) in their language, are fired at each other they form a ~1m wide blob of plasma with a peak density of 10^20/m^3 after around 40us, which is kept stable for around 1ms before instabilities set in, and the confinement is lost.

They say further heating mechanisms could be added such as neutral beam injectors (NBI), but I’m not sure this would maintain the favourable ion/electron temperature ratio needed for pB11 fusion

[jamesr]

Sorry, I didn’t mean to be flippant (I had just come back from the Pub when I posted it).

I assume you are suggesting if a pellet of fuel is inserted into the point where the colliding filaments normally form the focus. Whether the pellet is room temperature, frozen at a few Kelvin, or cooled further to near absolute zero to make a Bose Einstein condensate wouldn’t make much difference. The difference between 0.3, 3 or 300K and the 10^9K needed for fusion are all essentially 10^9K.

pressure = n*T, where n is the number density. For fusion you need the triple product of n*T*confinement_time to be greater than a critical value (dependent on the reaction in question). You always need the temperature to be high enough for the reaction to happen at any appreciable rate. So it’s not as simple as increasing density so you can lower the temperature, generally though if you can increase density you can decrease the required confinement time.

As for using the collapsing filaments of a plasma focus device to provide the energy to what is essentially inertial confinement fusion, instead of lasers is an interesting idea, but I think the axial symmetry of the plasma would mean the pellet would be compressed unevenly and squish out of the ends before it could be heated sufficiently.

[jamesr]

I’m not sure where to begin with this – but, no…

How can something be “pre-compressed”?? A Bose-Einstien condensate is by definition cold. It takes an enormous amount of energy to cool something so every atom is in it’s ground state. We want all the ions to have enough energy to overcome the coulomb barrier to fuse – you couldn’t get any further from this state as a BEC really.

[jamesr]

The hydrogen to boron ratio in diborane is closer to an optimal value as well I believe. I gather the sweet spot between fusion reaction rate and bremstrahlung losses is about 5:1 of p:B11.

What would a more or less fully dissociated partially ionized mixture naturally condense to?

I had always thought that the bulk gas in the chamber would, after a shot cool to a few thousand degrees, before the next pulse when operating at a high rep rate. Obviously during these experiments it will quickly cool to the chamber/electrode temperature. Would free boron & hydrogen atoms recombine to form complex molecules that could condense onto the walls.

[jamesr]

Here’s a few similar graphs from a recent talk I went to, showing demand from OECD, FSE(Former Soviet Union), and developing countries (primarily made up of India & China). Its a bit of and odd split, but shows a similar rise in demand. It assumed OECD rise in demand would be offset against efficiency savings

The other one is a different mix of energy production from an EDFA/TIMES model – it weighs a little too heavy to wind in my opinion. It also assumed fusion would not be cost effective until the availability of cheap uranium becomes a factor in 2090 or so.

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