Energy efficient proton production?

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 11:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Energy efficient proton production?

Post by Carl Willis » Sun Jun 21, 2009 3:23 am


>6x(10^23) protons at 161keV=161kW

The energy needed to accelerate one such proton is 161 keV or equivalently 2.6E-14 joules. The energy needed to accelerate 6E+23 of them would be 6E+23*2.6E-14 = 15.6 GJ. If you define the proton current then you can calculate the beam power. Otherwise, units of power do not come out of your calculation.

Let's try the other one:

>6x(10^23) Alpha particles at 3.76MeV+12x(10^23) Alpha paricles at 2.46MeV= 8.68MegaWatts

The first particle has 3.76 MeV of kinetic energy or equivalently 6E-13 J. The second and third particle each have 2.46 MeV (4E-13 J). All three collectively have 6E-13 + 4E-13 + 4E-13 = 1.4 pJ. 6E+23 of a set of these three particles has 840 GJ. The calculated quantity as before has units of energy, not power. It also tells you nothing about where breakeven is. It tells you that N times the kinetic energy of one particle is the total kinetic energy of N particles. In other words...not much.

>Working on the fact that fission reactors are only 40% efficient at converting energy to electricity, Any proposed fusion reaction has to be at least 5% efficient to reach break-even

This makes no sense to me. A power plant of any kind has a thermal efficiency that is less than unity and that's about the only generalization that can be made. It need not be limited to 40%. High-temperature gas cycles can be more efficient; Rankine steam cycles tend to be much less efficient unless superheat is added to the steam. Point is, the heat source could have Q(out)/Q(in) be arbitrarily larger than 1 (e.g. 1.000000001) and still work, as long as the heat source is at a high enough temperature and the cold sink at a low enough temperature. Carnot's theorem and all.

P-B11 is a classic, hashish PIPEDREAM as we know it on this site. No member has built SQUAT that accomplishes it, or even tried. And yet, we keep rehashing basic thermo and Bert-and-Ernie math in the discussions. I'm not trying to get personal or display an unwelcoming attitude. (Maybe I am displaying an unwelcoming attitude?) The minute someone does their background research and makes a hardware commitment on a worthy p-B11 project I may stop looking down my nose every time I hear its name.

-Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277

Quantum
Posts: 476
Joined: Fri Jun 19, 2009 12:30 am
Real name:

Re: Energy efficient proton production?

Post by Quantum » Sun Jun 21, 2009 4:19 am

I think you've missed the point, Carl....Either that or I have the wrong font.

David D Speck MD
Posts: 129
Joined: Sat Jan 26, 2008 7:05 pm
Real name: David D. Speck MD
Location: Auburn, NY

Re: Energy efficient proton production?

Post by David D Speck MD » Sun Jun 21, 2009 5:18 am

I was just reading the ORNL web page about their neutron spallation source. They dump 500 kW of protons into a target of liquid mercury to make a whole lotta neutrons in a hurry.

Of interest is the description of their proton source -- they negatively charge Hydrogen ions and accelerate them through a thin metal foil, which strips off the two electrons and leaves bare protons behind.

I wonder if this would be possible on an amateur scale.

Dave

User avatar
Chris Bradley
Posts: 2931
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Energy efficient proton production?

Post by Chris Bradley » Sun Jun 21, 2009 7:59 am

Negative ions through a foil is, I thought, normally the way to make a neutral beam, not a charged particle beam? I wonder why it'd help to strip 2?

Ash, if you pile MW of protons at a piece of 11B, statistically speaking you'll end up with no fusion at all. Almost all, bar a trillionth, will just scatter around and generate heat [destructive to the boron]. You need to come to understand this. beam protons into a lump of something isn't a fusion reactor - it is merely the way you learn how unreactive that really is.

User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 11:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Energy efficient proton production?

Post by Carl Willis » Sun Jun 21, 2009 8:44 am

Sorry, that happened when I tried to type Roman characters on a public Internet cafe computer here in Kobe, Japan. I thought I had it figured out because it looked right on my screen. Evidently not. I am going back to edit it now...

*Earlier post fixed. Small-to-medium-sized rant appended to it.*
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277

John Futter
Posts: 1455
Joined: Thu Apr 22, 2004 2:29 am
Real name: John Futter
Contact:

Re: Energy efficient proton production?

Post by John Futter » Sun Jun 21, 2009 9:14 am

Chris / Ash
Yes we use a negative ion source on our EN tandem
You have to to get the atoms De jour to go through it. A previous post from me on the activation of iron for wear coupons is a case in point for protons.
our unit uses an extremely thin carbon foil at the terminal in the middle of the machine to strip the electrons of the atoms selected, other machines use a recirculating gas stripper to do the same. The terminal is positive at 6MV so the ions get attracted towards it, on loosing their electrons going through the foil they want to get away from the positive terminal as they are now positively charged so the tandem gives a second 6MV push, the ions now have 12MV of push (for hydrogen) other elements of greater mass like silver we can strip more electrons off say up to 11 so the total acceleration is now 12, 1 going to the foil + 11 after the foil so you end up with a 72MeV silver beam.
Now back to your enquiry
If your ion source is working right the H2 will have been dissasociated into H+ ions. Neutral H2 if remaining will leak slowly out of the ion source and not be accelerated towards the H+ target area and will be pumped away and or mass selected by a Wein filter or mass selection magnet to make sure that only H+ ions get to the target.

Ash back to your previous answer/ question to my last post.
cold cathode or hot the ion source if working right keeps the ions bottled up in the centre via the external electromagnet so they do not touch the inner surfaces (anode) of the ion source. If the magnet is not strong enough the ion source interior would get sputtered by the active ions hitting it ( although the sputtering yield for H+ is lousy) For the back cathode and the front cathode (the one with the hole in it to extract the ions we use a material with high work function) we use Aluminium or Tantalum.
The cathodes have to be replaced every 100 hours of running but the anode surfaces only need a clean and this is when using Argon not hydrogen.

Our other accelerator the KN (single ended machine) uses H2, He, He3, D2 in an Rf excited ion source this ion source runs for about 18 months continuously before it needs service.

Remember the more + ions you produce the more they push against each other (repulsion) which means an ion source producing more needs a greater mag field to keep them compressed to the middle section. Also extracted beams of higher ion current will defocus further due to the same repulsive forces.

User avatar
Chris Bradley
Posts: 2931
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Energy efficient proton production?

Post by Chris Bradley » Sun Jun 21, 2009 11:04 am

John Futter wrote:
> Remember the more + ions you produce the more they push against each other (repulsion) which means an ion source producing more needs a greater mag field to keep them compressed to the middle section.
Do you get involved in the actual calculations looking at ion denisties? Various reading suggests the Brillouin limit is the one applicable to anaylsis of such situations - I believe - but I've also read academic treatments and experiments that say it can be a few orders of mag better than Brillouin suggests - and other that say the precise opposite!! What is your feeling for 'n' for a given B? Is Brillouin generally right, in practice?

Quantum
Posts: 476
Joined: Fri Jun 19, 2009 12:30 am
Real name:

Re: Energy efficient proton production?

Post by Quantum » Sun Jun 21, 2009 2:30 pm

"I was just reading the ORNL web page about their neutron spallation source. They dump 500 kW of protons into a target of liquid mercury to make a whole lotta neutrons in a hurry."

RAL use a similar system, but they use a Tungsten target....I have photos of it that I took while installing it, (the most recent ones were taken a few days before they first fired the proton beam to target) but I'm still trying to work out how to upload pics here.
(I also have photos of the beryllium neutron moderators, and the rest of their target system)

"they negatively charge Hydrogen ions and accelerate them through a thin metal foil, which strips off the two electrons and leaves bare protons behind. "

Thanks for that advice, I though something like that would be possible.

Quantum
Posts: 476
Joined: Fri Jun 19, 2009 12:30 am
Real name:

Re: Energy efficient proton production?

Post by Quantum » Sun Jun 21, 2009 2:44 pm

"if you pile MW of protons at a piece of 11B, statistically speaking you'll end up with no fusion at all. Almost all, bar a trillionth, will just scatter around and generate heat [destructive to the boron]. You need to come to understand this. beam protons into a lump of something isn't a fusion reactor - it is merely the way you learn how unreactive that really is. "

I did rather suspect that may be the case, but wondered if the energy levels of the protons were high enough (Giga-Watts?), that maybe the impact ebergy would be sufficient. While I respect your reasoning and advice, Do we know this for certain until it has been tried?

RAL use a solid Tungsten target for their beam, (I can look up the energies involved if you are interested), this produces 'a lot' of neutrons, which, after moderation, are then used to create pions, which, in turn, create muons. One of the things they are doing (RIKEN-RAL) is 'muon catalyzed fusion', which, although it is not what this site is about, may be of interest to some here.

http://riken.nd.rl.ac.uk/ral.html

User avatar
Chris Bradley
Posts: 2931
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Energy efficient proton production?

Post by Chris Bradley » Sun Jun 21, 2009 3:06 pm

Ash Small wrote:
> "if you pile MW of protons at a piece of 11B, statistically speaking you'll end up with no fusion at all. Almost all, bar a trillionth, will just scatter around and generate heat [destructive to the boron]. You need to come to understand this. beam protons into a lump of something isn't a fusion reactor - it is merely the way you learn how unreactive that really is. "
> Do we know this for certain until it has been tried?

Yes. Definitely. It was the first approach ever tried, by Oliphant, and, fortunately for him I guess, the rate of fusion reactions did not produce enough energy to provide an excess of energy to keep the reaction going. This is just what a fusor does, and does it with a 1E-9 inefficiency.

The way physicists refer to it is simply to say "cross-section[scattering]>>cross-section[fusion]" meaning a nucleus will scatter of another waaaaaay more often than it will fuse, so all that almost all the scattered energy just ends up as heat rather than powering a fusion reaction. So if you see "sigma[scattering]>>sigma[fusion]" in anything you read on the subject, then it's their shorthand for saying "beam-target fusion? you gotta be kidding".

....and that's not even counting the electrons that soak up the particles energy from ionisation.....

Post Reply