Author Topic: Fusion with space related aspects thread  (Read 949446 times)

Offline su27k

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Re: Fusion with space related aspects thread
« Reply #3640 on: 07/20/2022 11:50 am »
https://twitter.com/TAE/status/1549419593763921921

Quote
Milestone achieved—and surpassed! ✅

TAE Technologies’ state-of-the-art fusion research reactor Norman has achieved temperatures greater than 75 million° C while demonstrating unmatched real-time control of plasma. (1/6)



Norman exceeded expectations: Designed to keep plasma stable at 30M° C, the reactor was optimized to sustain plasma at more than 75M° C, 250% over its original goal. Here’s what plasma looks like inside Norman: (2/6)



Our next reactor Copernicus will target 100-150 million° C to demonstrate the viability of net energy generation from TAE’s approach. (3/6)



Fun fact about Norman: the plasma formed in its quartz tubes is accelerated to speeds of up to 670,000 mph—fast enough to circle the earth in 2 minutes 🌎 (4/6)



The Norman reactor was named for Dr. Norman Rostoker, TAE’s brilliant technology co-founder & professor @UCIrvine, who passed away in 2014. His vision for combining plasma physics with accelerator physics at the forefront of engineering technology still drives our progress. (5/6)



With a track record of over delivering on milestones and performance, TAE has attracted the support of visionary investors and to date has raised a total of $1.2 billion for its commercial fusion development using clean, safe, abundant hydrogen-boron fuel. http://bit.ly/3cdgMKK

Online Solarsail

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Re: Fusion with space related aspects thread
« Reply #3641 on: 08/16/2022 02:37 am »
New Atlas has an interesting, and quite detailed interview about Tri-Alpha's reactor:

https://newatlas.com/energy/tae-fusion-interview/

New to me is that their direct-energy-capture plans are markedly different from what Helion have talked about;  They want to use more or less photovoltaic cells to capture the X-ray light off of the plasma.

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #3642 on: 08/17/2022 08:53 am »
New Atlas has an interesting, and quite detailed interview about Tri-Alpha's reactor:

https://newatlas.com/energy/tae-fusion-interview/

New to me is that their direct-energy-capture plans are markedly different from what Helion have talked about;  They want to use more or less photovoltaic cells to capture the X-ray light off of the plasma.
Thats because TAE's machine is steady state (while Helion;s is pulsed) and on top of that is burning PB11. So they have a lot more Bremsstrahlung losses. Those are X-rays.

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #3643 on: 09/10/2022 06:33 pm »
New interview with Helion's David Kirtley with new footage of their facility.

Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3644 on: 10/21/2022 07:00 pm »
A bit of fun, using some discussion done here over the years.

https://sites.google.com/view/worldships/flight-of-the-firefly

A long term child of the Shear flow stabilized z-pinch.

Comments welcome.

Online InterestedEngineer

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Re: Fusion with space related aspects thread
« Reply #3645 on: 10/24/2022 01:47 am »
I quickly skimmed through 183 pages of thread and couldn't find any math on how to harness fusion for thrust.

Given the basic rocket physics, it seems like an insanely hard problem to solve, because the thermal energy waste will melt the spacecraft.

The equation, from kinematics, of the power of the exhaust plume for an impulsive thrust of interval ti for a ship of mass mship for a desired deltaV vdelta is:

Pe = 1/2 x mship x vdelta x vexhaust / ti

And the mass flow rate is:

mdot = mship * vdelta / ti /  vexhaust

So for example a 2kt ship with exhaust velocity of 20km/sec and 86400 second of thrust impulse and a deltaV of 10km/sec (i.e., Mars) yields a kinetic energy in the exhaust of 2.3GW and a mass flow rate of 11kg/sec.

Super efficient, yes, but the temperature of such an exhaust given an efficiency eff and specific heat cspecific is:

T = vexhaust2 / 2 / eff / cspecific

Which for an efficiency of 50% and hydrogen yields 28,600K, which will be plasma that will melt everything it touches.

Okay, magnetic nozzle you say.

One could try an exhaust all this thermal energy out the back like chemical rockets do, but by Wien's law and Stefan Boltzmann's law, those GW are going to be almost immediately radiated as ultraviolet at about 100nm wavelength

gigawatts of ultraviolet will heat up and destroy all surrounding materials.   1/r2 won't help you because by the time the exhaust has moved a few meters a large portion of the energy will have been emitted.

Forget fusion for a second.  The basic laws of physics as known since the middle of the early 20th century preclude exhaust velocities of 20,000+ km/sec at gigawatts of power.  It doesn't matter whether it's antimatter, fusion, or lightbulb fission or some magic source.

Perhaps one can use a film of hydrogen or other material to cool the perimeter of the exhaust, but then the mass flow gets you back to about the efficiency of a NERVA style fusion rocket (that's 47kg/sec of hydrogen with a deltaT of 3000k to absorb 2GW for example, so you've just got a slightly improved NERVA rocket).

Is this problem addressed anywhere in the literature?

Maybe film cooling of a quickly moving exhaust will work better than as described?  It just needs to get a few 10s of meters away from the ship, or 1mS.  But this calculator seems to indicate most of the GW will be emitted in the first few mS:   http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/cootime.html


NOTE: I picked the example because this is the minimum requirements to replace refueled Starships an a way that provides an economic and time-to-mars advantage.


« Last Edit: 10/24/2022 02:14 am by InterestedEngineer »

Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3646 on: 10/24/2022 02:29 am »
I quickly skimmed through 183 pages of thread and couldn't find any math on how to harness fusion for thrust.

Given the basic rocket physics, it seems like an insanely hard problem to solve, because the thermal energy waste will melt the spacecraft.

The equation, from kinematics, of the power of the exhaust plume for an impulsive thrust of interval ti for a ship of mass mship for a desired deltaV vdelta is:

Pe = 1/2 x mship x vdelta x vexhaust / ti

And the mass flow rate is:

mdot = mship * vdelta / ti /  vexhaust

So for example a 2kt ship with exhaust velocity of 20km/sec and 86400 second of thrust impulse and a deltaV of 10km/sec (i.e., Mars) yields a kinetic energy in the exhaust of 2.3GW and a mass flow rate of 11kg/sec.

Super efficient, yes, but the temperature of such an exhaust given an efficiency eff and specific heat cspecific is:

T = vexhaust2 / 2 / eff / cspecific

Which for an efficiency of 50% and hydrogen yields 28,600K, which will be plasma that will melt everything it touches.

Okay, magnetic nozzle you say.

One could try an exhaust all this thermal energy out the back like chemical rockets do, but by Wien's law and Stefan Boltzmann's law, those GW are going to be almost immediately radiated as ultraviolet at about 100nm wavelength

gigawatts of ultraviolet will heat up and destroy all surrounding materials.   1/r2 won't help you because by the time the exhaust has moved a few meters a large portion of the energy will have been emitted.

Forget fusion for a second.  The basic laws of physics as known since the middle of the early 20th century preclude exhaust velocities of 20,000+ km/sec at gigawatts of power.  It doesn't matter whether it's antimatter, fusion, or lightbulb fission or some magic source.

Perhaps one can use a film of hydrogen or other material to cool the perimeter of the exhaust, but then the mass flow gets you back to about the efficiency of a NERVA style fusion rocket (that's 47kg/sec of hydrogen with a deltaT of 3000k to absorb 2GW for example, so you've just got a slightly improved NERVA rocket).

Is this problem addressed anywhere in the literature?

Maybe film cooling of a quickly moving exhaust will work better than as described?  It just needs to get a few 10s of meters away from the ship, or 1mS.  Calculating the temperature decay rate of plasma is currently beyond my skillset, though I'm working on it.


NOTE: I picked the example because this is the minimum requirements to replace refueled Starships an a way that provides an economic and time-to-mars advantage.
It's a core problem of fusion propulsion.
It's been addresses extensively, but also handwaved away from time to time.  You are right that the primary solution is a magnetic nozzle.
The second solution, that is one of the key aspect of inertial confinement fusion, is that in inertial confinement there is a short period during which the material is hyperdense and is opaque to high energy photons.  The exact details may be handwavium or real science.  Unfortunately it falls into nuclear weapons research territory, part of which is not public.
The third element of the answer is to use an open nozzle, that lets much if the radiation pass through.

It's actually possible to cool in the Gigawatt levels.  I've joined a 'paper' of my efforts in that field, but plenty of others have explored this in detail.  The attempts at designing for these cooling levels gave the results you can see in the little story I wrote.

The Vista design (Vista fusion with Google Scholar) uses a solution close to what you propose and indeed gets back into nuclear fission territory.

Much of the fusion energy is in the kinetic motion on the neutrons and protons.  Once the acceleration phase is over, my (very limited) understanding is that there will be no more electromagnetic waves given off.  But to be honest, I just do the cooling part, the particle part I leave to the physicists.
« Last Edit: 10/24/2022 02:40 am by lamontagne »

Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3647 on: 10/24/2022 03:00 am »
Here is a link to my modest contribution to the field of fusion propulsion.

It's a work in progress that hasn't seen much progress recently, as I've been busy with other projects, and because I've hit my limits as far as understanding the science goes.

https://sites.google.com/view/worldships/accueil?authuser=0

Online InterestedEngineer

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Re: Fusion with space related aspects thread
« Reply #3648 on: 10/24/2022 07:02 am »
Here is a link to my modest contribution to the field of fusion propulsion.

It's a work in progress that hasn't seen much progress recently, as I've been busy with other projects, and because I've hit my limits as far as understanding the science goes.

https://sites.google.com/view/worldships/accueil?authuser=0

Good stuff, thanks!

The papers you attached/linked to don't address the Stefan-Boltzmann radiation given off by the plasma.  In fact they don't mention the temperature of the plasma, which would be necessary to calculate that power.

Then again, I may be barking about a non-existent problem, see https://physics.stackexchange.com/questions/415028/how-do-fusion-reactors-deal-with-blackbody-radiation .  I'm not sure if this applies to a fusion engine though, it's referring to ITAR.

It would be helpful if your comparison table listed the exhaust velocity.

I do see that aneutronic fusion was preferred, which results in less damage and heating, all of which is wasted energy.

The idea of active cooling horrifies me.  To expect compressors and pumps to operate for long periods of time seems like wishful thinking.  None of that stuff operates for years at a time here on Earth without regular maintenance, and they break all the time.  Jet engines are as good as it gets and that's 6000 hours between overhauls, and this doesn't include minor maintenance.

Offline edzieba

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Re: Fusion with space related aspects thread
« Reply #3649 on: 10/24/2022 08:09 am »
The ever-useful Atomic rockets has both derived formula for maximum engine power in terms of acceptable MW/m2 chamber areal heating (also arranged in terms of chamber size for a given power), along with a very extensive list of fusion engine designs.

Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3650 on: 10/24/2022 12:03 pm »

The idea of active cooling horrifies me.  To expect compressors and pumps to operate for long periods of time seems like wishful thinking.  None of that stuff operates for years at a time here on Earth without regular maintenance, and they break all the time.  Jet engines are as good as it gets and that's 6000 hours between overhauls, and this doesn't include minor maintenance.
Gas turbines and centrifugal refrigeration compressors go about twenty years without significant overhauls, but they do have yearly maintenance.
Of course you are right, maintenance is required and that is the whole point of my fusion story. 
https://sites.google.com/view/worldships/flight-of-the-firefly

Rate of failure was addressed in the 1980s Daedalus study, and the conclusion was that some form of artificial intelligence would be required.  This is still true today.  Once you have artificial intelligence capable of maintenance, then you can have systems that require maintenance.  Before that you need a system that will operate within the limit of the most likely failure, and that at best is a few thousand hours, and in some cases can be just a few minutes, as for some rocket engines.

Your horror is understandable,  common, but not necessarily justified. :D


Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3651 on: 10/24/2022 02:38 pm »
Here is a link to my modest contribution to the field of fusion propulsion.

It's a work in progress that hasn't seen much progress recently, as I've been busy with other projects, and because I've hit my limits as far as understanding the science goes.

https://sites.google.com/view/worldships/accueil?authuser=0

Good stuff, thanks!

The papers you attached/linked to don't address the Stefan-Boltzmann radiation given off by the plasma.  In fact they don't mention the temperature of the plasma, which would be necessary to calculate that power.

Then again, I may be barking about a non-existent problem, see https://physics.stackexchange.com/questions/415028/how-do-fusion-reactors-deal-with-blackbody-radiation .  I'm not sure if this applies to a fusion engine though, it's referring to ITAR.

It would be helpful if your comparison table listed the exhaust velocity.

I do see that aneutronic fusion was preferred, which results in less damage and heating, all of which is wasted energy.

The idea of active cooling horrifies me.  To expect compressors and pumps to operate for long periods of time seems like wishful thinking.  None of that stuff operates for years at a time here on Earth without regular maintenance, and they break all the time.  Jet engines are as good as it gets and that's 6000 hours between overhauls, and this doesn't include minor maintenance.
these is a table here:
https://sites.google.com/view/worldships/starships
Scroll down to the bottom of the page

Bremsstrahlung radiation is calculated for fusion engine designs.  I believe that corresponds to the radiation you are looking for.   The purpose of the nozzle is to convert the pressure from the temperature of the plasma into useful thrust, as for all rockets.

Online InterestedEngineer

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Re: Fusion with space related aspects thread
« Reply #3652 on: 10/24/2022 05:51 pm »
The ever-useful Atomic rockets has both derived formula for maximum engine power in terms of acceptable MW/m2 chamber areal heating (also arranged in terms of chamber size for a given power), along with a very extensive list of fusion engine designs.

That's the summary I was looking for, thanks!

A few things I've figured out while messing around with the thermal problems of aneutronic fusion:

1.  Black body radiation isn't as bad as I thought because plasma isn't a very good blackbody.
2.  Black body radiation doesn't happen instantly, there's an equation that gives you decay rates, and I plugged it into a spreadsheet, and only 1% of the thermal energy impacts the nozzle as waste heat using the worst case blackbody because the exhaust is going so fast that 1/r2 takes care of the rest of the thermal energy.   I didn't include Bremsstrahlung radiation in this though
3.   Film cooling may mitigate the X-ray problem from Bremsstrahlung or blackbody radiation, though it will reduce the Isp.  I don't see where anyone has addressed this in the documents you linked to, except in the anti-matter rocket.  I think they missed an important pressure calculation however.


I'm not quite convinced that the thermal energy of proton-boron or He3 is all captured by the plasma and turned into directed kinetic energy, however.   Will do more reading.


See http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/cootime.html
« Last Edit: 10/24/2022 06:31 pm by InterestedEngineer »

Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3653 on: 10/24/2022 06:59 pm »
The fusion reaction is overpowered for Interplanetary transportation.  Many designs suppose that propellant can be injected into the exhaust to get lower ISP but much more thrust, for a more appropriate performance.  Discovery II, for example.

In his Vista design for a Mars vehicle, Ourt raised the point that the fusion exhaust in a fusion drive might not be well coupled with extra propellant injected into the nozzle.  Which is why he surrounded his fusion pellets directly with extra mass.

Has there been any work done on that since Ourt's latest Vista papers?  Is this perhaps an outdated worry?

Offline sebk

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Re: Fusion with space related aspects thread
« Reply #3654 on: 10/25/2022 10:51 pm »
these is a table here:
https://sites.google.com/view/worldships/starships
Scroll down to the bottom of the page


I can't access the table (or in fact any table on your site):
"We're sorry. This document is not published." is all I could see

Offline lamontagne

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Re: Fusion with space related aspects thread
« Reply #3655 on: 10/25/2022 11:44 pm »
these is a table here:
https://sites.google.com/view/worldships/starships
Scroll down to the bottom of the page


I can't access the table (or in fact any table on your site):
"We're sorry. This document is not published." is all I could see
Thanks a million for testing this!  Of course all the tables worked for me :-[
I put all the tables into what I hope is a public mode.
Please let me know if this works and if you find anything useful.

If you have any suggestions for improvement I'm all ears!
« Last Edit: 10/25/2022 11:45 pm by lamontagne »

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #3656 on: 10/31/2022 03:09 pm »
ZAP has added a new "How it works" section to their website:
https://www.zapenergyinc.com/how-it-works

Online xanmarus

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Re: Fusion with space related aspects thread
« Reply #3657 on: 11/08/2022 09:03 am »
Dr. Matthew Moynihan talks about some general problems in the fusion industry

 

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