Terahertz Radiation To Enable Portable Particle Accelerators (www.desy.de)

Zothecula writes with this Gizmag story about an interdisciplinary team of researchers who have built the first prototype of a miniature particle accelerator that uses terahertz radiation. "Researchers at MIT in the US and DESY (Deutsches Elektronen-Synchrotron) in Germany have developed a technology that could shrink particle accelerators by a factor of 100 or more. The basic building block of the accelerator uses high-frequency electromagnetic waves and is just 1.5 cm (0.6 in) long and 1 mm (0.04 in) thick, with this drastic size reduction potentially benefitting the fields of medicine, materials science and particle physics, among others."

Comments

Who you gonna call?

[Anonymous Coward]

Why worry? Each one of us is carrying an unlicensed nuclear accelerator on his back.
- Dr. Venkman; Ghostbusters

YES!

[ememisya]

One small step for particle accelerators, one giant step for mankind! This brings us one step closer to the replicator!

Once the A/C's get tired of pop-culture references

[mmell]

I wonder if this could bring ion power within our reach as a propulsion mechanism?

so is this going show at 1060 west addison?

[Joe_Dragon]

so is this going show at 1060 west addison?

Re:so is this going show at 1060 west addison?

[Guy Harris]

I'd expect it to be more like the 5600 block of South Ellis Ave.

Re:so is this going show at 1060 west addison?

[preaction]

That's Wrigley Field

A boon to particle physicist hobbyists

[nojayuk]

Charlie Stross wrote a short story, "Dechlorinating the Moderator" a while back about a convention of hobbyist particle physics geeks using stuff like this to produce Higgs bosons in a hotel's banqueting suite.

Re:My ever shrinking HADRON

[tnk1]

I believe this advance actually makes linear accelerators better. I looked at the wording and they seem to focus on linear accelerators, which strongly implies to me that this is not as useful for loops.

Of course, that might mean that existing linear accelerators will be better, but that won't help with your LHCs out there.

Re:Once the A/C's get tired of pop-culture referen

[tnk1]

We already have ion engines. They just aren't all that useful in a gravity well, but pretty efficient outside of one.

prior art

[beckett]

see Spengler, E., Stantz, R., 1984

Sony sold them in the 80s

[LaughingRadish]

Big deal. Sony sold pocket-sized particle accelerators in the 1980s.

https://en.wikipedia.org/wiki/...

A 1959 tabletop accelerator

[602]

[Previously]

Re:Once the A/C's get tired of pop-culture referen

[angel'o'sphere]

We have ion engines since decades, e.g. as positioning engines in satellites.
We had a space probe using an ion engine to go to the moon and circle it.
You must be out of the loop for quite a while.
Welcome back!

Re:My ever shrinking HADRON

[angel'o'sphere]

WTF, this is not a 'linear accelerator', this is a synchrotron.
How fast do you think you get with an acceleration distance of less than an inch?

Re:My ever shrinking HADRON

[amRadioHed]

"Among the possible applications, Kärtner told us that the technology could in principle also be adapted to produce miniaturized but still powerful circular accelerators like the LHC."

Re:My ever shrinking HADRON

[Rising Ape]

The limitation for the LHC energy is the strength of the bending magnets, and for electron synchrotrons the limit is synchrotron radiation (which increases with the fourth power of energy, so more power in won't get you much further). It's not obvious how this can improve circular accelerators.

Re:Once the A/C's get tired of pop-culture referen

[pushing-robot]

The problem with ion drives is simple: F=mv and KE = 1/2mv^2.

The force (thrust) you get from a rocket is proportional to the velocity of its exhaust, but the energy you need goes up with the square of the velocity. The limitation on ion engines is the power source, not the engines themselves.

We are already using ion engines, though only for station-keeping (maintaining an existing orbit) or on small probes with big solar panels which can spend months or years performing orbital manoeuvres.

Subcritical fission reactors?

[Applehu Akbar]

Could this make possible a fission reacxtor design that requires a continuous input of neutrons (or protons) to keep the reaction going? To scram the reactor, just flick the Off switch instead of having to move moderator rods physically into place and then keep coolant circulating until most heat of decay is removed.

Re:Subcritical fission reactors?

[bughunter]

Technically that's still a critical reaction, just using a subcritical mass. This is sometimes called a critical assembly, esp when using neutron reflectors.

And this device accelerates electrons. Neutrons are hard to accelerate; the only means we have of doing that are using small fusion reactions created by accelerating ionized helium isotopes into targets with more H isotopes.

But yes, neutron acceleration can allow criticality in a much much smaller mass of fissile material, thus enabling backpack sized nuclear fission reactors... not that you'd want to get near one, or could lift one if it had adequate shielding. But it would be backpack sized.

Re:Subcritical fission reactors?

[Rei]

This is actually a thing. It's called an ADSR. They're an active research topic. The big thing that they need from their beam is POWER(TM). Designs usually call for something in the ballpark of 100MW.

Note that such a concept isn't *entirely* failsafe. You can be guaranteed to shut down the fission, as there's no chain reaction, but you're not just going to make all of the radioactive daughter products disappear - they'll keep decaying and releasing heat even after you hit the "off" switch. On the other hand, because of the use of a heavy external neutron flux, you do tend to burn up waste pretty well with an ADSR - which is one of the selling points.

Re:Subcritical fission reactors?

[samson13]

The ASDRs don't add much in terms of safety. You basically have the same meltdown risk from decay heat as with a critical reactor because you are producing the same amount of fission products because you are trying to produce the same amount of power.

There is a bit of a numbers game in trying to stay sub-critical.. You still need to play with control rods and burnable poisons etc to guarantee your reactor stays subcritical. You are aiming to get as close to critical as possible because your accelerator generated neutrons are expensive but things like changes in geometry, or chemistry can change the system enough to go critical. i.e. flooding adds water which is a moderator which means neutrons have a higher chance of being absorbed so your subcritical mass becomes critical or a building collapse puts something that reflects neutrons near the reactor core and it goes critical.

When a reactor has been running for a while there is lots of xenon produced which eats neutrons. You add a bit more fissile to get nearer to criticality and then if you stop your reactor the xenon poison decays then you go into critical. When a reactor has run for a while you breed some plutonium so your fissile inventory might increase enough to push you over into a critical mass..

Once you take risks from more regular refueling and ports for drive beams etc into account I'd guess that a critical mass reactor could be made safer, simpler and more reliable.

Not so easy

[joe_frisch]

There have been designs for high frequency accelerators for a long time. These range from normal ~few GHz machines like SLAC, to 10s of GHz (CLIC - proposed), to THz to direct optical acceleration. There are also plasma based 2-beam accelerators which have extremely high gradients (10 GeV/M).

There are some general trade-offs:

Higher frequency -> more energy / length, but lower beam charge and tighter tolerances, and usually lower efficiency. Depending on the application this may or may not be a good trade, but very high frequency accelerators have so far found limited practical application. Most applications for high energy also require fairly high beam power and good beam quality.

In particular high energy physics accelerators require very high average beam power (megawatts), which require high wall-plug efficiency, (to keep operating costs down). So far none of the high frequency accelerator designs look practical for this application. In addition for a high energy physics machine the final focus system is kilometers long, so even if the accelerators could shrink, it in no way results in a tiny machine.

There is a lot of interest in high frequency accelerators for medical and other low energy low power applications. This is a case where there are a number of ways to solve the problem and we need to see which technology is ultimately the cheapest / easiest. Here mm-wave is competing with lasers and other types.

For comparison, a conventional (x-band) 20MeV accelerator is 20cm long. The shielding for a 20MeV beam (which can generate neutrons) could easily be a meter of concrete.

I'm not knocking this technology at all, it may be very useful for some applications. I just want to counter the idea that it will transform particle accelerators.

Joe Frisch
SLAC

Re:Not so easy

[Rei]

Thanks for the comment, Joe, particularly for commenting about power density and efficiency, which I had just wondered about in an above post. Concerning the distance needed for focusing, however, isn't that highly application dependent? I mean, how much does, for example, an ADSR really care about focus? A subcritical fuel assembly isn't exactly a small target, and your evaporation neutrons are going to radiate out in pretty much any direction regardless even if the high energy secondaries keep going roughly along the original path.

This article has got me wanting to pick up the old GEANT4 simulation I was playing around with a couple months ago.... ;)

Re:Not so easy

[joe_frisch]

You are absolutely right that this depends a lot on the application. I'm from a high energy physics accelerator background so I tend to see things in those terms. Trying to ignore that bias I see as typical accelerator applications:

1) High energy physics. This is designed for electrons so we are talking about a linear collider (look up ILC for example). Those need very high energy (TeV scale), since we've already done up to 200GeV with LEP. Very high beam powers (the cross sections are low). and very tiny focal spots (same reason). The best final focus designs for a TeV scale collider are multi-kilometer long. A LOT of work has gone into this, so while there might be a trick people have looked very hard. I don't think high frequency machines make sense for this.

2) X-ray lasers. ( see LCLS) These need several GeV beams with extremely high stability and high phase space density. It would be difficult to get the high electron density with high frequency accelerators. Also, a 5 GeV accelerator is only 50M of X-band structures, and the the FEL laser itself is ~100M. So you would win some space, but not dramatically.

3). Nuclear physics. I don't know anything about this field. I don't know if low current beams are interesting.

4). Medical: typically 20MeV. This is a promising application. There is competition from laser accelerators (direct and plasma) which are in a similar stage of development. I don't know who wins.

5). Industrial: usually also low energy, but high power then medical. Maybe an option, but they usually aren't size constrained so conventional accelerators can be used .

6). ADSR: here and efficiency are everything. Need multi-megawatt beams- and protons which aren't very good for a mm-wave accelerator. I think ADSR is great, but the big technological problems are efficiency and reliability.

There may be a lot of other applications that I'm not aware of.

Re:Not so easy

[joe_frisch]

They probably assume the same techniques will be used as for other accelerators. Shielding. Interlocked doors, Radiation detectors etc.

The sophistication of these systems depends on the accelerator power and energy. Some are no more dangerous than doctor's X-ray machines, others can get near (small) reactor like levels of risk.

Re:Once the A/C's get tired of pop-culture referen

[Bengie]

Yes, if you double the exhaust velocity, you need to increase the energy by 4x assuming the same amount of exaust mass, but you gain more than 4x the acceleration due to efficiency. You have super linear gains because you conserve 100% of the increased energy, but you gain increase efficiency, allowing you to have better acceleration for the amount of energy you consume.

Re:My ever shrinking HADRON

[Rei]

The article talks about linear accelerators. Which I find really interesting because that's just a stunningly high gradient for a linac. If it doesn't come at a cost of efficiency (superconducting linacs being extremely efficient accelerators, unlike say the ultracompact plasma wave accelerators that have been being researched) or power density it could be a godsend to anything that needs a high-power ion or electron source - for example accelerator-driven fission, actinide burning, general spallation neutron sources, etc. Assuming it can operate in CW mode.... Even if it can't it'd be great for medical accelerators.

Heck, with gradients this high you could be putting linacs on spacecraft as ion engines and getting some nutty-high ISP figures.

Re:My ever shrinking HADRON

[Rei]

They're accelerating electrons, not photons. Electrons have mass and thus never hit "light speed", as that would be a state of infinite energy, among other problems.

Re:Once the A/C's get tired of pop-culture referen

[sconeu]

Someone may need to re-study his basic physics.

F = ma, not mv.

Re:Once the A/C's get tired of pop-culture referen

[hankwang]

He meant: F=(dm/dt)v for thrust and P=(dm/dt)v^2/2 for power. Alternatively p=mv for momentum and KE=mv^2/2. Your F=ma is not very relevant either for analyzing propulsion mechanisms.

Re:Particle accelerators are for cows.

[GerardAtJob]

http://orig06.deviantart.net/8... ?????

Re:Once the A/C's get tired of pop-culture referen

[jbengt]

Your F=ma is not very relevant either for analyzing propulsion mechanisms.

Unless you want to figure the acceleration of the space vehicle you get for a given force from the engine.

"just around the corner" like fusion

[peter303]

I've been reading articles about short accelerators for the past several decades, e.g. lasers, computer-pulsed EMF. Yet to see one to scale up to challenge existing accelerators.

Re:My ever shrinking HADRON

[angel'o'sphere]

But a synchrotron is not a linac :)

Re: My ever shrinking HADRON

[Rei]

Speak for yourself, my cat is a LINAC.

Completely unrelated topic: do you have any ideas on how to stop the SPCA from harassing you about so-called "disgusting and immoral body modifications to a pet"? Preferably a means that will cause them to rue the day that they got involved? I have a small LINAC, if that would help - I just need to find him, little Schrodinger is hiding somewhere under the bed right now and doesn't want to come out.