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

prior art

[beckett]

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

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

[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.

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

[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: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: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.