## Saturday, September 28, 2013 ... /////

### Accelerator inside a bumblebee

Californian and Colorado experts finally began to build it: early successes

Particle accelerators at the energy frontier are large and expensive. Yesterday, Google Maps revealed its StreetView visualization of the LHC tunnels and detectors. Those readers who have walked through the whole 27-kilometer tunnel by clicking their mouse are surely proud to be achieved e-tourists.

These devices are also expensive; the total cost of the LHC exceeded the annual budget deficit of the Czech Republic. We often think that things have to stay this way – and this belief also shapes our expectations about the experimental inaccessibility of certain questions – but we may be wrong. The microscopic structure on the finger above is what could replace the LHC, ILC, and their pals on a sunny day in the future. Perhaps. ;-)

As Phys.ORG told us last night, an interesting new paper in this direction was published in Nature.

The title of the paper by Peralta et al. is

Demonstration of electron acceleration in a laser-driven dielectric microstructure
They announce that other proponents of the paradigm just talked the talk but they, incredibly enough, also walk the walk. And they add some details:
Here we report high-gradient (beyond $250\MeV/{\rm m}$) acceleration of electrons in a DLA, a micro-fabricated dielectric laser accelerator. Relativistic ($60\MeV$) electrons are energy-modulated over $563 \pm 104$ optical periods of a fused silica grating structure, powered by a 800-nm-wavelength mode-locked Ti:sapphire laser. The observed results are in agreement with analytical models and electrodynamic simulations. By comparison, conventional modern linear accelerators operate at gradients of $10$–$30\MeV/{\rm m}$, and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately $1.6\MeV/{\rm m}$ (ref. 5). Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems. This would enable compact table-top accelerators on the $\MeV$-$\GeV$ ($10^6$–$10^9\eV$) scale for security scanners and medical therapy, university-scale X-ray light sources for biological and materials research, and portable medical imaging devices, and would substantially reduce the size and cost of a future collider on the multi-TeV ($10^{12}\eV$) scale.
So you see that with the higher frequencies (relatively to the RF i.e. radio frequencies that accelerate protons at the LHC), they may achieve much higher electric fields i.e. "gradients" (of the potential energy). The initial applications could be "lower-energy" ones but they are thinking about revolutionizing the high-energy physics colliders, too.

This is a 96-second video presentation of the advance, as posted at Nanowerk which also offers you an article. The trick is all about lasers and ridges. The ridges make the microscopic tunnel thinner in some regions than in others. In the thinner parts of the tunnel, the electric field is more concentrated, and therefore larger, as the whole structure oscillates with laser waves. The smaller, decelerating field in the thicker portions of the microscopic tunnel therefore play a smaller role and the net effect is acceleration.

Note that the gradient $250\MeV/{\rm m}$ is $0.25\TeV/{\rm km}$. You would need about four kilometers of such cool ridges (replacing a longer linear collider) to get to a $\TeV$ which is a high enough energy for electrons, of course assuming linearity. I kind of feel that this might be the future and the projects around 2020 will develop kilometers of nanostructures. ;-) The required linear tunnels already exist.

Via Viktor Kožený, Bahamas

#### snail feedback (13) :

Nah, I think this article shows cute nice developments that seem very helpful for building new accelerators, I would see it not so pessimistic.

Did you mean to say that string theory will become more important (I am not a native speaker and therefore not sure if I understood this right) ? With that I would happily agree of course :-D

Cheers

One thing that this makes me wonder about is how efficient this accelerator is(in terms of input energy to kinetic energy). Current accelerators designs are notoriously inefficient which limits the maximum luminosity they can achieve.

Even if no accelerator with a higher energy than the LHC is built, there might be a chance that this could lead to very high luminosity accelerators to make very accurate measurements of lower-energy parameters.

It could also be used to mass-produce particles which aren't normally abundant, like antimatter or muons which could be used for various experiments or possible applications. Miniaturization and a high acceleration gradient also means that relatively short-lived and slow-moving products of previous collisions could be accelerated quickly before they decay.

It is a great idea to use plasmons to accelerate electrons, with a linear particle accelerator "on a chip".
The plasmon oscillation are generated by laser, and the induced electric double layer generates the acceleration of the charged particles.
The problem is the change of the particle velocity, that need a different frequency of the laser for contiguous layers.
I am thinking that it is possible a generation of different laser frequency; the simplest method is to place side by side a great number of lasers with diffent lenght, to obtain different frequencies; a pratical laser can be obtained with a plane curved output coupler (with a stairway nanostructure), and a curved reflector (with a stairway nanostructure).
If the steps are right, and the chip structure have holes to permit the particle crossing, then the acceleration can be constant, and the velocity can be high.
I am thinking that a complete solid-state structure can be built (solid-state laser and linear accelerator on a chip).

The laser itself languished for many years as a solution looking for a problem.and now they are everywhere. That’s the way technology works.

It’s not at all far-fetched to imagine these gadgets (or something similar) in every home.

Even if you are right, mother nature will provide lots of opportunities for experimental high-energy physics. And you are probably wrong.

According to my naive understanding, the smaller the scale which you probe experimentally, the higher the energy required. I read somewhere that experiments at or near the Planck scale would require a galaxy-size accelerator -- something we will never be able to build. Why can't we use nature as our accelerator. We already send up high altitude balloons to measure what happens when cosmic rays impact the atmosphere (stratosphere, whatever.)

Can't astronomers look for cataclysmic events in deep space? The most massive black holes at the center of some galaxies are said to be on the order of billions of sun masses. When galaxies collide, every once in a while their respective humongous central black holes should collide, too. Surely the energy released in such a violent collision is immense... could it be high enough to yield data that helps to test a grand unified theory or even a theory of everything?

Very exciting news, indeed! High energy electrons may also cause a revolution in Transmission Electron Microscopy imaging, maybe going beyond atomic resolution. That would be an astonishing breakthrough for chemistry and materials science too!

Dear Eugene, to study particle physics at the energy frontier, you need the energy *per elementary particle* (pretty much equivalently, energy) to be huge. Whether the total energy of an astrophysical event is huge is mostly irrelevant for particle physics.

There are also cosmic rays bombing Earth whose energy is immense but the detectors are not built around these (random) collision points and the number of such events is too low (and the initial particles that cause them are often uncertain) so this can't really be used to learn much.

At energies over 60 MeV is the electron velocity practically constant and undistiguishable from c.

Which means that they would be small science by definition. And considering that scientists routinely lie to their funding agencies, one can be skeptical about these claims.

We will never again see facilities that cost tens of billions of dollars to build and that are staffed by thousands of scientists and engineers.

The reason is the welfare state and economic stagnation (which itself might be caused by the welfare state). Even collaborations of countries can no longer afford investments at those levels.

The US, which once planned Moon and Mars colonies, cannot put men into low earth orbit. The US is being forced to reduce its military just as Iran and China are gearing up for WWIII. Britain can't afford to put catapults on their two new carriers, and one of those will be mothballed upon completion.

So, if our mutual economic mess won't let us fund high priority activities, in which of the multiverses will we be able to fund Big Physics?

Okay, thanks. But the singularities at the center of black holes are infinitely small, aren't they? Can't they be considered elementary particles then? Or can the two singularities never touch because the closest two black holes can get to each other is when their respective event horizons touch?