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[ Narrator: ] Particle accelerators are powerful scientific tools that are used for research
in many fields: in particle physics at the highest...
... and most intense energies,
in nuclear physics,
in materials science,
and in biology and chemistry.
One of the most common methods for accelerating particles is with superconducting radiofrequency
cavities.
These SRF cavities build up strong electric fields that increase the energy of bunches
of particles in a beam.
And because they are made of superconducting materials, they only dissipate a tiny amount
of power in their surfaces.
[ Hasan Padamsee: ] The superconducting radiofrequency technology provides very high voltages over
these short distances at very low losses - at very low RF power losses, which means you
can leave on the radio frequency and the accelerating voltage, you can leave it on for all the time.
So first of all we need to get the metal in a very pure state.
And then we prepare the shapes and we weld them together.
Then after the cavity is ready, it's necessary to prepare the surface of the cavity in order
that it's very clean and we eliminate all of the material imperfections that naturally
come into the cavity when you're fabricating it.
So we have to go through a rigorous procedure of chemical etching to remove metal and impurities.
Then washing, and we use very high pressure water to rinse out the residues of the chemicals.
The pressure of the water is one hundred atmospheres of pressure.
And that cleans the surface completely.
And then after that, when the cavity is together, we need to assemble it in such a way that
it doesn't get dirty again.
Because any particles of dirt that fall into the cavity, when they see the high electric
and magnetic fields that are in this cavity, then they react badly to that so that a particle
of dust that may be sitting over here can actually emit electrons which then absorb
the energy in the cavity and the cavity fails.
And so when we assemble it, we assemble it in a class 100 or a class 10 clean room, which
means that one cubic foot of volume contains only one particle - one particle.
[ Narrator: ] Recent breakthroughs include nitrogen doping, a process where impurities
that actually improve performance are added to the superconductor itself.
This makes the cavities substantially more efficient.
New techniques like doping are evaluated through experiments on cavities and investigated using
advanced microscopy and materials analysis tools.
[ Martina Martinello: ] It's really interesting how these large SRF accelerators revolve around
the nanometer scale.
Indeed, the very surface of the cavity and its nanometer structures play a crucial role
in the achievable acceleration and efficiency.
For example, at Fermilab our group has pioneered surface treatment techniques like nitrogen
doping and niobium tin coating that can change the surface structure and impurity content,
leading to a large improvement in cavity performance.
However, in our labs, we make sure that this work on cavities goes hand in hand with the
material characterization and the understanding of radiofrequency superconductivity.
So it's a very exciting applied process of improving the performance of these accelerating
structures, it's oddly scientific and challenging.
It's what we call accelerator science.
[ Narrator: ] After surface treatment and assembly, the performance of the cavity is
carefully evaluated in a cryogenic vertical test stand.
The cavities are cooled to a few degrees above absolute zero, where the niobium material
becomes superconducting.
These cavities are assembled with vacuum piping, cryogenic lines, and other instrumentation
in a package called a cryomodule.
A large accelerator can require dozens of cryomodules.
Large SRF facilities currently under construction include a neutron source in Sweden, nuclear
physics experiments in Michigan and Korea, and X-ray lasers at SLAC in California and
DESY in Germany.
[ Marc Ross: ] Superconducting RF has been developed for application in linear accelerators
over the last twenty years with the goal in mind to really achieve the very highest energies
to study the basic components of the universe.
And it's been also found to be adaptable for different kinds of accelerators or different
kinds of science.
And as the accelerator we've been working on at Stanford is just such a linac which
operates in the steady state, or CW mode, for materials science.
The developments to allow this technology to reach higher and higher energies go hand
in hand with that.
And with the work that we now have under way, we have every intention of making an industrial,
practical technology capable of the purposes of high energy physics.
[ Narrator: ] One proposed accelerator, The International Linear Collider, would use thousands
of cavities to create particle collisions at extremely high energies.
Researchers could perform in-depth studies of the Higgs boson recently discovered at
the Large Hadron Collider and search for physics beyond the standard model.
[ Michael Peskin: ] So now we're setup to do a detailed exploration, to take our tweezers
and pick out these particles, one by one, and really understand their properties in
great detail.
The machine that will do it is is this one that you see behind you, based on the superconducting
RF technology that's being developed here at Fermilab.
With this machine, you can produce millions of individual Higgs bosons, understand their
structure and use them to prove the deepest mysteries of the universe.
[ Akira Yamamoto: ] An electron machine has very precise information, would give us very
precise information, so it should be built as a global effort.
We dream that this international linear collider will be realized, hopefully in Japan.
[ Narrator: ] Accelerators let scientists answer questions about what's happening in
our universe at the very smallest scales.
By advancing accelerator technology, we enable a new generation of machines that can probe
the frontiers of science - and illuminate a new view of our world.
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