Everything is a nail

Everything is a nail
October 7, 2010

There are many stories about how, if you possess a hammer, especially if it’s a good hammer, lots of things appear to be nails. If you were to replace the hammer with an accelerator, particularly a superconducting radiofrequency accelerator, I must confess that I have a tendency to see many opportunities as nails worth tapping.

A laboratory portrait of Jefferson Lab appeared in a recent edition of Nuclear Physics News . That article gave a fairly broad discussion of the range of nuclear physics conducted at the laboratory and also touched on the existence of a free-electron laser. The basis for the success in both of those fields is the excellence of the lab’s hammer, our superconducting radiofrequency technology.

Our nuclear physics accelerator, the Continuous Electron Beam Accelerating Facility, has performed superbly over the course of more than a decade. The machine design energy was 4 GeV. Recently, the accelerator has operated routinely at 6 GeV. The beam intensities can be very high, and extensive results, measurements of structure functions of nuclei and nucleons, have accrued. Nuclear measurements are the first nail.

Beams with very high polarization, in excess of 80 percent, are provided, with different polarization in different experimental halls on a routine basis. These have allowed the investigation of the distribution of spin in the nucleon. It has also encouraged the development of a parity violation program; this accesses the exchange of a Z boson interfering with that of a photon. So, given our particular hammer, the weak interaction also looks like a nail.

Over the past year, we have received several letters of intent and proposals, which have the goal of searching for so-called dark photons, the harbingers of dark matter. So, dark matter, a key concept in cosmology, also appears like a nail.

It turns out that the builders of our machine left space for us to install five extra cryomodules in each of the linear accelerators and to double their energy; so the hammer will get even better. We will be in a position to extend our nuclear physics studies to cover essentially all of the issues with the Bjorken x variable greater than 0.1 thus yielding a thorough knowledge of the valence quark region of the nucleon. The weak interaction work will also have the goal, for example through measurement of parity violation in Moller scattering, of achieving precisions comparable to those achieved by the LEP or SLAC-SLC/SLD program, or the W mass measurements at the Tevatron. Another nail.

It is worth noting also that the advances in the superconducting radiofrequency result in increased Quality Factors (Q values) which in turn reduces the cooling required and leads to the potential for high-power accelerators. This makes it possible to imagine using accelerator driven sub-critical reactor systems for nuclear power generation using, for example, a thorium cycle, or for re-burning spent fuel from existing reactors. This issue, given the current state of the planet, may be worth several nails, but certainly one.

The final nail I would like to point out is associated with photon science. As has been understood at DESY with their operation of FLASH and development of the XFEL machine, superconducting radiofrequency technology is a superb platform on which to build a free electron laser (FEL). At Jefferson Lab our free-electron laser, developed with support from the Office of Naval Research, and using the same cw approach as the nuclear physics accelerator, has operated with a power of 14 kW in the infrared. This device also uses energy recovery by deceleration. Recently we started operation of the device in the ultra-violet which provides useful power in 10 eV photons in the third harmonic. This is a clear precursor to a higher energy operation. With an upgrade of the existing device to a 300 MeV single pass linac, 600 MeV or even 900 MeV is possible with multiple passes. This could facilitate 100 eV photons, similar to FLASH but with higher power.

I think you can agree that given the beautiful superconducting radiofrequency technology available at Jefferson Lab, we have a hammer that makes the world look like a whole bed of nails. Predominantly this drives our nuclear physics program, but also gives us the potential to broaden our horizons.