Jefferson Labs

Today was the once-every-two-years open house for the Thomas Jefferson National Accelerator Lab, down in Newport News. I spent about three hours down there, walking around and looking at the exhibits. Basically, their facilities come down to two main devices, a laser and an accelerator.

Warning: High geek-speak quotient to follow.

The laser is a 10KW (soon to be 14KW) free electron infra-red laser. In the laser they cause an electron beam to oscillate up and down. Forcing the electrons to change the direction they are moving causes them to emit light. The light is bounced back and forth between mirrors. This interacts with the next group of electrons to make them give up even more energy. Eventually, this results in a cascade, and ZAP!

The electrons injected can only be used once in the loop of the device, because the act of giving up their energy to the laser places them out of phase for reuse. But what to do with a 200 MeV electron beam? Just dumping the beam is such a waste of electricity. So, they use the energy to provide the initial pump to another electron packet before finally dumping a now 100KeV electron beam, saving 95% of the power.

One of the presenters was asked "who paid for this?"
"The Navy."
"Why would the Navy be interested in this?"
"Let's just say, they'd like to be able to do some material processing at long range."
All the time the 'asker' is standing in front of a poster showing a laser beam shooting down a cruise missile. Duh! They said the beam can poke through 10 meters (?) of steel in one second.

The accelerator is the 6GeV (soon to be 12 GeV) Continuous Electron Beam Accelerator Facility. This is more of the traditional "atom smasher" that people know about. The electron beam is circulated, round and round, picking up 1 GeV each time. The photo shows where the electrons in each energy level are split out for the trip around the curved end of the accelerator.

Huh? Well, this is a continuous electron beam device. In other words they are always putting electrons into the loop, so some are low energy and some are very high energy. The curves at the end are lined with magnets to bend the electrons around the corner (see figure).

The magnetic field that would bend the high energy beam would we way to much for the low energy electrons, and they'd be knocked out of the machine. And vice-versa. So, they keep the high energy electrons (6 GeV) in the bottom beam, and send each of the other 4 energy levels through a different tube and set of magnets, as you can see happening to the right, here. The researchers pick which beam they want for their experiments, and have the electrons diverted into an experimental hall.

Amusingly, the staff narrating the trip kept avoiding mentioning anything about all the radiation security warnings posted about. Remember how I said if you bend an electron beam it gives off light? Well, imagine the electron beam is 3000 times as energetic as what they were using in that laser. The result is not pretty. Well, maybe it is pretty, but it's also pretty deadly. As in "deadly radiation" levels. Fortunately, stop the beam and the radiation stops too, which is why it was safe for us to tour there.

On a positive note, one of the accelerator scientists, after his spiel said "and I'd like to thank all of you folks for paying for this."
"I thought the Air Force paid for this part?"
"And where do you think they get their money? The Air Force doesn't make money, they just spend it."
The honesty, and acknowledgment of who was paying the bills, was refreshing.