Taylor Davidson, N4TD

An 80 MW final puts these hams at the top of the high-power list.

Many of us who have an interest in Amateur Radio are also attracted to technology-based professions. It is therefore not surprising to find 17 hams working at the Spallation Neutron Source (SNS). The SNS is a particle accelerator-based neutron source located at Oak Ridge National Laboratory in Oak Ridge, Tennessee.

A partnership of six national laboratories, sponsored by the US Department of Energy Office of Basic Energy Sciences, developed this facility. Studies of the atomic structure of materials are the focus of SNS research. It is a user facility available to corporate, university and governmental researchers from around the world.

Spall What?

Spallation is a technical term for knocking pieces off something with something else. Remember that time you were swinging your baseball bat in the house and accidentally hit that statue Aunt Jenny gave your mom? Remember how the head went flying across the floor? Well, that’s spallation.

At SNS, the process is a little more sophisticated. To create a neutron beam using spallation involves several steps. It starts with an ion source that produces negatively charged hydrogen ions consisting of a proton orbited by two electrons. The ions are injected into a linear accelerator, which raises them to very high energies. They then leave the accelerator and pass through a foil, which strips off each ion’s two electrons, converting it to a proton.

These protons pass into a ring where they accumulate in bunches. (The protons are the bat.) Each bunch of protons is released from the ring as a pulse (the swing). The high-energy proton pulses strike a heavy-metal target, which is a container of liquid mercury (the statue). The proton pulses slam into the mercury atoms and knock off neutrons (the head).

These spalled neutrons are moving pretty fast and need to be slowed down. To slow them, they are sent into a moderator like liquid hydrogen or methane. Once slowed down, the neutrons are guided to areas containing special instruments such as neutron detectors. Once there, neutrons of different energies are used in a wide variety of experiments.

Radio Research

There is a significant radio component to the Spallation Neutron Source. In the linear accelerator RF energy is applied to cavities, which are basically metal tubes, to grab and accelerate the ions. A series of these tubes cause the ion pulses to increase in velocity and energy as they travel down the accelerator. Ninety-one large klystron vacuum tubes generate the RF energy. Seven of these produce up to 2.5 MW each at 402.5 MHz. Another four klystrons provide up to 5 MW each at 805 MHz. The remaining 81 klystrons deliver up to 550 kW each to the cavities they drive. All these add up to a capability to deliver over 80 MW of RF power. That’s 47 db above a full gallon!

What Does It Do?

The beam of neutrons is used to study the structure of different materials. This has applications in physics, chemistry, engineering, medicine and biology. A few examples of neutron studies are:

•Engineering: the changes in the crystal structure of spinning turbine blades as they heat.

•Chemistry: the development of synthetic fibers for clothing.

•Physics: high-temperature superconducting materials.

•Medicine: the structure of synthetic molecules that may lead to drugs that can target diseased areas of the body.

•Biology: Research on the molecular structure of proteins, which aids the understanding of neurological and genetic diseases.

Hams of the SNS

The hams on staff at the SNS work in a variety of technical disciplines, including control systems engineering, RF engineering, beam diagnostics, survey and alignment, software engineering and cryogenics engineering. All of them agree that either their interest in ham radio helped steer them to a technical profession or their interest in things technical lead them to ham radio.

Photos by Genevieve Martin, SNS Communications Group.

Taylor Davidson, N4TD, an ARRL member, was first licensed in 1965 as WN4YIC soon upgrading to General to become WA4YIC Taylor took the final step to the Extra Class license in 1972 and changed his call to N4TD in ’77. His main ham interests are homebrewing, DXing (he is on the DXCC Honor Roll and has 5BDXCC), low power operating (DXCC) and digital modes especially RTTY (RTTY DXCC). Taylor has an MS in Engineering Technology and is the RF engineer for the SNS. He can be reached at PO Box 30506, Knoxville, TN 37930-0506, n4td@bellsouth.net.