Instrument Development Beam Line
HFIR’s new CG-1 beams test new ideas, techniques
Four new instrument development beam lines are in varying stages of development or completion at the Cold Guide 1 (CG-1) position, which views the HB4 Cold Source at HFIR.
The four beam lines, CG-1A, B, C, and D, are tucked into the far corner of the Cold Guide Hall, in building 7970. The beams are cheek by jowl with their more famous brothers, HFIR’s GP-SANS and Bio-SANS beam lines.
The CG-1 instruments are new. Very new. The brainchild of Lee Robertson, group leader for the Instrument Development Group, in the Neutron Facilities Development Division (NFDD), CG1 is the largest of the four guides housed in the Cold Guide Hall, and one day a full-fledged user instrument, like its neighbors, will be built there in its place.
“However, that’s down the road,” explained Greg Smith, Low-Q Scattering Group Leader and HFIR Operations Coordinator. “In the meantime, we had the most intense beam coming out of the cold source. So we decided to instrument that beam line.”
Because it is such a large beam, the HFIR team split it into four separate beams − four separate instruments. “It has all come together in the last few months. And it is temporary. It has a finite lifetime in that, if we get funding and the user community wants that beam port for a permanent instrument, then it will all go away,” Smith said.
“In the meantime we are going to use that to our best advantage, and test out some concepts.”
CG-1A, which began operating in January 2010, will be used to develop a SERGIS instrument prototype that employs the spin-echo scattering angle measurement technique. SERGIS, which is a relatively new concept, combines the spin-echo technique with reflectometry. SERGIS is particularly useful for the study of polymer systems, and researchers want to see if it has potential as a user instrument. It is currently under development at several neutron scattering facilities around the world.
“A lot of times, these techniques have a well-established pedigree as a technique, but they are looking for a science problem to really make them useful to the community and this is one of those,” Smith said. “We think we can learn a lot about polarized neutrons and spin echo encoding. Then we would build the real instrument, either at the SNS second target station or possibly here at HFIR.”
When it is commissioned, the CG-1B beam, a utility diffractometer, will be used to develop monochromators and analyzers, optical components that use diffraction. The researchers also hope to make it available to users to prepare their experiments, before moving on to their more cost-intensive and time-intensive user instrument. With this in mind, the table on the CG-1B has been designed to match the interface on the other HFIR instruments.
CG-1C is squeezed in beside 1D so closely that the two beams cannot be used at the same time. “The mission for beam line C is very similar to D,” Robertson explained. “It’s a monochromatic beam line: You can continuously vary the wavelength, using a double-bounce monochromator.” Its mission is optical component development.
CG-1C and 1D are a more general-purpose platform for exploring new ideas. CG-1D is a time-of-flight beam line, with a chopper for producing pulses of neutrons. It is much in demand for neutron imaging studies, essentially taking non-invasive images of the structure of materials, using neutrons rather than x rays.
CG-1D is also tasked with prototyping a new kind of powder diffractometer, which is part of the development work for the SNS second target station. And it will be used for low-energy cross section measurements, developing optical components,and characterizing 3He polarization cells.
“We have a collaboration with Gene Ice, in the Materials Science and Technology Division, to look at some nested focusing mirrors. He is well-known in the x ray optics community, and he is beginning to work with us on neutron optics,” Robertson said.
In another project, the CG-1D team is collaborating with a company in California, to build a MISANS enclosure. “It is good for looking at very, very, slow motions of materials, such as the dynamics of the particles in ferro-fluids, or protein folding,” Robertson said.
A Defense Advanced Research Projects Agency experiment is building a centrifuge that can be set on the CG-1D beam line to do neutron imaging of cells used to cool components in rotating space satellites.
The researchers are working fast because they don’t have a lot of time. “Our instrument can only be there until they are ready to install a user instrument,” Robertson said.
“But we are in the planning stages to build a similar facility at the SNS. There is a beam line 16B which is kind of hemmed in by its neighbors. There is not enough space to build a traditional neutron scattering instrument. Since no one else wants it, we think we can get it for development at the SNS.“
