About the Lab
The University of Wisconsin – Madison’s Ion Beam Lab (IBL) is home to our National Electrostatics Corporation 1.7 MV tandem Pelletron accelerator. Researchers at UW-Madison use this unique piece of equipment to advance research in the science of radiation damage of materials. We are proud to be a part of U.S. DOE Nuclear Science User Facilities (NSUF), which allows for researchers at other institutions to access this facility using either the Rapid Turnaround Experiment proposal process (https://nsuf.inl.gov/Page/rte) or the Consolidated Innovative Nuclear Research funding opportunity announcement (https://nsuf.inl.gov/Page/cinr).
The IBL accelerator system is made up of two ion sources, 45⁰ injector magnet, 1.7 MV tandem electrostatic linear accelerator, and finally a 22.5⁰ switching magnet with three analysis beamlines each ending with a custom sample chamber providing a wide array of capabilities.
Overview of Capabilities
Sample Geometry: We usually work with samples on the order of several millimeters across. The maximum rastered beam area is 20 X 20 mm. The size of the defocused ion beam is 1-3 mm in diameter. Sample thickness can vary from tens of microns to several millimeters.
Irradiation Temperature: We can provide conventional sample heating by mounting the sample to an in situ eclectic heater or via our custom 200W infrared laser heating system. We can also provide sample cooling via liquid or compressed air cooling of the sample stage. These techniques allow us to to maintain the irradiation temperature near room temperature or as high as 1000 ⁰C. Temperature is measured via type K thermocouples placed as close to the sample as possible and/or via dual-wavelength Williamson pyrometer which reads above 450 ⁰C.
Vacuum: Vacuum in the irradiation chamber is constantly monitored by ion gauge and is maintained at less than 1e-6 torr during irradiation. A residual gas analyzer can be used to monitor which gasses are present during irradiation.
Ion Species, Energy & Beam Current at Sample: We can provide up to 30 µA of 1.5 to 3.0 MeV protons. For heavy ions we often utilize the 2+ charge state to achieve energies up to 4.5 MeV. Most ion species are possible. Listed below is what we frequently do. Please inquire about desired ion species and we will determine what is feasible. Alpha particle irradiation is not currently available.
- Protons: 30 µA
- Nickel: 6 µA
- Tungsten: 500 nA
- Carbon: 12 µA
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Ion Sources
The NEC Toroidal Volume Ion Source (TORVIS) is a stable and reliable plasma ion source capable of producing many tens of microamps of negatively charged Hydrogen or Helium beam.
The NEC Source of Negative Ions through Cesium Sputtering (SNICS) is a versatile ion source capable of producing many species of ion beam. The many different cathode materials produce a wide range of beam currents, from tens of microamps to hundreds of nanoamps. Please inquire for information about specific beam species.
Irradiation with protons gives relatively flat damage profiles and has the benefit of more closely simulating neutron irradiation. Irradiation with heavy ions allows much faster damage rates and produces none of the sample activation of proton irradiation.
Accelerator
The NEC Pelletron accelerator is the heart of our lab. Low energy (~50 keV) negative ions from either ion source are accelerated toward the high voltage terminal. The terminal, housed inside a high pressure (60-80 psi) environment of insulating Sulphur hexafluoride gas, is held at constant positive voltage up to 1.7 megavolts by NEC’s eponymous pellet chain based mechanical charging system. Inside the terminal, electrons are removed by interactions with a stripper gas. Positively charged ions emerge and are then accelerated again, away from the high voltage terminal. The result is variety of useful energies and charge states ranging from 1.5 to 5.0 MeV.
High Energy Beamlines
The ion beam leaving the accelerator can be directed down one of three beamlines by the switching magnet. All three beamlines are equipped with NEC Faraday cups and beam profile monitors (BPM) to measure the current and cross-sectional distribution of the beam to be impinged on the sample. Adjustable apertures define the region to be irradiated and continuous current measurement of these apertures ensures the entire region is covered by the ion beam for the duration of the irradiation.
Both the left and middle beamlines are equipped with neutral beam trap deflectors and raster scanners operating at hundreds of hertz. This equipment creates a more uniform distribution of ion beam flux on the samples. Gaussian distributions (defocused beam) can be achieved simply by switching off the raster scanner and adjusting focusing elements.
Left Beamline
The left beamline is the Swiss army knife of the IBL. The 6” conflat flange at the end of the beamline can be built up and adapted to suit specific needs. The easily removable stage allows samples to be mounted, apertures adjusted, thermocouples installed to suit the irradiation plan. Beam heating can be complemented by a 220 W plate heater which can reach over 900⁰ C. Alternatively, beam heating can be offset by cooling with the closed loop propylene glycol chiller system for lower temperature irradiations down to room temperature. Temperatures are monitored by thermocouples mounted to the sample stage. We also have an in-situ thermal camera to provide information about surface temperatures and gradients during the irradiation.
Turbo pumps and an optional ion pump can maintain vacuum at or below 1 E-6 torr throughout the irradiation.
The left beamline can also be easily re-fitted with other chambers to suit other irradiation plans. For example, we have a chamber which holds a thin foil sample with high-temperature molten salt on the back side for in-situ irradiation of molten salt corrosion.
Middle Beamline
The middle beamline is purpose-built for high-throughput irradiation. The large (60 liter) chamber accommodates the large (15 cm X 15 cm) sample stage. Two linear drives allow for X-Y motion of the stage. This setup allows for the simultaneous loading of dozens of small samples, which can be irradiated consecutively without breaking vacuum.
The middle beamline’s temperature monitoring and control is custom built for precision. During irradiation, the 200 W IR laser provides direct heating of the sample surface while the dual wavelength pyrometer constantly measures the surface temperature. This equipment is integrated with LabView, such that sample temperature can be held steady to within 1 degree C by a software control loop.
As with the left beamline, aperture current is constantly measured to always ensure complete coverage of the beam flux region. Periodically, a faraday cup can interrupt the irradiation for a few seconds to measure the beam current directly.
An 850 L/s turbo pump mounted directly to the chamber can maintain vacuum at or below 1 E-6 torr throughout the irradiation.
Right Beamlne
The right beamline is currently in the process of being rebuilt. Stay tuned for exciting new capabilities!
UW-Madison can also offer neutron irradiation. Contact UW nuclear reactor https://reactor.engr.wisc.edu/.
