Development of a Portable, Differential-Absorption Spectrometer for Use at Underdiagnosed Electron Accelerators

Many small electron beam facilities exist around the United States which provide intense electron beams of several hundred mA into open air. These facilities can provide high dose rates for various measurements and are also convenient for experiments that require rapid changes in their set up, due to the ease of adjusting an experiment in open air. However, many of these facilities do not possess the means to identify the energy of their electron beam to a high precision, which limits the quality of data that can be obtained. We developed and commissioned a portable spectrometer called SPATC (a Spectrometer Purposed for Accelerator Testing and Certification), specifically to certify the beam energy of an accelerator while only requiring power from a wall outlet from the facility. SPATC is placed in front of the accelerator beam window in open air and measures the differential absorption of electrons as they stop in various thicknesses of aluminum. These data are then used to extract a central beam energy and beam distribution by comparing to simulated data in Geant4. This method for determining a beam energy was validated by comparing to magnetic spectrometer measurements and was found to agree well for three different energy electron beams. The design of SPATC and its commissioning experiment will be shown, along with the analysis procedure to extract beam energies. Finally, we will present ongoing work to improve the energy precision of this spectrometer.