Use of A Reconfigurable VME Module to Measure Beam Energy at the Los Alamos Proton Storage Ring

Custom instrumentation has been developed at the Los Alamos Neutron Science Center (LANSCE) to measure the Proton Storage Ring (PSR) beam energy. The PSR accumulates up to 4•10¹³protons from the linear accelerator for delivery to a spallation neutron source. The energy of the beam injected into the PSR must be adjusted so that the revolution frequency matches the ring buncher frequency, otherwise a large momentum spread will cause increased losses in high-dispersion areas such as the extraction line. Errors in injected beam energy appear as deviations from the ideal 2.8 MHz revolution frequency. A low-cost reconfigurable VME module developed at LANSCE has been configured to calculate the PSR revolution frequency in real-time. The module connects directly to a raw analog wall current monitor output and uses analog signal conditioning electronics, an analog to digital converter, field programmable gate arrays (FPGAs) and an embedded floating-point digital signal processor (DSP) to calculate the revolution frequency. The module is compliant with the EPICS based accelerator control system and calculation results are sent through the network to the control room. This is an improvement over the existing method of manually measuring the frequency with an oscilloscope. Accelerator physicists can now simply observe the PSR frequency, which is dependent on beam energy, on a control room display.