A next generation beam cooler and buncher has been developed and commissioned at NSCL to provide bunched, low energy spread ion beams for collinear laser spectroscopy of rare isotopes. Low energy spread beams reduce the Doppler broadening observed in the fluorescence spectrum, thus improving the resolution achievable in a measurement. Bunched beams permit the reduction of background in fluorescence spectra, thus dramatically improving the signal to noise ratio of the measurement. The beam cooler and buncher features a novel electrode design intended to simplify construction and maintenance, as well as permit the use of large radiofrequency (RF) amplitudes for more efficient beam cooling, especially in the case of high beam currents. A series of ion optical simulations were carried out to determine the design parameters and anticipated bunched beam characteristics. Additional studies using a prototype electrode structure and ion guide system were undertaken to test the performance of the proposed design. The ion guide also serves as a component of the NSCL gas stopping facility. Based on the results of simulation, prototype and ion guide test results, the BECOLA beam cooler and buncher was developed and commissioned. Buncher efficiency, bunched beam energy spread, time width, and transverse emittance were measured using a stable ion source. In addition, the BECOLA collinear laser spectroscopy facility and the beam cooler and buncher were commissioned using a beam of the rare isotope $^{37}$K. The results of ion optical simulations, prototype tests, ion guide studies, and BECOLA cooler and buncher characterization measurements are presented and discussed. The results indicate a successful commissioning of the beam cooler and buncher, along with the rest of the BECOLA facility, with a rare isotope beam, and the systematic studies indicate efficient delivery of low emittance, low energy spread bunched beams well suited for collinear laser spectroscopy.
Read
