ABSTRACT
Reported herein is development of a quadrupole mass spectrometer controller (MSC) with integrated radio frequency (rf) power supply and mass spectrometer drive electronics. Advances have been made in terms of the physical size and power consumption of the MSC, while simultaneously making improvements in frequency stability, total harmonic distortion, and spectral purity. The rf power supply portion of the MSC is based on a series-resonant LC tank, where the capacitive load is the mass spectrometer itself, and the inductor is a solenoid or toroid, with various core materials. The MSC drive electronics is based on a field programmable gate array (FPGA), with serial peripheral interface for analog-to-digital and digital-to-analog converter support, and RS232/RS422 communications interfaces. The MSC offers spectral quality comparable to, or exceeding, that of conventional rf power supplies used in commercially available mass spectrometers; and as well an inherent flexibility, via the FPGA implementation, for a variety of tasks that includes proportional-integral derivative closed-loop feedback and control of rf, rf amplitude, and mass spectrometer sensitivity. Also provided are dc offsets and resonant dipole excitation for mass selective accumulation in applications involving quadrupole ion traps; rf phase locking and phase shifting for external loading of a quadrupole ion trap; and multichannel scaling of acquired mass spectra. The functionality of the MSC is task specific, and is easily modified by simply loading FPGA registers or reprogramming FPGA firmware.
ABSTRACT
Long standing problems in the comparison of very accurate hyperfine-shift measurements to theory were partly overcome by precise measurements on few-electron highly charged ions. Still the agreement between theory and experiment is unsatisfactory. In this Letter, we present a radically new way of precisely measuring hyperfine shifts, and demonstrate its effectiveness in the case of the hyperfine shift of 4s1/2 and 4p1/2 in 207Pb53+. It is based on the precise detection of dielectronic resonances that occur in electron-ion recombination at very low energy. This allows us to determine the hyperfine constant to around 0.6 meV accuracy which is on the order of 10%.
ABSTRACT
A strong emission of characteristic M x rays is observed, without an M vacancy initially present, when slow highly charged ions (Ta(q+), q = 39--48) capture a single electron in single collisions with rare gas atoms (He). This is explained by the formation of bound doubly excited states through electron correlation. An elaborate theoretical treatment shows that bound doubly excited states are mixed with states where a Rydberg electron is bound in the core of a highly charged ion. It is striking that this occurs with a large probability (close to unity), and one needs to assume that higher Rydberg states are populated than predicted by the overbarrier model in order to explain the experimental results.
