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Low-energy multiply charged ions of the refractory elements tungsten and molybdenum have been produced and stored using a novel technique that couples laser ablation with a radio-frequency ion trap. The charge states of the ions stored range from q =+1 to +4 for tungsten and from q =+1 to +6 for molybdenum. Approximately 10' ions with energy less than 5X10 ' eV/amu are stored for a period in excess of 2 s. The technique can be used to store low-energy multiply charged ions of almost any element. In the last decade several techniques have been developed for the production of near-thermal-energy highly charged ions. Cocke' produced highly charged ions by the impact of swift heavy ions; this technique was later combined with ion storage to carry out experiments on low-energy charge transfer. ' More recently, Short et aI. have developed a technique that uses synchrotron radiation to produce near-room-temperature highly stripped ions of the noble gases after inner-shell excitation. In these experiments, however, choices of parent gases for the ions are limited, and only a few varieties of singly and multiply charged ions can be produced.Thermal energy multiply charged ions of refractory elements such as tungsten and molybdenum, so important to our current fusion energy program, have not been studied. Reported here is a novel yet simple approach that overcomes some of the limitations of earlier techniques. Useful quantities of low-energy multiply charged ions can be produced and stored for almost any element.The method combines the production of ions by laser ablation with ion trap techniques. Laser ablation has been used previously to produce both neutral atoms and ions from solids. Measures and Kwong have reported the production of neutral chromium atoms. Ehler, Irons, and Phaneuf reported the generation of multiply charged ions from a variety of target materials. The number and charge states of ions produced by laser ablation depends on the laser energy and the laser power density. The number produced per laser shot is large, typically ranging from 10' to 10' . To date only singly charged ions from laser ablation have been trapped.Johnson and Kwong' trapped Al+ in a cylindrical rf trap for the purpose of measurements of the lifetime of metastables. Knight" was able to capture Be+, C+, Al+, Fe+, and Pb+ ions in an electrostatic trap.The inability to trap multiply charged ions in the above-mentioned experiments most likely arises from the ions high kinetic energy (tens to hundreds of eV) relative to the traps low potential wells (a few eV). In order to trap multiply charged ions from ablation plasmas, it is therefore essential to reduce the kinetic energy of the ions. We have achieved the "cooling" of laser-ablated ions by using two separate beams that cross at right angles inside the ion trap. A few ions in one beam undergo collisions with ions from the other with the result that some of the scattered ions lose almost all their kinetic energy (and remain inside the trap) while others approximately double theirs (and ...

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Articles you may be interested inMultiphoton absorption by metal-metal long distance chargetransfer complexes in polar solvents Effective bridge spectral density for longrange biological energy and charge transfer Direct structural characterization of charge localization in metal to ligand charge transfer complexes AIP Conf.A novel method is described that combines the production of ions by laser ablation with an ion-trap technique for the measurement of thermal-energy charge-transfer rates of multiply charged ions and neutrals. The charge-transfer rate is determined by measuring the rate of loss of stored ions from the trap. Verification of the calibration of the apparatus is demonstrated through investigation of charge transfer of N z and N 2 +, which has been studied by another group. We also have made the first measurement on the thermal-energy charge-transfer coefficient of Ar and W2 + . The rate coefficient is 0.99(0.22) X 10 -Ii cm 3 s --1.

The radiative-decay rates of the 2s 2p( P')-2s2p ( P) intersystem transitions of C+ ions have been measured by recording the time dependence of the 233-nm emission. A cylindrical radiofrequency ion trap was used to store electron-impact-produced C ions. The time-dependent signals were analyzed by multiexponential least-squares fits to the data. The measured radiative-decay rates to the ground term are 146.4(+8.3, -9.2) s for Pi~q, 11. 6(+0.8, -1.7) s for Psych, and 51.2(+2.6, -3. 5) s for Psyq Com. parison of the measured values with theoretical values is presented.