Conny Carlberg

SMILETRAP : A Penning trap facility for precision mass measurements using highly charged ions

The precision of mass measurements in a Penning trap increases linearly with the charge of the ion. Therefore we have attached a Penning trap, named SMILETRAP, to the electron beam ion source CRYSIS at MSL. CRYSIS is via an isotope separator connected to an ion source that can deliver singly charged ions of practically any element. In CRYSIS charge state breeding occurs by intense electron bombardment. We have shown that it is possible to produce, catch and measure the cyclotron frequencies of ions in the charge region 1 + to 52 +. The relevant observable in mass measurements using a Penning trap is the ratio of the cyclotron frequencies of the ion of interest and ion used as a mass reference. High precision requires that the two frequencies are measured after one another in the shortest possible time. For reasons of convenience the precision trap operates at room temperature. So far it has been believed that warm traps working at 4K are required for high mass precision with exactly one ion in the trap at a time. In this paper we demonstrate that mass precision of a few parts in 10 1 0 also can be obtained in a warm trap at a pressure of about 5 × 10 - 1 2 mbar by stabilizing the pressure in the He-dewar, the trap temperature and the frequency synthesizer. In order to reduce the influence of changes of the magnetic field to a level below 10 1 0 , the scanning of the frequencies close to the resonances of both the ion of interest and the reference ion is done in a total time <2min. Trapping of ions is a statistical procedure, allowing more than one ion to be trapped in each measurement cycle. However, after completing the measurements it is possible to reject all information except for events based on 1 and 2 trapped ions. The procedures of producing, transporting, catching, exciting and measuring the cyclotron resonance frequencies of highly charged ions and the mass reference ions with the time-of-flight method are described. In routine measurements with I s excitation time lasting for about 24 h, atomic masses can be determined at an uncertainty of about 1 pbb. In the case of q/A doublet measurements a mass uncertainty close to 0.1 ppb can be obtained as illustrated by a mass measurement of 4 He 2 + . The mass measurements so far performed are either related to fundamental constants or to masses the accuracy of which is needed for some current questions in physics.

Determination of the 76Ge Double Beta Decay Q Value

The Q value of the (76)Ge double beta decay has been determined by measuring the masses of (76)Ge and (76)Se in a Penning trap using neon- and fluorinelike ions. The obtained masses are 75.921 402 758(96) u and 75.919 213 795(81) u, respectively. The systematic errors of these two determinations are nearly equal, and therefore, the remaining systematic uncertainty of the Q value is drastically reduced. A Q value of 2 039.006(50) keV was obtained improving the accuracy of the accepted value by a factor of 6.

The Stockholm–Mainz ion trap project

A new ion trap facility is described which is dedicated to studies of highly charged ions in a Penning trap. Such a trap will be connected to sources of highly charged ions, in particular the electron beam ion source CRYSIS, at the Manne Siegbahn Institute for Physics. The use of highly charged ions in a Penning trap increases the cyclotron frequency with a factor proportional to the charge which leads to a higher resolution. Also, the possibility to vary the charge state makes it possible to search for and identify different systematic effects. Thus, a substantial increase in accuracy can be expected. In addition, the combination of high charge state ions and a Penning trap allows new applications where one can take advantage of the controlled measuring situation, long observation time and high resolution detection. The initial priority will be given to high precision mass measurements of heavy stable ions. At a future stage, plans are to extend the use to other applications, such as charge exchange processes between neutrals and stored charged ions, electron impact ionization and exposure of clusters and molecules to highly charged ions as well as lifetime determinations of molecules and clusters.

Mass measurements of few-electron systems in Penning traps

The accuracy of the SMILETRAP mass spectrometer has been verified by a number of mass comparisons involving well-known masses. Our results for H2+,Ne6+,Ne9+,10+,Si12+,13+,14+,and Ar14+,16+ all agree within the statistical errors (0.3–1 ppb) with previous determinations. However, all measurements involving He give a deviation. The combined He1+,2+ data results in a mass deviation of +1.9 ±0.23 ppb. The uncertainty of the accepted He mass is 0.25 ppb, thus this represents a significant deviation. High statistics comparisons (statistical uncertainty <0.5 × 10-9utilizing different species (excluding He) and charge states agree within ±0.5 ppb. An analysis estimating the contribution from individual systematic error sources and other auxiliary tests does not allow a systematic error larger than ± 0.85 ppb. We conclude that for now we cannot rule out the presence of an unknown systematic error which in the He comparison results in a near 2 ppb deviation. Thus, as a safety measure we should exclude the He data when calculating the proton mass. The He discrepancy also forces us to give a larger limit of the systematic error of the proton mass than motivated by high statistics comparisons. However, due to the consistency of all other measurements and tests, it appears unlikely that this deviation should be present to the same extent in other comparisons. Thus, for now, after a preliminary analysis we report a proton mass = 1.007 276 466 72 ± 16 ± 85 u, where the errors are the weighted statistical errors and the estimated maximal systematical error, respectively. After a complete analysis we expect the systematic error to be reduced below ±0.5 ppb.

The smiletrap (Stockholm-Mainz-Ion-LEvitation-TRAP) facility

Described in this paper is an experimental facility which measures atomic masses by using multiply charged ions from an electron beam ion source. The ions are injected into a Penning trap and the cyclotron frequencies measured. A precision of 2×10−9 has been reached using highly charged carbon, nitrogen, oxygen and neon.

SMILETRAP — Atomic mass measurements with ppb accuracy by using highly charged ions

In the SMILETRAP facility externally produced highly charged ions are captured in a Penning trap and utilized for high precision measurements of atomic masses. Accuracy tests on a ppb level have been performed, using highly charged carbon, oxygen and neon ions. In all cases hydrogen ions served as a reference for the calibration and monitoring of the magnetic field in the trap. Deviations smaller than 3 ppb from the expected results were found in mass measurements of the16O and20Ne atomic masses. The proton atomic mass, determined from the reference measurements on hydrogen ions, is in good agreement with the accepted value [1]. A direct mass measurement on the86Kr-isotope, using trapped86Kr29+-ions is reported.

Precision mass measurements using highly charged ions from an electron beam ion source

The precision of mass determinations in a Penning trap increases linearly with the charge of the excited ion. The SMILETRAP mass spectrometer at the Manne Siegbahn Laboratory is a hyperboloidal Penning trap operating with highly charged ions delivered from an electron beam ion source. This combination of instruments uses ions in a destructive way and allows exchange of ion species in a few seconds with a total measuring cycle of about 1.5 min, during which the change of magnetic field is negligible. In the trap the cyclotron frequencies of a mass reference ion and the ion of interest are measured by driving their quadrupole frequencies. The principles of a Penning trap are briefly described, in particular, the merits of using highly charged ions. The resonance frequencies are determined by a time-of-flight method. We have shown that this method can reach a mass uncertainty close to 0.1 ppb using selected rather than cooled ions. In this way we have been able to measure the masses of several atoms with unc...

Accuracy tests of atomic mass measurements in a penning trap using externally produced highly charged ions

The SMILETRAP experimental set-up, a Penning trap mass spectrometer for highly charged ions, is described. Capture and observation of cyclotron frequencies of externally produced highly charged ions is demonstrated. Mass measurements utilizing different charge states and species to verify the consistency of the measurements are presented. A relative uncertainty <3 10−9 is attained in comparisons between highly charged 12C, 14N, 16O, 20Ne and singly charged H, H2 and H3 ions. The current limitations and future developments are discussed.

Precision mass measurements using a penning trap and highly charged ions produced in an electron beam ion source

A method for precision mass measurements in a Penning trap using highly charged ions produced in an electron beam ion source (CRYSIS) has been developed. The cyclotron frequencies for O8+, 7+, 6+, 5+ and Ar18+, 17+, 16+, 15+, 14+, 13+ ions have been determined by the excitation of the sum frequency v+ + v−. In addition to CRYSIS ions, H+, H2+ and He+ ions were produced by electron bombardment of the H2 rest gas or helium gas introduced through an UHV leak valve into an auxiliary ion trap (or a pre-trap). A technique for fast (seconds) interchanging of the ion species in the precision trap has been implemented to reduce the long term magnetic field drift.

Recent Progress with the SMILETRAP Penning Mass Spectrometer

The Penning trap mass spectrometer SMILETRAP has been considerably improved during the last two years. The helium pressure has been carefully stabilized and is now independent of irregular air pressure. The temperature of the hyperboloidal precision trap is stabilized to ±0.03°C. Remaining temperature instabilities are compensated by changes in the current of a warm coil surrounding the precision trap. The frequency synthesizer is now locked to GPS. This means that it is much easier to accurately measure resonances during several days. The improvements have demonstrated that in mass doublet measurements with an excitation time of 1 s it is possible to determine the mass of ions with q/A = 1/2 at an uncertainty to a few times of 0.1 ppb, using selected rather than cooled ions. In routine measurements lasting for one day it is possible to reach a mass uncertainty of 1 ppb. The masses of the following particles and atoms have been measured with uncertainties in the region 0.3–2 ppb: p, 3H, 3He, 4He, 22Ne, 28Si, 36Ar, 76Ge, 76Se, 86Kr and 133Cs. It has also been shown that though we are using a warm bore the trap pressure is sufficiently low to prevent electron capture from the rest gas for excitation times of 3 s and for ion charges as high as 50+.