Electrostatic Ion Beam Trap Research Articles

A bent electrostatic ion beam trap for simultaneous measurements of fragmentation and ionization of cluster ions

We describe a bent electrostatic ion beam trap in which cluster ions of several keV kinetic energy can be stored on a V-shaped trajectory by means of an electrostatic deflector placed between two electrostatic mirrors. While maintaining all the advantages of its linear counterpart [Zajfman et al., Phys. Rev. A 55, R1577 (1997); Dahan et al., Rev. Sci. Instrum. 69, 76 (1998)], such as long storage times, straight segments, and a field-free region for merged or crossed beam experiments, the bent trap allows for simultaneous measurement of charged and neutral fragments and determination of the average kinetic energy released in the fragmentation. These unique properties of the bent trap are illustrated by first results concerning the competition between delayed fragmentation and ionization of Al(n) (-) clusters after irradiation by a short laser pulse.

Radiative cooling ofAl4−clusters

The radiative cooling of isolated, negatively charged four-atom aluminum clusters has been measured using an electrostatic ion beam trap. Stored $\mathrm{Al}_{4}{}^{\ensuremath{-}}$ ions were irradiated by a short laser pulse at different times after their production in a hot ion source, and delayed electron emission was observed up to hundreds of microseconds after the laser pulse. The decay curves could be well reproduced using an Arrhenius decay law and allowed us to deduce the cluster temperatures at the time of the laser pulse. Using this sensitive molecular thermometer, the cluster temperature could be determined as a function of storage time. The radiation intensity is found to decrease from $40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{s}$ at $T=1400\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{s}$ at $500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with a temperature dependence as given by ${T}^{b}$ with $b=3.5\ifmmode\pm\else\textpm\fi{}0.2$---i.e., similar to what would be expected from a blackbody. This cooling behavior requires the presence of either electronic transitions or very collective infrared-active vibrations at transition energies around $\ensuremath{\sim}200\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$.

Lifetimes of the negative molecular hydrogen ions:H2−,D2−, andHD−

The lifetimes of three isotopologs of the molecular hydrogen anion have been measured using an electrostatic ion-beam trap. Much longer lifetimes (up to $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ for $\mathrm{D}_{2}{}^{\ensuremath{-}}$) than predicted by the most recent calculation are found, and it is proposed that more than one electronic state contributes to the overall lifetimes of these species.

Transverse kinematics of ions stored in an electrostatic ion beam trap

We present experimental results, as well as numerical simulations, for the transverse velocity distribution of ions stored in an electrostatic ion beam trap. The measurements indicate that the transverse velocity spread is about 1% of the longitudinal velocity, and that the ions fill the whole transverse stable phase space. We also demonstrate that ion losses from the trap due to multiple scattering with molecules from the residual gas is an important factor limiting the lifetime of the beam.

Size-dependent electron-impact detachment of internally cold Cn- and Aln- clusters.

The cross sections for electron detachment of internally cold Cn- and Aln- clusters were measured using an electrostatic ion beam trap fitted with an internal electron target. The measured electron-impact detachment cross sections for the Cn- (n = 1-9) clusters exhibit even-odd oscillations reflecting the binding energy trend, namely, higher cross sections for weaker binding. Surprisingly, however, these cross sections increase on the average with cluster size, n, in spite of the increase in electron binding. In contrast, the Aln- (n = 2-5) clusters follow the known scaling laws for electron detachment. We suggest that the size-dependent polarizability of these clusters is responsible for the observed behavior.

Dynamics of stored ions in an electrostatic ion beam trap

The motion of an ion bunch trapped between two electrostatic mirrors is described and the two main regimes, called dispersive and self-bunching, are characterized. Use of the delta-kick cooling method is demonstrated for the dispersive mode.

Phase-space manipulation of stored ions using theδ-kick method

We demonstrate compression of the velocity spread of a stored ion bunch in an electrostatic ion-beam trap, using the $\ensuremath{\delta}$-kick method. An analytical formula for the optimum pulse is derived and is used in the laboratory. A 20% reduction in the asymptotic velocity spread is observed after application of a single cooling pulse to a bunch of 4.2-keV ${\mathrm{Ar}}^{+}$ ions.

Self-bunching induced by negative effective mass instability in an electrostatic ionbeam trap

We demonstrate that the synchronization effect, which has been observedwhen a bunch of ions oscillates between two mirrors in an electrostaticion beam trap, can be explained as a negative effective mass instability.We derive simple necessary conditions for the existence of a regime inwhich this dispersionless behaviour occurs and demonstrate that, in thisregime, the ion trap can be used as a high resolution mass spectrometer.

Negative mass instability for interacting particles in a 1D box: theory and application.

We demonstrate that the synchronization effect observed [Pedersen et al., Phys. Rev. Lett. 87, 055001 (2001)]], when a bunch of ions oscillates between two mirrors in an electrostatic ion beam trap, can be explained as a negative mass instability. We derive simple necessary conditions for the existence of a regime in which this dispersionless behavior occurs and demonstrate that in this regime, the ion trap can be used as a high resolution mass spectrometer.

Fourier transform time-of-flight mass spectrometry in an electrostatic ion beam trap

We report on the application of an electrostatic ion beam trap as a mass spectrometer. The instrument is analogous to an optical resonator; ions are trapped between focusing mirrors. The storage time is limited by the residual gas pressure and reaches up to several seconds, resulting in long ion flight paths. The oscillation of ion bunches between the mirrors is monitored by nondestructive image charge detection in a field-free region and mass spectra are obtained via Fourier transform. The principle of operation is demonstrated by measuring the mass spectrum of trapped Ar+ and Xe+ particles, produced by a standard electron impact ion source. Also, mass spectra of heavier PEGnNa+ and bradykinin ions from a pulsed MALDI ion source were obtained. The long ion flight path, combined with mass-independent charge detection, makes this system particularly interesting for the investigation of large molecules.