Resistive cooling of highly charged ions in a Penning trap to a fluidlike state

Abstract

We have performed a detailed experimental study of resistive cooling of large ensembles of highly charged ions such as Ar 13+ in a cryogenic Penning trap. Different from the measurements reported in [M. Vogel et al., Phys. Rev. A 90, 043412 (2014)], we observe purely exponential cooling behavior when conditions are chosen to allow collisional thermalization of the ions. We provide evidence that in this situation, resistive cooling time constants and final temperatures are independent of the initial ion energy, and that the cooling time constant of a thermalized ion ensemble is identical to the single-ion cooling time constant. For sufficiently high ion number densities, our measurements show discontinuities in the spectra of motional resonances which indicate a transition of the ion ensemble to a fluid-like state when cooled to temperatures below approximately 14 K. With the final ion temperature presently being 7.5 K, ions of the highest charge states are expected to form ion crystals by mere resistive cooling, in particular not requiring the use of laser cooling. arXiv:1809.08606v1 [physics.atom-ph]

Electron Magnetic Moment in Highly Charged Ions: The ARTEMIS Experiment

“…From the width of the signal upon cooling, the temperature of the ion ensemble can be derived. This is true since under the present conditions, the thermalization of the ensemble via the Coulomb interaction is considerably faster than the resistive cooling . Also, the spectral width of the RLC circuit used for detection is negligible with respect to the width of the signal.…”

“…In this so‐called “creation trap,” ensembles of argon ions have been produced and cooled by resistive cooling of the axial motion . Typical spectra contain argon ions of charge states between 8 + and 16 + (see, e.g., the inset of Figure ) as well as tungsten ions of higher charge states that originate from the field emission tip.…”

“…The circuit is used for both cooling and detection and is resonant at a frequency of kHz with a quality factor of . Its inductance is about 3 mH, and hence in resonance it represents a resistance of The corresponding cooling time constant of the ions is given by where m is the ion mass, q is the ion charge, and mm is the effective distance of the electrodes used for cooling and detection. Under the present conditions, typical cooling time constants are of the order of a few seconds.…”

“…To illustrate the effect of resistive cooling, Figure shows the spectral width of the detected signal of Ar 11 + ions as a function of the cooling time (for details see ref. []), to which an exponential decay with a time constant of a few seconds can be fitted. This time constant is in agreement with theoretical expectations for the given conditions .…”

“…[]), to which an exponential decay with a time constant of a few seconds can be fitted. This time constant is in agreement with theoretical expectations for the given conditions . From the width of the signal upon cooling, the temperature of the ion ensemble can be derived.…”