Resonance coupling induced enhancement of indirect transverse cooling in a laser-cooled ion beam

Abstract

We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV 24 Mg þ . The longitudinal velocity distribution and the horizontal beam size of the laser-cooled 24 Mg þ ion beam with 280 nm laser light were simultaneously observed by the use of standard fluorescence-based techniques. Keeping the operation point at (2.068, 1.105), the synchrotron tune ( s ) was changed from 0.0376 to 0.1299. A strong decrease in the cooled horizontal beam size and a corresponding increase in the equilibrium cooled momentum spread were observed at the expected synchrobetatron resonance coupling condition of s ¼ 0:068, which is the first observation of a resonantly induced coupling for enhanced indirect transverse laser cooling of an ion beam, and is an important step towards creating a crystalline ground state of the beam.

Synchrobetatron resonant coupling mechanism in a storage ring

“…If the longitudinal (synchrotron) component of a beam is cooled, the transverse (betatron) component of the beam is also cooled since the longitudinal and the transverse freedoms are connected near the resonant point. This result is what we observed in our cooling experiment [3].…”

“…It was installed at the location of finite dispersion function (1.1 m) to couple synchrotron and horizontal betatron motions. The horizontal beam size was observed by a CCD camera and a photomultiplier [3]. Table I shows the main parameters of S-LSR.…”

“…1, is a synchrotron-type small storage ring at Kyoto University [2]. The synchrobetatron resonant coupling method was employed in S-LSR, in which the horizontal laser cooling was already observed [3]. Near the synchrobetatron resonant coupling point where the difference integer resonance condition was satisfied, an unexpected tune jump of the horizontal betatron tune was observed.…”

Simulation of longitudinal dynamics of laser-cooled and RF-bunched C 3+ ion beams at heavy ion storage ring CSRe

“…The laser cooling experiment of relativistic heavy ion beams at the CSRe has already been described in other paper [23]. For laser cooling experiments, 12 C 3+ ions were produced, accelerated, and finally injected into the CSRe at an energy of 122 MeV/u (at a velocity of 47% of the speed of light). A suitable laser overlaps the ion beams all along the straight section (~ 20 m) where the new Schottky-noise pick-up and optical diagnostic of UV-PMT and CPM are located.…”

“…So far, beams of several ion species have been cooled at heavy ion storage rings successfully, such as 7 Li + ion beams at the TSR in Heidelberg and the ASTRID in Aarhus, 24 Mg + ion beams at the S-LSR in Kyoto, and 12 C 3+ ion beams at the ESR in Darmstadt [10][11][12][13][14][15][16]. However, none of the laser cooling experiments has achieved phase-transition to obtain crystallized highly charged heavy ion beams, there are still many challenges to reach this states.…”