Physical Review Special Topics - Accelerators and Beams

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

Masao Nakao, 達也廣政, Hikaru Souda, M. Tanabe, Takehiro Ishikawa, Hiromu Tongu, A. Noda, Kouichi Jimbo, Tsuyoshi Shirai, M. Grieser, H. Okamoto, А. В. Смирнов

Published Nov 30, 2012• 8 citations

Publisher

Abstract

We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV $^{24}\mathrm{Mg}^{+}$. The longitudinal velocity distribution and the horizontal beam size of the laser-cooled $^{24}\mathrm{Mg}^{+}$ 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 (${\ensuremath{\nu}}_{s}$) 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 ${\ensuremath{\nu}}_{s}=0.068$, 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.

DOI: 10.1103/physrevstab.15.110102

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Physical Review Special Topics - Accelerators and Beams

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

Masao Nakao, 達也廣政, Hikaru Souda, M. Tanabe, Takehiro Ishikawa, Hiromu Tongu, A. Noda, Kouichi Jimbo, Tsuyoshi Shirai, M. Grieser, H. Okamoto, А. В. Смирнов

Published Nov 30, 2012• 8 citations

Publisher

Abstract

We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV

^{24}\mathrm{Mg}^{+}

. The longitudinal velocity distribution and the horizontal beam size of the laser-cooled

^{24}\mathrm{Mg}^{+}

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 (

{\ensuremath{\nu}}_{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

{\ensuremath{\nu}}_{s}=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.

DOI: 10.1103/physrevstab.15.110102

Related papers

Latest results of experimental approach to ultra-cold beam at S-LSR

Akira Noda, Masao Nakao, Hikaru Souda +7 more

Utilizing S-LSR which has a super-periodicity of 6 and is designed to be tough against resonant perturbation to the circulating beam, we have tried to approach as low as possible temperature with laser cooled 40 keV 24Mg+ ion beam. With the use of theoretically proposed Synchro-Betatron Resonance Coupling scheme, we have experimentally demonstrated the capability of active indirect transverse laser cooling. At first, the achieved transverse cooling efficiency was limited due to heating caused by intra-beam scattering (IBS). For the purpose of reduction of IBS heating, we have established a scheme tocontrol the circulating ion beam intensity down to ~104 by scraping the outskirt of the beam with the use of a horizontally moving scraper, which enabled us to cool down the transverse beam temperatures down to 20 K and 29 K for horizontal and vertical directions, respectively for the operation tune without H-V coupling. They were modified to be 40 K and 11 K by the horizontal and vertical coupling with the difference resonance with an excitation of a solenoid of 22.5 G, which were further improved to 7.0 K and 2.1 K adding deceleration by an induction accelerator of 6 mV/m using a -26 MHz detuned laser.Utilizing S-LSR which has a super-periodicity of 6 and is designed to be tough against resonant perturbation to the circulating beam, we have tried to approach as low as possible temperature with laser cooled 40 keV 24Mg+ ion beam. With the use of theoretically proposed Synchro-Betatron Resonance Coupling scheme, we have experimentally demonstrated the capability of active indirect transverse laser cooling. At first, the achieved transverse cooling efficiency was limited due to heating caused by intra-beam scattering (IBS). For the purpose of reduction of IBS heating, we have established a scheme tocontrol the circulating ion beam intensity down to ~104 by scraping the outskirt of the beam with the use of a horizontally moving scraper, which enabled us to cool down the transverse beam temperatures down to 20 K and 29 K for horizontal and vertical directions, respectively for the operation tune without H-V coupling. They were modified to be 40 K and 11 K by the horizontal and vertical coupling with the difference resonance with an excitation of a solenoid of 22.5 G, which were further improved to 7.0 K and 2.1 K adding deceleration by an induction accelerator of 6 mV/m using a -26 MHz detuned laser.

Jan 1, 20130 citations

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A longitudinal laser cooling of ion beams at about 5% of the velocity of light has been performed at the Heidelberg Test Storage Ring with various cooling schemes employing the spontaneous force. For a 7.29-MeV $^{9}\mathrm{Be}^{+}$ beam with an initial longitudinal temperature of 2700 K, the main characteristics of laser cooling in a storage ring are discussed. When undamped, the transverse betatron oscillations of the coasting ions limit the longitudinal temperature after laser cooling to typically 1 K. After damping the transverse motion by precooling the ions with an electron cooler, longitudinal temperatures of below 30 mK have been obtained in the subsequent laser cooling. In this case, the longitudinal ion-beam temperature can be understood as an equilibrium of the laser cooling rate with the heating rate due to intrabeam scattering. Moreover, single binary Coulomb collisions between the (still transversely hot) ions can cause such longitudinal velocity changes that ions are lost out of the critical capture range of the laser cooling force. In these two ways, intrabeam scattering imposes a substantial limit on the temperature or number of laser cooled ions in a storage ring. In our experiments, this process presently limits the ratio between the density-dependent Coulomb energy and the longitudinal thermal energy spread to a value on the order of 1, where liquid rather than gaseous behavior of the ion beam is expected to set in.A longitudinal laser cooling of ion beams at about 5% of the velocity of light has been performed at the Heidelberg Test Storage Ring with various cooling schemes employing the spontaneous force. For a 7.29-MeV $^{9}\mathrm{Be}^{+}$ beam with an initial longitudinal temperature of 2700 K, the main characteristics of laser cooling in a storage ring are discussed. When undamped, the transverse betatron oscillations of the coasting ions limit the longitudinal temperature after laser cooling to typically 1 K. After damping the transverse motion by precooling the ions with an electron cooler, longitudinal temperatures of below 30 mK have been obtained in the subsequent laser cooling. In this case, the longitudinal ion-beam temperature can be understood as an equilibrium of the laser cooling rate with the heating rate due to intrabeam scattering. Moreover, single binary Coulomb collisions between the (still transversely hot) ions can cause such longitudinal velocity changes that ions are lost out of the critical capture range of the laser cooling force. In these two ways, intrabeam scattering imposes a substantial limit on the temperature or number of laser cooled ions in a storage ring. In our experiments, this process presently limits the ratio between the density-dependent Coulomb energy and the longitudinal thermal energy spread to a value on the order of 1, where liquid rather than gaseous behavior of the ion beam is expected to set in.

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Physical Review LettersSep 2, 1991115 citations

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A simple method of cooling the transverse motion of an ion cloud in a linear Paul trap with a single axial laser is proposed. Transverse thermal oscillations of ions are indirectly damped by the longitudinal laser friction via an additional radio-frequency potential that resonantly couples two degrees of freedom. The fundamental mechanism of the present cooling scheme is theoretically described with the help of a harmonic oscillator model. It is shown that the indirect cooling rate can be considerably enhanced when the frequencies of the transverse and longitudinal ion oscillations satisfy a certain relation. The validity of theoretical predictions is confirmed through molecular dynamics simulations in which the detailed three-dimensional configuration of a typical Paul trap is incorporated.A simple method of cooling the transverse motion of an ion cloud in a linear Paul trap with a single axial laser is proposed. Transverse thermal oscillations of ions are indirectly damped by the longitudinal laser friction via an additional radio-frequency potential that resonantly couples two degrees of freedom. The fundamental mechanism of the present cooling scheme is theoretically described with the help of a harmonic oscillator model. It is shown that the indirect cooling rate can be considerably enhanced when the frequencies of the transverse and longitudinal ion oscillations satisfy a certain relation. The validity of theoretical predictions is confirmed through molecular dynamics simulations in which the detailed three-dimensional configuration of a typical Paul trap is incorporated.

Journal of the Physical Society of JapanAug 10, 20101 citation

Three-Dimensional Laser Cooling of Ion Beams Using a Wien Filter

Masahiro Ikegami, Hiroshi Sugimoto, H. Okamoto

Laser cooling of ion beams generally operates only upon the longitudinal motion of an ion beam. In order to extend this powerful dissipative force to the transverse directions, we consider introducing a Wien filter in a cooing straight section. It is theoretically shown that longitudinal cooling within a Wien filter naturally develops a transverse (mostly horizontal) cooling effect as well. Molecular dynamics simulations demonstrate that this method enables us to reach an ultralow-temperature state of a stored ion beam.Laser cooling of ion beams generally operates only upon the longitudinal motion of an ion beam. In order to extend this powerful dissipative force to the transverse directions, we consider introducing a Wien filter in a cooing straight section. It is theoretically shown that longitudinal cooling within a Wien filter naturally develops a transverse (mostly horizontal) cooling effect as well. Molecular dynamics simulations demonstrate that this method enables us to reach an ultralow-temperature state of a stored ion beam.

Journal of the Physical Society of JapanJul 10, 20081 citation

Parameter optimization for Doppler laser cooling of a low-energy heavy ion beam at the storage ring S-LSR

Kazuya Osaki, H. Okamoto

S-LSR is a compact ion storage ring constructed at Kyoto University several years ago. The ring is equipped with a Doppler laser cooling system aimed at beam crystallization. Bearing in mind hardware limitations in S-LSR, we try to find an optimum set of primary experimental parameters for the production of an ultracold heavy ion beam. Systematic molecular dynamics simulations are carried out for this purpose. It is concluded that the detuning and spot size of the cooling laser should be chosen around | $-$ |42 MHz and 1.5 mm, respectively, for the most efficient cooling of 40 keV | $^{24}$ |Mg| $^+$ | beams in S-LSR. Under the optimum conditions, the use of the resonant coupling method followed by radio-frequency field ramping enables us to reach an extremely low beam temperature on the order of 0.1 K in the transverse degrees of freedom. The longitudinal degree of freedom can be cooled to close to the Doppler limit; i.e., to the mK range. We also numerically demonstrate that it is possible to establish a stable, long one-dimensionally ordered state of ions.S-LSR is a compact ion storage ring constructed at Kyoto University several years ago. The ring is equipped with a Doppler laser cooling system aimed at beam crystallization. Bearing in mind hardware limitations in S-LSR, we try to find an optimum set of primary experimental parameters for the production of an ultracold heavy ion beam. Systematic molecular dynamics simulations are carried out for this purpose. It is concluded that the detuning and spot size of the cooling laser should be chosen around |$-$|42 MHz and 1.5 mm, respectively, for the most efficient cooling of 40 keV |$^{24}$|Mg|$^+$| beams in S-LSR. Under the optimum conditions, the use of the resonant coupling method followed by radio-frequency field ramping enables us to reach an extremely low beam temperature on the order of 0.1 K in the transverse degrees of freedom. The longitudinal degree of freedom can be cooled to close to the Doppler limit; i.e., to the mK range. We also numerically demonstrate that it is possible to establish a stable, long one-dimensionally ordered state of ions.

Progress of Theoretical and Experimental PhysicsMay 14, 20140 citations

We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV

^{24}\mathrm{Mg}^{+}

. The longitudinal velocity distribution and the horizontal beam size of the laser-cooled

^{24}\mathrm{Mg}^{+}

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 (

{\ensuremath{\nu}}_{s}

{\ensuremath{\nu}}_{s}=0.068

^{9}\mathrm{Be}^{+}

beam with an initial longitudinal temperature of 2700 K, the main characteristics of laser cooling in a storage ring are discussed. When undamped, the transverse betatron oscillations of the coasting ions limit the longitudinal temperature after laser cooling to typically 1 K. After damping the transverse motion by precooling the ions with an electron cooler, longitudinal temperatures of below 30 mK have been obtained in the subsequent laser cooling. In this case, the longitudinal ion-beam temperature can be understood as an equilibrium of the laser cooling rate with the heating rate due to intrabeam scattering. Moreover, single binary Coulomb collisions between the (still transversely hot) ions can cause such longitudinal velocity changes that ions are lost out of the critical capture range of the laser cooling force. In these two ways, intrabeam scattering imposes a substantial limit on the temperature or number of laser cooled ions in a storage ring. In our experiments, this process presently limits the ratio between the density-dependent Coulomb energy and the longitudinal thermal energy spread to a value on the order of 1, where liquid rather than gaseous behavior of the ion beam is expected to set in.

The interaction of laser-induced and intrabeam forces has been studied in a dense stored beam of 100-keV

^{7}\mathrm{Li}^{+}

ions. A fraction of the ions (\ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}4}$) exist in the metastable 1s2s

^{3}

S state. Using this state as a laser spectroscopic probe, we observe fast longitudinal heating in the injected, nonequilibrium distribution due to Coulomb scattering. Laser cooling of the metastable ions is ineffective during this heating period. The metastable fraction of the equilibrated beam is subsequently laser cooled to a longitudinal temperature of \ensuremath{\sim}1 mK, the lowest temperature ever reported in a stored ion beam.

-

|42 MHz and 1.5 mm, respectively, for the most efficient cooling of 40 keV |

^{24}

|Mg|

^+

| beams in S-LSR. Under the optimum conditions, the use of the resonant coupling method followed by radio-frequency field ramping enables us to reach an extremely low beam temperature on the order of 0.1 K in the transverse degrees of freedom. The longitudinal degree of freedom can be cooled to close to the Doppler limit; i.e., to the mK range. We also numerically demonstrate that it is possible to establish a stable, long one-dimensionally ordered state of ions.