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EXPERIMENTAL STRATEGY FOR REALIZATION OF 3-D BEAM ORDERING WITH USE OF TAPERED COOLING AT S-LSR *

A. Noda, Masashi Ikegami, Shinji Fujimoto, T. Shirai, Hikaru Souda, Mikio Tanabe, Hiromu Tongu, H. Okamoto, I. Meshkov, A. Ya. Smirnov

Published Jan 1, 2006• 3 citations
OpenAlex

Abstract

Experimental plan at S-LSR to realize ordered state with ultra-low temperature by application of laser cooling for 24Mg+ ions with kinetic energy of 35 keV has been surveyed. By normal mode with finite dispersion, 1 dimensional ordering and 2 dimensional zigzag structure of crystalline beam are expected if strong enough laser cooling force is applied with resonant coupling method. Three dimensional crystal is expected to be attained by the dispersion free mode with coupling cavity although limited at 1 layer level. With “tapered cooling ” utilizing Wien Filter, multi-layer 3 dimensional crystal state is expected to be realized.

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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 Physics•May 14, 2014•0 citations

Experimental approach to ultra-cold ion beam at S-LSR

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At S-LSR, abrupt reduction of momentum spread of 7 MeV proton beam to ~2 times 10-6at proton number of -2000 has been observed, which indicates phase transition to 1 dimensional ordered state. Attained proton temperatures after transition are 26 mueV and 1 meV for longitudinal and transverse directions, respectively, which compared with the corresponding values of 20 mueV and 34 meV for electron beam, indicates the magnetization of electron. Laser cooling of24Mg+has also been started and momentum spread of ~108ions is reduced to 2 times 10-4, saturated with the momentum transfer from transverse degree of freedom by intra-beam scattering.

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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.

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Masao Nakao, 達也 廣政, Hikaru Souda +9 more

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.

Physical Review Special Topics - Accelerators and Beams•Nov 30, 2012•8 citations
Experimental plan at S-LSR to realize ordered state with ultra-low temperature by application of laser cooling for 24Mg+ ions with kinetic energy of 35 keV has been surveyed. By normal mode with finite dispersion, 1 dimensional ordering and 2 dimensional zigzag structure of crystalline beam are expected if strong enough laser cooling force is applied with resonant coupling method. Three dimensional crystal is expected to be attained by the dispersion free mode with coupling cavity although limited at 1 layer level. With “tapered cooling ” utilizing Wien Filter, multi-layer 3 dimensional crystal state is expected to be realized.
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^{24}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.
At S-LSR, abrupt reduction of momentum spread of 7 MeV proton beam to ~2 times 10-6at proton number of -2000 has been observed, which indicates phase transition to 1 dimensional ordered state. Attained proton temperatures after transition are 26 mueV and 1 meV for longitudinal and transverse directions, respectively, which compared with the corresponding values of 20 mueV and 34 meV for electron beam, indicates the magnetization of electron. Laser cooling of24Mg+has also been started and momentum spread of ~108ions is reduced to 2 times 10-4, saturated with the momentum transfer from transverse degree of freedom by intra-beam scattering.
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.
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.
The crystallization of ion beams has recently been established in the rf quadrupole storage ring PALLAS (PAul Laser CooLing Acceleration System) for laser-cooled 24 Mg + ion beams at an energy of about 1 eV. Yet, unexpectedly sharp constraints had to be met concerning the confinement strength and the longitudinal laser cooling rate. In this paper, related and up to now unseen heating mechanisms are pinpointed for crystalline beams. The weak but inevitable diffusive transverse heating associated with the laser cooling process itself is investigated, possibly allowing the future measurement of the latent heat of the ion crystal. As a function of the beam velocity, the influence of bending shear on the attainability of larger crystalline structures is presented. Finally, rf heating of crystalline beams of different structure is studied for discontinuous cooling.
We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV 24Mg+^{24}\mathrm{Mg}^{+}24Mg+. The longitudinal velocity distribution and the horizontal beam size of the laser-cooled 24Mg+^{24}\mathrm{Mg}^{+}24Mg+ 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.