An approach with S-LSR at ICR, Kyoto University to attain an ordered structure for a circulating beam in a storage ring with a speed that is not negligible compared with the light velocity is described. An experimental approach for one-dimensional (1D) ordering of a 7MeV proton beam with the use of electron beam cooling is given first and then experimental plans to realize crystalline structures of 24 Mg + ions with a kinetic energy of 35keV by applying laser cooling are described together with computer-simulation results by a molecular dynamics (MD) code.

https://iopscience.iop.org/article/10.1088/1367-2630/8/11/288/pdf

Approach to ordered structure of the beam at S-LSR

It has been known theoretically that a charged-particle beam circulating in a storage ring exhibits an ``ordered'' configuration at the space-charge limit. Such an ultimate state of matter is called a crystalline beam whose emittance is ideally equal to zero except for quantum noise. This paper discusses how close one can come to various ordered states by employing currently available accelerator technologies. The dynamic nature of ultracold beams and conditions required for crystallization are briefly reviewed. Molecular dynamics simulations are performed to study the feasibility of this unique phenomenon, considering practical situations in general cooling experiments. It is pointed out that several essential obstacles must be overcome to reach a three-dimensional crystalline state in a storage ring. Doppler laser cooling of ion beams is also numerically simulated to explore the possibility of beam crystallization in an existing machine.

/pdf/feasibility-of-beam-crystallization-in-a-cooler-storage-ring-1pfllzwgq8.pdf

Feasibility of beam crystallization in a cooler storage ring

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.

https://link.aps.org/pdf/10.1103/PhysRevSTAB.15.110102

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

The efficient focusing, bunching and acceleration of high current, low energy heavy ion beams in an RFQ accelerator have been investigated. The considerations on the choice of the working frequency for increasing the beam current are introduced. Designed using an unconventional procedure, this 20 emA RFQ will be able to work with A/q
 ≤ 60 ion beams in the β range of 0.002–0.016. The beam dynamics simulation shows that the design fulfills all requirements with good beam quality and a compact structure.

Efficient focusing, bunching, and acceleration of high current heavy ion beams at low energy

In this paper, a new technical scheme of high-voltage, long-pulse generator, mostly based on solid-state power devices, including magnetic pulse compressor, Blumlein-type rolled strip pulse-forming line (RSPFL) and inductive voltage adder (IVA), is proposed and investigated numerically and experimentally. The generator has potential advantages of high average power level, high repetitive rate capability, long lifetime, and long pulse achievability, which meet the requirements of military and industrial application of the pulsed power technology. Specifically, a two-stage magnetic pulse compressor was set up with iron-based amorphous cores. Total compression ratio of the device is approximately 12 and the achieved voltage efficiency is up to 92%. Low impedance, long-duration Blumlein-type RSPFL was established with characteristic impendence and electrical length of 3 Ω and 100 ns, respectively. Mylar film was selected as the solid-state dielectric. Increased by a four-stage IVA, typical quasi-square pulse was obtained with peak current of 2.3 kA and duration over 200 ns. As the resistance of the dummy load was measured to be 60 Ω, the peak voltage was approximately 138 kV. Experiments show reasonable agreement with numerical analysis.

A high-voltage, long-pulse generator based on magnetic pulse compressor and Blumlein-type rolled strip pulse forming line

A possible method to realize a dispersion-free storage ring is described. The simultaneous use of a magnetic field $\mathbf{B}$ and an electric field $\mathbf{E}$ in bending regions, where the two fields are set perpendicular to each other, enables us to control the effect of momentum dispersion. When the relation $(1+1/{\ensuremath{\gamma}}_{0}^{2})\mathbf{E}(\ensuremath{\rho})=\ensuremath{-}{\mathbf{v}}_{0}\ifmmode\times\else\texttimes\fi{}\mathbf{B}$ is satisfied for a beam with the velocity ${v}_{0}$, the linear dispersion can be completely eliminated all around the ring. It is shown that the acceleration and deceleration induced by the electrostatic deflector counteracts the heating mechanism due to the shearing force from dipole magnets. The dispersion-free system is thus beneficial to producing ultracold beams. It looks probable that the technique will allow one to achieve three-dimensional crystalline beams. At ICR Kyoto University, an ion cooler storage ring S-LSR oriented for various beam physics purposes is now under construction. The application of the present idea to S-LSR is discussed and the actual design of the dispersionless bend is given.

/pdf/heavy-ion-storage-ring-without-linear-dispersion-3q05drrpqi.pdf

Heavy ion storage ring without linear dispersion

Phase space compression of stored ions in storage rings is very important to attain high quality beam. The two most widely used cooling techniques are stochastic cooling and electron cooling. Historically these two methods have been considered complementary in their dependence on the beam and machine parameters. In general, it is accepted that stochastic cooling is well suited for hot ion beams(halo cooling) while electron cooling is more efficient for rather cool ion beams(core cooling). In this work we will present the results of experimental investigations on the possibility of an efficient electron cooling scheme for hot ion beams. Our ultimate goal is to show that conventional electron cooling can be supplemented with adequate relative velocity sweeping techniques in order to achieve efficient cooling even in the case of hot ion beam. The experiments were carried out with the storage ring TSR at MPI fur Kernphysik in Heidelberg. Two different cooling methods have been studied with the purpose of reducing the cooling time of an ion beam with a large momentum spread of ∆P/P=1%. The results of the schemes using an induction accelerator to accelerate the ion beam towards the active region of the cooling force, and the sweeping of the velocity of the electron beam through the velocity range of the ion beam by ramping the cathode voltage are presented. Both methods were tested with a carbon ion beam C of kinetic energy 73.3MeV. Significant reduction of the longitudinal cooling time to 0.65 and 0.35 s is achieved with “induction accelerator sweep” and “electron velocity sweep” methods respectively, compared with 2.9s for conventional cooling. We also show that these two schemes are in fact physically equivalent as shown in figure 1.

/pdf/electron-cooling-of-hot-ion-beams-2sfyjhs3mu.pdf

Electron cooling of hot ion beams

Laser cooling has been applied for Mg ion beam with the kinetic energy of 40 keV. By application of laser light with the wave length of 280 nm of the power ~50mW, the ion longitudinal temperature has been cooled down to 3. 6 Kelvin for ion number of 3x10, which is considered to be limited due to heat transfer from transverse degree of freedom to longitudinal one. Longitudinal and transverse temperatures are found to be coupled linearly. By application of synchro-betatron coupling, the coupling between longitudinal and transverse temperature has been tried to be increased on purpose to cool down the transverse temperature by the laser cooling, indication of which has been experimentally observed for bunched beam cooling.

Recent status of laser cooling for Mg realized at S-LSR

Design of New Compact Cooler Ring at ICR, Kyoto University

24aYA-3 Electron Cooling of Ion Beams with Large Momentum Spread

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