Kyoto ICR, Uji, Kyoto
MPI-K, Heidelberg
AEC, Chiba
JINR, Dubna, Moscow Region
NIRS, Chiba-shi
The ion storage ring, S-LSR in Kyoto University has an electron beam cooler and a laser cooling system. The electron cooler for S-LSR was designed to maximize the cooling length in the limited drift space of the ring. The effective cooling length is 0.44 m, while the total length of the cooler is 1.8 m. The commissioning of the electron cooling was started from October 2005. The 7 MeV proton beam from the linac was used and the first cooling was observed on October 31. The momentum spread became 2×10-4 and the beam diameter was 1.2 mm with the particle number of 2×108 and the electron current of 60 mA. The various experiments have been carried out using the electron cooling at S-LSR. The one-dimensional ordering of protons is one of the important subjects. The momentum spread and the beam size were observed while reducing the particle number. They were measured by the Schottky noise spectrum and the scraper. The particle number was measured by the ionization residual gas monitor. Abrupt jumps in the momentum spread and the Schottky noise power were observed for protons at a particle number of around 2000. The beam temperature was 0.17 meV and 1 meV in the longitudinal and transverse directions at the transition particle number, respectively. The normalized transition temperature of protons is close to those of heavy ions at ESR. The lowest momentum spread below the transition was 1.4×10-6, which corresponded to the longitudinal beam temperature of 0.026 meV (0.3 K). It is close to the longitudinal electron temperature. The transverse temperature of the proton beam was much below that of electrons (34 meV). It is the effect of the magnetized electron.
Kyoto ICR, Uji, Kyoto
MPI-K, Heidelberg
JINR, Dubna, Moscow Region
NIRS, Chiba-shi
Ion storage and cooler ring, S-LSR, has been designed to enable the investigation of coldest possible ion beams with use of various beam cooling schemes such as an electron beam cooling and the laser cooling. Electron beam cooling of 7 MeV protons and laser cooling of 40 keV Mg ions have been applied up to now. The first laser cooling applied to ~108 Mg ions with the induction accelerator voltage of ~6 mV reduced the momentum spread (1 σ) from 1.7×10-3 to 2.9×10-4, which is considered to be saturated by the momentum transfer from transverse degree of freedom to the longitudinal one due to intra-beam scattering. The laser cooling force has been improved from the above one more than one order of magnitude owing to the precise alignment between the laser and Mg ion beam. Recent measurement with frequency shift of the laser showed the enhancement of the coherent signals in odd harmonics of the revolution frequency picked up with an electrostatic beam monitor and detailed measurements of various harmonics have been performed with changing the resolution bandwidth of the spectrum analyzer, although the origin of such coherency is not yet identified up to now. For the purpose of measurement of lowest possible temperature attainable by the laser cooling, measurement with reducing the ion numbers of Mg is needed, which has been blocked by the difficulty of observing the Schotty signal of such a low intensity beam. So as to cope with this situation, development of observing system of emitted light by the transition from the upper level to the ground state with the use of photomultiplier has been performed, which recently succeeded in detection of clear signals coming from the oriented process. Activities above mentioned will be presented together with the forth coming experimental results on laser cooling.
