Development of a gas cell-based laser ion source for RIKEN PALIS

Size: px

Start display at page:

Download "Development of a gas cell-based laser ion source for RIKEN PALIS"

Louisa McDowell
5 years ago
Views:

1 Hyperfine Interact (2013) 216: DOI /s Development of a gas cell-based laser ion source for RIKEN PALIS T. Sonoda M. Wada H. Tomita C. Sakamoto T. Takatsuka T. Noto H. Iimura Y. Matsuo T. Kubo T. Shinozuka T. Wakui H. Mita S. Naimi T. Furukawa Y. Itou P. Schury H. Miyatake S. Jeong H. Ishiyama Y. Watanabe Y. Hirayama Published online: 22 February 2013 Springer Science+Business Media Dordrecht 2013 Abstract We developed a prototype laser ionization gas cell with a beam extraction system. This device is for use of Pasitic Laser Ion-Source (PALIS), which will be implemented into RIKEN s fragment separator, BigRIPS as a part of SLOWRI. Offline resonant laser ionization for stable Co, Cu, Fe, Ni, Ti, Nb, Sn, In and Pd inside the gas cell, ion extraction and transport to the high-vacuum region via SPIG and QMS have been confirmed (Sonoda et al, Nucl Instrum Meth B 295:1, 2013). Keywords Laser ion source Gas cell Resonant laser ionization Gas jet Proceedings of the 6th International Conference on Laser Probing (LAP 2012), Paris, France, 4 8 June T. Sonoda (B) M. Wada T. Kubo Y. Matsuo S. Naimi SLOWRI Team, Nishina Center for Accelerator-Based Science, RIKEN, 2-1 Hirosawa, Wako, Saitama , Japan tetsu@riken.jp H. Tomita C. Sakamoto T. Takatsuka T. Noto Faculty of Engineering, Nagoya University, Nagoya , Japan H. Iimura Japan Atomic Energy Agency (JAEA), Tokaimura , Japan T. Shinozuka T. Wakui Cyclotron and Radioisotope Center, Tohoku University, Sendai , Japan H. Mita Y. Itou P. Schury Department of Physics, Tsukuba University, Tsukuba , Japan T. Furukawa Department of Physics, Tokyo Metropolitan University, Tokyo , Japan H. Miyatake S. Jeong H. Ishiyama Y. Watanabe Y. Hirayama High Energy Accelerator Research Organization (KEK), Tsukuba , Japan

104 T. Sonoda et al. Main RI-beam Unused RI-beam Laser for resonant ionization degrader Beam energy 10MeV/u 300MeV/u ev gon gas 1 bar Low-energy beam F1/F2 SLIT Fig.

2 104 T. Sonoda et al. Main RI-beam Unused RI-beam Laser for resonant ionization degrader Beam energy 10MeV/u 300MeV/u ev gon gas 1 bar Low-energy beam F1/F2 SLIT Fig. 1 Schematic of the laser ionization gas catcher setup. Without disturbing the main beam, an unwanted portion of the beam is stopped in the gas cell 1 Introduction Radioactive ion beam (RIB) facilities based on the in-flight production technique provide a wide variety of exotic nuclei without restrictions on lifetimes or chemical properties. An essential requirement for present and future RIB facilities is to transform this high-energy beam into a low-energy, low-emmitance beam. This opens up opportunities to study ground state properties of exotic nuclei by low-energy RI-beam experimental techniques, such as laser spectroscopy and ion trapping. At RIKEN, an universal slow RI-beam facility, SLOWRI, based on a gas catcher cell with an RF-carpet ion guide [2], was assigned as one of the principal facilities of RIBF. A novel method, named PALIS (Pasitic RI-beam production by Laser Ion- Source) [3] was also approved as an extension of SLOWRI, to expand the usability and reduce experimental costs by utilizing unused RI-beams produced by projectile fragmentation or in-flight fission. Using this scheme, it will be possible to perform low-energy RI-beam experiments alongside every on-line BigRIPS experiment. A schematic view of PALIS gas cell is shown in Fig. 1. We will place one compact gas cell on the side of the main beam path in the focal plane in a fragment separator, BigRIPS [4]. The gas cell will be filled with 1 bar gas whereby most injected ions can be neutralized. A rotatable degrader located in front of the cell will adjust the beam energy to efficiently stop the ions inside the cell. The neutralized atoms will be transported by gas flow toward the exit of the cell, where the atoms can be reionized by laser radiations [5]. We have estimated that RI-beams with energies up to 10 MeV/A have a stopping range within the length of the gas cell (25 cm), while the

3 Li Li He He H H Cl S S S P Si Si Si Al MgMgMg Na Ne Ne Ne F O O O N N C C B B Be Ca K Cl S Zn Cu Ni Ni Ni Ni Co Fe Fe Fe Fe Mn Cr Cr Cr V Ti Ti Ti Ti Ti Sc Ca Ca Ca Ca K Ge Ga Zn Zn Zn Cu Ni Kr Kr Br Se Se Se Se As GeGe Ge Ge Ga Ru Mo MoMoMoMoMo Nb Zr Zr Zr Zr Y Sr Sr Sr Sr Rb Kr Kr Kr Kr Br Se Cd Cd Ag Pd Pd Pd Pd Rh Ru Ru Ru Ru Ru Ru Te Te Sb Sn Sn Sn Sn Sn Sn Sn Sn In Cd Cd Cd Cd Cd Ag Pd Pd Sm Nd Nd Pr Ce Ce Ce La Ba Ba Ba Ba Ba Ba Ba Cs Xe Xe Xe Xe Xe Xe Xe I Te Te Te Sb Sn Sn Nd Nd Eu Sm Nd W W Ta Hf Hf Hf Hf Hf Lu Yb Yb Yb Yb Yb Yb Yb Tm Er Er Er Er Er Er Ho Dy Dy Dy Dy Dy Dy Dy Tb GdGdGdGdGd Gd Eu Sm Sm Pt Ir Os Os Os Os Re W Tl Hg Hg Hg Hg Hg Hg Au Pt Pt Pt Pt Ir Os Bi Pb Pb Pb Tl Hg U Development of a gas cell-based Laser Ion Source for RIKEN PALIS 105 primary beam: U 100pnA Xe 500pnA Kr 500pnA Pb Ca Ni Sn 10 7 ions/s 1 ions/s Fig. 2 Expected yields of low-energy unstable nuclei at PALIS evacuation time of the cell (gas cell volume 500 cm 3, 1 mm exit hole) will allow a half-life of 100 ms to be extracted with 20 % efficiency. In separation procedure of fragment separator, all contaminant ions with slightly different A/Z are stopped in the slit at the first focal point of the separator (F1) and dozens of isotopes in the vicinity of the desired isotope are stopped in the slit at the second focal point (F2). Our aim is to collect those isotopes abandoned in the slits by this laser ionization gas catcher. Thusly produced low-energy RI-beams can be utilized for low-energy RI-beam experiments, whenever BigRIPS experiments are in operation. Importantly, this will be achieved with no restriction from the beam time allocation. 2 Estimated PALIS yields The expected PALIS yields of unstable nuclei with realistic intensity of primary beams in available elements by laser ionization are shown in Fig. 2. The estimation includes efficiencies attributed to individual process, such as the stopping in gas cell (40 %), laser ionization (10 %) and decay loss for short-lived nuclei. It should be also noted that such slow RI-beams should be very pure compared to that of the other ISOL facilities or in-flight separator facilities. This is because PALIS has three different types of separation: one is the A/Z separation made at BigRIPS, the second is the Z separation via laser ionization and the final is the A separation at the mass separator. These three separation methods are orthogonal to each other.

4 106 T. Sonoda et al. Fig. 3 Cut-away view of the prototype gas cell and the differential pumping system for Pasitic RI-beam production by Laser Ion-Source (PALIS) We will be free from the isobaric contamination which is often a serious problem in ISOL facilities. 3 Prototype gas cell and a beam extraction system A prototype gas cell and a beam extraction system has been developed. A conceptual sketchisshowninfig.3. The system is composed of four parts: a laser ionization gas cell, a differential pumping system, a quadrupole mass separator and a detector station comprising a CEM. A novel implementation of differential pumping, in combination with a sextupole ion beam guide (SPIG) [6], has been developed. A few small scroll pumps create a pressure difference from 1000 hpa 10 3 Pa within a geometry drastically miniaturized compared to conventional systems. This system can utilize a large exit hole for fast evacuation times, minimizing the decay loss for short-lived nuclei during the extraction from buffer gas cell, while sufficient gas cell pressure is maintained for stopping high energy RI-beams. We have tested ionization inside the gas cell for several stable elements which was performed by a two-step excitation scheme. Novel spectroscopy experiments such as in-gas cell laser spectroscopy [7] andin gas-jet laser spectroscopy [8, 9] have been started for the off-line test in combination with Ti:Sa laser system, collaborated with Nagoya University. This spectroscopy technique will also be applied to evaluate the neutron damage to the nuclear reactor through measurement of the abundant ratio of metastable Nb produced by inelastic neutron scattering from stable Nb [10].

5 Development of a gas cell-based Laser Ion Source for RIKEN PALIS Conclusion We have introduced the concept and some feasibility studies for PALIS project. It describes the proof of principle studies for a resonant laser ionization gas cell for stable elements: Co, Cu, Fe, Ni, Ti, Nb, Sn, In and Pd that utilizes a novel differential pumping method, based on the use of a few small scroll pumps [1]. The miniaturization of the differential pumping system, along with the ability to use higher gas pressures, will enable an installation of the parasitic laser ion source (PALIS) in the limited space of the BigRIPS fragment separator. The availability of PALIS system will result in a manyfold increase in the available beam time. More details of this first phase development is reported in [1]. References 1. Sonoda, T., et al.: Nucl. Instrum. Methods B 295, 1 (2013) 2. Wada, M., et al.: Nucl. Instrum. Methods B 204, 570 (2003) 3. Sonoda, T., et al.: AIP Conf. Proc. 1104, 132 (2009) 4. Kubo, T.: Nucl. Instrum. Methods B 204, 97 (2003) 5. Kudryavtsev, Yu., et al.: Nucl. Instrum. Methods B 114, 350 (1996) 6. Xu, H.J., et al.: Nucl. Instrum. Methods A 333, 274 (1993) 7. Cocolios, T.E., et al.: Phys. Rev. Lett. 103, (2009) 8. Sonoda, T., et al.: Nucl. Instrum. Methods B 267, 2918 (2009) 9. Ferrer, R., et al.: Nucl. Instrum. Methods B (2012) 10. Takatsuka, T., et al.: LAP2012 Proceedings (2012)

Restoration of Rl-beams from a projectile fragment separator by Laser Ionization gas Catcher -PALIS-

Restoration of Rl-beams from a projectile fragment separator by Laser Ionization gas Catcher -PALIS- T. Sonoda'', M. Wada""', A. Takamine'', K. Okada", P. Schury", A. Yoshida, T. Kubo, Y. Matsuo, T. Furukawa,