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We have begun searching for the new super-heavy element (SHE) with Z=119 at RIKEN Heavy Ion LINAC (RILAC). To overcome the small production cross section of vanadium (V) beam on the curium target, the project requires a very powerful V beam. In order to optimize the beam intensity of V with the charge state of 13+, we have investigated the effects of the amount of V vapor, the power of 18- and 28-GHz microwaves, and the strength of the mirror field. While no significant effect was seen by changing the mirror field Bext from 1.4 T to 1.6 T, the amount of V vapor and the microwave power strongly affected. Based on the correlation between the V-vapor and the microwave power, we obtained a 600-euA V(13+) beam with the V consumption rate of 24 mg/h and the microwave power of 2.9 kW in order to execute about 1-month SHE experiment. Furthermore, because such strong mirror field enhances the transverse beam emittance, it is important to control the emittance with small reduction of the intensity. We have successfully controlled the beam emittance by using three pairs of slits (triplet slits) in LEBT by eliminating the peripheral beam components in both of the x-x’ and y-y’ phase spaces., Proceedings of the 24th International Workshop on ECR Ion Sources, ECRIS2020, East Lansing, MI, USA

At RIKEN Nishina Center, the SRILAC project has been launched for the search experiments of super-heavy-elements with atomic numbers of 119 and higher. The main points of the SRILAC project are as follows. Superconducting RIKEN Linear Accelerator (SRILAC) was newly installed at downstream of existing accelerator (RIKEN Linear Accelerator: RILAC) to enhance beam energy. Additionally, a new RIKEN 28-GHz superconducting electron cyclotron resonance ion source has been implemented at the frontend of SRILAC to increase beam intensity. With that, the SRILAC control system requires corrections and upgrades to the shortcomings of previous RILAC control system, for example control methods for electromagnet power supplies, an machine protection system and an archive system. Moreover, there was also a issue to be solved for methods of integration with small LabVIEW-based systems. To operate efficiently in the SRILAC project, a distributed control system utilizing EPICS should be adopted as in RIBF, a higher-level application protocol needs to be integrated to EPICS Channel Access protocol. In this conference, we report the system implementation, developed tool in detail about SRILAC project., Proceedings of the 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2021, Shanghai, China

Recent efforts at the RIKEN RI Beam Factory (RIBF) are aimed at increasing the beam intensity for very heavy ions such as xenon and uranium. This paper presents upgrade programs carried out over the past few years, including modifications of the RF cavities of the RIKEN Ring Cyclotron and improvements of the charge stripper. The current performance of the RIBF accelerators and future plans to further increase the beam intensity are also presented., Proceedings of the 22nd International Conference on Cyclotrons and their Applications, Cyclotrons2019, Cape Town, South Africa

To produce intense metal ion beams (e.g. Ti¹³⁺, V¹²⁺,13+, U³⁵⁺ ) for super heavy element search and RIBF experiments at RIKEN, we tried to optimize the RIKEN 28 GHz SC-ECRIS performance. Based on the scaling low and 'high B mode' operation, we systematically measured the beam intensity of various heavy ions as a function of Binj, Br and Bext with 28 and 18 GHz microwaves. In these experiments, we observed that (1) optimum Binj>1.6~2 Bext, (2) optimum Br>1.2~1.4 Bext and (3) optimum Bext is dependent on the charge state and ion spices as described by scaling low. We also observed same tendency for 18 GHz liquid-He-free SC-ECRIS. Using this systematics, we obtained ~400μA of V¹³⁺ at the RF power of 2kW (28 GHz) and very low Bext (~1.4 T with 28 GHz). For long term operation (one month), we successfully produced very stable beam of 100~200 μA of V¹³⁺ ion. Following the success, we constructed new 28 GHz SC-ECRIS for super heavy element search experiments. In this contribution, we report the experimental results in detail and how to produce intense metal ion beams., Proceedings of the 23th Int. Workshop on ECR Ion Sources, ECRIS2018, Catania, Italy

For synthesizing the new elements heavier than Z=118 at RIKEN, production of the intense metallic ion beams (e.g., Ti, V and Cr ion beams) were strongly required. To meet the requirements, we systematically studied the optimization of RIKEN 28 GHz SC-ECRIS performance. Using these results, we produced ~400 μA of V¹³⁺ ion beam at the RF power of 2 kW (28 GHz) and very low Bext (~1.4 T for 28 GHz). For long term operation, we successfully produced the intense stable beam (100~200 microA). To further push this project forward, new super-conducting RF cavities are now under construction in the downstream of RIKEN heavy-ion linac (RILAC) to increase the beam energy. In this project, we also constructed new 28 GHz SC-ECRIS based on these results in order to increase the beam intensities. In addition, to inject the high quality beam into the upgraded RILAC, three sets of movable slits to control the size of the transverse emittance of the beam are installed in the low energy beam transport (LEBT). In this contribution, we present the status of new 28 GHz ECRIS and LEBT. We also present the results of the systematic study and the production of the intense metallic ion beams., Proceedings of the 14th Int. Conf. on Heavy Ion Accelerator Technology, HIAT2018, Lanzhou, China

In order to accelerate uranium beams at the RI-beam Factory (RIBF) at RIKEN, U³⁵⁺ ions are extracted from a 28 GHz superconducting ECR ion source by using a high-temperature oven. Our high temperature oven uses a tungsten crucible joule-heated with a large DC current. The crucible is heated to a temperature of approximately 2000°C to achieve a UO2 vapor pressure of 0.1'1 Pa. We encountered the following problems since 2013: 1) the ejection hole of the crucible was blocked with UO2, 2) local over-heating in the upper and lower rods supporting the crucible, and 3) the supporting rods were bent and broken by an electromagnetic force because of the reduction of tungsten strength in the long-term operation at high temperature. We overcame the above problems, and moreover by doubling the volume of the crucible, the high-temperature oven has been used for the ion source operation for the RIBF experiments since the first use in the autumn of 2016. In this contribution, we report the design changes in the new crucible, and the results of the long-term operation. Moreover, we also present the practical use of the high-temperature oven for vanadium beams for the super heavy element search., Proceedings of the 23th Int. Workshop on ECR Ion Sources, ECRIS2018, Catania, Italy

In RIBF project, a superconducting linac will be implemented in order to enhance the beam energy necessary for promoting super heavy element experiment. A new 28 GHz electron resonance ion source has been installed upstream of them. Its control system will be consisted of Yokogawa FA-M3 series which is a porgrammble logic controller (PLC) with EPICS because of many achievements in case of RIBF control system. On the other hand, in the previous system with PLCs there was a disadvantage of low reliability for communications between PLC stations. Additionally, some devices (eg, oven, mivoc etc.) are changed for the generation of various kind of ions each times, therefore higher expandability is required. In the new system, we have designed the control system by utilizing star topology fieldbus for communications between the PLC stations to establish safety and expandability. In this conference, we report on the details of the system., Proceedings of the 12th Int. Workshop on Emerging Technologies and Scientific Facilities Controls, PCaPAC2018, Hsinchu, Taiwan

Present status and recent developments of RIKEN RI Beam Factory will be presented., Proceedings of the 14th Int. Conf. on Heavy Ion Accelerator Technology, HIAT2018, Lanzhou, China

The Radioactive Isotope Beam Factory (RIBF) is the cyclotron based accelerator facility for nuclear science, completed in the end of 2006. Now RIBF can provide the most intense RI beams. Continuous efforts since the first beam has increased the beam intensity and made stable operation. In 2016, 49.8 pnA (3×10¹¹/sec) of uranium ion beam could be extracted from the final accelerator SRC with energy of 345 MeV/u. An intensity upgrade program has been proposed to increase the intensity of uranium ion by more than twenty. The program includes two subjects. First, space charge limit of the beam intensity in the low energy ring cyclotron (RRC) should be increased by replacing the existing resonators with the new one to get higher accelerating voltage. The second is skip of the first stripper, requiring a new ring cyclotron (FRC) just after the first stripper to increase the maximum magnetic rigidity so as to accept low charge state. This presentation show a conceptual design of the new cyclotron with some issues to realize the intensity upgrade., Proceedings of the 21st Int. Conf. on Cyclotrons and their Applications, Cyclotrons2016, Zurich, Switzerland

Recent efforts concerning the accelerators of the RIKEN RI Beam Factory (RIBF) have been directed towards achieving higher heavy-ion beam intensities. As shown at the IPAC2014 conference, the intensities of these ion beams have improved significantly following the construction of the new injector, RILAC2, which is equipped with a 28-GHz superconducting ECR ion source, development of the helium gas stripper, and upgrading of the bending power of the fRC. In this respect, this paper presents the subsequent upgrade programs conducted in the past two years, such as the development of a new charge stripper for uranium beam and a new acceleration scheme of krypton beam. The current performance level of the RIBF accelerator complex, as well as a future plan to further increase the beam intensities, are also presented., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The RIKEN heavy ion linac (RILAC) is composed of a variable-frequency Wideröe linac, an 18 GHz ECR ion source, a variable-frequency folded-coaxial radio frequency quadrupole linac (FC-RFQ) as a pre-injector, and a Charge-State Multiplier system (CSM) as a booster. The operation of RILAC was started to supply heavy ion beams for experiments in 1981. The 18 GHz ECR ion source and the FC-RFQ were installed in 1996. The CSM was installed in 2000. The maximum beam energy, boosted by the CSM, is 6.0 MeV/nucleon. A GAs-filled Recoil Isotope Separator (GARIS) was moved from the E1 experiment room of the RRC to the No. 1 target room of the RILAC in 2000. In RIKEN Nishina center, the experiment on the super-heavy element (Z=113) search was carried out at RILAC from September 2003 to October 2012. As a result, three events for Z=113 have been successfully observed. The heavy-ion beam acceleration at RIKEN for the super-heavy element search will be reported., Proceedings of the 13th Heavy Ion Accelerator Technology Conference, HIAT2015, Yokohama, Japan

In the past two years, we tried to improve the performance of the RIKEN 28GHz SC-ECRIS for production of intense U ion beam. Usually, we used the sputtering method to produce U ion beam. Last year, we produced ~200e μA of U³⁵⁺ at the injected RF power of ~2.6kW, when slightly adding the U vapor with high temperature oven. For RIKEN RIBF experiment, we produced ~110 e μA of U³⁵⁺ beam with sputtering method longer than one month without break. In this case, we surly need very stable beam to increase the transmission efficiency in the accelerators and avoid the any damage of the components of the accelerator due to the high power beam. In this contribution, we will report the beam intensity of highly charged U ions as a function of various parameters (magnetic field strength, RF power, sputtering voltage etc.) and the effect of these parameters on the beam stability in detail. We also present the experience of the long term operation of the ion source for the RIKEN RIBF experiments., Proceedings of the 22nd Int. Workshop on ECR Ion Sources, ECRIS2016, Busan, Korea

In the RIKEN 18-GHz electron cyclotron resonance ion source, the practical use of low-temperature oven was achieved for the supply of metallic beams. At the RIKEN Radioisotope Beam Factory, Ca-48 beam is one of the important beams, as a primary beam to produce the secondary beam of neutron-rich medium-heavy nuclei. In order to enhance the intensity and stability of Ca-48 beam, we newly introduced a low-temperature oven and so-called "hot liner." A mixture of CaO and Al powders was placed into the crucible of the oven and heated to produce metallic calcium by a reductive reaction. We succeeded in high-intensity and stable supply of Ca-48 beam, as well as the reduction of material consumption rate. In addition, we succeeded in the supply of Zn-70 beam using the low-temperature oven. In supplying Zn-70 beam, only the ZnO powder was placed into the crucible, and the hot liner was not used. In this contribution, the configuration of low-temperature oven, the effect of the hot liner, the supply situations of Ca-48 and Zn-70 beams for a long-term experiment, and the attempts to supply other metallic beams using the low-temperature oven will be reported., Proceedings of the 13th Heavy Ion Accelerator Technology Conference, HIAT2015, Yokohama, Japan

Recent efforts concerning the RIBF accelerators in RIKEN have been directed towards achieving higher beam intensities of very heavy ions such as uranium and xenon. As presented in the last IPAC conference in 2013, the intensities of these ion beams have significantly improved due to the construction of a new injector, RILAC2, which is equipped with a 28-GHz superconducting ECR ion source, the development of a helium gas stripper, and upgrading of the bending power of the fRC. In this light, this paper presents the subsequent upgrade programs carried out in the last couple of years, such as developments of a new air stripper for xenon beams and a micro-oven for metallic ions. The current performance level of the RIBF accelerator complex, as well as a future plan to further increase the beam intensities, are also presented., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The RI beam factory at RIKEN Nishina Center needs high intensity of uranium ion beams. We constructed a new injector, RILAC2, which would provide several hundred times higher intensity. As a part of the RILAC2, we designed the low energy beam transport, LEBT, from the superconducting ECR ion source to the RFQ entrance. In this paper we present its requirements and problems, and show our design as the solutions to them. Especially we focus a technique of a pair of two solenoids to treat a rotational operation and a focusing operation independently. Based on this design, the LEBT was completed in March 2010. The RILAC2 will be operational this fall., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The next generation heavy ion accelerator facility, such as the RIKEN RIBF, requires great variety of high charged heavy ions with a magnitude higher beam intensity than currently achievable. In the last decade, performance of the ECR ion sources has been dramatically improved with increasing the magnetic field and RF frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key components (magnetic field configuration, gas pressure etc) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and the technology, we successfully constructed the new 28GHz SC-ECRIS which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. In the test experiment, we obtained the direct evidence that the field gradient and the zone size strongly affect the beam intensity. It concludes that the gentler field gradient and large ECR zone size gives intense beam of highly charged heavy ions from ECR plasma. In this contribution, we report the systematic study of these effects on the beam intensity of highly charged heavy ions., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The RI beam factory at RIKEN Nishina Center needs high intensity of uranium ion beams. We have used so far the RFQ pre-injector upstream of the linac system, in which the extraction voltage of the ECR ion source is as low as 5.7 kV for the uranium beam. However, for much higher intensity beams from a newly developed superconducting ECR ion source, such a low voltage was expected to significantly increase their emittance due to the space charge effect. To reduce this effect, we prepared a new pre-injector line of 127 kV for uranium beams by placing the ion source on a high-voltage terminal. In this paper we present the design of the 127 kV medium energy beam transport, MEBT, and show the measured results through the line., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

A new additional injector (RILAC2) is constructed at RIKEN Nishina Center in order to enable the independent operation of the RIBF experiments and super-heavy element synthesis. The RILAC2 consists of a 28 GHz superconducting ECR ion source, a low-energy beam transport with a pre-buncher, a four-rod RFQ linac, a rebuncher, three DTL tanks, and strong Q-magnets between the rf resonators for the transverse focusing. Very heavy ions with m/q of 7 such as ¹³⁶Xe²⁰⁺ and ²³⁸U³⁵⁺ will be accelerated up to the energy of 680 keV/u in the cw mode and be injected to the RIKEN Ring Cyclotron without charge stripping. The RFQ linac, the last tank of the DTL, and the bunchers have been converted from old ones in order to save the cost. Construction of the RILAC2 started at the end of the fiscal 2008. The RFQ and DTLs will be installed in the AVF cyclotron vault and be tested in March 2010. The ECR ion source and low-energy beam transport will be set on the RILAC2 in 2010 summer, and the first beam will be accelerated in 2010 autumn. We will present the details of the linac part of RILAC2 as well as the progress of construction which includes the result of high power test of resonators., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan