RIKEN, Wako, Saitama
The Radioactive Isotope Beam Factory at RIKEN Nishina Center is a next generation facility which is capable of providing the world’s most intense RI beams over the whole range of atomic masses. Three new ring cyclotrons have been constructed as post-accelerators for the existing facility in order to provide the intense heavy ion beam for the RI beam production by using a in-flight separation method. The beam commissioning of RIBF was started at July 2006 and we succeeded in the first beam extraction from the final booster cyclotron, SRC, by using 345 MeV/nucleon aluminum beam on December 28th 2006. The first uranium beam with energy of 345 MeV/nucleon was extracted from the SRC on March 23rd 2007. Various modifications for equipments and many beam studies were performed in order to improve the transmission efficiency and to gain up the beam intensity. Consequently, the world’s most intense 0.4 pnA 238U beam with energy of 345 MeV/nucleon and 170 pnA 48Ca beam with energy of 345 MeV/nucleon have been provided for experiments.
RIKEN, Wako, Saitama
In 2008, the RIKEN RI-Beam Factory (RIBF) succeeded in providing heavy ion beams of 48Ca and 238U with 170 particle-nano-ampere and 0.4 particle-nano-ampere, respectively, at an energy of 345 MeV/u. The transmission efficiency through the accelerator chain has been signifcantly improved owing to the continuous efforts paid since the first beam in 2006. From the operational point of view, however, the intensity of the uranium beam should be much increased. We have, therefore, constructed a superconducting ECR ion source which is capable of the microwave power of 28 GHz. In order to reduce the space-charge effects, the ion source was installed on the high-voltage terminal of the Cockcroft-Walton pre-injector, where the beam from the source will be directly injected into the heavy-ion linac by skipping the RFQ pre-injector. The test of the ion source on the platform has started recently with an existing microwave source of 18 GHz. This pre-injector will be available in October 2009. We will show further upgrade plan of constructing an alternative injector for the RIBF, consisting of the superconducting ECR ion source, an RFQ, and three DTL tanks. An RFQ linac, which has been originally developed for the ion-implantation application will be reused for the new injector. Modification of the RFQ as well as the design study of the DTL are under progress. The new injector, which will be ready in FY2010, aims at independent operation of the RIBF experiments and super-heavy element synthesis.
RIKEN, Wako
A highly sensitive beam current monitor with an HTS (High-Temperature Superconducting) SQUID (Superconducting QUantum Interference Device) and an HTS current sensor, that is, an HTS SQUID monitor, has been developed for use of the RIBF (RI beam factory) at RIKEN. Unlike other existing facilities, the HTS SQUID monitor allows us to measure the DC of high-energy heavy-ion beams nondestructively in real time, and the beam current extracted from the cyclotron can be recorded without interrupting the beam user's experiments. Both the HTS magnetic shield and the HTS current sensor were dip-coated to form a Bi2 - Sr2 - Ca2 - Cu3 - Ox (Bi-2223) layer on 99.9 % MgO ceramic substrates. In the present work, all the fabricated HTS devices are cooled by a low-vibration pulse-tube refrigerator. These technologies enabled us to downsize the system. Prior to practical use at the RIBF, the HTS-SQUID monitor was installed in the beam transport line of the RIKEN ring cyclotron to demonstrate its performance. As a result, a 20 μA 40Ar15+ beam intensity (63 MeV/u) was successfully measured with a 500 nA resolution. Despite the performance taking place in an environment with strong gamma ray and neutron flux radiations, RF background and large stray magnetic fields, the measurements were successfully carried out in this study. This year, the HTS SQUID monitor was upgraded to have aresolution of 100 nA and was reinstalled inthe beam transport line, enabling us to measure a 4 μA 132Xe20+ (10.8 MeV/u) beam and a 1 μA 132Xe41+ (50.1 MeV/u) beam used for the accelerator operations at RIBF. Hence, we will report the results of the beam measurements an the present status of the HTS SQUID monitor.