Isomers and high-spin structures in the N

The high-spin structures and isomers of the N=81 isotones 135Xe and137Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in 136 Xe+238 U and (ii) 136 Xe + 208 Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the 136 Xe+ 198PtMNT reaction employing the γ-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a 11 B+130Te fusion-evaporation reaction with the HORUS γ-ray array at the University of Cologne. The high-spin level schemesof 135Xe and 137 Ba are considerably extended to higher energies. The 2058-keV (19/2−) state in 135 Xe is identified as an isomer, closing a gap in the systematics along the N=81 isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of B(E2,19/2−→15/2−)=0.52(6 ) W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels

STF-2 Cryomodule Performance and New Input Coupler R&D; for ILC

The high power test for STF -2 cryomodule with twelve cavities has completed successfully in 2015. It became clear the average accelerating gradient was 30.3 MV/m, eight cavities achi eved above 31.5 MV/m as the ILC specification, and three cavities had the significant performance degradation by heavy field emission due to the additional clean room work in t he STF tunnel. As the following next steps, there are the LFD (Lorenz Force Detuning) measurem ent, LFD compensation by piezo, and long ru n for check of stable operation at high gradient. In th e long run around 32 MV/m, each cavity without degradation showed the stable operation with the successful LFD compensation by piezo and RF feedback system. On the other hand, from the view point of pl ug-compatibility for the input coupler in the ILC, new STF input couplers with 40mm of input port were re -designed, fabricated and high -power -tested successfully. Moreover, for the lower cost study, another input couplers with coating -free ceramic will be also tested soon in the collaboration of CERN and KEK. In this presentation, the detailed results for STF -2 Cryomodule t est and 40mm input couplers are reported

1 mA Stable Energy Recovery Beam Operation with Small Beam Emittance

A compact energy-recovery linac (cERL) have been operating since 2013 at KEK to develop critical components for ERL facility. Details of design, construction and the result of initial commissioning are already reported*. This paper will describe the details of further improvements and researches to achieve higher averaged beam current of 1 mA with continuous-wave (CW) beam pattern. At first, to keep the small beam emittance produced by 500 kV DC-photocathode gun, tuning of low-energy beam transport is essential. Also, we found some components degrades the beam quality, i.e., a non-metallic mirror which disturbed the beam orbit. Other important aspects are the measurement and mitigation of the beam losses. Combination of beam collimator and tuning of the beam optics can improve the beam halo enough to operate with 1 mA stably. The cERL has been operated with beam energy at 20 MeV or 17.5 MeV and with beam rep-rate of 1300 MHz or 162.5 MHz depending on the purpose of experiments. In each operation, the efficiency of the energy recovery was confirmed to be better than 99.9 %.10th International Particle Accelerator Conferenc

The First Beam Recirculation and Beam Tuning in the Compact ERL at KEK

Superconducting(SC)-linac-based light sources, which can produce ultra-brilliant photon beams in CW operation, are attracting worldwide attention. In KEK, we have been conducting R&D; efforts towards the energy-recovery-linac(ERL)-based light source* since 2006. To demonstrate the key technologies for the ERL, we constructed the Compact ERL (cERL)** from 2009 to 2013. In the cERL, high-brightness CW electron beams are produced using a 500-kV photocathode DC gun. The beams are accelerated using SC cavities, transported through a recirculation loop, decelerated in the SC cavities, and dumped. In the February of 2014, we succeeded in accelerating and recirculating the CW beams of 4.5 micro-amperes in the cERL; the beams were successfully transported from the gun to the beam dump under energy recovery operation in the main linac. Then, precise tuning of beam optics and diagnostics of beam properties are under way. We report our experience on the beam commissioning, as well as the results of initial measurements of beam properties

Construction and commissioning of the compact energy-recovery linac at KEK

Energy-recovery linacs (ERLs) are promising for advanced synchrotron light sources, high-power free electron lasers (FELs), high-brightness gamma-ray sources, and electron–ion colliders. To demonstrate the critical technology of ERL-based light sources, we have designed and constructed a test accelerator, the compact ERL (cERL). Using advanced technology that includes a photocathode direct current (DC) electron gun and two types of 1.3-GHz-frequency superconducting cavities, the cERL was designed to be capable of recirculating low emittance (1 mm mrad) and high average-current (10 mA) electron beams while recovering the beam energy. During initial commissioning, the cERL demonstrated successful recirculation of high-quality beams with normalized transverse emittance of 0.14 mm mrad and momentum spread of 1.2 10−4 (rms) at a beam energy of 20 MeV and bunch charge below 100 fC. Energy recovery in the superconducting main linac was also demonstrated for high-average-current continuous-wave beams. These results constitute an important milestone toward realizing ERL-based light sources