Kyoto ICR, Uji, Kyoto
JAEA/Kansai, Kizu-machi Souraku-gun Kyoto-fu
JAEA, Ibaraki-ken
NIRS, Chiba-shi
Funding: This work is supported by Advanced Compact Accelerator project by MEXT of Japanese Government and 21COE of Kyoto University, Center for Diversity and Universality in Physics.
By the phase rotation with the use of rf electric fields created by two gap resonator synchronous to a pulse laser, the energy spread of the laser-produced ions can be reduced*. In addition, owing to the curved structure of the electric field line in the gaps of the phase rotator, radial focusing effect is found also to exist. In order to extend the applicable energy of the phase rotation to the region where such laser produced protons can be directly applied for cancer therapy, multi-gap resonator with higher frequency has been proposed. By controlling the relative phases between the pulse laser and the electric fields in the gaps of phase rotator, we can create peaks in the energy spectrum simultaneously focusing in the radial direction.
* Japanese Journal of Applied Physics (Express Letter), 46 (2007) L717-L720
Kyoto ICR, Uji, Kyoto
ILL, Grenoble
RIKEN, Wako, Saitama
KEK, Tsukuba
University of Tokyo, Tokyo
JAEA, Ibaraki-ken
Kyoto University, Kyoto
ICEPP, Tokyo
We are developing a modulating permanent magnet sextupole lens to focus pulsed cold neutrons. It is based on the extended Halbach configuration to generate stronger magnetic field. In order to adjust the strength, the magnet is divided into two nested co-axial rings, where the inner ring is fixed and the outer ring can be rotated. Synchronizing the modulation with neutron beam pulse suppresses the chromatic aberration. These devices largely improve the utilization efficiency of neutrons, which makes even small linac based neutron sources practical. We have fabricated a half-scale model and studied its strength, torque and temperature rise during the operation. The main causes of the temperature rise are eddy-current loss in the poles made of soft magnetic material in inner ring and hysteresis loss. A laminated structure reduced the eddy-current loss. The temperature rise was suppressed to about half of the former model. We now study their B-H curve to optimize the thickness of the sheet. Annealing of the material is supposed to reduce the hysteresis loss, which will be tested soon. The experimental results of very-cold neutrons focusing with the half-scale model are also described.
Kyoto ICR, Uji, Kyoto
KEK, Ibaraki
A final focus quadrupole (FFQ) doublet of ILC should have excellent properties such as strong focusing, compactness and less vibrations. In a baseline design, superconducting magnet is supposed to be used, which may have some vibrations traveling through liquid helium. It may not be suitable for FFQ of ILC unless the vibration effect is proven to be negligible. Since the five-disc-singlet proposed by Gluckstern satisfies these properties including continuous adjustability, we are developing a FFQ aiming at a beam test at ATF2. Although the x-y coupling effect is carefully cancelled in the design, fabrication errors or rotation errors may break the cancellation. We are estimating the effect of these errors on the beam size at the interaction point. Two methods are currently carried out. The first one is transfer matrix calculations, which neglects fringing field and higher multipole components. The second one is beam-tracking calculation in measured or calculated magnetic field. The fabricated magnet is under adjustment measuring the magnetic field. The recent results will be presented.
Kyoto ICR, Uji, Kyoto
We aim to develop a small and high intensity proton source for a compact accelerator based neutron source. Because this proton source shall be located close to RFQ for simplification, ratio of H+ to molecular ions such as H2+ or H3+ must be large. Therefore we select ECR ion source with permanent magnet as a small and high intensity ion source. ECR ion sources can provide high H+ ratio because of their high plasma temperature. Using permanent magnets makes the ion source small and running cost low. Because there is no hot cathode, longer MTBF is expected. Usually, gas is fed into ion sources continuously, even if ion sources run in pulse operation mode. But, continuous gas flow doesn't make vacuum in good level. So, we decided to install pulse gas valve directly to the plasma chamber. Feeding the gas only when the ion source is in operation reduces the gas load to the evacuation system and the vacuum level can be kept high. Recent experimental results will be presented.
Kyoto ICR, Uji, Kyoto
KEK, Ibaraki
Inspections of superconducting rf cavities seem essential in achieving high achieving gradient. The inspection of interior surface of a superconducting rf cavity with high enough resolution to find defects more than several tens microns is achieved by our high resolution camera system. This system revealed undiscovered defects at just inner sides of the locations predicted by passband-mode and thermometry measurements. This system will help to improve cavity fabrication processs and their yield. This system will be delivered world wide for that purpose. We are planning to widen our activity in this field: developments of new termometry system with easy installation and less cabling and high sensitivity Eddy Current Surface Inspection system for bare niobium sheets. The detailed systems and some preliminary data obtained from the systems will be presented.