Katsuhiro Dobashi

Design of a polarized positron source for linear colliders

We propose a design of a polarized positron source for linear colliders. The design is based on electron–positron pair creation from polarized g-rays which are produced by Compton scattering of circularly polarized laser light off a highenergy electron beam. Polarized positrons are created from those g-rays incident on a thin conversion target. A future linear collider of the TeV-energy region requires an extraordinary large number of positrons (B1 � 10 10 positrons/ bunch) in a multi-bunch time structure. To meet these requirements, our design employs a high-current, low-emittance electron beam of 5:8 GeV; 10 CO2 lasers, and 200 laser–electron collision-points. At each collision point, a pair of specially designed parabolic mirrors is installed to achieve efficient head-on collisions. This system allows us to produce high-intensity polarized g-rays, which effectively generate high-intensity polarized positrons with the magnitude of polarization greater than 50%: r 2003 Elsevier Science B.V. All rights reserved.

Polarized positron source for the linear collider, JLC

Abstract A comprehensive description of a polarized positron project is presented in terms of physics motivations for utilizing a polarized positron in electron–positron collider experiments, a proof-of-principle experiment and a conceptual design of a polarized positron source for the future linear collider JLC. In order to verify a proposed method of creating highly polarized positron beams via successive two fundamental processes, i.e. Compton scattering and pair creation, we have been performing basic experiments both at KEK and BNL. First observation of positrons was made at KEK using an electron beam of 1.26 GeV and a laser of 2.33 eV. High-intensity picosecond X-rays were also generated at BNL using a specially designed Compton chamber. In order to realize polarized positron beams of the JLC which have considerably high intensity, i.e. 0.7×10 10 e + / pulse and a complicated multi-bunch structure, we have achieved a possible scheme for the Compton scattering system and a positron capture section into an L-band linac.

Dual-Energy X-Ray CT by Compton Scattering Hard X-Ray Source

We are developing a compact Compton scattering hard X-ray source by the X-band linac and YAG lasers at Nuclear Professional School, University of Tokyo. The compact hard X-ray source can produce tunable monochromatic hard X-rays for 10 - 40 keV. The monochromatic hard X-rays are very useful in large fields of medical and biological sciences. We are planning to carry out dual-energy X-ray CT, which enables us to obtain 3D distribution of effective atomic number Zeffand electron density ρein a matter. The hard X-ray source has an advantage in the dual-energy X-ray CT. The X-ray energy can be changed quickly by introducing a fundamental-frequency and a second-harmonic-frequency lasers. It is indispensable to change the X-ray energy quickly for medical imaging, but it is very difficult to achieve the quickness with a large SR light source and others. The information on the atomic number and electron density will be used for radiation treatment planning as well as for identification of materials in a nondestructive test. We examined applicability of the dual-energy X-ray CT for low to medium Z elements (Z ≤ 38) by considering the X-ray energy profile generated by the Compton scattering hard X-ray source.

Generation of positrons via pair-creation from Compton scattered gamma-rays

Abstract An important role of positron (e + ) polarization in future linear colliders is discussed in terms of effective polarization, which is closely related to the clear observation of interesting reaction processes in e − e + collisions. In order to verify our proposed method, in which highly polarized e + can be generated through Compton scattering of laser light off a relativistic electron (e − ) beam, we performed an experiment to prove the principle and observed e + productions for the first time. It was found that the production rates of e + are not only consistent with those of e − and γ-ray but also in good agreement with numerical estimations.

Erratum to “Design of a polarized positron source for linear colliders”

Erratum Erratum to ‘‘Design of a polarized positron source for linear colliders’’ T. Omori*, T. Aoki, K. Dobashi, T. Hirose, Y. Kurihara, T. Okugi, I. Sakai, A. Tsunemi, J. Urakawa, M. Washio, K. Yokoya KEK: High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba-shi, Ibaraki 305-0801, Japan Advanced Research Institute for Science and Engineering of Waseda Univ., Tokyo 169-8555, Japan Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachioji-shi, Tokyo 192, Japan National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba-shi, Chiba 263-8555, Japan Sumitomo Heavy Industries, 2-1-1 Yado, Tanashi-shi, Tokyo 188-8585, Japan

Review of Advanced Accelerator Concepts R & D in Japan

More than 15 Japanese laboratories are dedicated to the advanced and compact accelerator development. Some use ultra‐intense lasers and others use microwave concepts. As for the laser electron accleration, the topics are the capillary acceleration and the mono‐energetic acceleration. The laser ion acceleration is also active. As well, the compatization is proceeding of the current rf accelerator. The National Institute for Radiological Science is promoting an advanced accelerator concept project mainly for the medical application.

Compton scattering of laser off electron beams to generate polarized positron beams for future linear colliders

We observed positron (e+) production for the first time on the basis of the new idea that (gamma) -rays produced via Compton scattering of laser lights off electron (e-) beams of 1.26 GeV/c provided by the ATF damping ring can create pairs of e+ and e-. It is verified that the production rates of e+- and (gamma) -rays are consistent with each other as well as in good agreement with theoretical predictions. We also attain a conceptual design of a polarized e+ source for the future linear collide JLC which requires high intensity e+ beams with a complicated time structure of multi-bunching.