Yoshisato Funahashi

Photon generation by laser-Compton scattering at the KEK-ATF

We performed a photon generation experiment by laser-Compton scattering at the KEK-ATF,aiming to develop a Compton based polarized positron source for linear colliders. In the experiment, laser pulses with a 357 MHz repetition rate were accumulated and their power was enhanced by up to 250 times in the Fabry-Perot optical resonant cavity. We succeeded in synchronizing the laser pulses and colliding them with the 1.3 GeV electron beam in the ATF ring while maintaining the laser pulse accumulation in the cavity. As a result, we observed 26.0 +/- 0.1 photons per electron-laser pulse crossing, which corresponds to a yield of 10(8) photons in a second

Photon Generation by Laser-Compton Scattering Using an Optical Resonant Cavity at the KEK-ATF Electron Ring

We studied gamma-ray generation by the laser-Compton scattering using a Fabry-Perot optical resonant cavity at the KEK-ATF electron storage ring. The laser power was enhanced up to 388 W in the optical resonant cavity with an injection power of 7 W in the ATF operation environments. The yield of photons for a crossing of a laser pulse and an electron bunch was 3.3 +/- 0.6, which was consistent with a numerical estimate. In this paper, we report construction, installation and future prospect toward the polarized positron generation for the International Linear Collider.

The Development of a Superconducting RF Electron Microscope

Fig. 2: 2-mode cavity We are developing a new type of electron microscope (EM), which adopts RF acceleration in order to exceed the energy limit of DC acceleration used in conventional EMs. It enables us to make a high voltage EM more compact and to examine thicker specimens, and possibly to get better spatial resolution. It also provides an ability to observe transient processes by employing a state of the art laser photocathode technology as electron source. Low energy dispersion ∆E/E, e.g. 1.0×10−6 or better, is required for good spatial resolution in EMs, while it is usually between 1.0×10−3 to 1.0×10−4 in accelerators. We have thus designed a special type of cavity that can be excited with the fundamental and second harmonic frequencies simultaneously; TM010 and TM020. With the 2-mode cavity, the energy dispersion of the order of 1.0×10−5 would be obtained by modifying the peak of accelerating field to be flattened. We also adopt a superconducting cavity in order to operate the EM in CW mode, so that we can obtain a beam flux comparable to conventional EMs. In addition, we can make the operation more stable. As the proof-of-principle of our concept, we are developing a prototype using a 300 keV transmission electron microscope (TEM), to which a new photocathode gun and the 2-mode cavity are attached(Fig.1). Now we have already manufactured the cavity(Fig.2). We have done the beam dynamics simulation using General Particle Tracer(GPT), using the realistic electromagnetic field of the gun and the cavity. As a result, it has been found that we can reduce the energy dispersion ∆E/E from 2.04×10−4 to 3.68× 10−5 with 2-mode cavity. Then we can get the spatial resolution of 376pm, which is only about 50% deterioration of the existing 300keV TEM, which is much smaller than 818pm, the expected value of 1-mode cavity. The required electric fields are 8.21MV/m for TM010, 9.25MV/m for TM020. The designed Q-values are 1.86 × 10 for TM010(1.3002GHz), 1.00 × 10 for TM020(2.5999GHz). Performance evaluation tests has shown that the maximum electric fields are (8.75±0.73)MV/m for TM010, (7.80±0.33)MV/m for TM020. And the measured Q-values are (1.41± 0.45)× 10 for TM010, (0.78± 0.12)× 10 for TM020. It proves that manufactured cavity’s Q-values are close to designed ones, therefore we can say that the manufacturing process of our specially-shaped cavity has been confirmed. The measured resonant frequencies are 1.2963GHz for TM010, 2.5851GHz for TM020, so that the frequency ratio is 1.994. Then next task is to modify the cavity in order to tune the frequencies. And gun is now under construction. The goal of this year is to acquire the electron beam from the cathode. APPC12 The 12th Asia Pacific Physics Conference