Y. Enomoto

Positron accumulation and manipulation for antihydrogen synthesis

Our group ASACUSA-MUSASHI has established an efficient way for accumulating antiprotons in the cusp trap, a combination of an anti-Helmholz superconducting coil and a multi-ring electrode trap. The last piece for synthesizing antihydrogens in the cusp trap is positron. We have developed a compact system to effectively accumulate positrons based on N2 gas-buffer scheme with a specially designed high precision cylindrical multi-ring electrode trap. Millions of positrons were accumulated in the pre-accumulator just using polycrystalline tungsten moderators. The accumulated positrons were transported as a pulsed beam via three guiding coils and caught in the cusp trap under cryogenic and ultra high vacuum conditions without serious loss. Confinement of two kinds of numerous antiparticles, e.g., 108 positrons and 107 antiprotons, in the cusp trap becomes feasible.

Mirror actuation design for the interferometer control of the KAGRA gravitational wave telescope

KAGRA is a 3-km cryogenic interferometric gravitational wave telescope located at an underground site in Japan. In order to achieve its target sensitivity, the relative positions of the mirrors of the interferometer must be finely adjusted with attached actuators. We have developed a model to simulate the length control loops of the KAGRA interferometer with realistic suspension responses and various noises for mirror actuation. Using our model, we have designed the actuation parameters to have sufficient force range to acquire lock as well as to control all the length degrees of freedom without introducing excess noise.

Standard quantum limit of angular motion of a suspended mirror and homodyne detection of a ponderomotively squeezed vacuum field

Compared to the quantum noise in the measurement of the translational motion of a suspended mirror using laser light, the quantum noise in the measurement of the angular motion of a suspended mirror has not been investigated intensively despite its potential importance. In this article, an expression for the quantum noise in the angular motion measurement is explicitly derived. The expression indicates that one quadrature of the vacuum field of the first-order Hermite-Gaussian mode of light causes quantum sensing noise and the other causes quantum back-action noise, or in other words the first-order vacuum field is ponderomotively squeezed. It is also shown that the Gouy phase shift the light acquires between the mirror and the position of detection of the light corresponds to the homodyne angle. Therefore, the quantum back-action noise can be canceled and the standard quantum limit can be surpassed by choosing the appropriate position of detection analogously to the cancellation of quantum radiation pressure noise by choosing an appropriate homodyne angle.

Observation of reduction of radiation-pressure-induced rotational anti-spring effect on a 23 mg mirror in a Fabry–Perot cavity

Although quantum radiation pressure noise could limit the sensitivity of the second-generation gravitational wave detectors, it has not been observed in a broad frequency band and its reduction methods have not been proven yet. A promising way to observe quantum radiation pressure noise is to store high power light in an optical cavity with a tiny mirror. However, anti-spring torque caused by radiation pressure of the light acting on the tiny mirror could make the system unstable, and it is generally difficult to attach actuators to the tiny mirror for stabilization. Hence a new method to overcome this anti-spring torque has been developed. In the new method, the other mirror of the cavity is controlled so that the position of the resonant light at the tiny mirror is fixed to decrease the anti-spring torque and stabilize angular motion of the tiny mirror. With the new method, it was successfully observed that the anti-spring torque caused by radiation pressure was suppressed in the present experiment with a 23 mg mirror, where resonant frequency of angular motion of the tiny mirror increased towards the mechanical resonant frequency.

Observation of Ultra‐Slow Antiprotons using Micro‐channel Plate

Our group ASACUSA‐MUSASHI has succeeded in accumulating several million antiprotons and extracting them as monochromatic ultra‐slow antiproton beams (10 eV–1 keV) at CERN AD. We have observed ultra‐slow antiprotons using micro‐channel plates (MCP). The integrated pulse area of the output signals generated when the MCP was irradiated by ultra‐slow antiprotons was 6 times higher than that by electrons. As a long‐term effect, we also observed an increase in the background rate presumably due to the radioactivation of the MCP surface. Irradiating the antiproton beams on the MCP induces antiproton‐nuclear annihilations only on the first layer of the surface. Low‐energy and short‐range secondary particles like charged nuclear fragments caused by the “surface nuclear reactions” would be the origin of our observed phenomena.

Towards the production of anti-hydrogen beams

Recently, the production of low energy anti-hydrogen atoms in the cusp trap with the use of 150eV antiproton beams from the MUSASHI trap was reported. The purpose of producing low energy anti-hydrogen atoms in a cusped magnetic field is to extract a polarized anti-hydrogen beam to a field free region, so that the hyperfine structure of anti-hydrogen atoms can be measured.

Radial Compression of a Non‐neutral Plasma in a Non‐uniform Magnetic Field of a Cusp Trap

Spectroscopic comparison of antihydrogen and hydrogen atoms is one of the best candidates for the stringent tests of the CPT symmetry, and intensive studies are being carried out by using Antiproton Decelerator at CERN. The ASACUSA collaboration has constructed a superconducting cusp trap for the formation, trapping and extraction of antihydrogen atoms, where a quadrupole magnetic field is generated by a pair of anti‐Helmholtz coils with anti‐parallel currents. The cusp configuration is considerably advantageous for the extraction of spin‐polarized and ground‐state antihydrogen beams that are ideal for the spectroscopic measurements of hyperfine structures of the ground state of antihydrogen. For the effective generation of antihydrogen atoms, it is essential to form high density and stable plasmas of antiproton and positrons. In this study, we applied a rotating electric field to an electron plasma in the inhomogeneous cusp magnetic field, and demonstrated the effective radial compression of a non‐neutra...

Developments of the cusp trap to synthesize antihydrogen atoms for high precision spectroscopy of ground state hyperfine splitting

We have been developing a so-called cusp trap to synthesize antihydrogen atoms, and to make high precision microwave spectroscopy. The cusp trap consists of an anti-Helmholtz coil and a multi-ring trap, which yield axially symmetric magnetic and electric fields. This axial symmetry is quite important to realize stable confinements of antiproton and positron plasmas, which guarantees stable operation during the antihydrogen synthesis.