|Budget Amount *help
¥289,000,000 (Direct Cost : ¥262,000,000、Indirect Cost : ¥27,000,000)
Fiscal Year 2002 : ¥44,200,000 (Direct Cost : ¥34,000,000、Indirect Cost : ¥10,200,000)
Fiscal Year 2001 : ¥72,800,000 (Direct Cost : ¥56,000,000、Indirect Cost : ¥16,800,000)
Fiscal Year 2000 : ¥27,000,000 (Direct Cost : ¥27,000,000)
Fiscal Year 1999 : ¥37,000,000 (Direct Cost : ¥37,000,000)
Fiscal Year 1998 : ¥40,000,000 (Direct Cost : ¥40,000,000)
Fiscal Year 1997 : ¥68,000,000 (Direct Cost : ¥68,000,000)
Search for dark matter axions over the mass range of 11 μeV is in progress with Rydberg atoms in a resonant cavity at low temperature. Along with the search, efforts have been devoted to improve the detection efficiency by modifying a number of parts of the experimental apparatus. Specifically the following improvements were obtained for increasing the detection efficiency: 1) Reduction of the stray electric field around the cavity and the field ionization detector regions, 2) Reduction of the motional Stark effect on the broadening of the resonant width for the Rydberg states in a cavity by eliminating the magnetic field in the region of the cavity and the detector. In addition the effect of the collisions between the Rydberg atoms and the ground state Rb atoms on the selective field ionization performance was carefully examined to improve the selectivity. For these improvements, further cleaning of the inside of the cavity and of the detector system were carefully tried and shielding of the magnetic field around the field ionization detection region was especially improved by incorporating a number of sheets made of NbTi-Nb-Cu complex. Also we improved the pulsed field ionization performance to get better detection efficiency.
We also somewhat modified the structure of metal post system in the cavity to get more uniform electric field mode in the cavity, thus improving the detection efficiency. Installing a sextupole magnet to increase the intensity of the atomic beam and to select and polarize the atomic hyperfine state was also examined to increase the overall detection efficiencies. With these efforts, the overall detection efficiency was increased and these improvements enabled us to shorten the necessary time to search for axions. No axion signals have been definitely observed at the mass region investigated.