Direct measurement of the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ reaction cross section near stellar energies

The $^{12}$C$+^{4}$He$\to^{16}$O$+\gamma$ reaction is one of the key reactions in stellar He-burning, but its total cross section at stellar energy (Ecm $=$ 0.3 MeV) has not been measured yet, in spite of many experiments made in the world for about a half century. At Kyushu University Tandem accelerator Laboratory (KUTL), we have been making direct measurement of the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ total cross section below Ecm $=$ 2.4 MeV for about 20 years. We have measured the total cross section at Ecm $=$ 2.4, 1.5 and 1.2 MeV. Now we are preparing to measure the cross section at 1.0 MeV. The direct measurement was made from Ecm $=$ 5 MeV down to 1.9 MeV at Ruhr University, Bochum. We use a pulsed $^{12}$C beam and a windowless $^{4}$He target, and detect all the $^{16}$O recoils in a charge state. A usually continuum $^{12}$C beam from our tandem accelerator is pulsed by a pre-buncher, a main buncher, and a beam chopper. Our tandem accelerator was designed to be used at the acceleration voltage of 6-10 MV. For the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ experiment we need to use it at 1.3-1.8 MV where beam transmission is very low, then we have invented an acceleration-deceleration method for the tandem accelerator. We have developed a blow-in windowless He target based on an original idea. To separate $^{16}$O recoils from the $^{12}$C beam, we developed a recoil-mass separator. To reject $^{12}$C backgrounds, we developed a long-time chopper, and an ionization chamber. Now, we are preparing to measure time-of-flight of $^{16}$O recoils and $^{12}$C backgrounds. Many original instruments and the experimental results will be presented. Finally we discuss what are necessary for future direct measurement of the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ total cross section below 1.0 MeV, down to 0.7 MeV. A dynamitron accelerator and hard-working researchers may be inevitable.