Simulation study and modification of the MAIKo+ active-target field cage

We aim to determine the rate of the triple-alpha reaction in dense conditions. To do this, we're investigating the transition of ¹²C from the Hoyle state to its grand state via the neutron up- scattering. Since the direct measurement of the above reaction is impossible, we're measuring the time-reversal reaction and using the principle of detailed balance.

The MAIKo active-target TPC is suited to detect the low-energy decay particles from the ¹²C excited state. A test experiment of MAIKo using a neutron beam at E_n=14 MeV in 2020 showed promising results, validating our method.

To improve the statistical accuracy of the measurement, we developed a larger version, MAIKo+, with dimensions of 30.7 × 30.7 × 30.0 cm³. Simulations show that MAIKo+ could boost our yields by about 10 times, which was confirmed by another test experiment in 2022.

In the test experiment with MAIKo+, we observed the worse angular resolution for the decay particles than expected. This could be attributed to the distortion in the track data measured with MAIKo+. We aim to solve this by modifying our TPC field cage based on the electric field simulation. We will present the electric field calculation of the MAIKo+ field cage conducted using the simulation tool Garfield++. Additionally, performance tests of the MAIKo+ TPC after the modification will be discussed.