Development of Bounce-Time-Based Orbit-Following Monte-Carlo Code

We developed a bounce-time (BT)-based orbit-following Monte-Carlo code as an extension of the OFMC code in QST. In the BT-based method, we take a bounce time as a time step of the orbit following. The time step is ~ 100 times longer than the gyro period which is a typical time step for the conventional guiding-center (GC) method. In the BT-based method, an accurate and simple estimation of a poloidal projection of the bounce orbit and a staying time are essential. An expression for the orbit gives us an orbit shape by a small calculation with the difference of less than 1% of the minor radius, compared with the GC method with the same fast ion parameters. And an approximate expression for the staying time also gives us the staying time with a good accuracy for our purpose. We can see a good agreement between calculation results for the BT-based method and those for the GC method in an axisymmetric condition. The BT-based method is 70–140 times faster than the GC method, depending on the slowing-down time.