Modification of JT-60 NBI system from quasi-perpendicular to tangential injection

Modification of the JT-60 NBI system from quasi-perpendicular to tangential injection is studied. The motivation is that the ripple loss of fast ions would be substantial with the present quasi-perpendicular NBI in the upgraded JT-60 since in the upgrading modification the tokamak vacuum vessel is replaced to a larger bore one while toroidal coils are unchanged and hence toroidal field ripples at the periphery of plasmas increase. How many units of the present seven pairs of upper and lower units should be modified, and then how to combine them to inject beams through limited ports are discussed. The modification is optimized to utilize present beam line components as many as possible but is found to be still a complex task. This is because all present components are specialized to the present large slant angle of ±35.5 degrees. In this report, studies are presented on the necessity and the method of the modification. (author)