Background: The deflection magnet is one of the key components of the neutral beam injector

it is installed in the neutral beam injector vacuum chamber. While the neutral beam injector works

the heat generated by current running through exciting coils of deflection magnet must be taken away by the cooling water simultaneously. Purpose: In order to meet the requirements of the developing nuclear fusion researches

the neutral beam injector must work steadily

providing neutral beam of high energy

high power continuously. The cooling abilities of the deflection magnets must be enhanced. Methods: The water cooling structure of excitation coils of the original deflection magnet was optimized by adding a pair of water taps in each primary coil

and the tests were made to check the cooling capbilities of the improved exciting coils. Results: When the neutral beam injector runs at the state of long pulse

improved water cooling structures take away the heat generated by the exciting coils timely. The improvement of the cooling abilities of the coils was successful. Conclusion: The temperature difference between the inlet and outlet of the cooling water pipe is about 21 oC

and the surface temperature of deflection magnet coil is about 45 oC. Abstract