paris iter international project build prototype nuclear fusion reactor southern france say face delay trump administration reconsider budget cut seven partner europe unite state china india japan russia south korea launch international thermonuclear experimental reactor iter 10 years ago project experience years delay budget overrun iter hop generate power process similar nuclear fusion power sun unlike exist nuclear reactors produce energy split atoms iter director-general bernard bigot washington talk u.s. administration say u.s. 2017 contribution cut plan 105 million 50 million 2018 contribution plan 120 million 63 million unite state already spend billion prototype reactor schedule contribute another 1.5 billion 2025 iter schedule run first operational test respect deadlines begin respect end bigot tell reuters telephone bigot say follow letter french president emmanuel macron president donald trump august trump ask administration reconsider issue hope decision weekend week say u.s. provide necessary fund 2018 impact entire project add early year iter total budget revise upwards 18 22 billion euros 21-26 billion u.s. share nine percent trump administration conduct review civilian nuclear policy include research development inform u.s. policy toward iter future say shaylyn hynes spokeswoman u.s. department energy u.s. energy secretary rick perry tell macron understand history scale project say bigot say trump cut u.s. energy department budget department reduce fund u.s. company make iter components iter member countries finance manufacture iter components via national company part ship france assemble iter cadarache southern france site iter main u.s. supplier california-based general atomics build central solenoid 18-metre tall pillar-like magnet one first components instal 2020. project half way towards first test super-heated plasma 2025 first full-power fusion 2035. iter say nuclear fusion produce nuclear waste like traditional nuclear power plant much safe operate challenge replicate sun fusion earth enormous critics say remain unclear whether technology work eventually commercially viable iter nuclear fusion project face delay trump budget cut