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In 1950 – 1951 I.E. Tamm and A.D. Sakharov in the Soviet Union , first discussed a tokamak-like approach .
 I.E. Tamm, A.D. Sakharov, Soviet Union
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
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Text: {0} 
Answer:
 I.E. Tamm, A.D. Sakharov, Soviet Union