Complex sentence: The archival research is primarily undertaken by PhD and graduate students, who prepare for each mission by spending several months at the US Holocaust Memorial Museum studying the Soviet archives of the Extraordinary State Commission of 1944 and the archives of German Trials from Ludwisburg, Germany.
Split into simpler sentences: The archival research is primarily undertaken by PhD and graduate students. The students spend several months at the US Holocaust Memorial Museum, where they study the Soviet archives of the Extraordinary State Commission of 1944 and the archives of German Trials from Ludwisburg, Germany.