First of all, there are no people named "Sakadeans". The Scythians were sometimes called the "Saka" according to the Encyclopedia Britannica. https://www.britannica.com/topic/Scythian.
As for the Khazarian mass conversion, Encyclopaedia Britannica has this to say:
Textual witnesses dating from the 9th and 10th centuries claim the Khazars adopted Judaism in the 8th century. These texts are not without problems, however, and lack of archaeological or other physical evidence indicating a mass conversion has called both the extent and historicity of this conversion into doubt.
Regarding the Ashkenazim, Bastethotep beat me to it again:
Ashkenazi, plural Ashkenazim, from Hebrew Ashkenaz (“Germany”), member of the Jews who lived in the Rhineland valley and in neighbouring France before their migration eastward to Slavic lands (e.g., Poland, Lithuania, Russia) after the Crusades (11th–13th century) and their descendants. After the 17th-century persecutions in eastern Europe, large numbers of these Jews resettled in western Europe, where they assimilated, as they had done in eastern Europe, with other Jewish communities.
https://www.britannica.com/topic/Ashkenazi