I found a web page that says that it was discovered by Tesla in 1890, is that true or generally acknowledged?
Isn't 1890 too early a date?
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See listing here: Index of Early Bremsstrahlung Articles
The earliest items are: patents filed by Tesla in 1891 and 1892. And papers (by others, not Tesla) in Philosophical Magazine in 1891.
The term Bremsstrahlung is said to be coined by Arnold Sommerfeld in 1909. Cannot access this chapter but the abstract is available. It must have the original reference. https://link.springer.com/chapter/10.1007/978-3-540-70626-7_23