The charts above are from a newly-released Morning Consult Poll. It was done between January and March of this year and questioned 85,000 respondents is the 50 states.
One should be careful in stating the popularity of these senators in the nation as a whole. Each senator was rated only by the residents of his/her own state -- not the nation as a whole. For instance, the most popular senator in this poll was Bernie Sanders (at 75% approval), but that is only the opinion of people in his state of Vermont. I seriously doubt he would be rated anywhere near that high in the entire nation.
In fact, I think the popularity of every senator would be lower on a national basis. It would be interesting to see how each senator is rated nationally though.