Summer Research with Advisor or at National Lab? I have the option of doing research with my advisor this summer (yay, funding!) or working with a collaborator at a highly-regarded national lab (a research position, but called an internship). I have worked at this lab two summers ago, and it was very enjoyable, fairly productive, and I networked with people with whom I would love to work with in the future. I realized that this kind of work in this environment would be my dream job. To work there, however, I almost need a PhD (it's possible with a MS, but a PhD is obviously more competitive). Working at the lab has built friendships and has provided several networking opportunities since. 

Unfortunately, the summer research at the lab doesn't further my dissertation. Working with my advisor does. 

Should I go for the position at the lab for the summer, or should I stay and do research? If I wanted to work with the internship, how would I breach the topic with my advisor?
One unfortunate by-product of the increasingly specialized nature of doctoral research is the tendency to put on "blinders" when it comes time to work on the dissertation: PhD students tend to forget that there are things to study and learn about outside the field of the dissertation. (For example, I always have a few students who complain in the course evaluation "I'm studying X; I shouldn't have to take this mandatory course!")

However, in spite of this, research is becoming inherently more interdisciplinary and interconnected. So having additional experience—and additional contacts—outside your main field can only help you in the long run, if you're planning to pursue a "knowledge-based" career. 

That said, this is definitely a matter you should bring up with your advisor. This early in your career, it's probably not such a big deal to do something else for the summer. But you should still check if there are some important counterarguments (related to funding or project sponsorship).