How to say no to more work as a PhD student so I can graduate
I think your most realistic option is to have an honest discussion with your advisor about your goals and expectations.
Tell them that you’d like to graduate by 20xx, and you think your work on A B C was fulfilling and interesting. You feel like you can really build a narrative around these projects that would culminate in a good thesis within the timeframe set above. Given your goal, you feel like starting a new project at this time will be detrimental to your progress.
Ideally your advisor would totally see it your way and you’ll graduate into the sunset. Realistically: advisors tend to be overzealous at times and can exert a lot of pressure over their students. A reasonable advisor would leave the choice to you; a clever one will make you believe that it’s a really good idea to start this new project (you don’t have enough material now, your CV will be amazing with the new project accomplished...). So a lot of this depends on the dynamics you have with your advisor.
I would not go over their head unless you’re willing and able to switch advisors. Its hard to get back to a good working relationship after something like that.
I will try to establish my own independence and capacity to successfully graduate with a plan (by 20yy I plan to submit these results, draft by Jan 20zz and so on).
Good luck!
Lots of good advice in @Spark's answer. I would add that you might suggest mentoring an new student to take over the project when you are gone. You can advise them on the design while you focus on writing your last two papers. This is a reasonably common practice, at least in the fields I have worked in. This should have a number of advantages from all perspectives:
- Your adviser will get your help training the new student to take over which means they will have 5 more years of work on the project rather than just the 1.5 they can get from you.
- It takes the burden of the new project off your shoulders while still providing a mechanism for the work to get done.
- If it isn't worth your adviser's efforts to recruit a new student for the project, then it shouldn't be worth your time either. Making your adviser have to make the first effort toward moving the project forward will demonstrate how much they really care about making it happen.
- By helping the new student, you might be able to get your name on some of their papers even after you graduate.
Adding on to Sparks answer, it would be helpful to provide context to your planned graduation date. A reason to graduate by a certain date presented with reasoning from a different angle makes it more difficult for the professor to counter argue.
Drawing reasons for example from:
- Family - presence needed, marriage or impending split/divorce, pregnancy or desire to get pregnant by a certain age due to fertility
- Work - money needed, job offer, etc
- Visa - although this is specific to your case
- Relocation - plan to move elsewhere for some reason or another
Whether you actually are going to carry through with the reasoning and how truthful the reasoning is up to you. Just try not to be blatantly false that you'll get caught