You can spend up to three terms out of your mandatory nine working away from Cambridge if your need to use another library, research documents, etc. However, it is not advisable to leave in your first year and you must apply for permission well in advance. For more detailed information, see Applying to Work Away from Cambridge from the Board of Graduate studies (BoGS). Discuss it with your supervisor and tutor then fill in the application form, which can be dowloaded from CamSIS self-service:
If you need leave of absence for other reasons, including illness, maternity, family problems or training/fellowship elsewhere, you can apply for intermission for up to three full-time terms. After consulting your tutor and supervisor, you can obtain the form from CamSIS . If you intermit or work away from Cambridge, you will be exempt from the university composition fee (and often also the college fee) for each term of absence. However, funded students will usually also have to waive or hold over your research grant as well. Someone who wants to work away from Cambridge during their nine terms who has started after October 2010, now no longer has the option to waive fees.