US Tourist Visa - Ties to the UK

Hi I am a Nigerian student in the UK and i want to apply for a US tourist visa. However i want to know if i demonstrate strong ties to the UK and what documents are required to show this. I moved to the Uk in 2005 and i have been studying ever since. A-Levels (2yrs), Bachelors (3 yrs), masters (1 year), PhD (4+ years). I am still doing my PhD but i submitted my thesis in july but i still have a Viva at the end of November and i dont officially complete my PhD until middle of january 2016. I also recently obtained my indefinite leave to remain in september. Do i have enough ties to the Uk to apply for a US tourist visa for october 28. I filled in the application i was travelling 8th of November to return for the 15th of November. My Viva/defence date is 27th. I can get my supervisor to put this in writing. My fear is that they can assume that my PhD is almost over and i want to run to the US. Should the UK indefinite leave not negate this? Pls advice. I also have been granted 3 previous US tourist visa before while i was studying in the UK. I have been to the US on three occasions and never overstayed.