documents required for longest possible tourist visa

If you don't have the invitation letter, then round-trip air tickets and hotel booking are required except for your passport, application form and a recent passport photo. For applying a multiple type, your previous entry records on your passport are useful. And you may provide other valid documents that prove you really need to stay that long. Theoretically, you can apply for a 12 multiple-entry L type. The duration of stay is decided by the consular officers. Usually, it is 30 days.