For the beta release of the updated campaign structure you will not be able duplicate an entire campaign, but can duplicate ad sets and ads as follows:
Ad sets can be duplicated within the same campaign with the same format, targeting, budget, and schedule details. Ad sets can only be duplicated within the same campaign. Please note: Any ads within the ad set will not be duplicated and will need to be reuploaded to the duplicated ad set.
Ads can be duplicated within the same ad set with the same audio or video file, companion image, call-to-action, and click-through URL. Ads can only be duplicated within the same ad set.
In order to duplicate an ad set or ad you must select a specific campaign or ad set in which you would like to duplicate the new ad set or ad into. This is denoted by the 1x at the top of the dashboard within each tab.
More campaign management help: