Jetstream allocations are awarded exclusively through the eXtreme Science and Engineering Discovery Environment (XSEDE). XSEDE provides XSEDE User Portal (XUP) accounts free of charge. XSEDE allocations require that the Principal Investigator (PI) be a US-based researcher.
A guide with more detail on Jetstream allocations is available online at https://portal.xsede.org/web/guest/resources/overview. Samples of successful requests are available here, https://portal.xsede.org/allocations/research .
You'll need to have an XSEDE Portal account to apply for an allocation. If you already have an XSEDE Portal account, skip to the box titled "Apply for an XSEDE allocation".