If I’m not wrong, there isn’t exactly a portable version of TOR per se. If you download the installer on to a USB and install it on the USB itself, then it becomes a portable download. If you download it on your PC and install it, it installs in the PC. Remember, the TOR Browser is not like conventional apps (at least in Windows as far as I know). All the required files and modules are installed in a single folder which can be deleted if you want to remove the app (as opposed to a classic uninstall process).