Can I make Help Center Articles Private to Agents Only?

Can I make Help Center Articles Private to Agents Only?

I want to use the Help Center for internal only documentation that would not be shared with customers who are portal users, just agents. Our default permissions are public/read/write. Is there a way to do this? Assuming I can manage the permissions of the Help Center, is there a way for me to create certain content that is available to portal users (or to specific portal users) vs. what articles would be available to agents?