Here is a link to a company that sells straight-up ginger juice. Good quality, from my personal experience. They add citric acid, presumably as a mold inhibitor/preservative, but other than that it's pure.
Most of the articles I find on the internet talk about the whole root form rather than the juice. The same site has a section of articles regarding the benefits of ginger for health.
When I was doing ginger shots, I was working as the nutritionist at a large scale health food co-op. They juiced ginger and I took 1-3 ounces a day. Zesty! Packed a punch but made me feel great. Now that I am working independently, I juice my own and either take it straight or mixed with other vegetable juices.
Hope this information is useful. Thank you for being such a positive influence on this forum. I admire your objectivity. Have a great day!