There have been some posts here, and some reports at conferences, about ketamine. Here's a link to one, from a beloved CB member, "Ricardo." https://clusterbusters.org/forums/topic/4780-ketamine-conference-talk/#comment-50317 You can probably find more by putting ketamine into the search box, top right side of the page.
FWIW, there's a pharma drug, rapastinel, not yet on the market but due fairly soon (next year or two), that works on ketamine receptors without ketamine side effects. So, far, in extensive clinical trials (not for CH, but for depression), zero side effects, period. I have some high hopes for this, though it might, please Lord, be surpassed in efficacy and sooner availability by the monoclonal antibodies currently being tested with what seems to be good promise against migraine and CH. https://en.wikipedia.org/wiki/Rapastinel