On March 23rd 1989 Martin Fleischmann and Stanley Pons stunned the world by announcing that had achieved fusion at room temperature on a table-top chemistry experiment - so called "cold fusion". This experiment involved conducting electricity through heavy water and into solid palladium metal (electrolysis) - something that a high school student could in principle do.
Despite the apparent simplicity, the experiments were difficult to reproduce and took 10 weeks to perform. Experimental replications were made over many months in reputable labs, e.g. Los Alamos and SRI international, but the failed high-profile replication attempts done over several days at MIT and Caltech won the day.
Cold fusion was an anathema to fusion physicists. Not only was it considered impossible to produce useful amounts of fusion at low temperatures, but the expected fusion radiation would have killed anyone in the lab. Reasonable skepticism turned into dogmatic opposition where cold fusion scientists were ridiculed in public and accused of being incompetent, delusional and fraudulent.
Despite the words of Nobel prize winner and theoretical nuclear physicist, Julian Schwinger, who cautioned "The circumstances of cold fusion are not those of hot fusion" , the community had made up its mind. Mainstream journals quickly stopped accepting cold fusion papers for review and research drifted into the fringe.
30 years on, the basic science of cold fusion - now called Low Energy Nuclear Reactions (LENR) - has advanced significantly. We now know:
However, we are still missing experiments that are simultaneously reproducible, controllable and produce useful amounts of power.
Finding that "sweet spot" is now the goal.
More technical details
Challenged by one of my physics friends to build a cold fusion demonstration for under £1000, I decided to attempt to replicate the work of Les Case [1-3]. He made cold fusion / LENR happen in a pressurised container of deuterium gas at 3.4 atmospheres at 200C with palladium and coconut shell carbon.
You can follow the progress of my work by visiting to my experimental log on GitLab.
 P. Hagelstein et.al, Appendix B Results of Case Experiments at SRI (2004). (This was Submitted to DoE as part of their second review on LENR)