 As beta is a measure of economic merit, a practical tokamak based fusion reactor must be able to sustain a beta above some critical value, which is calculated to be around 5%.Through the 1980s the understanding of the high-n instabilities grew considerably.Shafranov and Yurchenko first published on the issue in 1971 in a general discussion of tokamak design, but it was the work by Wesson and Sykes in 1983 and Francis Troyon in 1984 that developed these concepts fully.