Toroidal Alfven eigenmodes and a new class of modes, the Alfven cascades, e
xcited by energetic ions are observed in the JET tokamak. Measurements of t
hese Alfven instabilities are used to solve the inverse problem of identify
ing the plasma parameters using the dependence of the Alfven spectrum on eq
uilibrium parameters. Crown copyright (C) 2001 Published by Elsevier Scienc
e B.V. All rights reserved.