The published article incorrectly contains a placeholder reference to an equation (“(??)”) on page 2, paragraph 2, line 4:
“The high-beta, β ~ 1, regime has been explored previously in the context of asymptotic magnetohydrodynamic (MHD) equilibria by solving the Grad–Shafranov equation in the limit 
$\epsilon/(\beta q^2)\ll1$ (Hsu, Artun & Cowley 1996) where 
$\epsilon$ is the aspect ratio of the tokamak and q is the safety factor defined in (??):.”
The placeholder (“(??)”) should have been replaced by a pinpoint reference to equation 2.2 (“(2.2)”), as follows:
“The high-beta, β ~ 1, regime has been explored previously in the context of asymptotic magnetohydrodynamic (MHD) equilibria by solving the Grad–Shafranov equation in the limit 
$\epsilon/(\beta q^2)\ll1$ (Hsu, Artun & Cowley 1996) where 
$\epsilon$ is the aspect ratio of the tokamak and q is the safety factor defined in (2.2).”
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