TITLE: Is every finite separable extension of a strictly henselian DVR totally ramified?
QUESTION [5 upvotes]: Let $R$ be a discrete valuation ring with field of fraction $K$ and residue field $k$ and let $K'$ be a finite and separable extension of $K$.
If $R$ is henselian ("Hensel's lemma holds", e.g. if it is complete) and $k$ is algebraically closed then the extension $K'|K$ is totally ramified (from Hensel's lemma if follows that there's just one prime lying above the prime of $R$ and since $k$ is algebraically closed there's no residual extension).
What happens if we assume only that $R$ is strictly henselian (i.e. that $k$ is only separably closed)?
Equivalently: does it exist a finite separable extension $K'$ of $K$ such that the residual extension is a nontrivial inseparable extension?
I believe that such an extension should exist.
Moreover, can we find a Galois extension with this property?
Can we do this both in characteristics $(0,p)$ and $(p,p)$?

REPLY [3 votes]: Let $k$ a separably closed imperfect field of char. $p$. Fix $t \in k$ for which $X^p - t \in k[X]$ has no root in $k$.
Set $K = k((s))$, and form the extension $L = K(y) \supset K$ obtained by adjoining to $K$ a root $y$ of the poly. $f(Y) = Y^p + sY - t \in K[Y]$. 
Write $A = k[[s]]$ for the integers of $K$. Since the image of $f(Y)$ in $k[Y] = (A/sA)[Y]$ is irreducible, $f(Y)$ is irreducible in $A[Y]$ and hence in $K[Y]$. Since $f'(Y) = s \ne 0$, it follows that $L/K$ is separable.
Now write $B$ for the integral closure of $A$ in $L$; thus $y \in B$. Denoting by $\pi$ a uniformizer for the DVR $B$, note that $s \in \pi B$. Thus the image of $y$ in $\ell = B/\pi B$ is a $p$-th root of $t$, so $\ell$ is a proper (purely) inseparable extension of $k$.
EDIT:  In hindsight, it seems that with minor tweaking the same argument gives an answer in the "mixed characteristic" case.
Indeed, let $t \in k$ as before, and now let $A$ a complete (or Henselian) DVR with residue field $k$ and with fractions $K$ of char. 0. Now choose an element
$\tau \in A$ whose image in $k$ is $t$. Let $\sigma \in A$ be a uniformizer,
and set $f(Y) = Y^p + \sigma Y - \tau \in A[Y]$.  Then as before the extension $L = K(y)$ of $K$ is separable, where $y$ is a root of $f(Y)$. And the residue extension is again inseparable.