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# another symbol: \iotaslash or \iotabar

• To: math-font-discuss@cogs.susx.ac.uk
• Subject: another symbol: \iotaslash or \iotabar
• From: vieth@convex.rz.uni-duesseldorf.de (Ulrik Vieth)
• Date: Wed, 25 Aug 93 16:33:48 +0200

Although I don't want to make it a habbit, pestering you with new
symbols every week, here's another one I'd like to consider:

\iotabar and/or \iotaslash (very similar to \hbar and/or \hslash)

* Usage:

In plasma physics, especially in fusion reserarch, $\iotabar$ and/or
$\iotaslash$ are used to denote the rotational transform of magnetic
field lines in toroidal plasma confinements. Like $\hbar$ in quantum
mechanics, $\iotabar$ is defined as

\iotabar = \iota / 2\pi

where $\iota$ is the inverse of a so-called quality factor $q$.
(Incidently, one branch of plasma physicsist prefers to use $q$
while the other branch prefers $\iotaslash$, I just can't remember
which were the tokamak physicsts and the stellerator physicists.)

* References:

In a quick, but not extensive, search through the library, I found
examples of its use in

J.Wesson: Tokamaks, Oxford Univ. Press

and probably some other specialist books on fusion machines.
(Look for keywords like rotational transform and quality factor.)

I've also seen some books where the author used clumsy expressions
like $2\pi/\iota$ repeatedly, probably for lack of a suitable
$\iotabar$ symbol.

* TeXnicalities:

In principle, $\iotabar$ is constructed similar to $\hbar$ by putting
a little bar across the stem. However the plain.tex macro for $\hbar$
can't be used for $\iotabar$ since it needs to be lowered as well.

To avoid problems in complicated constructions, separate glyphs like
$\hbar$ and $\hslash$ in msbm would be preferable, but that adds
another two glyphs to the MC font, or even four more if it's included
in both the italic and the upright greek. However, there are certainly
some people in a rather specialized field, who would definitely like
to see $\iotabar$ and/or $\iotaslash$ included. Maybe $\hbar$ in QM
is more common, but somehow that's a rather specialized field, too.

Now, it's up to you to decice.

Greetings,

Ulrik.

P.S. A general question: would it be a good idea to post a query
about the need for specialized symbols on some of the major sci.*
newsgroups? Quite a lot of people in math, physics, etc use TeX
for their papers, but most of them aren't aware of this working
group. So questions to this list like: Do we really need this
or that symbol?'' probably don't reach a wide enough audience.