.. _QE Coverage:

QE Coverage
===========

.. contents:: Table of Contents
  :local:

.. figure:: /images/QECoverage.png
   :alt: QECoverage.png
   :align: right
   :width: 455

Overview
--------

QECoverage is a small planning tool to allow inelastic neutron scattering users
to determine graphically the momentum / energy transfer limits for a given
spectrometer and fixed energy.

Options
------------------

To use, select the geometry (direct or indirect) and instrument from the tabs
and drop-down menu. For direct geometry spectrometers, an incident energy (Ei)
in meV must be given; for indirect geometry machines, the final energies are
fixed at a few values which must be selected from the drop-down menu. Only positive
values of Ei are permitted. Several Q-E trajectories can be plotted simultaneously
by providing several Ei values separated by commas.

To overplot the calculated Q-E trajectories, set the "Plot Over" check box.

The plot range is from Emin to Ei for direct, and from -Ef to Emax for indirect
geometry spectrometers, and Emin and Emax may be inputted in the appropriate text
box. If the input for Emin is invalid or bigger than min(Ei), then Emin is
automatically set to Emin = -max(Ei)/2 for direct (indirect) geometry.

You can choose to create a 1D Mantid workspace for latter plotting using the
"Create Workspace" check box.

In addition, for HYSPEC, where the detector bank can be rotated, an additional
parameter **S2** denoting the scattering angle of the center of the detector
bank is required. The detectors extend over 60 degrees, so the two theta limits
will be taken from max([0, abs(s2)-30]) to abs(s2)+30.

The Q(E) trajectory is calculated from the kinematic conditions:

:math:`\Delta E = E_i - E_f`

and

:math:`\frac{\hbar^2 \mathbf{Q}^2}{ 2 m_n } = E_f + E_i - 2 \sqrt{E_i E_f} \cos{2\theta}`

which is then solved for known :math:`E_i` (:math:`E_f`) for direct
(indirect) geometry.

.. categories:: Interfaces