**********************
PMT 2D Uniformity Scan
**********************

=========
Rationale
=========

The PMT response is mostly measured with perpendicular light incident on the
middle of the photocathode. This measurement aims to characterize the PMT
response over the whole photocathode relative to the behavior at the center.

This is done by comparing accumulated charges at each scan point to the center.
Since we compare charges, this measurement is done at MPE level.

=====
Setup
=====

The PMT is mounted inside the 2D scan box as in the gain vs. HV scan. The
oscilloscope used is the R&S RTO1044 next to *ratafia*. Its settings for this
measurement can be found in Ayumis
:download:`sheet <../../downloads/main_1p.pdf>`.

Aim for an average of 60-70 photoelectrons when setting the laser intensity.

===============
Running the DAQ
===============

The DAQ lives in a *jupyter notebook*, which is located at::

    /home/icecube/measurements/daq/notebooks/2d_cathode_scan.ipynb

It records 200 DEgg waveforms for every scanpoint on a 2D grid in zenith and
azimuth. The binning is very fine, with 72 bins in azimuth and 64 bins in
zenith. The motors are automatically controlled and will return to the central
position after the scan is done.

========
Analysis
========

To get an overview of commands to run for the analysis of the data, see::

    /home/icecube/measurements/analysis/workspace/cathode_scan/README

First, the waveforms are processed, then tables for the uniformity scan are
built. Finally, a 2D polar plot is made to show the uniformity of the cathode.

.. container:: toggle

    .. container:: header

        **Show/Hide typical plot**

    .. figure:: ../../images/plots/pmt_uniformity/cemap_sq0291_20190603.png
        :align: right

        Example polar uniformity plot