STRIP polarimeter tuning

This repository contains a number of Python program which can be used to analyze the Strip tuning data. These data have been acquired during the unit tests done in the laboratories at the University of Milano Bicocca in 2017.

The following programs have been implemented so far:

1. Striptun reads the data acquired with the Keithley machine used at the Bicocca labs and produces a report containing the tuning parameters of the six HEMTs used in Strip's polarimeters.
2. Tnoise reads the data acquired during the so-called «Y-factor» test and runs an analysis to determine the gain and the noise temperature of the polarimeter.
3. Average output determines the average output of a test. It is mainly used to study the data acquired with all six HEMTs turned off, in order to estimate the average ADU offset to be removed from the PWR data.

All the programs save the results of their calculations in JSON files, and they are able to produce reports in Markdown and HTML formats. The Markdown format is useful when used in conjunction with the program Pandoc, as it can be easily converted to a variety of other formats (LaTeX, Microsoft Word, etc.).

This repository contains a database of the parameters used during the tests in Bicocca (https://github.com/lspestrip/striptun/blob/master/polarimeter_info.yaml), which is used by the scripts listed above. Any operator should update this file any time a new polarimeter is tested. If you do not have access rights to this repository, you should fork the repository, make your changes, and open a pull request.

Installation

All the programs need the following packages:

• Mako (templating engine)
• Markdown (markdown to HTML conversion)
• Matplotlib (plotting library)
• NumPy (vector/matrix operations)
• SciPy (interpolation)
• SimpleJSON (JSON export)
• Xlrd (Excel file importing)

If you are using Anaconda Python, you can install them using the command conda:

conda install mako markdown matplotlib numpy scipy simplejson xlrd

In any other case, you can use pip:

pip install mako markdown matplotlib numpy scipy simplejson xlrd

Striptun

This program can be used to find the optimal setpoint for the HEMT biases of a polarimeters. It tries to balance the two legs by computing the transconductance of each amplifying stage. It requires the full set of Excel files produced by the Keithley apparatus.

Usage

The program does not need to be installed. Just run it with the following parameters:

python striptun.py POLARIMETER_NAME INPUT_PATH OUTPUT_PATH

The meaning of the parameters is the following:

• POLARIMETER_NAME is a string identifying the polarimeter (e.g., STRIP07)
• INPUT_PATH is the name of the directory containing the files produced by Keithley (usually the name is prove_DC, or something similar)
• OUTPUT_PATH is the name of the directory that will contain the report (if the directory does not exist, it will be created silently)

At the end of the execution, the directory OUTPUT_PATH will contain the following files:

1. A JSON file named striptun_results.json, containing the results of the analysis;
2. A Markdown file named striptun_report.md;
3. An HTML file named striptun_report.html.

Example

The following is the beginning of an HTML report produced by the script striptun.py:

How the program works

The program runs the following steps:

1. Read all the Excel files saved by Keithley
2. From the Vd versus Id curve, compute TransHEMT (see below) and plot Vd versus TransHEMT
3. Plot Vd versus Ig and Vg versus Id
4. Set Vd to 0.9 V and find Id ≈ 4 mA (Q1, Q6), Id ≈ 7 mA (Q2, Q5)
5. Find TransHEMT for the Vd and Id found in the previous step
6. Set Vd to 0.9 V and find Id ≈ 6 mA for Q3
7. Find the configuration which maximizes the match between the product of the transconductances across the two legs (Q1→Q2→Q3 and Q6→Q5→Q4)
8. Save all the plots
9. Generate a Markdown report and an HTML report

Transconductance

The formula used to compute transconductance is the following:

TransHEMT = 1e3 * (Id2 - Id1) / ((Vg2 - Vg1) - 1e4 * (Ig2 - Ig1))

where pairs like (Id1, Id2) refer to two consecutive lines with different values of Vg. The factor 1e4 is a resistance, and its presence seems to be due to the partitor.

Tnoise

Two programs are implemented to compute the noise temperature. The first one, tnoise_step1.py, automatically detects the time spans where the signal of the polarimeter was stable enough to assume thermal equilibrium. The output of this program is used by the second program, tnoise_step2.py, to run a frequentist/Bayesian analysis on the data and extract the best value of the gain and noise temperature of the amplifier.

Usage (step 1)

To run the first program, use the following parameters:

python tnoise_step1.py POLARIMETER_NAME INPUT_FILE_NAME OUTPUT_PATH

The meaning of the parameters is the following:

• POLARIMETER_NAME is a string identifying the polarimeter (e.g., STRIP07)
• INPUT_FILE_NAME is the name of the text file containing the raw data (in tabular format) acquired during the test.
• OUTPUT_PATH is the name of the directory that will contain the report (if the directory does not exist, it will be created silently)

At the end of the execution, the directory OUTPUT_PATH will contain the following files:

1. A JSON file named tnoise_results.json, containing the results of the analysis;
2. A Markdown file named tnoise_report.md;
3. An HTML file named tnoise_report.html.

The most important result saved by this program is a list of the regions in the data file where the signal is stable enough to be used in the next step of the analysis, the determination of the gain and the noise temperature for the polarimeter.

Usage (step 2)

To run the second program, you must have ran tnoise_step1.py first, as it requires the JSON file containing the list of temperature steps. The data for the test must have been saved in the test database as well: if this is not the case, you must provide a custom test database in YAML format (through the --test-db-path switch).

The code supposes the following model:

PWR = 1/4 * (1/2 * (G_A^2 + G_B^2) * (T_A + T_B + 2 T_N) ± trig * G_A * G_B * (T_A - T_B) )

where G_A and G_B are the gains of the two legs of the polarimeter, in , T_A and T_B are the brightness temperatures of the two loads, trig is either cosΔφ or sinΔφ, the term due to the phase difference of the two phase shifter states. The value of trig, as well as the sign of ±, depend on the power output and the configuration of the phase switches. The code automatically finds which is the case by determining the number of the «blind channel», i.e., the channel that stays fixed while load B is changing. The code tries to find a simultaneous fit for these three parameters:

• 1/2 * (G_A^2 + G_B^2) is the average gain of the polarimeter, in K/ADU
• G_A * G_B is the product of the gains of the polarimeter, in K/ADU
• T_N is the overall noise temperature, equal to (G_A^2 * T_A + G_B^2 * T_B) / (G_A^2 + G_B^2)

The usage of tnoise_step2.py is the following, use --help to get full help about all the (many) command-line switches:

python tnoise_step2.py POLARIMETER_NAME RAW_FILE TNOISE1_RESULTS OUTPUT_PATH

The meaning of the parameters is the following:

• POLARIMETER_NAME is the name of the polarimeter. This must match the entry in the test database polarimeter_info.yaml.
• RAW_FILE is the text file containing all the data acquired during the test
• TNOISE1_RESULTS is the JSON file produced by tnoise_step1.py, which contains the analysis of the data in RAW_FILE
• OUTPUT_PATH is the name of the directory where results will be saved. This can be the same directory as the one created by tnoise_step1.py, as there will be no clashes in file names.

By default, the code runs a frequentist analysis of the data, which assumes that errors are Gaussian and is extremely fast; the Gaussian hypothesis has been tested on real data and holds with large confidence. The code is able to run a Bayesian analysis through a Monte Carlo Markow Chain (MCMC) approach, which is much slower but potentially more insightful. To run the MCMC analysis, use the --mcmc flag.

Average output

This small program does exactly what it says: it computes the average of the columns PWR0, PWR1, PWR2, and PWR3 in the raw text files acquired in Bicocca. The name of the script is output_average.py, use the --help flag to get the command-line help.

Biases

This program produces a HTML report containing the configuration of the HEMT biases used during a test. Its usage is similar to the other scripts in the repository.