This notebook was created by Sergey Tomin for Workshop: Designing future X-ray FELs. Source and license info is on GitHub. August 2016.
Ocelot is a multiphysics simulation toolkit designed for studying FEL and storage ring based light sources. Ocelot is written in Python. Its central concept is the writing of python's scripts for simulations with the usage of Ocelot's modules and functions and the standard Python libraries.
Ocelot includes following main modules:
Ocelot extensively uses Python's NumPy (Numerical Python) and SciPy (Scientific Python) libraries, which enable efficient in-core numerical and scientific computation within Python and give you access to various mathematical and optimization techniques and algorithms. To produce high quality figures Python's matplotlib library is used.
It is an open source project and it is being developed by physicists from The European XFEL, DESY (Germany), NRC Kurchatov Institute (Russia).
We still have no documentation but you can find a lot of examples in ocelot/demos/
Ocelot is designed for researchers who want to have the flexibility that is given by high-level languages such as Matlab, Python (with Numpy and SciPy) or Mathematica. However if someone needs a GUI it can be developed using Python's libraries like a PyQtGraph or PyQt.
For example, you can see GUI for SASE optimization (uncomment and run next block)
In [1]:
from IPython.display import Image
#Image(filename='gui_example.png')
All IPython (jupyter) notebooks (.ipynb) have analogues in the form of python scripts (.py).
All these notebooks as well as additional files (beam distribution, wakes, ...) you can download here.
The tutorial includes 4 simple examples dediacted to beam dynamics. However, you should have a basic understanding of Computer Programming terminologies. A basic understanding of Python language is a plus.
numpy version 1.8 or later: http://www.numpy.org/scipy version 0.15 or later: http://www.scipy.org/matplotlib version 1.5 or later: http://matplotlib.org/ipython version 2.4 or later, with notebook support: http://ipython.orgThe easiest way to get these is to download and install the (very large) Anaconda software distribution.
Alternatively, you can download and install miniconda. The following command will install all required packages:
$ conda install numpy scipy matplotlib ipython-notebookAdd ../your_working_dir/ to PYTHONPATH
Windows 7: go to Control Panel -> System and Security -> System -> Advance System Settings -> Environment Variables. and in User variables add ../your_working_dir/ to PYTHONPATH. If variable PYTHONPATH does not exist, create it
Variable name: PYTHONPATH
Variable value: ../your_working_dir/
$ export PYTHONPATH=**../your_working_dir/**:$PYTHONPATHin command line run following commands:
$ ipython notebookor
$ ipython notebook --notebook-dir="path_to_your_directory"or
$ jupyter notebook --notebook-dir="path_to_your_directory"
In [2]:
import IPython
print('IPython:', IPython.__version__)
import numpy
print('numpy:', numpy.__version__)
import scipy
print('scipy:', scipy.__version__)
import matplotlib
print('matplotlib:', matplotlib.__version__)
import ocelot
print('ocelot:', ocelot.__version__)
In [3]:
from __future__ import print_function
# the output of plotting commands is displayed inline within frontends,
# directly below the code cell that produced it
%matplotlib inline
# import from Ocelot main modules and functions
from ocelot import *
# import from Ocelot graphical modules
from ocelot.gui.accelerator import *
In [4]:
# defining of the drifts
D1 = Drift(l=2.)
D2 = Drift(l=0.6)
D3 = Drift(l=0.3)
D4 = Drift(l=0.7)
D5 = Drift(l=0.9)
D6 = Drift(l=0.2)
# defining of the quads
Q1 = Quadrupole(l=0.4, k1=-1.3)
Q2 = Quadrupole(l=0.8, k1=1.4)
Q3 = Quadrupole(l=0.4, k1=-1.7)
Q4 = Quadrupole(l=0.5, k1=1.3)
# defining of the bending magnet
B = Bend(l=2.7, k1=-.06, angle=2*pi/16., e1=pi/16., e2=pi/16.)
# defining of the sextupoles
SF = Sextupole(l=0.01, k2=1.5) #random value
SD = Sextupole(l=0.01, k2=-1.5) #random value
# cell creating
cell = (D1, Q1, D2, Q2, D3, Q3, D4, B, D5, SD, D5, SF, D6, Q4, D6, SF, D5, SD, D5, B, D4, Q3, D3, Q2, D2, Q1, D1)
hint: to see a simple description of the function put cursor inside () and press Shift-Tab or you can type sign ? before function. To extend dialog window press +
The cell is a list of the simple objects which contain a physical information of lattice elements such as length, strength, voltage and so on. In order to create a transport map for every element and bind it with lattice object we have to create new Ocelot object - MagneticLattice() which makes these things automatically.
MagneticLattice(sequence, start=None, stop=None, method=MethodTM()):
other paramenters we will consider in tutorial N2.
In [5]:
lat = MagneticLattice(cell)
# to see total lenth of the lattice
print("length of the cell: ", lat.totalLen, "m")
Uses:
To calculate twiss parameters you have to run twiss(lattice, tws0=None, nPoints=None) function. If you want to get a periodic solution leave tws0 by default.
You can change the number of points over the cell, If nPoints=None, then twiss parameters are calculated at the end of each element. twiss() function returns list of Twiss() objects.
In [6]:
tws=twiss(lat)
# to see twiss paraments at the begining of the cell, uncomment next line
# print(tws[0])
# to see twiss paraments at the end of the cell, uncomment next line
print(tws[-1])
In [7]:
len(tws)
Out[7]:
In [8]:
# plot optical functions.
plot_opt_func(lat, tws, top_plot = ["Dx", "Dy"], legend=False, font_size=10)
plt.show()
# you also can use standard matplotlib functions for plotting
#s = [tw.s for tw in tws]
#bx = [tw.beta_x for tw in tws]
#plt.plot(s, bx)
#plt.show()
In [9]:
# you can play with quadrupole strength and try to make achromat
Q4.k1 = 1.18
# to make achromat uncomment next line
# Q4.k1 = 1.18543769836
# To use matching function, please see ocelot/demos/ebeam/dba.py
# updating transfer maps after changing element parameters.
lat.update_transfer_maps()
# recalculate twiss parameters
tws=twiss(lat, nPoints=1000)
plot_opt_func(lat, tws, legend=False)
plt.show()