Exercice 4 - linac

The example 4 illustrates the simulation of a linac head. We first show a full simulation, then split it into two parts. The first part aims at obtaining a phase-space (PhS) from electron source to a plane just before the MLC. The second part makes use of this PhS as a source.

Single step simulation (very slow)

Go into folder linac and run the simulations Gate mac/main.mac

This simulation describe the irradiation of a waterbox from the linac head from the electron source. Look a the geometry and describe what is simulated. Explain the source. Explain the physical processes that occur. Investigate the time needed to obtain a dose distribution in the waterbox with a correct statistical uncertainty.

(Figure from [Grevillot2011])

Two-steps simulation (create PHSP)

Now run the simulation Gate mac/main-write-PhS.mac

Look a the geometry and describe what is simulated. Explain the source. Analyse the PhS with root: once the simulation is completed, type root to enter the root mode. Then, type TBrowser t to obtain a windows that will allow you to load the PhS. Explain what is the content of this PhS. Comment and look at the variance reduction technique in the macro file : what is the splitting ? Why ? Look at the options for generating a PhS, comment them. To exit root, type .q.

Two-steps simulation (use PHSP)

Run the simulation Gate mac/main-read-PhS.mac

This simulation uses the PhS as input, describe it. Compare the time needed to obtain a correct statistical uncertainty in the waterbox. You can use the phase-space in the folder results.MD6k/ that was computed with more particles.

Analysis

Use the python notebook to display and analyse the phase-space file. The notebook is named phsp.ipynb in the linac/ folder. In this notebook, you will find the module uproot that allows to read root file and get the data as numpy array.