# DepositionPointCharge

Status | Functional |

Maintainers |
Simon Spannagel (simon.spannagel@cern.ch) |

Output Objects |
DepositedCharge MCParticle |

## Description

Module which deposits a defined number of charge carriers at a specific point within the active volume the detector. The number of charge carriers to be deposited can be specified in the configuration.

Two different source types are available:

- The
`point`

source deposits charge carriers at a specific point in the sensor, which can be configured via the`position`

parameter with three dimensions. The number of charge carriers deposited can be adjusted using the`number_of_charges`

parameter. - The
`mip`

model allows to deposit charge carriers along a straight line through the sensor, perpendicular to its surface. Charge carriers are deposited linearly along this line with a configurable number of electron-hole pairs per length. The number of steps through the sensor can be configured using the`number_of_steps`

parameter, the position can be given in two dimensions via the`position`

parameter and the number of charge carriers per length are taken from the`number_of_charges`

parameter.

This module supports three different deposition models:

- In the
`fixed`

model, charge carriers are always deposited at exactly the same position, specified via the`position`

parameter, in every event of the simulation. This model is mostly interesting for development of new charge transport algorithms, where the initial position of charge carriers should be known exactly. - In the
`scan`

model, the position where charge carriers are deposited changes with every event. The scanning positions are distributed such, that the volume of one pixel cell is homogeneously scanned. The total number of positions is taken from the total number of events configured for the simulation. If this number doesn’t allow for a full illumination, a warning is printed, suggesting a different number of events. The pixel volume to be scanned is always placed at the center of the active sensor area. The scan model can be used to generate sensor response templates for fast simulations by generating a lookup table from the final simulation results. - In the
`spot`

model, charge carriers are deposited in a Gaussian spot around the configured position. The sigma of the Gaussian distribution in all coordinates can be configured via the`spot_size`

parameter. Charge carriers are only deposited inside the active sensor volume.

Monte Carlo particles are generated at the respective positions, bearing a particle ID of -1. All charge carriers are deposited at time zero, i.e. at the beginning of the event.

## Parameters

`model`

: Model according to which charge carriers are deposited. For`fixed`

, charge carriers are deposited at a specific point for every event. For`scan`

, the point where charge carriers are deposited changes for every event. For`spot`

, depositions are smeared around the configured position.`number_of_charges`

: Number of charges deposited. This refers to the total number of charge carriers for the source type`point`

and defaults to 1. For the`mip`

source type, this value is interpreted as charge carriers per length deposited in the sensor and defaults to`80/um`

. It should be noted that without units specified, this value will be interpreted in the framework base units, in this case`/mm`

.`number_of_steps`

: Number of steps over the full sensor thickness at which charge carriers are deposited. Only used for`mip`

source type. Defaults to 100.`source_type`

: Modeled source type for the deposition of charge carriers. For`point`

, charge carriers are deposited at the position given by the`position`

parameter. For`mip`

, charge carriers are deposited along a line through the full sensor thickness. Defaults to`point`

.`position`

: Position in local coordinates of the sensor, where charge carriers should be deposited. Expects three values for local-x, local-y and local-z position in the sensor volume and defaults to`0um 0um 0um`

, i.e. the center of first (lower left) pixel. When using source type`mip`

, providing a 2D position is sufficient since it only uses the x and y coordinates. If used in scan mode, it allows you to shift the origin of each deposited charge by adding this value. If the scan is only performed in one or two dimensions, the remaining coordinate will constantly have the value given by`position`

.`spot_size`

: Width of the Gaussian distribution used to smear the position in the`spot`

model. Only one value is taken and used for all three dimensions.`scan_coordinates`

: Coordinates to scan over, a combination of x, y, z. Only used for the`scan`

model. Defaults to`x y z`

, i.e. all three spatial coordinates. The`position`

parameter is used to determine the value of the coordinates that are not scanned over if a partial scan is requested, and the start offset of the scan for the other coordinates.`mip_direction`

: Vector giving the direction of the line along which deposits are made when the`mip`

source type is used. Defaults to`0 0 1`

, i.e. along the z-axis. The`position`

keyword gives a point that the line of depositions will cross through with this direction.

### Plotting parameters

`output_plots`

: Determines if output plots should be generated. Disabled by default.`output_plots_bins_per_um`

: Number of bins per micrometer in all directions in the 2D histograms used to plot deposition position. Only used if`output_plots`

is enabled.

## Usage

Example configuration for a point source at a defined position around which 100 charge carriers are deposited with a Gaussian distribution:

```
[DepositionPointCharge]
source_type = "point"
model = "spot"
position = -10um 10um 0um
spot_size = 3um
number_of_charges = 100
```

Example configuration for a point source scanned over the x and y cooridantes, with a fixed z coordinate of 10 micrometers (with the sensor center at 0):

```
[DepositionPointCharge]
source_type = "point"
model = "scan"
scan_coordinates = x y
position = 0um 0um 10um
number_of_charges = 100
```

Example configuration for a MIP-like energy deposition along a line at a fixed position, with 63 electron-hole pairs deposited per micrometer of sensor material:

```
[DepositionPointCharge]
source_type = "mip"
model = "fixed"
position = -10um 10um
number_of_steps = 100
number_of_charges = 63/um
```