@Detector¶

The @Detector module is a submodule of the @Radiation tool. This module configures the radiation detector to use, and sets properties such as its position, viewing direction, field-of-view, spectral range and more.

When specifying detector position, the following illustration of the coordinate system assumed in SOFT can be useful:

Summary of options¶

Option	Description
`aperture`	Aperture size / square side length
`direction`	Viewing direction / detector plane normal vector
`optics`	Detector optics settings
`position`	Position relative to tokamak point-of-symmetry
`vision_angle`	Detector vision angle (field-of-view (half) opening angle)
`spectrum`	Spectral range configuration of detector
`roll`	Angle between \(\hat{e}_1\) and the horizontal plane.

Detector plane basis¶

The detector plane is spanned by two vectors which we refer to as \(\hat{e}_1\) and \(\hat{e}_2\). Together with the detector viewing direction (or normal vector) \(\hat{n}\) they form an orthonormal basis in space. The vectors \(\hat{e}_1\) and \(\hat{e}_2\) are used for several purposes, but one of the more important purposes is for spanning the camera images that this @RadiationOutput produces.

The vector \(\hat{e}_1\) is defined so that it always lies in the horizontal plane when the roll angle is zero. Its mathematical definition is

\[\begin{split}\hat{e}_1 = \begin{cases} \hat{y}\cos\vartheta + \hat{z}\sin\vartheta, \quad&\text{ if } \hat{n}\cdot\hat{y} = 0,\\ \left[ \hat{x}\left(\hat{n}\cdot\hat{y}\right) - \hat{y}\left( \hat{n}\cdot\hat{x} \right)\right]\cos\vartheta + \hat{z}\sin\vartheta, \quad&\text{ otherwise}. \end{cases}\end{split}\]

where \(\vartheta\) denotes the angle between \(\hat{e}_1\) and the horizontal plane (the “roll angle”). From this, \(\hat{e}_2\) is defined so that \((\hat{e}_1, \hat{e}_2, \hat{n})\) form a right-handed orthonormal basis:

\[\hat{e}_2 = \hat{n}\times\hat{e}_1.\]

The values of both of these vectors are output on stdout by SOFT during execution.

Example configuration¶

This example configuration of a detector corresponds to wide-angle visible camera located in the midplane of a medium-sized tokamak:

@Detector example_detector {
    aperture     = 0.006;              # in meters
    direction    = 0, 1, 0;            # x,y,z
    position     = 0, 1.7, 0;          # x,y,z (relative to point of symmetry)
    vision_angle = 1.25 fov;           # Field-of-view (half) opening angle
    spectrum     = 440e-9, 790e-9, 40; # Lower wavelength (m), Upper (m), Number of points
}

Options¶

aperture¶: Default value: None

Allowed values: Any positive real number

Size of detector aperture. All detectors are modeled as squares in SOFT, with the aperture specified here corresponding to the square side length.

direction¶: Default value: None

Example line: direction = 1.3, -0.25, 0;

Allowed values: Any real 3-vector except null

Detector viewing direction, i.e. normal vector of the detector plane. This vector is normalized internally by SOFT to become a unit vector, and does not have to specified as a unit vector.

optics¶: Default value: korger

Allowed values: korger

Specifies which model to use for the detector optics. At the moment, the detector optics in principle only specifies whether or not to apply any polarization filters, but could in principle in the future be used to apply any kind of detector transfer function. For now, the default value of this option is the only possible one, and so there is no need to set this option specifically.

position¶: Default value: None

Example line: position = 0, -1.069, 0;

Allowed values: Any real 3-vector except null

Detector position relative to the tokamak point-of-symmetry. Units used for the vector components are meters.

vision_angle¶

Default value: None
Example line: vision_angle = 0.75 image;
Allowed values: Real number, optionally followed by either fov or image

Specifies the half opening angle of the field-of-view. If only a number is given, then it is implied that the fov opening angle is specified.

A camera image will be a square inscribed in the circular field-of-view. By appending image after the real number, you indicate that the given vision angle is the minimum angle between a vector extending from the detector to the side of the image, and the detector normal. In a 2D top view, if a cone with the specified image vision angle was plotted, this would correspond exactly to the edges of the observed image.

spectrum¶

Default value: no
Example line: spectrum = 785e-9, 795e-9, 10;
Allowed values: (i) Vector of two positive real numbers and one positive integer, or (ii) no

Sets the limits and resolution of the detector spectral range. If the number of spectral points is 0, or if this parameter is assigned the boolean no value, the detector will have an infinite spectral range.

The numbers given to the spectral range specify (i) the lower spectral bound, (ii) the upper spectral bound, and (iii) the number of points on the interval. The units of the bounds depend on the emission model used. The synchrotron emission models will assume that the spectrum limits are wavelengths given in units of meters. The bremsstrahlung models assume that the spectrum limits are photon energies, given in normalized units (normalized to \(m_e c^2\), the electron mass times speed-of-light squared).

roll¶

Default value: 0
Example line: roll = 0.1 cw;
Allowed values: Real number, optionally followed by either cw or ccw

Specifies the angle in radians by which the image x axis, \(\hat{e}_1\) is rotated with respect to the horizontal plane (the x/y plane). By default, this parameter is 0, so that \(\hat{e}_1\cdot\hat{z} = 0\). If no direction is specified, a positive angle corresponds to rotation in the counter-clockwise (CCW) direction.

Optionally, the direction of rotation can be explicitly specified by appending either cw (positive angle in clockwise direction) or ccw (positive angle in counter clockwise direction) after the roll angle.