[ Identification | Description | Input parameters | Links ]

# The `ESS_moderator` Component

A parametrised pulsed source for modelling ESS long pulses.

## Identification

- Site:
- Author: P Willendrup and E Klinkby, February 2014, derived from K Lefmann ESS_moderator_long
- Origin: DTU
- Date:

## Description

    Produces a time-of-flight spectrum, from the ESS parameters
    Chooses evenly in lambda, evenly/exponentially decaying in time
    Adapted from ESS_moderator_long by: K Lefmann, 2001

    Updates and simplified interface:

    The spectrum from the source(s) is defined via the sourcedef string input parameter which allows these values:

    sourcedef="2001", legacy "Mezei moderators" from the original F. Mezei documents
    "ESS reference moderator characteristics for generic instrument performance evaluation", but rescaled to ESS TDR frequency, pulselength and power.
    sourcedef="TDR", Mezei moderators, with a wavelength-dependent correction term to the cold flux, derived from
    2012 MCNPX calculations by ESS neutronics group. Corrections calculated by K Lieutenant (Vitess) and
    implemented here by E Klinkby. NOTE: uses the 2001 brilliance for the thermal moderator!
    sourcedef="2014", updated brilliance using formulation by Troels Schoenfeldt, including support for the "pancacke", i.e. flat geometry.
    sourcedef="2015", updated brilliance using formulation by Troels Schoenfeldt, new butterfly baseline.

    The component can use target_index for focusing to a given beam port. Use an Arm() and ROTATED to position
    relatively to the moderator.
    The component relies on the new ess_source-lib which is expected to become further enriched during design-finaliziation and construciton of the ESS.

    Note that this component does not implement "engineering reality" and currently uses a coordinate system centered on the moderator assembly. An
    updated moderator component which references the "Moderator focus coordinate system" will be released later during the spring of 2016.

    Derived from ESS_moderator_long which was debugged intensively against Mezei note (4/12 2000) and VitESS @ Rencurel 2006.

    -----------------------------------------------
    Correction by J. Saroun, NPI Rez:
    1) version 2015: accepts negative port angles
    2) version 2015: weight by cosine of the port angle
    Warning: The negative beamport angle is not taken into acccount by mcplot

    %VALIDATION
    Mezei-modererators validated against VitESS and Mezei note (4/12 2000) @ Rencurel 2006
    Benchmarked against multiple versions of ESS moderator group simulation data 2013-2015

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default |
isleft | 1 | Fraction of thermal neutrons generated at the "left" moderator slab in case of "2013" or "2014" | 0.9 |
Lmin | AA | Lower edge of wavelength distribution |  |
Lmax | AA | Upper edge of wavelength distribution |  |
cold_frac | 1 | Fraction of neutron statistics from cold source. It is implicitely assumed that supermirror allows each beamline to choose the desired fraction of cold and thermal neutrons (i.e. extreme idealization). | 1.0 |
dist | m | Distance from source to focusing rectangle; at (0,0,dist) | 0 |
focus_xw | m | Width of focusing rectangle |  |
focus_yh | m | Height of focusing rectangle |  |
target_index | 1 | relative index of component to focus at, e.g. next is +1 this is used to compute 'dist' automatically. | 0 |
tmax_multiplier | 1 | Defined maximum emission time at moderator, tmax= tmax_multiplier * ESS_PULSE_DURATION. Only in combination with sourcedef="2013", "2014" or "2015" | 3 |
yheight_c | m | Height of the cold source | 0.12 |
yheight_t | m | Height of the thermal source | 0.12 |
n_pulses | 1 | Number of pulses simulated. 0 and 1 creates one pulse. The integrated intensity is constant | 1 |
acc_power | MW | Accelerator power in MW | 5 |
beamport_angle | deg | Direction within the beamport sector (0 < angle < extraction_opening for 2014, -extraction_opening/2 < angle < extraction_opening/2 for 2015) to direct neutrons. For sourcedef="2015", the only allowed values are 5,15,...,55 degrees measured from the central point. | -1 |
sourcedef | string | ESS source "database", values: "TDR", "2001", "2013", "2014", "2015" | "2015" |
xwidth_c | m | Width / arc-length opening of the cold source. | 0.1 |
xwidth_t | m | Edge of thermal source | 0.18 |
extraction_opening | deg | Width of extraction-area in degrees (60 or 120 degrees). 120 deg only in combination with sourcedef="2014" and "2015". | 120 |

AT ( | , | , |  | ) RELATIVE |  |
ROTATED ( | , | , |  | ) RELATIVE |

## Links

- Source code for `ESS_moderator.comp`.

[ Identification | Description | Input parameters | Links ]