[ Identification | Description | Examples | Input parameters | Links ]
NXdisk_chopper ComponentOne component per physical disc, however many openings it has. `DiskChopper` describes `nslit` *identical, evenly spaced* openings so a chopper whose openings are neither identical nor evenly spaced has to be emitted as a GROUP of several components. This component takes the edges directly, so one disc is one component and corresponds to one NeXus group. It also stops. `DiskChopper` replaces a zero frequency with `omega = 1e-15`, which leaves the disc permanently *open* rather than parked; here `nu = 0` means the disc is stationary with its zero mark at `park_angle`, and a ray passes only if an opening happens to be in front of the beam. That is what a commissioning run with a parked chopper actually does. Geometry follows `DiskChopper`: the beam crosses the disc a distance `radius - yheight/2` from the spindle, and rays are located by `atan2(x, y + delta_y)` about that crossing. Where the beam crosses the disc is `beam_angle`, measured from the zero mark in the same sense as `slit_edges` and `park_angle`. The default of 0 puts the beam at the top of the disc, which is the only thing `DiskChopper` can express -- so a caller that used to turn the whole component about its own z to bring the right part of the disc to the top can stop, and say the angle instead. A disc hanging above its beam is `beam_angle = 180`.
| Name | Unit | Description | Default | |
| slit_edges | deg | opening and closing edge of each slit, from the disc's zero mark, in pairs | ||
| n_edges | 1 | number of entries in slit_edges; must be even and non-zero | 0 | |
| radius | m | outer radius of the disc | 0.35 | |
| yheight | m | radial clearance of the openings across the whole window; 0 means they reach the spindle | 0 | |
| xwidth | m | chord width of the beam window; 0 leaves the opening unrestricted | 0 | |
| nu | Hz | signed rotation frequency; 0 parks the disc at park_angle | 0 | |
| delay | s | when the disc's zero mark is on the beam | 0 | |
| park_angle | deg | where the zero mark stands while parked; only read when nu is 0 | 0 | |
| beam_angle | deg | where the beam crosses the disc, from the zero mark, in the same sense as slit_edges; 0 puts the beam at the top of the disc | 0 | |
| zero_angle | deg | from the component's +y axis to the top-dead-centre pickup; with beam_angle it says which way the spindle lies | 0 | |
| jitter | s | timing jitter applied to each ray | 0 | |
| abs_out | 1 | absorb rays that miss the disc entirely | 0 | |
| verbose | 1 | -1: silent, 0: errors, 1: warnings, 2: info, 3: details | 0 |
| AT ( | , | , | ) RELATIVE | |||
|---|---|---|---|---|---|---|
| ROTATED ( | , | , | ) RELATIVE |
NXdisk_chopper.comp.
[ Identification | Description | Examples | Input parameters | Links ]
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