method 

&DRIFT: INTEGRATION-PARAMETERS: method


NO-PROJECTION

No special treatment when approaching the wire, hence the value of ncloud is not relevant.

INTEGRATION

As soon as the cloud enters the 'ncloud' zone, the following is done:

Complete integration over the cloud of the local distance to the wire divided by the local drift velocity.

The longitudinal diffusion over the remaining distance to the wire is added to the estimate.


CENTRAL-VELOCITY-INTEGRATION

As soon as the cloud enters the 'ncloud' zone, an integration similar to INTEGRATION is carried out, but the drift velocity is always taken to be the drift velocity at the centre of the cloud.

The longitudinal diffusion over the remaining distance to the wire is added to the estimate.

[This is currently the default method.]


LONGITUDINAL-DIMENSION

When the cloud centre enters the 'ncloud' zone, the dimension of the cloud over a line through cloud centre and wire centre is taken as measure of diffusion spread.

The longitudinal diffusion over the remaining distance to the wire is added to the estimate.

The longitudinal dimension is in principle the dimension that matters, but in the presence of a strong magnetic field, the cloud rapidly rotates near the wire. At the same time, the cloud stretches to the point of becoming almost one-dimensional. A small rounding error in the cloud alignment, can make the dimension along the axis pointing to the wire, very small.

For this reason, this method is not recommended, unless the cloud trap radius is very large (in which case the velocity estimates are likely to be inaccurate).


LARGEST-DIMENSION

This is similar to LONGITUDINAL-DIMENSION but the cloud size is taken to be the largest cross section of the cloud.

The longitudinal diffusion over the remaining distance to the wire is added to the estimate.

For reasons explained under LONGITUDINAL-DIMENSION, this method must be considered superior, provided the cloud-trap radius is small.


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Formatted on 21/01/18 at 16:55.