Transverse Damping coming from EnergyLoss element

[lcarver]

Hello @lfarv and @lnadolski ,

In the EnergyLoss element, the radiation damping is equal in the horizontal and vertical planes (and half in longitudinal) corresponding to damping partitions of [1, 1, 2].

It would be nice if we could specify the damping partition numbers in order to have the correct damping times given by this element. I'm not sure of the best way to implement this.

As a reminder: the analytical formula for the damping time is given by

tau = 2 * E0 * T0 / ( j * U0 )

[lcarver]

The intended usage of this is explained a bit more in PR #643 .

[lfarv]

It seems that there is some misunderstanding on the use of the EnergyLoss element. It is not meant to summarise all the radiation effects in a ring. It's a single, straight, thin, non-focusing radiating element. Look at it as a "thin wiggler". This element has no contribution to the I4. Its contribution to I2 has been introduced in the analytical formulae so that the damping times obtained by tracking and analytical are in agreement. Concerning emittances and energy spread, nothing is done: for ohmienvelope, the generalisation of the computation of diffusion matrices has already been discussed but is on hold, and for analytic, it is probably possible to do something… For the time being, the computed emittances are correct only if the element is in a non-dispersive section.

To summarise the use of this element:

• it has nothing to do neither with include fast_ring generation from a list of machine parameters (tunes, chromaticities, ac, U0, etc) #606 nor Simple ring model #643,
• it gives correct damping times,
• it should be used in non-dispersive sections, otherwise the computed emittances are wrong,
• standard plane wigglers have a vertical focusing effect, but not this element. This could be easily added once the choice of a meaningful attribute to describe it is done.

[swhite2401]

Can we improve documentation then? Is it possible to include your comment above in the docstring?

I would not include any 'specific' feature to this element but rather add the possibility to 'lose' energy in existing ID elements.