RBEN vs SBEN

[libov]

Dear all,

I'm confused about E1 and E2 meaning in RBEN and SBEN.

From the SBEN description in the manual, it looks to me as it's the angle between the nominal orbit and the edge of the magnet
Thus, in a sector magnet it's E1=E2=0; if we have a rectangular magnet and particles enter in perpendicularly to one side, it should be E1=0, E2=<bending angle>, is that right?

Is there any difference in E1 and E2 meaning in RBEN compared to SBEN?
The manual says, RBEN is implemented as SBEN; if I make, say, optimisation and store the resulting lattice, Elegant will change
RBEN to SBEN - ok, but it will also modify E1 and E2, thus the meaning should be different.

Example: I want to have a rectangular magnet, with electrons hitting the dipole normally;
thus, the exit angle (angle between the electrons leaving the dipole and the normal to it's exit edge) will be equal the bending angle (6 degrees in my example)
I set therefore D1: RBEN, L=1.02, ANGLE=0.06, E1 = 0, E2=0.06, ORDER=1
According to Elegant, it's equivalent to
SBEN,L=1.020153016066525,ANGLE=0.06,E1=0.03,E2=0.09,ORDER=1

Somehow I can't make sense out of it. Why is E1=0.03 in SBEN, shouldn't it be zero?

Either my definition of RBEN or my understanding of E1 and E2 is wrong.

Any help is greatly appreciated!!

Cheers,
Slava

[michael_borland]

Slava,

The angles E1 and E2 for RBEN are relative to the rectangular case. For SBEN, they are relative to the sector case. I.e.,

! Rectangular bends
BR1: RBEN,L=1,ANGLE=0.5,E1=0,E2=0
BR2: SBEN,L=1,ANGLE=0.5,E1=0.25,E2=0.25

! Sector bends
BS1: RBEN,L=1,ANGLE=0.5,E1=-0.25,E2=-0.25
BS2: SBEN,L=1,ANGLE=0.5

Note that these elements are not exactly equivalent, because for RBEN the L is the straight-line length (chord), whereas for SBEN L is the arc length.

--Michael