rf_setup return <0 values for Ss & Sdelta

Moderators: cyao, michael_borland

Post Reply
Philippe Piot
Posts: 79
Joined: 20 Aug 2008, 13:18
Location: Northern Illinois University & Argonne National Laboratory
Contact:

rf_setup return <0 values for Ss & Sdelta

Post by Philippe Piot » 18 Apr 2018, 16:07

Hello,
I was wondering what is the meaning of Ss0 and Sdelta0 and how they are computed in rf_setup. For the example attached I am puzzled as the rf_setup returns negative values for these two variables. Also, I am surprised by the magnitude of Sdelta [O(10**-10)] assuming there is just an issue with the sign. If I just use these value as input for my sddsbeam, I see the beam is longitudinally mismatched. It there an easy way to find out the ideal initial longitudinal beam parameter to be matched and avoid large oscillation in bunch length and energy spread?
Thank you, -- Philippe.
Attachments
test_multiturn.tar
(101.5 KiB) Downloaded 148 times

michael_borland
Posts: 1795
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: rf_setup return <0 values for Ss & Sdelta

Post by michael_borland » 11 May 2018, 11:45

Philippe,

The problem is that the code wasn't properly handling negative momentum compaction. I fixed this and attach the revised source code.

Also, I now use eta=alpha-1/gamma^2, whereas before I just used alpha. Doesn't make a significant difference in most cases.

--Michael
Attachments
twiss.cc.gz
(42.35 KiB) Downloaded 147 times

Philippe Piot
Posts: 79
Joined: 20 Aug 2008, 13:18
Location: Northern Illinois University & Argonne National Laboratory
Contact:

Re: rf_setup return <0 values for Ss & Sdelta

Post by Philippe Piot » 16 May 2018, 04:39

Michael,
Thank you. The signs are fixed but I am still just confused by the meaning of Sz0 and Sdelta0 are these the expected equilibrium bunch length and relative energy spread? Thank you, -- Philippe.

michael_borland
Posts: 1795
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: rf_setup return <0 values for Ss & Sdelta

Post by michael_borland » 16 May 2018, 07:48

Philippe,

Here's the code that compiles with the present release of elegant.

Ss0 and Sdelta0 are indeed the equilibrium values of the bunch length (in meters) and fractional momentum spread.

--Michael
Attachments
twiss.cc.gz
(42.35 KiB) Downloaded 171 times

Post Reply