Difference in Touschek lifetime

[ranamonikaa]

Hi,
For a bare lattice with identical superperiods, the Touschek lifetime should ideally be the same regardless of whether you specify s_end as one superperiod length or leave it unspecified (assuming it defaults to the whole ring) in the momentum_aperture command. However, I am seeing significant difference in the Touschek lifetime for these two cases although the momentum aperture is consistent in both the cases.
What could be causing this discrepancy? and what should be the correct way of setting the momentum _aperture command.

-Monika

[ranamonikaa]

I have attached the lte and ele files below.

[michael_borland]

Monika,

Could you also upload your .mmap files for the two cases, along with the touschekLifetime commands you used?

Thanks--Michael

[ranamonikaa]

Hi, sorry for the late reply.
I have attached the mmap files for both the cases.
The touschek lifetime command I used is:
touschekLifetime -twiss=A2.twi -aperture=A2.mmap A2.lt -charge=0.2 -coupling=0.01 -rf=volt=7.0,harm=1600

Thanks.
-Monika

[michael_borland]

Monika,

The problem is that the computation of bunch length doesn't work correctly for a partial ring. If you use the -length option to provide the bunch length instead of the -rf option, you'll get essentially the same answer for both the full ring and the partial ring.

It should be possible to improve this by having the user specify the number of superperiods. I'll look into that.

--Michael

[ranamonikaa]

Hi,
Even after replacing -rf with the bunch length, the Touschek lifetime is still different for both the cases (i.e., for a single superperiod and the entire ring). . Furthermore, the .lt file shows the same bunch length for both cases suggesting that the computation of the bunch length is correct even for a partial ring. So, the difference in Touschek lifetime is still not clear to me.

Thanks

-Monika

[michael_borland]

Monika,

I get different results. Here's my script

Code: Select all

#!/bin/bash

touschekLifetime -twiss=A2Twiss.twi -aperture=A2.mmap A2.tlife -charge=0.2 -coupling=0.01 -rf=volt=7,harm=1600
sddsprintout -parameter=sigmaz -parameter=tLifetime A2.tlife -title="Full LMA and twiss files with -rf option"

touschekLifetime -twiss=A2TwissUnit.twi -aperture=A2_unit.mmap A2_unit.tlife -charge=0.2 -coupling=0.01 -rf=volt=7,harm=50 
sddsprintout -parameter=sigmaz -parameter=tLifetime A2_unit.tlife -title="Unit LMA and twiss files with -rf option"

length=`sdds2stream -parameter=sigmaz A2.tlife`
touschekLifetime -twiss=A2TwissUnit.twi -aperture=A2_unit.mmap A2_unit.tlife -charge=0.2 -coupling=0.01 -length=`rpnl $length 1e-3 /`
sddsprintout -parameter=sigmaz -parameter=tLifetime A2_unit.tlife -title="Unit LMA and twiss files with -length option"

and the output

Code: Select all

Full LMA and twiss files with -rf option
sigmaz (m) =        2.631383e-03  tLifetime (hour) =  1.746720e+01

Unit LMA and twiss files with -rf option
sigmaz (m) =        4.458803e-04  tLifetime (hour) =  2.925825e+00

Unit LMA and twiss files with -length option
sigmaz (m) =        2.631383e-03  tLifetime (hour) =  1.726689e+01

You can see that the bunch length and lifetime are different (and wrong) in the second case (unit LMA/twiss plus -rf option), but correct in the third case (unit LMA/twiss plus -length option).

--Michael

[ranamonikaa]

I don't get the same result as you for the unit cell case. Maybe I'd install the latest elegant version and then try again.
Thank you so much.

-Monika