Octupole element for particle tracking

[vitben]

Hello,

thanks for developing such a good code! I am performing particle tracking of a 6D distribution. The beamline have a set of sextupole and octupole elements. When performing the tracking, I noticed that there is not difference in the case when I include the octupoles and when I do not. Here below you can find the python code for the tracking with and without octupoles.

`# initialization of tracking method
%autoreload
from my_lattice import *
method = {"global": SecondTM}

# for first order tracking uncomment next line
# method = {"global": TransferMap}

lat_t1 = MagneticLattice(cell1, start=None, stop=None, method=method)

navi = Navigator(lat_t1)
p_array = deepcopy(p_array_init)
start = time.time()
tws_track1, p_array1 = track(lat_t1, p_array, navi, calc_tws=True)
print("\n time exec:", time.time() - start, "sec")

lat_t2 = MagneticLattice(cell2, start=None, stop=None, method=method)

navi = Navigator(lat_t2)
p_array = deepcopy(p_array_init)
start = time.time()
tws_track2, p_array2 = track(lat_t2, p_array, navi, calc_tws=True)
print("\n time exec:", time.time() - start, "sec")

tau1 = np.array([p.tau for p in p_array1])*1000
dp1 = np.array([p.p for p in p_array1])*1000
x1 = np.array([p.x for p in p_array1])*1000
xp1 = np.array([p.px for p in p_array1])*1000
y1 = np.array([p.y for p in p_array1])*1000
yp1 = np.array([p.py for p in p_array1])*1000

tau2 = np.array([p.tau for p in p_array2])*1000
dp2 = np.array([p.p for p in p_array2])*1000
x2 = np.array([p.x for p in p_array2])*1000
xp2 = np.array([p.px for p in p_array2])*1000
y2 = np.array([p.y for p in p_array2])*1000
yp2 = np.array([p.py for p in p_array2])*1000

The octupoles elements I use are defined as follow:

O_1=  Octupole(l = 0.2 , k3 =-328.29496694078165, tilt = 0, eid = 'O_1')
O_2= Octupole(l = 0.2, k3 =-208.57373589036763, tilt = 0, eid = 'O_2')
O_3=   Octupole(l = 0.2, k3 =2844.666880229662, tilt = 0, eid = 'O_3')

Do you have any ideas of what the issue could be?

Thanks a lot for your help!

[sergey-tomin]

hi, the issue is that Octuple is 3d order element and by default we activate first order maps for all elements. To make Octuple work you need to specify for it a different map. method = {"global": SecondTM, Octupole: KickTM}

see more details in tutorial. https://nbviewer.org/github/ocelot-collab/ocelot/blob/dev/demos/ipython_tutorials/small_useful_features.ipynb#TM

Sergey.

[vitben]

Hi Sergey,

Thanks for the very quick answer. Now it works perfectly.

Best,

Vittorio