class Photons():
"""
Integrate over the beam and create the photons
"""
def __init__(self):
pass
def initialize(self, lattice):
# read settings
settings = Settings()['generator']['photons']
self._enabled = settings['enabled']
self._full_events = settings['full_events']
self._nth_step = settings['nth_step']
self._time = settings['time']
self._energy_cutoff = settings['energy_cutoff']
self._sigma_h = settings['sigma']['horizontal']
self._sigma_v = settings['sigma']['vertical']
self._stepsize_h = 2.0 * self._sigma_h / settings['steps']['horizontal']
self._stepsize_v = 2.0 * self._sigma_v / settings['steps']['vertical']
self._crossing_angle = Settings()['machine']['crossing_angle']
self._region_enabled = settings['region']['enabled']
if settings['region']['range'][0] < settings['region']['range'][1]:
self._region_left = settings['region']['range'][0]
self._region_right = settings['region']['range'][1]
else:
self._region_left = settings['region']['range'][1]
self._region_right = settings['region']['range'][0]
self._target_zone_enabled = settings['target_zone']['enabled']
self._target_zone_radius = settings['target_zone']['radius']
self._target_zone_boundary = settings['target_zone']['boundary']
# create synchrotron radiation power spectrum PDF
self._spectrum = Spectrum()
self._spectrum.initialize(settings['spectrum']['resolution'],
settings['spectrum']['cutoff'],
settings['spectrum']['seed'],
settings['spectrum']['interpolation'])
# internal parameters
self._lattice = lattice
self._call_count = 0
self._dl = 0.0
# internal constants and pre-calculated factors
self._alpha = 1.0 / 137.035999074
self._speed_of_light = 2.99792458e8 # [m/s]
self._hbar = 6.58211928e-25 # [GeV s]
self._gamma = Settings()['machine']['beam_energy'] / 510.998928e-6
self._current = Settings()['machine']['beam_current'] * 6.241508e18
self._num_photon_factor = (5.0 / (2.0*math.sqrt(3))) * \
self._gamma * self._alpha * \
self._current * self._time
self._crit_e_factor = 3.0 / 2.0 * self._speed_of_light * \
self._hbar * (self._gamma**3)
def create(self, step, beam, output, hepevt):
if not self._enabled:
return
# accumulate steps only inside magnets and, if enabled,
# inside the region
if (not step.in_vacuum) and \
(not self._region_enabled or \
(self._region_enabled and \
step.s0ip >= self._region_left and step.s0ip <= self._region_right)):
self._dl += step.dl
self._call_count += 1
# radiate photons if the n-th step is reached,
# the current step is on a magnet to vacuum boundary,
# or the region is enabled and the step leaves the region
if (self._call_count >= self._nth_step) or \
(self._call_count > 0 and step.on_boundary) or \
(self._region_enabled and self._call_count > 0 and step.ds < 0.0 and \
step.s0ip <= self._region_left) or \
(self._region_enabled and self._call_count > 0 and step.ds > 0.0 and \
step.s0ip >= self._region_right):
self._integrate_beam(math.fabs(self._dl),
step, beam,
output, hepevt)
self._dl = 0.0
self._call_count = 0
def write_spectrum(self, output):
self._spectrum.write(output)
def _intersect_target_zone(self, vertex, direction):
"""
Target zone is an z-axis aligned cylinder with an inner and an outer
radius and a lower and upper boundary. This code intersects a line with
the cylinder, not a ray! That's ok for the SyncRad Generator, as this
shouldn't introduce too many false intersections as long as the generation
is done in a way such that the photons travel towards the IP.
"""
# calculate slopes
if math.fabs(direction[2]) > 0.0000000001:
slope_xz = direction[0] / direction[2]
slope_yz = direction[1] / direction[2]
else:
slope_xz = 0.0
slope_yz = 0.0
# calculate the distance from the z-axis (radius) that the ray has at the
# lower and upper z-boundary of the cylinder.
def calc_radius2(boundary):
x_b = slope_xz*(boundary-vertex[2]) + vertex[0]
y_b = slope_yz*(boundary-vertex[2]) + vertex[1]
return x_b**2 + y_b**2
r_low = calc_radius2(self._target_zone_boundary[0])
r_up = calc_radius2(self._target_zone_boundary[1])
# since it is a z-axis aligned cylinder, the radius can simply be compared
# to the cylinder radii, in order to check for the intersection of the ray.
radius2 = [self._target_zone_radius[0]**2, self._target_zone_radius[1]**2]
return ((r_low < radius2[1]) and (r_up > radius2[0])) or \
((r_up < radius2[1]) and (r_low > radius2[0]))
def _integrate_beam(self, dl, step, beam, output, hepevt):
"""
integrate over the beam profile
"""
total_number_photons = 0
total_number_photons_cut = 0
k1s = []
for region in self._lattice.get(step.s0ip):
idx = region.index(step.s0ip)
k1s.append([region.k1(idx), region.sk1(idx)])
hsize, vsize, ch, cv = beam.size()
prob_norm_1 = 1.0 / (2.506628 * hsize * vsize)
prob_norm_2 = 1.0 / (2.0*math.pi * hsize * vsize)
weight_factor = self._stepsize_h * self._stepsize_v * hsize * vsize
xstep = self._stepsize_h * hsize
ystep = self._stepsize_v * vsize
xs_max = self._sigma_h * hsize
ys_max = self._sigma_v * vsize
cx_s = math.sin(self._crossing_angle)
cx_c = math.cos(self._crossing_angle)
xs = -1.0 * self._sigma_h * hsize + 0.5*xstep
while xs <= xs_max:
ys = -1.0 * self._sigma_v * vsize + 0.5*ystep
while ys <= ys_max:
# calculate local radius
local_gh = step.gh
local_gv = step.gv
for k1 in k1s:
local_gh += (k1[0] * xs) - (k1[1] * ys)
local_gv += (k1[0] * ys) + (k1[1] * xs)
rho_inv = math.sqrt(local_gh**2 + local_gv**2)
# calculate weight
prob = 0.0
nsigh = xs / hsize
nsigv = ys / vsize
# beam profile. Either Talman tails or Gaussian
if (math.fabs(nsigv) > 5.0) and (beam.emitv / beam.emith < 0.2):
prob = prob_norm_1 * math.exp(-0.5*nsigh**2) * \
math.exp(-7.4 -1.2*math.fabs(nsigv))
else:
prob = prob_norm_2 * math.exp(-0.5*(nsigh**2 + nsigv**2))
weight = prob * weight_factor
# calculate number of radiated photons
num_photons = int(self._num_photon_factor * rho_inv * weight * dl)
total_number_photons += num_photons
if num_photons > 0:
# calculate critical energy
crit_e = self._crit_e_factor * rho_inv
# calculate vertex
vx = (cx_c*(step.xip+xs)) + (cx_s*step.zip)
vy = step.yip+ys
vz = (cx_c*step.zip) - (cx_s*(step.xip+xs))
# calculate momentum
px_temp = -step.zip * ((math.pi - step.xip_prime) + (ch * xs))
py_temp = -step.zip * (step.yip_prime + (cv * ys))
pz_temp = -step.zip
# rotate momentum into Geant4 space
px = (cx_c*px_temp) + (cx_s*pz_temp)
py = py_temp
pz = (cx_c*pz_temp) - (cx_s*px_temp)
norm = 1.0/math.sqrt(px**2 + py**2 + pz**2)
# if the target zone feature is on, only write events if
# the photons will hit the zone.
if (not self._target_zone_enabled) or \
(self._target_zone_enabled and \
self._intersect_target_zone([vx, vy, vz], [px, py, pz])):
# if full event writing is turned on, get the energies
# for all radiated photons and write them into the
# event file
if self._full_events:
energies = self._spectrum.random(crit_e, num_photons,
self._energy_cutoff)
if len(energies) > 0:
evt = hepevt.event(vx, vy, vz)
for e in energies:
evt.add(px*e*norm, py*e*norm, pz*e*norm)
evt.commit()
total_number_photons_cut += len(energies)
else:
evt = hepevt.event(vx, vy, vz,
num_photons=num_photons,
critical_e=crit_e)
evt.add(px*norm, py*norm, pz*norm)
evt.commit()
ys += ystep
xs += xstep
output.write(["%f:%i:%i:%e:%e:%e:%e\n"%(step.s0ip,
total_number_photons,
total_number_photons_cut,
step.x, step.y,
step.xp, step.yp)])