Add compt_scale as a user parameter.

xfields/beam_elements/beambeam3d.py

@@ -181,6 +181,7 @@ class BeamBeamBiGaussian3D(xt.BeamElement):
          #bhabha
          'flag_bhabha': xo.Int64,
          'compt_x_min': xo.Float64,
+         'compt_scale': xo.Float64,
          'flag_beamsize_effect': xo.Int64,
 
          #lumi
@@ -251,6 +252,7 @@ def __init__(self,
 
                     flag_bhabha=0,
                     compt_x_min=1e-4,
+                    compt_scale=1.,
                     flag_beamsize_effect=1,
 
                     flag_luminosity=0,
@@ -330,6 +332,7 @@ def __init__(self,
              slices_other_beam_sqrtSigma_{135}{135}_beamstrahlung (float array): Array storing the per-slice standard deviations of x (=1), y (=3) and zeta (=5) of the opposing bunch, in the unboosted accelerator frame. Length of the array is the number of longitudinal slices. Used for beamstrahlung only. 
              flag_bhabha (int): Flag to simulate small angle radiative Bhabha scattering. 1: ON (quantum), 0: OFF
              compt_x_min (float): Low energy cut on virtual photon spectrum, used for Bhabha, in units of [gamma^-2] where gamma is the rel. Lorentz factor.
+             compt_scale (float): Scaling factor to scale up photon generation, used for Bhabha.
              flag_beamsize_effect (int): Flag to simulate beamsize effect, used for Bhabha. 1: ON, 0: OFF. Results in ~factor 2 reduction in cross section.
              flag_luminosity (int): Flag to record soft-Gaussian luminosity per bunch crossing in a buffer. Luminosity will be in units of [m^-2].
              slices_other_beam_{x,px,y,py,zeta,pzeta}_center_star (float array): Array storing the per-slice centroid variables of the opposing bunch, in the unboosted accelerator frame. Length of the array is the number of longitudinal slices. 
@@ -465,7 +468,7 @@ def __init__(self,
         )
 
         # initialize bhabha
-        self._init_bhabha(flag_bhabha, compt_x_min, flag_beamsize_effect)
+        self._init_bhabha(flag_bhabha, compt_x_min, compt_scale, flag_beamsize_effect)
 
         self._init_luminosity(flag_luminosity)
 
@@ -635,9 +638,10 @@ def flag_beamstrahlung(self, flag_beamstrahlung):
                     'needs to be correctly set')
         self._flag_beamstrahlung = flag_beamstrahlung
 
-    def _init_bhabha(self, flag_bhabha, compt_x_min, flag_beamsize_effect):
+    def _init_bhabha(self, flag_bhabha, compt_x_min, compt_scale, flag_beamsize_effect):
         self.flag_beamsize_effect = flag_beamsize_effect
         self.compt_x_min = compt_x_min
+        self.compt_scale = compt_scale
         self.flag_bhabha = flag_bhabha # Trigger property setter
 
     @property
@@ -649,6 +653,8 @@ def flag_bhabha(self, flag_bhabha):
         if flag_bhabha == 1:
             if self.compt_x_min <= 0:
                 raise ValueError('compt_x_min must be larger than 0')
+            if self.compt_scale <= 0:
+                raise ValueError('compt_scale must be larger than 0')
         self._flag_bhabha = flag_bhabha
 
     def _init_luminosity(self, flag_luminosity):

xfields/beam_elements/beambeam_src/beambeam3d.h

@@ -103,9 +103,11 @@ void do_bhabha(BeamBeamBiGaussian3DData el, LocalParticle *part,
       py_photon = py_slice_star;
       pzeta_photon = pzeta_slice_star;
 
+      const double compt_scale = BeamBeamBiGaussian3DData_get_compt_scale(el); // [1] can be used to scale up photon generation for tests
+
       // for each virtual photon get compton scatterings; updates pzeta and energy vars inside
       compt_do(part, bhabha_record, bhabha_table_index, bhabha_table,
-               e_photon, compt_x_min, q2,
+               e_photon, compt_x_min, compt_scale, q2,
                x_photon, y_photon, S, px_photon, py_photon, pzeta_photon,
                *wgt, px_star, py_star, pzeta_star, q0);
 

xfields/headers/bhabha_spectrum.h

@@ -250,6 +250,7 @@ double compt_select(LocalParticle *part,
 void compt_do(LocalParticle *part, BeamBeamBiGaussian3DRecordData bhabha_record, RecordIndex bhabha_table_index, BhabhaTableData bhabha_table,
               double e_photon,           // [GeV] single equivalent virtual photon energy before Compton scattering
               const double compt_x_min,  // [1] scaling factor in the minimum energy cutoff
+              double compt_scale,        // [1] can be used to scale up photon generation for tests
               double q2,                 // [GeV^2] single equivalent virtual photon virtuality
               double x_photon, double y_photon, double z_photon,  // [m] (boosted) coords of the virtual photon
               double vx_photon,          // [1] transverse x momentum component of virtual photon (vx = dx/ds/p0)
@@ -284,7 +285,6 @@ void compt_do(LocalParticle *part, BeamBeamBiGaussian3DRecordData bhabha_record,
     double e_photon_prime, px_photon_prime, py_photon_prime;      // [GeV, GeV/c] scattered (real) Compton photon momenta
     double e_loss_primary;            // [GeV] energy lost from one photon emission
     double eps = 0.0;                 // 1e-5 in guinea, used due to limited resolution of RNG in the past
-    const double compt_scale = 1;     // [1] can be used to scale up photon generation for tests
     const double compt_emax = 200;    // [GeV] upper cutoff on e_e_prime from guineapig
     const double pair_ecut = 0.005;   // [GeV] lower cutoff on e_e_prime from guineapig
     double r1, r2;  // [1] uniform random numbers