Ejemplo n.º 1
0
 def test_transverse_damper(self):
     '''
     Track through a transverse damper
     '''
     bunch_cpu = self.create_all1_bunch()
     bunch_gpu = self.create_all1_bunch()
     dampingrate_x = 0.01
     dampingrate_y = 0.05
     damp = TransverseDamper(dampingrate_x, dampingrate_y)
     self.assertTrue(self._track_cpu_gpu([damp], bunch_cpu, bunch_gpu),
                     'Tracking TransverseDamper CPU/GPU differs')
Ejemplo n.º 2
0
    def _install_damper(self):

        pp = self.pp

        if pp.enable_transverse_damper:
            # setup transverse damper
            from PyHEADTAIL.feedback.transverse_damper import TransverseDamper

            damper = TransverseDamper(dampingrate_x=pp.dampingrate_x,
                                      dampingrate_y=pp.dampingrate_y)
            self.machine.one_turn_map.append(damper)
            self.n_non_parallelizable += 1
            self.dampers = [damper]
        else:
            self.dampers = []
# PARAMETERS FOR LONGITUDINAL MAP
# =======================
alpha           = 1.9e-3
Q_s             = 0.0035
h1, h2          = 4620, 9240
V1, V2          = 4.5e6, 0e6
dphi1, dphi2    = 0, np.pi
p_increment     = 0 * e/c * circumference/(beta*c)

#longitudinal_map = LinearMap([alpha], circumference, Q_s)

# CREATE DAMPER
# =============
dampingrate_y = 10 #40
damper = TransverseDamper(dampingrate_x, dampingrate_y)

# CREATE BEAM
# ===========
macroparticlenumber = 100000

charge    = e
mass      = m_p
intensity = 1.5e11

R         = circumference/(2*np.pi)
eta       = alpha-1/gamma**2
beta_z    = np.abs(eta)*R/Q_s
epsn_x    = 2e-6
epsn_y    = 2e-6
epsn_z    = 2.5
Ejemplo n.º 4
0
    def init_all(self):

        self.n_slices = pp.n_slices

        # read the optics if needed
        if pp.optics_pickle_file is not None:
            with open(pp.optics_pickle_file) as fid:
                optics = pickle.load(fid)
                self.n_kick_smooth = np.sum(
                    ['_kick_smooth_' in nn for nn in optics['name']])
        else:
            optics = None
            self.n_kick_smooth = pp.n_segments

        # define the machine
        from LHC_custom import LHC
        self.machine = LHC(n_segments=pp.n_segments,
                           machine_configuration=pp.machine_configuration,
                           beta_x=pp.beta_x,
                           beta_y=pp.beta_y,
                           accQ_x=pp.Q_x,
                           accQ_y=pp.Q_y,
                           Qp_x=pp.Qp_x,
                           Qp_y=pp.Qp_y,
                           octupole_knob=pp.octupole_knob,
                           optics_dict=optics,
                           V_RF=pp.V_RF)
        self.n_segments = self.machine.transverse_map.n_segments

        # compute sigma
        inj_opt = self.machine.transverse_map.get_injection_optics()
        sigma_x_inj = np.sqrt(inj_opt['beta_x'] * pp.epsn_x /
                              self.machine.betagamma)
        sigma_y_inj = np.sqrt(inj_opt['beta_y'] * pp.epsn_y /
                              self.machine.betagamma)

        if pp.optics_pickle_file is None:
            sigma_x_smooth = sigma_x_inj
            sigma_y_smooth = sigma_y_inj
        else:
            beta_x_smooth = None
            beta_y_smooth = None
            for ele in self.machine.one_turn_map:
                if ele in self.machine.transverse_map:
                    if '_kick_smooth_' in ele.name1:
                        if beta_x_smooth is None:
                            beta_x_smooth = ele.beta_x1
                            beta_y_smooth = ele.beta_y1
                        else:
                            if beta_x_smooth != ele.beta_x1 or beta_y_smooth != ele.beta_y1:
                                raise ValueError(
                                    'Smooth kicks must have all the same beta')

            if beta_x_smooth is None:
                sigma_x_smooth = None
                sigma_y_smooth = None
            else:
                sigma_x_smooth = np.sqrt(beta_x_smooth * pp.epsn_x /
                                         self.machine.betagamma)
                sigma_y_smooth = np.sqrt(beta_y_smooth * pp.epsn_y /
                                         self.machine.betagamma)

        # define MP size
        nel_mp_ref_0 = pp.init_unif_edens_dip * 4 * pp.x_aper * pp.y_aper / pp.N_MP_ele_init_dip

        # prepare e-cloud
        import PyECLOUD.PyEC4PyHT as PyEC4PyHT

        if pp.custom_target_grid_arcs is not None:
            target_grid_arcs = pp.custom_target_grid_arcs
        else:
            target_grid_arcs = {
                'x_min_target':
                -pp.target_size_internal_grid_sigma * sigma_x_smooth,
                'x_max_target':
                pp.target_size_internal_grid_sigma * sigma_x_smooth,
                'y_min_target':
                -pp.target_size_internal_grid_sigma * sigma_y_smooth,
                'y_max_target':
                pp.target_size_internal_grid_sigma * sigma_y_smooth,
                'Dh_target': pp.target_Dh_internal_grid_sigma * sigma_x_smooth
            }
        self.target_grid_arcs = target_grid_arcs

        if pp.enable_arc_dip:
            ecloud_dip = PyEC4PyHT.Ecloud(
                slice_by_slice_mode=True,
                L_ecloud=self.machine.circumference / self.n_kick_smooth *
                pp.fraction_device_dip,
                slicer=None,
                Dt_ref=pp.Dt_ref,
                pyecl_input_folder=pp.pyecl_input_folder,
                chamb_type=pp.chamb_type,
                x_aper=pp.x_aper,
                y_aper=pp.y_aper,
                filename_chm=pp.filename_chm,
                PyPICmode=pp.PyPICmode,
                Dh_sc=pp.Dh_sc_ext,
                N_min_Dh_main=pp.N_min_Dh_main,
                f_telescope=pp.f_telescope,
                N_nodes_discard=pp.N_nodes_discard,
                target_grid=target_grid_arcs,
                init_unif_edens_flag=pp.init_unif_edens_flag_dip,
                init_unif_edens=pp.init_unif_edens_dip,
                N_mp_max=pp.N_mp_max_dip,
                nel_mp_ref_0=nel_mp_ref_0,
                B_multip=pp.B_multip_dip,
                enable_kick_x=pp.enable_kick_x,
                enable_kick_y=pp.enable_kick_y)

        if pp.enable_arc_quad:
            ecloud_quad = PyEC4PyHT.Ecloud(
                slice_by_slice_mode=True,
                L_ecloud=self.machine.circumference / self.n_kick_smooth *
                pp.fraction_device_quad,
                slicer=None,
                Dt_ref=pp.Dt_ref,
                pyecl_input_folder=pp.pyecl_input_folder,
                chamb_type=pp.chamb_type,
                x_aper=pp.x_aper,
                y_aper=pp.y_aper,
                filename_chm=pp.filename_chm,
                PyPICmode=pp.PyPICmode,
                Dh_sc=pp.Dh_sc_ext,
                N_min_Dh_main=pp.N_min_Dh_main,
                f_telescope=pp.f_telescope,
                N_nodes_discard=pp.N_nodes_discard,
                target_grid=target_grid_arcs,
                N_mp_max=pp.N_mp_max_quad,
                nel_mp_ref_0=nel_mp_ref_0,
                B_multip=pp.B_multip_quad,
                filename_init_MP_state=pp.filename_init_MP_state_quad,
                enable_kick_x=pp.enable_kick_x,
                enable_kick_y=pp.enable_kick_y)

        if self.ring_of_CPUs.I_am_the_master and pp.enable_arc_dip:
            with open('multigrid_config_dip.txt', 'w') as fid:
                if hasattr(ecloud_dip.spacech_ele.PyPICobj, 'grids'):
                    fid.write(repr(ecloud_dip.spacech_ele.PyPICobj.grids))
                else:
                    fid.write("Single grid.")

            with open('multigrid_config_dip.pkl', 'w') as fid:
                if hasattr(ecloud_dip.spacech_ele.PyPICobj, 'grids'):
                    pickle.dump(ecloud_dip.spacech_ele.PyPICobj.grids, fid)
                else:
                    pickle.dump('Single grid.', fid)

        if self.ring_of_CPUs.I_am_the_master and pp.enable_arc_quad:
            with open('multigrid_config_quad.txt', 'w') as fid:
                if hasattr(ecloud_quad.spacech_ele.PyPICobj, 'grids'):
                    fid.write(repr(ecloud_quad.spacech_ele.PyPICobj.grids))
                else:
                    fid.write("Single grid.")

            with open('multigrid_config_quad.pkl', 'w') as fid:
                if hasattr(ecloud_quad.spacech_ele.PyPICobj, 'grids'):
                    pickle.dump(ecloud_quad.spacech_ele.PyPICobj.grids, fid)
                else:
                    pickle.dump('Single grid.', fid)

        # setup transverse losses (to "protect" the ecloud)
        import PyHEADTAIL.aperture.aperture as aperture
        apt_xy = aperture.EllipticalApertureXY(
            x_aper=pp.target_size_internal_grid_sigma * sigma_x_inj,
            y_aper=pp.target_size_internal_grid_sigma * sigma_y_inj)
        self.machine.one_turn_map.append(apt_xy)

        if pp.enable_transverse_damper:
            # setup transverse damper
            from PyHEADTAIL.feedback.transverse_damper import TransverseDamper
            damper = TransverseDamper(dampingrate_x=pp.dampingrate_x,
                                      dampingrate_y=pp.dampingrate_y)
            self.machine.one_turn_map.append(damper)

        # We suppose that all the object that cannot be slice parallelized are at the end of the ring
        i_end_parallel = len(
            self.machine.one_turn_map) - pp.n_non_parallelizable

        # split the machine
        sharing = shs.ShareSegments(i_end_parallel, self.ring_of_CPUs.N_nodes)
        myid = self.ring_of_CPUs.myid
        i_start_part, i_end_part = sharing.my_part(myid)
        self.mypart = self.machine.one_turn_map[i_start_part:i_end_part]
        if self.ring_of_CPUs.I_am_a_worker:
            print 'I am id=%d/%d (worker) and my part is %d long' % (
                myid, self.ring_of_CPUs.N_nodes, len(self.mypart))
        elif self.ring_of_CPUs.I_am_the_master:
            self.non_parallel_part = self.machine.one_turn_map[i_end_parallel:]
            print 'I am id=%d/%d (master) and my part is %d long' % (
                myid, self.ring_of_CPUs.N_nodes, len(self.mypart))

        #install eclouds in my part
        my_new_part = []
        self.my_list_eclouds = []
        for ele in self.mypart:
            my_new_part.append(ele)
            if ele in self.machine.transverse_map:
                if pp.optics_pickle_file is None or '_kick_smooth_' in ele.name1:
                    if pp.enable_arc_dip:
                        ecloud_dip_new = ecloud_dip.generate_twin_ecloud_with_shared_space_charge(
                        )
                        my_new_part.append(ecloud_dip_new)
                        self.my_list_eclouds.append(ecloud_dip_new)
                    if pp.enable_arc_quad:
                        ecloud_quad_new = ecloud_quad.generate_twin_ecloud_with_shared_space_charge(
                        )
                        my_new_part.append(ecloud_quad_new)
                        self.my_list_eclouds.append(ecloud_quad_new)
                elif '_kick_element_' in ele.name1 and pp.enable_eclouds_at_kick_elements:

                    i_in_optics = list(optics['name']).index(ele.name1)
                    kick_name = optics['name'][i_in_optics]
                    element_name = kick_name.split('_kick_element_')[-1]
                    L_curr = optics['L_interaction'][i_in_optics]

                    buildup_folder = pp.path_buildup_simulations_kick_elements.replace(
                        '!!!NAME!!!', element_name)
                    chamber_fname = '%s_chamber.mat' % (element_name)

                    B_multip_curr = [0., optics['gradB'][i_in_optics]]

                    x_beam_offset = optics['x'][i_in_optics] * pp.orbit_factor
                    y_beam_offset = optics['y'][i_in_optics] * pp.orbit_factor

                    sigma_x_local = np.sqrt(optics['beta_x'][i_in_optics] *
                                            pp.epsn_x / self.machine.betagamma)
                    sigma_y_local = np.sqrt(optics['beta_y'][i_in_optics] *
                                            pp.epsn_y / self.machine.betagamma)

                    ecloud_ele = PyEC4PyHT.Ecloud(
                        slice_by_slice_mode=True,
                        L_ecloud=L_curr,
                        slicer=None,
                        Dt_ref=pp.Dt_ref,
                        pyecl_input_folder=pp.pyecl_input_folder,
                        chamb_type='polyg',
                        x_aper=None,
                        y_aper=None,
                        filename_chm=buildup_folder + '/' + chamber_fname,
                        PyPICmode=pp.PyPICmode,
                        Dh_sc=pp.Dh_sc_ext,
                        N_min_Dh_main=pp.N_min_Dh_main,
                        f_telescope=pp.f_telescope,
                        N_nodes_discard=pp.N_nodes_discard,
                        target_grid={
                            'x_min_target':
                            -pp.target_size_internal_grid_sigma * sigma_x_local
                            + x_beam_offset,
                            'x_max_target':
                            pp.target_size_internal_grid_sigma * sigma_x_local
                            + x_beam_offset,
                            'y_min_target':
                            -pp.target_size_internal_grid_sigma * sigma_y_local
                            + y_beam_offset,
                            'y_max_target':
                            pp.target_size_internal_grid_sigma * sigma_y_local
                            + y_beam_offset,
                            'Dh_target':
                            pp.target_Dh_internal_grid_sigma * sigma_y_local
                        },
                        N_mp_max=pp.N_mp_max_quad,
                        nel_mp_ref_0=nel_mp_ref_0,
                        B_multip=B_multip_curr,
                        filename_init_MP_state=buildup_folder + '/' +
                        pp.name_MP_state_file_kick_elements,
                        x_beam_offset=x_beam_offset,
                        y_beam_offset=y_beam_offset,
                        enable_kick_x=pp.enable_kick_x,
                        enable_kick_y=pp.enable_kick_y)

                    my_new_part.append(ecloud_ele)
                    self.my_list_eclouds.append(ecloud_ele)

        self.mypart = my_new_part

        if pp.footprint_mode:
            print 'Proc. %d computing maps' % myid
            # generate a bunch
            bunch_for_map = self.machine.generate_6D_Gaussian_bunch_matched(
                n_macroparticles=pp.n_macroparticles_for_footprint_map,
                intensity=pp.intensity,
                epsn_x=pp.epsn_x,
                epsn_y=pp.epsn_y,
                sigma_z=pp.sigma_z)

            # Slice the bunch
            slicer_for_map = UniformBinSlicer(n_slices=pp.n_slices,
                                              z_cuts=(-pp.z_cut, pp.z_cut))
            slices_list_for_map = bunch_for_map.extract_slices(slicer_for_map)

            #Track the previous part of the machine
            for ele in self.machine.one_turn_map[:i_start_part]:
                for ss in slices_list_for_map:
                    ele.track(ss)

            # Measure optics, track and replace clouds with maps
            list_ele_type = []
            list_meas_beta_x = []
            list_meas_alpha_x = []
            list_meas_beta_y = []
            list_meas_alpha_y = []
            for ele in self.mypart:
                list_ele_type.append(str(type(ele)))
                # Measure optics
                bbb = sum(slices_list_for_map)
                list_meas_beta_x.append(bbb.beta_Twiss_x())
                list_meas_alpha_x.append(bbb.alpha_Twiss_x())
                list_meas_beta_y.append(bbb.beta_Twiss_y())
                list_meas_alpha_y.append(bbb.alpha_Twiss_y())

                if ele in self.my_list_eclouds:
                    ele.track_once_and_replace_with_recorded_field_map(
                        slices_list_for_map)
                else:
                    for ss in slices_list_for_map:
                        ele.track(ss)
            print 'Proc. %d done with maps' % myid

            with open('measured_optics_%d.pkl' % myid, 'wb') as fid:
                pickle.dump(
                    {
                        'ele_type': list_ele_type,
                        'beta_x': list_meas_beta_x,
                        'alpha_x': list_meas_alpha_x,
                        'beta_y': list_meas_beta_y,
                        'alpha_y': list_meas_alpha_y,
                    }, fid)

            #remove RF
            if self.ring_of_CPUs.I_am_the_master:
                self.non_parallel_part.remove(self.machine.longitudinal_map)
    def init_all(self):
        
        print('Exec init...')
        
        from LHC_custom import LHC
        self.machine = LHC(n_segments = n_segments, machine_configuration = machine_configuration,
                        Qp_x=Qp_x, Qp_y=Qp_y,
                        octupole_knob=octupole_knob)
        self.n_non_parallelizable = 1 #RF

        inj_optics = self.machine.transverse_map.get_injection_optics()
        sigma_x_smooth = np.sqrt(inj_optics['beta_x']*epsn_x/self.machine.betagamma)
        sigma_y_smooth = np.sqrt(inj_optics['beta_y']*epsn_y/self.machine.betagamma)

        if flag_aperture:
            # setup transverse losses (to "protect" the ecloud)
            import PyHEADTAIL.aperture.aperture as aperture
            apt_xy = aperture.EllipticalApertureXY(x_aper=target_size_internal_grid_sigma*sigma_x_smooth, 
                                                   y_aper=target_size_internal_grid_sigma*sigma_x_smooth)
            self.machine.one_turn_map.append(apt_xy)
            self.n_non_parallelizable +=1 

        if enable_transverse_damper:
            # setup transverse damper
            from PyHEADTAIL.feedback.transverse_damper import TransverseDamper
            damper = TransverseDamper(dampingrate_x=dampingrate_x, dampingrate_y=dampingrate_y)
            self.machine.one_turn_map.append(damper)
            self.n_non_parallelizable +=1
            
        if enable_ecloud:
            print('Build ecloud...')
            import PyECLOUD.PyEC4PyHT as PyEC4PyHT
            ecloud = PyEC4PyHT.Ecloud(
                    L_ecloud=L_ecloud_tot/n_segments, slicer=None, slice_by_slice_mode=True,
                    Dt_ref=5e-12, pyecl_input_folder='./pyecloud_config',
                    chamb_type = 'polyg' ,
                    filename_chm= 'LHC_chm_ver.mat', 
                    #init_unif_edens_flag=1,
                    #init_unif_edens=1e7,
                    #N_mp_max = 3000000,
                    #nel_mp_ref_0 = 1e7/(0.7*3000000),
                    #B_multip = [0.],
                    #~ PyPICmode = 'ShortleyWeller_WithTelescopicGrids',
                    #~ f_telescope = 0.3,
                    target_grid = {'x_min_target':-target_size_internal_grid_sigma*sigma_x_smooth, 'x_max_target':target_size_internal_grid_sigma*sigma_x_smooth,
                                   'y_min_target':-target_size_internal_grid_sigma*sigma_y_smooth,'y_max_target':target_size_internal_grid_sigma*sigma_y_smooth,
                                   'Dh_target':.2*sigma_x_smooth},
                    #~ N_nodes_discard = 10.,
                    #~ N_min_Dh_main = 10,
                    #x_beam_offset = x_beam_offset,
                    #y_beam_offset = y_beam_offset,
                    #probes_position = probes_position,
                    save_pyecl_outp_as = 'cloud_evol_ring%d'%self.ring_of_CPUs.myring,
                    save_only = ['lam_t_array', 'nel_hist', 'Nel_timep', 't', 't_hist', 'xg_hist'],
                    sparse_solver = 'PyKLU', enable_kick_x=enable_kick_x, enable_kick_y=enable_kick_y)
            print('Done.')



        # split the machine
        i_end_parallel = len(self.machine.one_turn_map)-self.n_non_parallelizable
        sharing = shs.ShareSegments(i_end_parallel, self.ring_of_CPUs.N_nodes_per_ring)
        i_start_part, i_end_part = sharing.my_part(self.ring_of_CPUs.myid_in_ring)
        self.mypart = self.machine.one_turn_map[i_start_part:i_end_part]

        if self.ring_of_CPUs.I_am_at_end_ring:
            self.non_parallel_part = self.machine.one_turn_map[i_end_parallel:]
            

        #install eclouds in my part
        if enable_ecloud:
            my_new_part = []
            self.my_list_eclouds = []
            for ele in self.mypart:
                if ele in self.machine.transverse_map:
                    ecloud_new = ecloud.generate_twin_ecloud_with_shared_space_charge()
                    
                    # we save buildup info only for the first cloud in each ring
                    if self.ring_of_CPUs.myid_in_ring>0 or len(self.my_list_eclouds)>0:
                        ecloud_new.remove_savers()
                    
                    my_new_part.append(ecloud_new)
                    self.my_list_eclouds.append(ecloud_new)
                my_new_part.append(ele)

            self.mypart = my_new_part
            
            print('Hello, I am %d.%d, my part looks like: %s. Saver status: %s'%(
                self.ring_of_CPUs.myring, self.ring_of_CPUs.myid_in_ring, self.mypart, 
                [(ec.cloudsim.cloud_list[0].pyeclsaver is not None) for ec in self.my_list_eclouds]))
Ejemplo n.º 6
0
def run(intensity, chroma=0, i_oct=0):
    '''Arguments:
        - intensity: integer number of charges in beam
        - chroma: first-order chromaticity Q'_{x,y}, identical
          for both transverse planes
        - i_oct: octupole current in A (positive i_oct means
          LOF = i_oct > 0 and LOD = -i_oct < 0)
    '''

    # BEAM AND MACHINE PARAMETERS
    # ============================
    from LHC import LHC
    # energy set above will enter get_nonlinear_params p0
    assert machine_configuration == 'LHC_6.5TeV_collision_2016'
    machine = LHC(n_segments=1,
                  machine_configuration=machine_configuration,
                  **get_nonlinear_params(chroma=chroma, i_oct=i_oct))

    # BEAM
    # ====
    epsn_x = 3.e-6  # normalised horizontal emittance
    epsn_y = 3.e-6  # normalised vertical emittance
    sigma_z = 1.2e-9 * machine.beta * c / 4.  # RMS bunch length in meters

    bunch = machine.generate_6D_Gaussian_bunch_matched(n_macroparticles,
                                                       intensity,
                                                       epsn_x,
                                                       epsn_y,
                                                       sigma_z=sigma_z)

    print("\n--> Bunch length and emittance: {:g} m, {:g} eVs.".format(
        bunch.sigma_z(), bunch.epsn_z()))

    # CREATE BEAM SLICERS
    # ===================
    slicer_for_slicemonitor = UniformBinSlicer(50,
                                               z_cuts=(-3 * sigma_z,
                                                       3 * sigma_z))
    slicer_for_wakefields = UniformBinSlicer(500,
                                             z_cuts=(-3 * sigma_z,
                                                     3 * sigma_z))

    # CREATE WAKES
    # ============
    wake_table1 = WakeTable(
        wakefile,
        [
            'time',
            'dipole_x',
            'dipole_y',
            'quadrupole_x',
            'quadrupole_y',
            # 'noquadrupole_x', 'noquadrupole_y',
            'dipole_xy',
            'dipole_yx',
            # 'nodipole_xy', 'nodipole_yx',
        ])
    wake_field = WakeField(slicer_for_wakefields, wake_table1)

    # CREATE DAMPER
    # =============
    dampingrate = 50
    damper = TransverseDamper(dampingrate, dampingrate)

    # CREATE MONITORS
    # ===============
    try:
        bucket = machine.longitudinal_map.get_bucket(bunch)
    except AttributeError:
        bucket = machine.rfbucket

    simulation_parameters_dict = {
        'gamma': machine.gamma,
        'intensity': intensity,
        'Qx': machine.Q_x,
        'Qy': machine.Q_y,
        'Qs': bucket.Q_s,
        'beta_x': bunch.beta_Twiss_x(),
        'beta_y': bunch.beta_Twiss_y(),
        'beta_z': bucket.beta_z,
        'epsn_x': bunch.epsn_x(),
        'epsn_y': bunch.epsn_y(),
        'sigma_z': bunch.sigma_z(),
    }
    bunchmonitor = BunchMonitor(
        outputpath + '/bunchmonitor_{:04d}_chroma={:g}'.format(it, chroma),
        n_turns,
        simulation_parameters_dict,
        write_buffer_every=100)
    slicemonitor = SliceMonitor(
        outputpath + '/slicemonitor_{:04d}_chroma={:g}'.format(it, chroma),
        n_turns_slicemon,
        slicer_for_slicemonitor,
        simulation_parameters_dict,
        write_buffer_every=1,
        buffer_size=n_turns_slicemon)

    # TRACKING LOOP
    # =============
    machine.one_turn_map.append(damper)
    machine.one_turn_map.append(wake_field)

    # for slice statistics monitoring:
    s_cnt = 0
    monitorswitch = False

    print('\n--> Begin tracking...\n')

    # GO!!!
    for i in range(n_turns):

        t0 = time.clock()

        # track the beam around the machine for one turn:
        machine.track(bunch)

        ex, ey, ez = bunch.epsn_x(), bunch.epsn_y(), bunch.epsn_z()
        mx, my, mz = bunch.mean_x(), bunch.mean_y(), bunch.mean_z()

        # monitor the bunch statistics (once per turn):
        bunchmonitor.dump(bunch)

        # if the centroid becomes unstable (>1cm motion)
        # then monitor the slice statistics:
        if not monitorswitch:
            if mx > 1e-2 or my > 1e-2 or i > n_turns - n_turns_slicemon:
                print("--> Activate slice monitor")
                monitorswitch = True
        else:
            if s_cnt < n_turns_slicemon:
                slicemonitor.dump(bunch)
                s_cnt += 1

        # stop the tracking as soon as we have not-a-number values:
        if not all(np.isfinite(c) for c in [ex, ey, ez, mx, my, mz]):
            print('*** STOPPING SIMULATION: non-finite bunch stats!')
            break

        # print status all 1000 turns:
        if i % 1000 == 0:
            t1 = time.clock()
            print('Emittances: ({:.3g}, {:.3g}, {:.3g}) '
                  '& Centroids: ({:.3g}, {:.3g}, {:.3g})'
                  '@ turn {:d}, {:g} ms, {:s}'.format(
                      ex, ey, ez, mx, my, mz, i, (t1 - t0) * 1e3,
                      time.strftime("%d/%m/%Y %H:%M:%S", time.localtime())))

    print('\n*** Successfully completed!')