Commit d2b871c1 authored by Zolnierczuk, Piotr's avatar Zolnierczuk, Piotr
Browse files

more or less working flippers 

need to get the absolute scale right
parent 9a627140

pysen/echo/flippers.py

+35 −19
Original line number Diff line number Diff line
@@ -8,23 +8,26 @@ import scipy.optimize as opt 
from numpy import sqrt, cos



try:

    from ..constants import (PI, MU_0, HMN, GAMMA_N)

    from ..constants import (PI, MU_0, HMN, OMEGA_N)

except ImportError:

    from scipy import constants as _const

    PI      = np.pi

    MU_0    = 4e-7*PI

    HMN     = _const.Planck/_const.neutron_mass

    GAMMA_N = _const.physical_constants['neutron gyromag. ratio'][0]

    OMEGA_N = _const.physical_constants['neutron gyromag. ratio'][0]/HMN







_pisqrt2  = PI/sqrt(2)

PISQRT2 = PI/sqrt(2)



def rxx13(omega_z, omega_x):

    """omega.z**2 cos(omega.x**2+omega.z**2) + omega.x**2"""

    omega_x, omega_z = omega_x**2, omega_z**2 # compute the squares

    return omega_z*cos(sqrt(omega_x+omega_z)) + omega_x



def current_sheet(turns_density):

    "magnetic field of an infinite current sheet per unit current"

    return MU_0/2*turns_density





class BaseFlipper:

    "Base flipper class"

    def __init__(self, name, position=0, thickness=0.01, turns_density=1):
@@ -38,9 +41,14 @@ class BaseFlipper: 
        "the flipper"

        return f"{self.name:8s} (pos={self.position:g}m d={self.thickness:g}m n={self.turns_density:g})"



    def current(self, lam):

        "flipper current"

        return HMN/GAMMA_N * PI/(MU_0*self.turns_density*self.thickness*lam)

    def current(self, arg, rotation=None):

        """calculate flipper current

            arg      - wavelength or magnetic field (if rotation is None)

            rotation - rotation angle in radians (if given arg is wavelength)

            returns current in Amperes

        """

        bfield = arg if rotation is None else rotation/(OMEGA_N*self.thickness*arg)

        return bfield/current_sheet(self.turns_density)/2 # factor of 2 for two sheets per flipper





class FlipperPi(BaseFlipper):
@@ -57,26 +65,30 @@ class FlipperPi(BaseFlipper): 


        (bx_ext, _ , bz_ext) = (0, 0, 0) if b_ext is None else b_ext



        sigma = HMN * PI/(self.thickness*GAMMA_N)

        sigma = PI/OMEGA_N/self.thickness

        f0 = sqrt((sigma/lam0)**2 - bx_ext**2) - bz_ext

        fl = sqrt((sigma/lam )**2 - bx_ext**2) - bz_ext



        return fl/f0



    def current(self, arg, rotation=PI):

        "flipper current"

        return super().current(arg, rotation=rotation)



class FlipperPi2(BaseFlipper):

    """Simple pi/2-flipper class """



    def current(self, lam):

    def current(self, arg, rotation=PISQRT2):

        "flipper current"

        return super().current(lam)/sqrt(2)

        return super().current(arg, rotation=rotation)



    @staticmethod

    def curve(lam, lam0, **_kwargs):

        """pi/2-flipper ramp curve

        lam  - array of neutron wavelengths

        lam0 - reference wavelength (lambda_max at SNS-NSE)"""

        lam     = np.asarray(lam)

        omega_x = _pisqrt2*lam/lam0

        lam     = np.atleast_1d(lam)

        omega_x = PISQRT2*lam/lam0

        omega_z = np.asarray([opt.newton(rxx13,PI/2,args=(x,)) for x in omega_x])

        return omega_z/omega_x
@@ -107,17 +119,21 @@ def tof_curve(flipper, lmax, dlam, points, sample_to_source, **kwargs): 
    lam     = (lam[1:]+lam[:-1])/2

    tofmax  = dhmn * lmax

    tofmax  = tofmax - int(tofmax*freq)/freq

    zeroidx = int(np.round(points*tofmax*freq))-1

    zeroidx = int(np.round(points*tofmax*freq))



    # the "curve"

    curve = flipper.curve(lam, lmax, b_ext=b_ext)

    cmin, cmax = min(curve), max(curve)



    # ramp currents

    ramp  = curve[-1] + np.arange(nrewind+1)/(nrewind+1)*(curve[0]-curve[-1])

    # keep at max

    hold  = np.ones((ngap-nrewind-1,))*curve[0]

    ramp  = np.arange(1,nrewind+1)/(nrewind+1)*(cmax-cmin) + cmin



    # keep at max

    hold  = np.ones((ngap-nrewind+1,))*cmax

    #

    # build and roll the curve

    curve = np.hstack((ramp, hold, curve))

    curve = np.roll(curve, zeroidx)

    curve = np.hstack((ramp, hold, curve[1:])) # drop the first point

    curve = np.roll(curve, zeroidx)/cmin # normalize to cmin

    #

    return curve

# End of file

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