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Commit 8e88c4e2 authored by Keon Hee KIM's avatar Keon Hee KIM
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Updated CircularResistiveWall class to replace numerical integrations with an... 

Updated CircularResistiveWall class to replace numerical integrations with an analytical forms for improved performance.
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mbtrack2/impedance/resistive_wall.py
+ 60
− 52
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......@@ -5,7 +5,7 @@ Define resistive wall elements based on the WakeField class.
import numpy as np
from scipy.constants import c, epsilon_0, mu_0
from scipy.integrate import quad
from scipy.special import wofz
from mbtrack2.impedance.wakefield import Impedance, WakeField, WakeFunction
......@@ -45,7 +45,7 @@ class CircularResistiveWall(WakeField):
Resistive wall WakeField element for a circular beam pipe.
Impedance from approximated formulas from Eq. (2.77) of Chao book [1].
Wake function formulas from [2].
Wake function formulas from [2, 3].
Parameters
----------
......@@ -71,7 +71,11 @@ class CircularResistiveWall(WakeField):
----------
[1] : Chao, A. W. (1993). Physics of collective beam instabilities in high
energy accelerators. Wiley.
[2] : Skripka, Galina, et al. "Simultaneous computation of intrabunch and
[2] : Ivanyan, Mikayel I. and Tsakanov, Vasili M. "Analytical treatment of
resistive wake potentials in round pipes." Nuclear Instruments and Methods
in Physics Research Section A: Accelerators, Spectrometers, Detectors and
Associated Equipment 522, no. 3 (2004): 223-229.
[3] : Skripka, Galina, et al. "Simultaneous computation of intrabunch and
interbunch collective beam motions in storage rings." Nuclear Instruments
and Methods in Physics Research Section A: Accelerators, Spectrometers,
Detectors and Associated Equipment 806 (2016): 221-230.
......@@ -126,9 +130,11 @@ class CircularResistiveWall(WakeField):
def LongitudinalWakeFunction(self, time, exact=False, atol=1e-20):
"""
Compute the longitudinal wake function of a circular resistive wall
using Eq. (22), or approxmiated expression Eq. (24), of [1]. The
approxmiated expression is valid if the time is large compared to the
characteristic time t0.
using Eq. (11), of [1], or approxmiated expression Eq. (24), of [2].
The approxmiated expression is valid if the time is large compared
to the characteristic time t0.
Eq. (11) in [1] is completely equivalent to Eq. (22) in [2].
If some time value is smaller than atol, then the fundamental theorem
of beam loading is applied: Wl(0) = Wl(0+)/2.
......@@ -151,31 +157,40 @@ class CircularResistiveWall(WakeField):
References
----------
[1] : Skripka, Galina, et al. "Simultaneous computation of intrabunch and
[1] : Ivanyan, Mikayel I. and Tsakanov, Vasili M. "Analytical treatment of
resistive wake potentials in round pipes." Nuclear Instruments and Methods
in Physics Research Section A: Accelerators, Spectrometers, Detectors and
Associated Equipment 522, no. 3 (2004): 223-229.
[2] : Skripka, Galina, et al. "Simultaneous computation of intrabunch and
interbunch collective beam motions in storage rings." Nuclear Instruments
and Methods in Physics Research Section A: Accelerators, Spectrometers,
Detectors and Associated Equipment 806 (2016): 221-230.
"""
wl = np.zeros_like(time)
idx1 = time < 0
wl[idx1] = 0
if exact == True:
idx2 = time > 20 * self.t0
idx2 = time == 0
idx3 = np.logical_not(np.logical_or(idx1, idx2))
wl[idx3] = self.__LongWakeExact(time[idx3], atol)
idx4 = np.isclose(0, time, atol=atol)
factor = 4 * self.Z0 * c / (np.pi * self.radius**2) * self.length
wl[idx2] = 0.25 * factor
wl[idx3] = self.__LongWakeExact(time[idx3], factor)
wl[idx4] *= 0.5
else:
idx2 = np.logical_not(idx1)
wl[idx2] = self.__LongWakeApprox(time[idx2])
wl[idx2] = self.__LongWakeApprox(time[idx2])
return wl
def TransverseWakeFunction(self, time, exact=False):
"""
Compute the transverse wake function of a circular resistive wall
using Eq. (25), or approxmiated expression Eq. (26), of [1]. The
approxmiated expression is valid if the time is large compared to the
characteristic time t0.
using Eq. (11), of [1], or approxmiated expression Eq. (26), of [2].
The approxmiated expression is valid if the time is large compared
to the characteristic time t0.
Exact expression (Eq. (25) from [1]) is corrected by factor (c * t0).
Eq. (11) in [1] is completely equivalent to Eq. (25) in [2].
Corrected the typos in the last two terms in exact expression
(Eq. (11), of [1]).
Parameters
----------
......@@ -191,66 +206,59 @@ class CircularResistiveWall(WakeField):
References
----------
[1] : Skripka, Galina, et al. "Simultaneous computation of intrabunch and
[1] : Ivanyan, Mikayel I. and Tsakanov, Vasili M. "Analytical treatment of
resistive wake potentials in round pipes." Nuclear Instruments and Methods
in Physics Research Section A: Accelerators, Spectrometers, Detectors and
Associated Equipment 522, no. 3 (2004): 223-229.
[2] : Skripka, Galina, et al. "Simultaneous computation of intrabunch and
interbunch collective beam motions in storage rings." Nuclear Instruments
and Methods in Physics Research Section A: Accelerators, Spectrometers,
Detectors and Associated Equipment 806 (2016): 221-230.
"""
wt = np.zeros_like(time)
idx1 = time < 0
wt[idx1] = 0
if exact == True:
idx2 = time > 20 * self.t0
idx2 = time == 0
idx3 = np.logical_not(np.logical_or(idx1, idx2))
wt[idx3] = self.__TransWakeExact(time[idx3])
factor = ((8 * self.Z0 * c**2 * self.t0) / (np.pi * self.radius**4) *
self.length)
wt[idx3] = self.__TransWakeExact(time[idx3], factor)
else:
idx2 = np.logical_not(idx1)
wt[idx2] = self.__TransWakeApprox(time[idx2])
wt[idx2] = self.__TransWakeApprox(time[idx2])
return wt
def __LongWakeExact(self, time, atol):
wl = np.zeros_like(time)
factor = 4 * self.Z0 * c / (np.pi * self.radius**2) * self.length
for i, t in enumerate(time):
val, err = quad(lambda z: self.__function(t, z), 0, np.inf)
wl[i] = factor * (
np.exp(-t / self.t0) / 3 * np.cos(np.sqrt(3) * t / self.t0) -
np.sqrt(2) / np.pi * val)
if np.isclose(0, t, atol=atol):
wl[i] = wl[i] / 2
def __LongWakeExact(self, t, factor):
wl = np.real(factor / 12 * ( 4 * np.exp(-1 * t / self.t0)
* np.cos(np.sqrt(3) * t / self.t0)
+ wofz(1j * np.sqrt(2 * t / self.t0))
- wofz(np.exp(1j * np.pi / 6) * np.sqrt(2 * t / self.t0))
- wofz(-1 * np.exp(-1j * np.pi / 6) * np.sqrt(2 * t / self.t0)) ) )
return wl
def __TransWakeExact(self, time):
wt = np.zeros_like(time)
factor = ((8 * self.Z0 * c**2 * self.t0) / (np.pi * self.radius**4) *
self.length)
for i, t in enumerate(time):
val, err = quad(lambda z: self.__function2(t, z), 0, np.inf)
wt[i] = factor * (
1 / 12 *
(-1 * np.exp(-t / self.t0) * np.cos(np.sqrt(3) * t / self.t0) +
np.sqrt(3) * np.exp(-t / self.t0) *
np.sin(np.sqrt(3) * t / self.t0)) - np.sqrt(2) / np.pi * val)
def __TransWakeExact(self, t, factor):
wt = np.real(factor / 24 * ( 2 * np.exp(-1 * t / self.t0)
* ( np.sqrt(3) * np.sin(np.sqrt(3) * t / self.t0)
- np.cos(np.sqrt(3) * t / self.t0) )
+ wofz(1j * np.sqrt(2 * t / self.t0))
+ np.exp(-1j * np.pi / 3) * wofz( np.exp(1j * np.pi / 6)
* np.sqrt(2 * t / self.t0) )
+ np.exp(1j * np.pi / 3) * wofz( -1 * np.exp(-1j * np.pi / 6)
* np.sqrt(2 * t / self.t0) ) ) )
return wt
def __LongWakeApprox(self, t):
wl = -1 * (1 / (4 * np.pi * self.radius) * np.sqrt(self.Z0 * self.rho /
(c * np.pi)) /
t**(3 / 2)) * self.length
wl = -1 * (1 / (4 * np.pi * self.radius) *
np.sqrt(self.Z0 * self.rho / (c * np.pi)) /
t**(3 / 2)) * self.length
return wl
def __TransWakeApprox(self, t):
wt = (1 / (np.pi * self.radius**3) *
np.sqrt(self.Z0 * c * self.rho / np.pi) / t**(1 / 2) *
self.length)
np.sqrt(self.Z0 * c * self.rho / np.pi) / t**(1 / 2) *
self.length)
return wt
def __function(self, t, x):
return ((x**2 * np.exp(-1 * (x**2) * t / self.t0)) / (x**6 + 8))
def __function2(self, t, x):
return ((-1 * np.exp(-1 * (x**2) * t / self.t0)) / (x**6 + 8))
class Coating(WakeField):
......
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