From 9cbba893e543a4b0389883af2c95fdf80663bea5 Mon Sep 17 00:00:00 2001
From: Kevin Kuns <kevin.kuns@ligo.org>
Date: Thu, 14 Jan 2021 16:16:41 -0500
Subject: [PATCH] add infinite volume residual gas damping
---
gwinc/ifo/aLIGO/__init__.py | 9 +++--
gwinc/ifo/aLIGO/ifo.yaml | 2 +
gwinc/ifo/noises.py | 80 +++++++++++++++++++++++++++++++------
gwinc/noise/residualgas.py | 43 ++++++++++++++++++--
4 files changed, 114 insertions(+), 20 deletions(-)
diff --git a/gwinc/ifo/aLIGO/__init__.py b/gwinc/ifo/aLIGO/__init__.py
index 821e4887..961f88fa 100644
--- a/gwinc/ifo/aLIGO/__init__.py
+++ b/gwinc/ifo/aLIGO/__init__.py
@@ -30,9 +30,12 @@ class ExcessGas(nb.Budget):
)
noises = [
- ExcessGasH2,
- ExcessGasN2,
- ExcessGasH2O,
+ ExcessGasScatteringH2,
+ ExcessGasScatteringN2,
+ ExcessGasScatteringH2O,
+ ExcessGasDampingH2,
+ ExcessGasDampingN2,
+ ExcessGasDampingH2O,
]
diff --git a/gwinc/ifo/aLIGO/ifo.yaml b/gwinc/ifo/aLIGO/ifo.yaml
index eca5e990..28666445 100644
--- a/gwinc/ifo/aLIGO/ifo.yaml
+++ b/gwinc/ifo/aLIGO/ifo.yaml
@@ -37,11 +37,13 @@ Infrastructure:
pressure: 4.0e-7 # Pa
mass: 3.35e-27 # kg; Mass of H_2 (ref. 10)
polarizability: 7.8e-31 # m^3
+ TestMassPressure: 4e-7
N2:
pressure: 1.33e-8
mass: 4.65e-26
polarizability: 1.79e-30
+ TestMassPressure: 4.65e-8
H2O:
pressure: 1.33e-8
diff --git a/gwinc/ifo/noises.py b/gwinc/ifo/noises.py
index 17f83d4a..f3467595 100644
--- a/gwinc/ifo/noises.py
+++ b/gwinc/ifo/noises.py
@@ -764,7 +764,7 @@ class ExcessGas(nb.Noise):
def calc(self):
cavity = arm_cavity(self.ifo)
- n = noise.residualgas.residual_gas_cavity(
+ n = noise.residualgas.residual_gas_scattering(
self.freq, self.ifo, cavity, self.ifo.Infrastructure.ResidualGas)
# FIXME HACK: it's unclear if a phase noise in the arms like
# the excess gas noise should get the same dhdL strain
@@ -779,55 +779,109 @@ class ExcessGas(nb.Noise):
return n * 2 / sinc_sqr
-class ExcessGasH2(nb.Noise):
- """Excess gas for H2
+class ExcessGasScatteringH2(nb.Noise):
+ """Excess gas scattering for H2
"""
style = dict(
- label='H2',
+ label='H2 scattering',
color='xkcd:red orange'
)
def calc(self):
cavity = arm_cavity(self.ifo)
species = self.ifo.Infrastructure.ResidualGas.H2
- n = noise.residualgas.residual_gas_cavity(
+ n = noise.residualgas.residual_gas_scattering(
self.freq, self.ifo, cavity, species)
dhdl_sqr, sinc_sqr = dhdl(self.freq, self.ifo.Infrastructure.Length)
return n * 2 / sinc_sqr
-class ExcessGasN2(nb.Noise):
- """Excess gas for N2
+class ExcessGasScatteringN2(nb.Noise):
+ """Excess gas scattering for N2
"""
style = dict(
- label='N2',
+ label='N2 scattering',
color='xkcd:emerald'
)
def calc(self):
cavity = arm_cavity(self.ifo)
species = self.ifo.Infrastructure.ResidualGas.N2
- n = noise.residualgas.residual_gas_cavity(
+ n = noise.residualgas.residual_gas_scattering(
self.freq, self.ifo, cavity, species)
dhdl_sqr, sinc_sqr = dhdl(self.freq, self.ifo.Infrastructure.Length)
return n * 2 / sinc_sqr
-class ExcessGasH2O(nb.Noise):
- """Excess gas for H2O
+class ExcessGasScatteringH2O(nb.Noise):
+ """Excess gas scattering for H2O
"""
style = dict(
- label='H2O',
+ label='H2O scattering',
color='xkcd:water blue'
)
def calc(self):
cavity = arm_cavity(self.ifo)
species = self.ifo.Infrastructure.ResidualGas.H2O
- n = noise.residualgas.residual_gas_cavity(
+ n = noise.residualgas.residual_gas_scattering(
self.freq, self.ifo, cavity, species)
dhdl_sqr, sinc_sqr = dhdl(self.freq, self.ifo.Infrastructure.Length)
return n * 2 / sinc_sqr
+
+
+class ExcessGasDampingH2(nb.Noise):
+ """Residual gas damping for H2
+
+ """
+ style = dict(
+ label='H2 damping',
+ color='xkcd:red orange',
+ linestyle='--',
+ )
+
+ @nb.precomp(sustf=precomp_suspension)
+ def calc(self, sustf):
+ species = self.ifo.Infrastructure.ResidualGas.H2
+ n = noise.residualgas.residual_gas_damping(
+ self.freq, self.ifo, species, sustf)
+ return 4 * n
+
+
+class ExcessGasDampingN2(nb.Noise):
+ """Excess gas damping for N2
+
+ """
+ style = dict(
+ label='N2 damping',
+ color='xkcd:emerald',
+ linestyle='--',
+ )
+
+ @nb.precomp(sustf=precomp_suspension)
+ def calc(self, sustf):
+ species = self.ifo.Infrastructure.ResidualGas.N2
+ n = noise.residualgas.residual_gas_damping(
+ self.freq, self.ifo, species, sustf)
+ return 4 * n
+
+
+class ExcessGasDampingH2O(nb.Noise):
+ """Excess gas damping for H2O
+
+ """
+ style = dict(
+ label='H2O damping',
+ color='xkcd:water blue',
+ linestyle='--',
+ )
+
+ @nb.precomp(sustf=precomp_suspension)
+ def calc(self, sustf):
+ species = self.ifo.Infrastructure.ResidualGas.H2O
+ n = noise.residualgas.residual_gas_damping(
+ self.freq, self.ifo, species, sustf)
+ return 4 * n
diff --git a/gwinc/noise/residualgas.py b/gwinc/noise/residualgas.py
index 61cb962f..bdf31f5e 100644
--- a/gwinc/noise/residualgas.py
+++ b/gwinc/noise/residualgas.py
@@ -7,18 +7,18 @@ from numpy import sqrt, log, pi
from .. import const
-def residual_gas_cavity(f, ifo, cavity, species):
- """Residual gas noise strain spectrum in an evacuated cavity.
+def residual_gas_scattering(f, ifo, cavity, species):
+ """Residual gas noise strain spectrum due to scattering.
Noise caused by the passage of residual gas molecules through the
- laser beams in a cavity.
+ laser beams in a cavity due to scattering.
:f: frequency array in Hz
:ifo: gwinc IFO structure
:cavity: arm cavity structure
:species: molecular species structure
- :returns: arm displacement noise power spectrum at :f:
+ :returns: arm strain noise power spectrum at :f:
The method used here is presented by Rainer Weiss, Micheal
E. Zucker, and Stanley E. Whitcomb in their paper Optical
@@ -55,3 +55,38 @@ def residual_gas_cavity(f, ifo, cavity, species):
zint[zint < 0] = 0
return zint
+
+
+def residual_gas_damping(f, ifo, species, sustf):
+ """Noise due to residual gas damping for one test mass
+
+ :f: frequency array in Hz
+ :ifo: gwinc IFO structure
+ :species: molecular species structure
+ :sustf: suspension transfer function structure
+
+ :returns: displacement noise
+ """
+ kT = ifo.Infrastructure.Temp * const.kB
+ mass = species.mass
+ radius = ifo.Materials.MassRadius
+ thickness = ifo.Materials.MassThickness
+ thermal_vel = sqrt(kT/mass) # thermal velocity
+
+ # pressure near the test mass
+ # possibly different from the pressure in the arms due to outgassing near
+ # the test mass
+ if 'TestMassPressure' in species:
+ pressure = species.TestMassPressure
+ else:
+ pressure = species.pressure
+
+ # infinite volume viscous damping coefficient for a cylinder
+ # table 1 of https://doi.org/10.1016/j.physleta.2010.06.041
+ beta_inf = pi * radius**2 * pressure/thermal_vel
+ beta_inf *= (1 + thickness/(2*radius) + pi/4)
+
+ # convert force to displacement noise using the suspension susceptibility
+ noise = 4 * kT * beta_inf * abs(sustf.tst_suscept)**2
+
+ return noise
--
GitLab