NLC - The Next Linear Collider Project
Seismometer Mechanical
Design - update 6/18/03
Phase I – Spring Design, Fab Bench-top unit
Phase II – Vac chamber/RF feed-thrus
Phase III – Internal RF details, etc
NLC - The Next Linear Collider Project
Background
• Requirements
– <1nm integrated noise above 0.1 hz
( ~2x10-9 m/s2/Hz1/2)
– high frequency limit > 60hz
– small size (must fit inside detector)
– non-magnetic
• No commercial sensors available
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Initial Concept
f1 = 1.1 hz
f2 = 6.8 hz
Mass: 65gm, tungsten
Beam: L = 5 in
Spring: BeCu .004” x .6” x 2”
Problem: low freq second mode due to curvature of spring under load
Solution: pre-bend spring so it’s flat when loaded (Æf2 ~ 100 hz)
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Pre-bent Spring
Pre-bent Spring
BeCu Alloy 25, .004 in thick
deflection = 81o
stress = 125 ksi (.75 σyp)
creep rate (est) = .014% to .1 %/month
2nd mode ~ 100 hz
Y-shape beam raises freq of transverse bending mode to >100 hz
Flat Spring for Horizontal Unit
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Creep Test
Creep data not available for room temperature
Extrapolate creep rate from high temp stress relaxation data
Creep Test – to verify
Flat & Pre-bent Springs - shown
Also testing long-term stability in twisting
1.5 years of data so far
Results (see plot): Creep rate ~ max calculated
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Seismometer - Schematic
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
CAD model of Benchtop Unit
BeCu Spring
Electrodes
.25in FR4
PC Board
Cylindrical joint for
initial alignment
Picomotor for creep
compensation
Y-shaped beam
Tungsten Mass
Electrode Assy on
adjustable 3-point mount
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Phase I – Benchtop Unit
upper
electrode
beam
spring
mass
Lower
electrode
picomotor
horizontal set-up
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Thermal Sensitivity, Damping
• Spring elastic modulus varies with temperature
o
– dE/dT = -5000 psi/ F
o
o
– dY/dT = .0015 in/ F = 3.9e4 nm/ F
– effect verified in creep test
• Remedies
– insulate enclosure
– Au plate enclosure interior and spring
– possible interior thermal radiation shields
• Air in electrode gap damps motion
– Q ~1
• Remedy
– Operate in vacuum e-4 torr --> Q ~100
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Phase II – Vac Chamber, etc
New:
1.
Picomotor
a. HV rated
b. new brackets, etc
2. Vac chamber (to reduce
air damping)
a. o-ring seals
b. windows
c. feed-thrus, SMB
d. new cables .047” coax
e. Au plated (thermal)
3. Springs
a. Au plated (thermal)
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Phase II – Electrical Feed-thrus
PICOMOTOR
LINEAR POT
RF DRIVEN
SPLIT
.047 CABLES
HARD-SOLDERED
RF DRIVE
DELAY LINE
ELECTROSTATIC DRIVE
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Phase II in situ
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Phase III mods in progress
NONCONDUCTIVE
BEAM & MASS
ELECTRODES
MISC
MECHANICAL
MODS
FEED-THRUS
PCB SPLITTER
/DELAY
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Phase III Mods
• Misc Mechanical
– ease assembly, simplify feed-thrus, etc
• PCB Delay/Splitter
– improved RF
– predictable delay
• Electrodes
– accommodate new wiring
– increased capacitance
• Beam & Mass
– non-conductive to prevent eddy currents
– Beam: ceramic, carbon or boron composite
– Mass: W-loaded ceramic or epoxy
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Splitter/Delay board
Approximate delay =
1.1 ns for .063”
PTFE/glass strip-line
board
Twisted pair interface
to electrodes
Eric Doyle 6/18/03
NLC - The Next Linear Collider Project
Beam & Mass Materials Issues
To minimize effect of eddy currents:
Beam:
- stresses low (ANSYS result)
- need high stiffness, low weight, low conductivity
- materials considered: ceramic, CFC, BFC
Mass:
- need high density, low conductivity, ability to plate conductive surface
- materials considered: W-loaded ceramic or epoxy, Thoria, HfO2
Eric Doyle 6/18/03