Inertial Sensor Development for a 1 TeV Linear Collider

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Inertial Sensor Development for a 1 TeV Linear
Collider

• Eric Doyle, Josef Frisch, Linda Hendrickson,
  Thomas Himel, Thomas Markieweicz, Justin May,
  Richard Partridge, Andrei Seryi
• Work Supported by Department of Energy Contract
  DE-AC03-76SF0515

The proposed 1 TeV X-band electron / positron
linear collider will produce beams with
approximately 1 nanometer vertical sizes at the
collision point. The final focusing magnets for
this accelerator must be held relative to each
other at the nanometer level. Beam Beam
interactions provide a signal for a high gain
feedback for frequencies below 1Hz, but
additional stabilization is required at higher
frequencies. One option is to use inertial
sensors (geophones) to provide a feedback signal.
Requirements Noise lt 1 nanometer integrated
above 1Hz. Frequency response 0.1Hz to 50Hz.
Must operate in 1 Tesla magnetic field Compact -
202010 cm
Technology RF capacitive position
sensing Position feedback through DSP Feedback
force -gt measured acceleration BeCu spring,
Ceramic moving parts
Prototype sensor
Parameters Test mass 40 grams Suspension
frequency 1.5Hz Mechanical Q gt100 Theoretical
thermal mechanical noise lt1.510-10M/s2/Hz1/2. Cap
acitor Sensor gap 300 microns Theoretical
thermal electronic noise lt thermal noise Vacuum
ltfew microns
Technical Issues Creep Spring must be operated
at high stress to maximize unwanted 2nd mode
frequency (from ANSYS simulations) Lifetime of
sensor limited by creep of spring. Tests at
design 75 of yield stress give creep life gt20
years.
Creep chart
Technical Issues Magnetic sensitivity Housing,
fixed supports Non-magnetic stainless,
Aluminum Motor (for creep / temperature
compensation) Piezoelectric motor (PicomotorTM),
nonmagnetic in final system Cantilever
Prototype uses Aluminum cantilever. (conductor
dB/dt problem) Final version uses Aluminum Oxide
cantilever Mass Tungsten in prototype (magnetic
in first prototype!) Final version HfO2 9.8g/cc,
(heaviest non-radioactive ceramic)
Technical Issues Creak High spring stress can
produce creak Also ,early prototype had problems
with creak in support components (support
position pot)
Technical Issues Temperature Sensitivity Non-mag
netic requirement prevents the use of
temperature compensated spring materials.
Calculated temperature sensitivity .01 M/s2 /
C, 10 nano-degree temperature variation (during
measurement time) would limit resolution. Design
incorporates multiple thermal filters, gold
plating for radiation shielding. Temperature
variations probably major noise source below
0.1Hz.
Preliminary Data not verified! Initial testing
of sensor vs. Strekheisen STS-2. Testing done in
noisy lab environment high Frequency noise
(5-100Hz) exceeds sensor feedback actuator
strength. Noise floor lt10-8m/s2/sqrt(Hz) Noise
1/f corner 0.1Hz.
Future Work Test in quiet location Install
fully non-magnetic components Try reduced spring
stress to reduce creak. Add temperature
stabilization