Inertial Sensor Development for a 1 TeV Linear Collider

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

Requirements

Noise: < 1 nanometer integrated above 1Hz.Frequency response: 0.1Hz to 50Hz. Must operate in 1 Tesla magnetic fieldCompact - ~20×20×10 cm

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.

Technology:

RF capacitive position sensingPosition feedback through DSPFeedback force -> measured accelerationBeCu spring, Ceramic moving parts

Parameters

Test mass 40 gramsSuspension frequency 1.5HzMechanical Q >100Theoretical thermal mechanical noise <1.5×10-10M/s2/Hz1/2.Capacitor Sensor gap ~300 micronsTheoretical thermal electronic noise < thermal noiseVacuum <few microns

Prototype sensor

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 >20 years.

Creepchart

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)

75% y.p. springs: flat (ch4) & pre-bent (ch6) displ. vs timecompared to max and min predicted rates

00.020.040.060.080.1

0.120.140.160.180.2

0 200 400 600 800 1000

elapsed time (days)

displacement (in)

pre-bent

flat

min rate

max rate

Technical Issues: Temperature Sensitivity

Non-magnetic requirement prevents the use of temperaturecompensated 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.

Future Work:

Test in quiet locationInstall fully non-magnetic componentsTry reduced spring stress to reduce creak.Add temperature stabilization

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 <~10-8m/s2/sqrt(Hz)Noise 1/f corner ~0.1Hz.