STABILISATION AND PRECISION POINTING QUADRUPOLE MAGNETS IN THE COMPACT LINEAR COLLIDER S. Janssens, P. Fernandez Carmona, K. Artoos, C. Collette, M. Guinchard The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD * ULB

Scope: Compact Linear Collider (CLIC) 2  Lepton collider complementary to LHC  Linear due to energy loss in turn  1 chance for collisions CLIC:  Vert. Beam size 1nm at ip  Hor. Beam size 40 nm at ip  For high collision rate

Scope: CLIC 3 The main beam accelerator: Accelerating structure:  To accelerate the beam Quadrupole magnets:  Mass kg  Length mm  200 T/m  To focus the beam after accelerating structures Problem: Misalignment of quadrupoles due to:  Ground motion  External forces (watercooling, ventilation,…) Result:  Beam-Beam offset (missing each other)  Beam growth (fewer collisions) Accelerating structure

Stabilisation Requirements Goal for 3992 CLIC Main Beam Quadrupoles:  Stability vertical magnetic axis 1.5 nm int. 1Hz  Stability lateral magnetic axis 5 nm int. 1 Hz 4 Type 4: 2m, 400 kgType 1: 0.5 m, 100 kg A. Samoshkin Additional requirements:  Modify position of quadrupoles:  Range ± 5 μ m  Increments 10 to 50 nm  Precision ± 0.25 nm  Available Space  Compatibility alignment  Transportability  Stray magnetic fields + radiation DNA 2 nm

Characterisation ground vibration 5 Cultural noise -Human activity -Incoherent -Highly variable Earth noise - Coherent Micro seismic peak -> Sea waves Reduced by Method 1: Beam based feedback Deeper tunnel 2-5 nm int. 1Hz Reduction needed <100 Hz Method 2: vibration isolation

Active Isolation Strategies Add virtual mass Feedback control principle

Sky-hook damper (D.C. Karnopp, 1969 ) Active Isolation Strategies Feedback control principle

Position feedback would be great ! Active Isolation Strategies Feedback control principle Chosen configuration:  Piezo actuator  Vibration sensor on top (Position Feedback)  Additional vibration sensor on the bottom (Feedforward)

Simplified modelling 9 Modelling efforts:  Different controllers  Flexibility of the magnet  Coarse alignment stage  Combination  Introduction of a joint Parametric 2D modelling:  Number of legs  Leg attachements points  Leg Angles  Additional support structures (Shear pins, bellow,…)

 Advantages  Flexibility  Easy reuse of IP  Noise only added at ADC and DAC  Disadvantages  Single events upsets  Higher latency  Expensive  High power  Advantages  Minimum latency  Simplicity  Less radiation effects expected  Disadvantages  Fixed configuration 10 Digital implementationAnalogue implementation Hybrid controller S. Janssens, P. Fernandez, A&T Sector Seminar, Geneva, 24 November 2011

11 Controller electronics: Hybrid 2 analogue chains + positioning offset Local electronics ADCs digitize signals For remote monitoring Communication to remote control center with optical fiber S. Janssens, P. Fernandez, A&T Sector Seminar, Geneva, 24 November 2011 Configurable parameters Gain Feedforward Gain Feedback Lag pole and zero frequencies Lead pole and zero frequencies Output offset (positioning) Feedforward low pass filter frequency SPI

12 Hybrid controller schematic Digital S. Janssens, P. Fernandez, A&T Sector Seminar, Geneva, 24 November 2011

13 Testbenches used 1 d.o.f. (membrane) 2 d.o.f. (xy-guide) Type 1 Water-cooled magnet

14 Results Vibration isolation results Type 1 magnet:  Basic set-up  Magnet on  Watercooling nominal  0.5 nm integrated r.m.s.

15 Testbenches used Xy-guide prototype:  Seismometer feedback and feedforward (similar results)  Testing of mechanical two leg proposal with shear pins  Same actuators and mass as final design  Positioning tests with multiple sensor crosscheck (vertical while moving laterally) Positioning results:  nm hard to measure  Good repeatability  Precision within +/ nm  Interferometer drift

Full type 1 and Type 4 prototype 16  Type 1 (100 kg) prototype finished (re)construction  Type 4 (400 kg) prototype produced

Current study 17 New absolute vibration sensor:  Larger bandwidth  Better luminosity performance (after filter adjustment)  Under magnet  Or collocated with actuator  Adapted to accelerator environment Controllerluminosity loss No stabilization68% Seismometer FB maximum gain13% Seismometer FB medium gain6% Seismometer FB maximum gain +FF4% Inertial reference mass11% Inertial reference. mass. + HP filter3% =>0.7% Courtesy of J. Pfingstner

Current study 18 Vibration sensor requirements:  Resonance frequency: 5 Hz +/- 1 Hz  Maximum overshoot d max : 2  Spurious modes: >100 Hz  Sensitivity: [V/ μm]  Operating temperature: °C  Temperature sensitivity: 1 μ m/°C  Humidity: 20-80%  Radiation level Gy/year  Stray magnetic fields  Maximum defined noise curve based on simulations

PACMAN subjects 19 Increasing range of actuators to mm:  Reduce time between realignment  Increase robustness against temperature changes  Larger range to use quadrupoles as dipoles  With similar precision! Required redesigns:  New actuator/New combination of actuators  New guidance system  Adapted relative measurement system A. Samoshkin

Conclusions 20  A feedback + feedforward system with stiff piezo actuator was chosen to cope with external forces on the system to the nano metre level.  It was demonstrated with models and in a test bench that it is technically feasible to stabilise and position a mass better than the required level at 1Hz.  A concept design of the stabilisation support based on the validated actuator pair with is being constructed.

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