Very Forward Detectors Workshop on beam position monitoring and detector alignment

24 April 2007BPM WS summary D. Swoboda2 FP420 BPM workshop Scope  Scope:  assess adequate technology for FP420 requirements  Criteria:  accuracy, resolution, acquisition speed (b-b)  Concept of alignment monitoring and detector positioning  Development time/cost  Resources:  i.e. available experts for mechanical layout, integration, electronics

24 April 2007BPM WS summary D. Swoboda3 Workshop structure  FP 420 Requirements  Alignment requirements  detector Alignment  moving beam pipe  Alignment strategies of other movable LHC detectors  FP 220 Alignment requirements  TOTEM Alignment  LHCb-VELO  Beam Position Monitors  BPM design  Signal Processing for BPMs  DESY experience with BPMs and moving beampipes  Discussion and conclusions

24 April 2007BPM WS summary D. Swoboda4 Basic considerations  Environment variables:  Cryostat, floor, pumps, …  Bake 300 deg C  Hi vs. Lo Q:  Hi Q impracticable for long LHC bunches (ringing)  Lo Q  long decay time  Calibration on-line;  Requires special calibration run  Beam intensity dependent

24 April 2007BPM WS summary D. Swoboda5 Proposals  Electrostatic pickups  cheap, available, limited development (electronics)  Integrate single bunch measurement over many turns  LHC BPM capable of bunch tagging  Multiplex electrode readings in single channel  89 μsec revolution time  full acquisition at > 1 Hz  Use moving + fix BPMs  No problems over 10 yrs with moving beam pipe

24 April 2007BPM WS summary D. Swoboda6 Different BPM types  Electrostatic  Button  Electromagnetic coupler  Resistive  Inductive  Cavity  Re-entrant cavity Image current HOM HF electron beams

24 April 2007BPM WS summary D. Swoboda7 BPM overview ElectrostaticButtonStrip lineWCMInductiveCavity Re-entr. Cavity LinearityVery goodBadGood SensitivityGood Very good Load imp.High50Ω FE close?YesNo Feed-thru’sYes NoYesyes Long. ImpBad Very good Good BadGood CostExpensiveCheapMedium

24 April 2007BPM WS summary D. Swoboda8  The ability to minimize the beam position errors  Error sources:  mechanic, magnetic and electronics  Offset for centered beam should be minimized  Beam based alignment techniques  Electronics error sources:  Impedance mismatching on interconnecting cables  Electromagnetic interference and noise on the input stage  Non-linearity and beam intensity dependence  Channels gain differences and calibration errors  Digitizer granularity Parameters: Accuracy

24 April 2007BPM WS summary D. Swoboda9 Parameters: Resolution  Important in colliding machines for luminosity  Minimum position difference that can be resolved  Single shot:  Averaged:  Limiting factors:  At low level, it depends on the input noise and the BW  For large signals, on the ADC resolution and the time jitter  State of art resolutions :  Single shot: < 0.02% of N a (few micron)  Averaged : < 20 ppm of N a (sub-micron)

24 April 2007BPM WS summary D. Swoboda10 Parameters: Stability  The measurement’s uncertainty will affect the global resolution of system.  Stability versus input signal  Stdev from a series of digitized positions measured over the whole dynamic range.  Position temperature coefficient  Slope of the position drift versus temperature  Long term position stability  Stdev of a series of digitized positions versus time

24 April 2007BPM WS summary D. Swoboda11 Parameters: Sensitivity & Dynamic  Sensitivity:  minimum input level (> 10 7 p/b)  Dynamic  different beam intensities conditions  maximum input level (saturation) versus  minimum input level (signal to noise ratio)  Processors using a discrimination level will not be limited by the S/N ratio, the lower limit being determined by the discriminator's threshold.

24 April 2007BPM WS summary D. Swoboda12 Parameters: Acquisition time  capability of resolving individual bunches and the absolute resolution of the processor  Several elements contribute to build-up this time:  The LP and BP filters  The switching and acquisition time (MPX processors)  The PLL’s time to synchronize (synchronous detector)  The AGC’s set-up time (constant sum)  The S&H circuit and the ADC’s conversion time

24 April 2007BPM WS summary D. Swoboda13 Signal processing methods beam position amplitude ratio  The beam position is uniquely related to the amplitude ratio of the induced signals on opposite electrodes.  Processing methods for position calculation:  Difference over Sum (  )  Analog and Digital process  Amplitude to phase/ time  Passive analog process  Log-ratio (logA-logB)  Active analog process

24 April 2007BPM WS summary D. Swoboda14 => Sub micron orbit stability => 0.2  m resolution at 300 Hz bandwidth Very close cooperation with WP Feedback. Decision: Before buying extensive tests of electronic necessary: Slow orbit resolution Fast data readout for fast orbit feedback. Part I: Readout electronic Same system also used in Diamond, Soleil. Planned for ALBA, ESRF… BPM for fast orbit correction

24 April 2007BPM WS summary D. Swoboda15 a slight touch of the cables may have led to jumps in the position value. This was proved online by watching the readout values, but no dedicated experiment was recorded. However, in the data one can find these kinds of jumps but we can correlate it no more with touches. Fig. 12 shows such a jump of  m but offline observations had shown some  m jumps, too. Jump of x-position ESRF with Libera some kind of slow oscillations, which are also visible in other samples. The setup was done in a way to avoid influenced from real beam oscillations, but this might be an residual effect of real beam oscillations or effects from LIBERA itself (1/f noise?). Note that the amplitude of these oscillations is very small (≈ 0.01 mm).

24 April 2007BPM WS summary D. Swoboda16 Beam structures

24 April 2007BPM WS summary D. Swoboda17 MPX description  Conceived for closed orbit of stable stored beams  The input signals are sequentially multiplexed into a single receiver  Multi-stage configuration of GaAs switches (Channels isolation >50 dB)  A BP filter selects the largest line of the spectrum  Pre-amplifier with AGC. Large input dynamic (>80 dB) and gain control (>50 dB) Noise Figure difficult to optimize.  Active mixer, driven by a frequency synthesizer, down convert to standard IF  IF amplifier with AGC and synchronous detection, by comparing the phase of a sample of carrier signal with a reference signal via a VCO in a phase lock loop (VLSI)  BP filter to suppress side-bands (100 kHz > BW< 1MHz).  De-multiplexer, Track & Hold and active matrix produce 7 signals (A, B, C, D, Sum, X, Y) store theirs values in four analog memories

24 April 2007BPM WS summary D. Swoboda18 Wide Band Time Normaliser

24 April 2007BPM WS summary D. Swoboda19 WPS Monitoring  Experience from HERA:  Long wires disturbed always any kind of service on magnets, water, cables, …  due to services, wires often got huge offsets, shorts, dismounted, … NO LONG WIRES IN PETRAIII

24 April 2007BPM WS summary D. Swoboda20 MOTOR LVDT Linear Guide Silicium Cerenkov Emergency Spring (for emergency) (for measurement moving) Moving Table Integration Detector & Movement

24 April 2007BPM WS summary D. Swoboda21 Position Monitoring Inductive Eddy Current

24 April 2007BPM WS summary D. Swoboda22 PU with reduced „working aperture”  A „collimator arrangement” to reduce the PU „working aperture”  If the jaw distance can be reduced to some 10 mm, then the „normalized accuracy” drops to 10 -3, which is much more reasonable  One PU electrode on one unit with the Si detector, giving excellent relative positioning  Jaw relative position measured with optical means  Possible dynamic jaw positioning with respect to the beam  Some know-how could be quickly transferred from the collimator people, especially if they could think about using a similar idea for the collimator system