OPTIONS FOR THE DESIGN OF A NEW PICK-UP AND SCHEDULE G. Kotzian, LIU-SPS High Bandwidth Damper Review, July 30, 2013

HBTFB - High Bandwidth Transverse Feedback Wideband feedback system (GHz bandwidth) Intra-bunch GHz transverse feedback system Help stabilize beam against Ecloud and TMCI effects Under development with LARP supported by: US-LARP CERN SPS LIU Project Analog Front End Analog Back End Signal Processing BPM Kicker Power Amp ADC DAC Beam transverse position pre-processed sampled position “slices” calculated correction data correction signal pre-distortiondrive signal

OVERVIEW A.Design Considerations B.Strip-line Pick-up Options Coupler type pick-ups Current PU: Exponential coupler BPW(A) Strip-line BPCL Long Strip-line Option Variation of strip-line for scrubbing beam optimization B.Alternative PUs Electromagnetic PU: Position Sensitive Wall Current Monitor Exotic (i.e. electro-optic) PUs Faltin-type (not treated today) C.Schedule On-going activities Possible Roadmap

Design considerations Option to split system into several bands to cover entire frequency range  Centre frequencies of instabilities moving during acceleration  Adequate adjustment of loop delay and for all bands (5 deg approx. ~14 ps)  Overlap of bands becomes delicate Option for direct digitization with high bandwidth ADCs (GSPS)  Direct representation of beam transverse motion  Gain and phase equalization realizable using digitally implemented filters  Loop delay adjustment follows acceleration Analog BW: 10 MHz – 2 GHz Lower end covered by classical damper (dipole mode, large injection oscillations require strong damping) Upper limit defined by Nyquist frequency for subsequent sampling (fs > 4 GSPS) SPS 200 MHz RF System: 5ns bucket length With 4 GSPS  20 slices/bucket NB: observed signal is always position x intensity  holds information on longitudinal and transverse motion

Design considerations SCOPE: PU design; requires taking into account properties of pre-processing chain (cables, filters, attenuators/amplifiers, orbit suppression signal processing) GOAL: provide analog representation of beam transverse position for direct digitization with high bandwidth ADC (few GSPS) Equalizer BPM ADC Passive Closed Orbit Suppression 7/8’’ transmission line Equalizer 7/8’’ transmission line Delay adjustment

Coupler type pick-ups ^ |Z T (  )|  … ZTZT Frequency Domain Z T (  ) = Z T j sin(  ) e -j  /2 ^ f=1/(2  ) L Beam  = 2 L/c  load or short notches in freq. response PU output voltage, matched in 50 Ω direct representation of the bunch profile logarithmic scale: dBMax(1V/m), 70 dB range

Current PU: Exponential Stripline (BPWA) (Courtesy W. Höfle, SPS Studies WG - August 5, 2008) Four such couplers installed in SPS (four electrodes at 45 degrees) … but: phase response not linear with frequency ! Developed for SPS by T. Linnecar, Reference: CERN-SPS-ARF-SPS/78/17 Special case: no notches in frequency response due to tapering of electrodes

Exponential PU – Beam response w/o coaxial transmission linewith coaxial transmission line Gaussian bunch Ideal PU response Reversed PU PU response with dispersive and corrugated cable  shows ringing in time domain Ringing due to cable TF

Bunchlet in BPWA 2 short bunches, 5ns spaced PU response w/o cables Reversed PU PU response with dispersive and corrugated cable Observation: BWPA length of 375 mm was chosen to just separate two successive bunches no mixing when bunches are split; however not so evident when closer May need another iteration taking into account the implemented or an improved phase compensation K. Pollock, Signal Equalizer for SPS ECloud/TMCI Instability Feedback Control System (Courtesy W. Höfle)

Exponential strip-line BPW (A/B) Advantages mechanically short L = 375 mm no notches in frequency response due to tapering of electrodes 4 electrodes, can be wired horizontally or vertically Limitations Vacuum chamber cut-off frequency for TE11 mode at 1.64 GHz (D=107mm, BPWA/BPWB) resp GHz (D=155mm, BPW) phase response not linear, thus group delay frequency dependent; need to compensate for PU response and cable dispersion impedance variation & matching was difficult to control in the design (T. Linnecar)  production of matching not perfect 1 of the 4 existing devices may be damaged, will be inspected during LS1  For MDs and demonstrator system OK; fully functional system: what are better options? NamePositionDescriptionDiameter/TE11 cut-off BPW317.98horizontal PU, 3x H-183; for beam observation in CCR155 mm / GHz BPWA319.01vertical PU (reversed), used as vertical kicker (RF injected in downstream end)107 mm / 1.64 GHz BPWA319.31vertical PU, 3x H-183, 2x 6dB attn. at each coupling port; for beam observation in CCR, may be damaged  inspection during LS1 107 mm / 1.64 GHz BPWB321.01vertical PU, 6 dB/12W attn. at each coupling port; H-183 hybrids replaced by two resistive combiners ( ) 107 mm / 1.64 GHz

Strip-line BPCL Courtesy: R. Steinhagen

Long strip-line Option calculations based on: J-P. Papis, L. Vos, CERN SL/91-g (BI) BPWA BPCL stay-clear aperture limit

Long strip-line – Option II

Variation of strip-line for scrubbing beam optimization Challenge in direct representation of bunch profiles using coupler-type PUs: the residual reflection spoils the response.  exponential coupler uses tapered electrodes  long strip-line with delayed reflection Quest: Absorb the residual reflection in bulk material Studies on-going … localized load material with adjusted bulk conductivity

Position Sensitive Wall-Current Monitor Option BPM based on M. Gasior design AB-Note BDI: A proposal for an Inductive Pick-Up for Measuring the Position and Current of Proton Beams in the Transfer Lines between the Linac 2 and the PSB adapted from and based on an inductive pick-up (IPU), developed for position and current measurement in CTF3 Bandwidth starting from 100 kHz up >1 GHz should be feasible 1-10 Ohm loading, differential L~70 nH taken from: M. Gasior, AB-Note BDI Provided by R. Steinhagen 100 kHz1 GHz  Scale this version to fit to the SPS vacuum chamber

EO-PBM – Electro-Optical Pick-Up Working principle similar to LCD/TFT screen: particle beam modulates crystal birefringence (double refracting) → intensity of two laser beams A & B, position ~ (A-B)/(A+B) Pro: very wide-band signal, no beam power issues, true DC response (alt. AGM?) Only lab tests for the full assembly until now Hope to have a in-vacuum prototype ready for post-LS1 → to be published SPS-LSS4.421SPS-ECA4 P A P A p-beam 532/1550 nm Laser MM or SM (not matched) OM4 (matched) DAQ: Scope & Multiband-Inst._Mon. Σ & Δ tunnel EO-Hybrid Analog FE x2 locally stabilised ΔT< 0.1-1°C (Courtesy R. Steinhagen)

On-going activities Pick-up design 3D-EM simulations and documentation of long strip-line design Verification using HFSS and CST Microwave/Particle Studio Evaluation of “terminated” strip-line performance (also thermal simulation including losses) Optimization for length reduction/tapering of electrodes Closed Orbit Suppression  suppression of common mode signal  to avoid amplifier saturation and good usage of dynamic range (digitization) Fact-finding: programmable step attenuators with required resolution 0.1 dB/step Preparation of hardware & firmware development (for use with VME form factor) Coaxial transmission lines New smooth-wall coaxial transmission lines installed during LS1(lower dispersion than corrugated cables) Characterisation measurement method utilizes “synthetic TDR” via commercial VNAs (high sensitivity) Equalize cable length (equal pairs of same length for pick-up A and B outputs)

Possible Roadmap New Pick-up design Finalize EM-design until end down selection which PU to be realized Produce design drawings in Prototyping and lab testing , to be ready for installation at the latest in LS2 Closed orbit suppression Start HW development after fall 2013 Possible synergies with other active projects, e.g. damper HW upgrade project Finalize HW and firmware in 2014 Ready for tests with beam in the SPS after LS1 Coaxial transmission lines May require new analog compensation filters Adapt analog front-end for optimum signal levels to fast ADCs

THANK YOU FOR YOUR ATTENTION!

Button electrodes - Variant of electrostatic electrodes signal current flowing onto (behind) the electrode beam velocity current of a centred pencil beam voltage onto termination R termination resistance