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Claire Simon

Reentrant Beam Position Monitors DITANET Topical Workshop on Beam Position Monitors 16 th – 18 th January 2012. Claire Simon. Introduction. Two types of BPMs based on a radiofrequency reentrant cavity are developed :.

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Claire Simon

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  1. Reentrant Beam Position MonitorsDITANET Topical Workshop on Beam Position Monitors16th – 18th January 2012 Claire Simon

  2. Introduction Two types of BPMsbased on a radiofrequencyreentrantcavityare developed: • One monitor is developed for the E-XFEL (Thirsty two of those monitors will be installed in E-XFEL cryomodules): • aperture of 78 mm • designed to work at cryogenic temperature in a clean environment • can get a high resolution and the possibility to perform bunch to bunch measurements. • One prototype is installed in a warm part in the • Free electron LASer in Hamburg (FLASH), at DESY.. and shown a resolutionResolutionmeasured around 4 µm with 1 nC and • dynamic range around ± 5 mm. • The second monitor is developed for the probe beam (CALIFES) of CLIC Test Facility (CTF3) at CERN: • aperture of 18 mm • operatedin single bunch and multi-bunches modes. Re-entrant BPM (left) installed on the linac FLASH.

  3. E-XFEL - Accelerator Complex 17.5 GeV 100 accelerator modules 800 accelerating cavities 1.3 GHz / 23.6 MV/m 25 RF stations 5.2 MW each

  4. Cold BPM (unit cell) Schematicfrom D. Noelle • 100+1 (Injector) Modules along machine with 32 re-entrant BPMs • Injector 1M+3rd: Button2x • Linac 1 4M: Button4x(1unit) • Linac 2 12M: 2xReentrant2x(1unit), 2xButton4x(1 unit) • Linac 3 84M: 14x Reentrant2x(1 Unit), 14 x Button 4x (2 Unit)

  5. HOM absorber bellows BPM quadrupole gate valve Cold Reentrant BPM for the E-XFEL Specifications Single bunch resolution (RMS): 50 µm Drift over 1 hour: 5 µm Max. resolution range: ± 3 mm Reasonable signal range : ± 10 mm Linearity: 10% Transverse alignment tol. (RMS): 300 µm Charge dependence : 50 µm Collaboration between DESY, PSI and CEA Saclay

  6. Design • Arranged around the beam tube and forms a coaxial line which is short circuited at one end. • Cavity fabricated with stainless steel as compact as possible : • 170 mmlength (minimized to satisfy the constraints imposed by the cryomodule)78 mm aperture. Cu-Be RF contacts welded in the inner cylinder of the cavity to ensure electrical conduction. Feedthroughs are positioned in the re-entrant part to reduce the magnetic loop coupling and separate the main RF modes (monopole and dipole) Dowel pins to adjust transverse alignment with quadrupole Twelve holes of 5 mm diameter drilled at the end of the re-entrant part for a more effective cleaning. Signal from one pickup

  7. Test bench in CryHolab Test in a horizontal cryostat at Saclay (Cryholab) BPM He tube to cool down BPM integrated in CRYHOLAB. CRYHOLAB. Reflection and transmission measurements

  8. Feedthroughs • Feedthroughs mounted on BPM body with Conflat gaskets • Brazed ceramic • Manufacturing Process • Machining of feedthroughs(carried out by company) • Cryogenic test in N2 according to: (carried out by company and by CEA Saclay to check) • Transport of feedthroughs to DESY • Particle cleaning of feedthroughs • RGA and leak test of feedthroughs in clean room (ISO5) at DESY • Cold test procedure for feedthroughs • Feedthroughs leak tested • Feedthroughs plunged into LN2 • Operation repeated 3 times • Feedthroughs leak tested

  9. Process steps for the reentrant cavity BPM (1) • Firing at 950°C and machining body (carried out by company) • Copper coating (acid bath) of 2 parts (carried out by company). • Using of tools to protect reentrant part and outside parts which are not copper coated. • Ultrasonic bath + Heat treatment 300°C for 1 h + visual check • Thickness measurement 12 µm ± 2 µm with 1 µm of Nickel to do the contact • between stainless steel and copper • Welding of RF contacts and EB welding of 2 parts composing the BPM (carried out by company) • Cleaning, leak test and RGA (carried out by CEA/Saclay) • Cleaning in US bath • Leak test: leak rate must be <= 1*10-10mbar l /s • Residual gas analyze : sum of residual gases with mass < 45 not exceed 10-3 • of total pressure which is ≤ 10-8mbar • Process in clean room ISO5 (carried out by DESY) • Particle Cleaning, Residual gas analyze, Transport to ISO3 • Process in clean room ISO3 (carried out by DESY) • Assembly of quad and BPM • High pressure rinsing of quad-BPM assembly • Assembly feedthroughs and checking • Assembly of quad-BPM unit with valve and pump tube with valve • Leak check and RGA spectrum total unit • Packing and Transport to Saclay BPM Mounting in an XFEL prototype cryomodule

  10. First RFFE prototype installed • First RFFE electronics prototypedesigned with a reference frequency of 9.028 MHz installed at FLASH • Digital electronics 8-channel Fast ADC with 14 bits resolution used. 9.028 MHz 9.028 MHz Frame of re-entrant RFFE electronics

  11. Beam measurements with first RFFE prototype Calibration results from horizontal (left) and vertical (right) steering at 0.5 nC • Good linearity in a range ±3 mm • RMS resolution ~ 10 µm on Y channel with beam jitter • ~ 48 µm on X channel with beam jitter

  12. Cavity BPM Hardware Concept ByCourtesyof Raphael Baldinger, Goran Marinkovic More information, pleasesee E-XFEL/SwissFEL BPM Electronics‘ talk PAUL SCHERRER INSTITUT 2 Reentrant Cavity RF front-ends, GPAC as digital back-end.

  13. Second RFFE prototype Option: for charge < 0.1 nC

  14. Evolution of the second prototype • E-XFEL infra- structure requirement: spacing will be N*111ns, with N=integer and >=2 • Reference frequency : 216 MHz and then adding of a frequency divider to get 9 MHz • Adding of crystal oscillator on PCB board in backup if reference signal 216 MHz fails • Give a flag, showing something is wrong with the 216 MHz •  No exact value of the position – error position high • New design of sum channel with band pass filter at the dipole mode frequency and IQ demodulation •  Normalize position signal to reference (amplitude and phase) • if small beam time arrival moved can be determined. •  change of phase can be determined • Adding of ADC clock (design from M. Stadler/PSI) • Adding of Hot Swap control design with new components (design from R. Kramert and R. Baldinger/PSI) • Interfaces: “Two I2C buses” to control all RFFE functions • Differential outputs integrated on PCB board • Option 2 charge ranges: low charge (from 100 pC to 20 pC) • adding switches, variable attenuator and amplifier on X and Y channels

  15. ΔT =1µs 20 mV 20 ns RF signal measured at one pickup 40 ns Time Resolution • Damping time is given by using the following formula : fd: dipole mode frequency Qld: loaded quality factor for the dipole mode With • Considering the system (cavity + signal processing), the time resolution is determined, since the rising time to 95% of a cavity response corresponds to 3τ. IF signal behind Lowpass Filter on channel Δ Time resolution for re-entrant BPM 100 bunches read by the re-entrant BPM

  16. CALIFES linac – Probe Beam of CTF3 Specifications Energy ~ 170 MeV Emittance< 20 .mm.mrad Charge per bunch : 0.6 nC Energy spread: <2% Number of bunches : 1- 32 – 226 Bunch charge (single/multi bunch): 0.6 nC/ 6 nC/Nb Bunch length (rms) : 0.75ps Initial /final bunch spacing :5.3/1.8 ps, 1.6/0.5 mm Train length: 21 - 150 ns Train spacing (rep. rate): 5 Hz 6 BPMs are installed on the CALIFES linac Collaboration between CERN and CEA Saclay

  17. Reentrant Cavity BPM for CALIFES • Cavity fabricated with titanium and as compact as possible : • ~125 mmlength and 18 mm aperture • 4 mmgap BPM Reentrant Part • Bent coaxial cylinder designed to have: • a large frequency separation between monopole and dipole modes • a low loop exposure to the electric fields

  18. RF Characteristics Due to machining, dipole mode frequencies are different for each BPMs. Standard deviation on the dipole mode: ~ 10 MHz • With Matlab and the HFSS calculator, we computed R/Q Ratio. • and k=w/c R: the Shunt impedance and Q: the quality factor E field H field

  19. Signal Processing for CALIFES BPM • Hybrids installed close to BPMs in the CLEX • Multiport switches used to have one signal processing electronics • to control six BPMs. • Analog electronics with several steps to reject the monopole mode Hybrid couplers • RF electronics used synchronous detection with an I/Q demodulator.

  20. Beam tests • To calibrate the BPM: • Beam is moved with one steerer. • Calculate for each steerer setting, the relative beam position in using a transfer matrix between steerer and BPM (magnets switched off to reduce errors and simplify calculation). • Average of 15 points for each steerer setting. Calibration results from horizontal (left) and vertical (right) steering Good linearity in a range±1.5 mm • RMS resolution: ~58 µm on the Y channel with beam jitter • ~98 µmon the X channel with beam jitter

  21. Summary • E-XFEL reentrant BPM: • Mechanics (BPM body/Cavity + feedthroughs) under construction • Second RFFE prototype under construction • Tests at FLASH going on • CALIFES re-entrant BPM: • In using with beam • Special thanks to CERN, DESY, PSI and CEA/Saclay Colleagues for their collaboration to CALIFES and E-XFEL reentant BPMs • Thank you for your attention

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