16/01/12DITANET Topical Workshop on Beam Position Monitors Reentrant Beam Position Monitors DITANET Topical Workshop on Beam Position Monitors 16 th – 18 th January 2012 Claire Simon

16/01/12DITANET Topical Workshop on Beam Position Monitors Introduction Two types of BPMs based on a radiofrequency reentrant cavity are 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 resolution Resolution measured 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  operated in single bunch and multi-bunches modes. Re-entrant BPM (left) installed on the linac FLASH.

16/01/12DITANET Topical Workshop on Beam Position Monitors E-XFEL - Accelerator Complex 17.5 GeV 800 accelerating cavities 1.3 GHz / 23.6 MV/m 25 RF stations 5.2 MW each 100 accelerator modules

16/01/12DITANET Topical Workshop on Beam Position Monitors Cold BPM (unit cell) (Injector) Modules along machine with 32 re-entrant BPMs  Injector 1M+3 rd : 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) Schematic from D. Noelle

16/01/12DITANET Topical Workshop on Beam Position Monitors Cold Reentrant BPM for the E-XFEL quadrupole BPM bellows HOM absorber gate valve 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

16/01/12DITANET Topical Workshop on Beam Position Monitors 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 mm length (minimized to satisfy the constraints imposed by the cryomodule) 78 mm aperture. Eigen modesF (MHz)QlQl (R/Q) l (Ω) at 5 mm (R/Q) l (Ω) at 10 mm Measured Calculated Monopole mode Dipole mode Twelve holes of 5 mm diameter drilled at the end of the re-entrant part for a more effective cleaning. Feedthroughs are positioned in the re-entrant part to reduce the magnetic loop coupling and separate the main RF modes (monopole and dipole) Signal from one pickup Cu-Be RF contacts welded in the inner cylinder of the cavity to ensure electrical conduction. Dowel pins to adjust transverse alignment with quadrupole

16/01/12DITANET Topical Workshop on Beam Position Monitors Test bench in CryHolab Test in a horizontal cryostat at Saclay (Cryholab) He tube to cool down BPM BPM integrated in CRYHOLAB. CRYHOLAB. Frequency (MHz)Ql Measured in Cryholab at 300 K Estimated at 6 K Measured in Cryholab at 6 K Monopole mode Dipole mode Reflection and transmission measurements

16/01/12DITANET Topical Workshop on Beam Position Monitors Feedthroughs  Feedthroughs mounted on BPM body with Conflat gaskets  Brazed ceramic Manufacturing Process 1.Machining of feedthroughs (carried out by company) 2.Cryogenic test in N2 according to: (carried out by company and by CEA Saclay to check) 3.Transport of feedthroughs to DESY 4.Particle cleaning of feedthroughs 5.RGA and leak test of feedthroughs in clean room (ISO5) at DESY Cold test procedure for feedthroughs 1. Feedthroughs leak tested 2. Feedthroughs plunged into LN2 3. Operation repeated 3 times 4. Feedthroughs leak tested

16/01/12DITANET Topical Workshop on Beam Position Monitors Process steps for the reentrant cavity BPM (1) 1.Firing at 950°C and machining body (carried out by company) 2.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 3.Welding of RF contacts and EB welding of 2 parts composing the BPM (carried out by company) 4.Cleaning, leak test and RGA (carried out by CEA/Saclay)  Cleaning in US bath  Leak test: leak rate must be <= 1* mbar l /s  Residual gas analyze : sum of residual gases with mass < 45 not exceed of total pressure which is ≤ mbar 5. Process in clean room ISO5 (carried out by DESY)  Particle Cleaning, Residual gas analyze, Transport to ISO3 6.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

16/01/12DITANET Topical Workshop on Beam Position Monitors Frame of re-entrant RFFE electronics First RFFE prototype installed  First RFFE electronics prototype designed with a reference frequency of MHz installed at FLASH  Digital electronics 8-channel Fast ADC with 14 bits resolution used MHz

16/01/12DITANET Topical Workshop on Beam Position Monitors 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 Beam measurements with first RFFE prototype

16/01/12DITANET Topical Workshop on Beam Position Monitors Cavity BPM Hardware Concept 2 Reentrant Cavity RF front-ends, GPAC as digital back-end. By Courtesy of Raphael Baldinger, Goran Marinkovic More information, please see E-XFEL/SwissFEL BPM Electronics‘ talk PAUL SCHERRER INSTITUT

16/01/12DITANET Topical Workshop on Beam Position Monitors Second RFFE prototype Option: for charge < 0.1 nC

16/01/12DITANET Topical Workshop on Beam Position Monitors  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 Evolution of the second prototype

16/01/12DITANET Topical Workshop on Beam Position Monitors  Damping time is given by using the following formula : Time Resolution Damping Time cavity only Time resolution cavity + electronics BPM9.4 ns40 ns With fd: dipole mode frequency Q l d: loaded quality factor for the dipole mode  Considering the system (cavity + signal processing), the time resolution is determined, since the rising time to 95% of a cavity response corresponds to 3τ. Time resolution for re-entrant BPM RF signal measured at one pickup ΔT =1µs 100 bunches read by the re-entrant BPM 20 ns 20 mV 40 ns IF signal behind Lowpass Filter on channel Δ

16/01/12DITANET Topical Workshop on Beam Position Monitors CALIFES linac – Probe Beam of CTF3 6 BPMs are installed on the CALIFES lina c 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: ns Train spacing (rep. rate): 5 Hz Specifications Energy ~ 170 MeV Emittance < 20 .mm.mrad Charge per bunch : 0.6 nC Energy spread: <2% Number of bunches : – 226 Collaboration between CERN and CEA Saclay

16/01/12DITANET Topical Workshop on Beam Position Monitors Reentrant Part Reentrant Cavity BPM for CALIFES Bent coaxial cylinder designed to have:  a large frequency separation between monopole and dipole modes  a low loop exposure to the electric fields Cavity fabricated with titanium and as compact as possible : ~125 mm length and 18 mm aperture 4 mm gap BPM

16/01/12DITANET Topical Workshop on Beam Position Monitors E field H field RF Characteristics With Matlab and the HFSS calculator, we computed R/Q Ratio. and k=w/c R: the Shunt impedance and Q: the quality factor Due to machining, dipole mode frequencies are different for each BPMs. Standard deviation on the dipole mode: ~ 10 MHz Eigen modes F (MHz)QlQl (R/Q) (Ω) Calculated with HFSS in eigen mode Measured in the CLEX Calculated with HFSS in eigen mode Measured in the CLEX Calculated Offset 5 mm Calculated Offset 10 mm Monopole mode Dipole mode

16/01/12DITANET Topical Workshop on Beam Position Monitors 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.

16/01/12DITANET Topical Workshop on Beam Position Monitors 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. Good linearity in a range ± 1.5 mm RMS resolution: ~58 µm on the Y channel with beam jitter ~98 µm on the X channel with beam jitter Calibration results from horizontal (left) and vertical (right) steering

16/01/12DITANET Topical Workshop on Beam Position Monitors 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