An Inductive PickUp IPU for Beam Position and

An Inductive Pick-Up (IPU) for Beam Position and Current Measurement Marek GASIOR, CERN, AB/BDI email: marek. gasior@cern. ch 6 th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators 5 – 7 May 2003, Mainz, Germany Contributed Talk #01 M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement

An Inductive Pick-Up (IPU) for Beam Position and Current Measurement Marek GASIOR, CERN, AB/BDI email: marek. gasior@cern. ch § M. Gasior, CERN Third CLIC Test Facility § Evolution from a WCM to an IPU § IPU Design and Model § Active Hybrid Circuit § Results An Inductive Pick-up for Beam Position and Current Measurement 2

Third CLIC Test Facility (CTF 3) Delay Loop, f’ = f 2, I’B = IB 2 1. 5 s bunch train 5 pieces of 140 ns Drive Beam Linac (f =1. 5 GHz, IB = 3. 5 A) A 1. 5 s bunch train, some 2300 pulses Drive Beam Decelerator Main Beam Accelerator Combiner Ring, f” = f’ 5, I”B = I’B 5 5 pieces of 140 ns 1 train of 140 ns Requirements for a DBL Beam Position Monitor: § Low cut-off frequency at least 10 k. Hz to limit a droop of the 1. 5 s pulse to about 10 % § High cut-off frequency at least 100 MHz to observe fast beam movements (rise time some 3 ns) § The bandwidth 10 k. Hz – 100 MHz means 4 decades § The pick-up structure must be as transparent as possible for the beam and corresponding longitudinal coupling impedance should be low in the GHz range M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 3

Wall Current Monitor (WCM) principle § § § The BEAM current is accompanied by its IMAGE A voltage proportional to the beam current develops on the RESISTORS in the beam pipe gap The gap must be closed by a box to avoid floating sections of the beam pipe The box is filled with the FERRITE to force the image current to go over the resistors The ferrite works up to a given frequency and lower frequency components flow over the box wall M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 4

WCM as a Beam Position Monitor § § § For a centered BEAM the IMAGE current is evenly distributed on the circumference The image current distribution on the circumference changes with the beam position Intensity signal ( ) = resistor voltages summed Position dependent signal ( ) = voltages from opposite resistors subtracted The signal is also proportional to the intensity, so the position is calculated according to / Low cut-offs depend on the gap resistance and box wall (for ) and the pipe wall (for ) inductances M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 5

A Beam Position Sensitive WCM § A position sensitive WCM is still used in the CERN PS § It contains 96 resistors of 10 in 32 groups of 3 in series), V /IB 1 § Position measurement bandwidth is 9 MHz – 1. 5 GHz (2. 2 decade) § Current measurement bandwidth is 3 MHz – 1. 5 GHz (2. 7 decade) G. C. Schneider, A 1. 5 GHz Wide-Band Beam Position and Intensity Monitor for the Electron-Positron Accumulator (EPA), CERN/PS 87 -9 (BT), 1987 M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 6

A new design: Inductive Pick-Up (IPU) M. Gasior, CERN § An eight electrode “tight” design to avoid resonances in the GHz range § The electrodes cover 75 % of the circumference § The electrode internal diameter is only 9 mm larger then the vacuum chamber of 40 mm and it is occupied by the ceramic insertion (alumina) § The transformers are as small as possible to gain high frequency cut-off with many turns § The transformers are mounted on a PCB § The connection between the electrodes and the cover is made by screws § Electrode diameter step is occupied by the ceramic tube § The tube is titanium coated on the inside An Inductive Pick-up for Beam Position and Current Measurement 7

Inductive Pick-Up – A Low Frequency Model § Electrodes are combined in pairs so that each transformer sees half of the load § Frequency low cut-offs are limited by connection parasitic resistances § Each transformer has one calibration turn (not shown) n = 30, RS 7 giving RT 0. 1 and RP 4 m f. L 150 Hz (RP with L 5 H) f. L 10 k. Hz (RP with L 70 n. H) The electrode signal high cut-off frequency is beyond 300 MHz M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 8

Inductive Pick-Up New Design § The ceramic tube is coated with low resistance titanium layer, resistance: end-to-end 10 , i. e. 15 /� § Primary circuit has to have small parasitic resistances (Cu pieces, Cu. Be screws, gold plating) § Tight design, potential cavities damped with the ferrite § The transformers are mounted on a PCB and connected by pieces of microstrip lines (minimizing series inductances) M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 9

Active Hybrid Circuit (AHC) M. Gasior, CERN § More than four decades of bandwidth required § High Common Mode Rejection Ratio needed, at least -40 d. B at 100 MHz § Active circuit with a differential amplifier § AD 8129 – “active feedback” architecture, i. e. one feedback network needed § Datasheet CMRR is -42 d. B at 100 MHz § Bandwidth 200 MHz with a gain of 10 An Inductive Pick-up for Beam Position and Current Measurement 10

Active Hybrid Circuit – Performance M. Gasior, CERN § The CMRR at 100 MHz is as high as 55 d. B (datasheet 42 d. B) § The CMRR for frequencies below 10 MHz is limited by the measurement setup § signal high cut-off frequency about 200 MHz An Inductive Pick-up for Beam Position and Current Measurement 11

IPU and AHC – Frequency Characteristics § A wire method with a 50 coaxial setup which the IPU is a part § signal – flat to 0. 5 d. B within 5 decades, almost 6 decades of 3 d. B bandwidth (no compensation) § signal – 5 decades (four decades + one with an extra gain for low frequencies) BW: 300 Hz – 250 MHz ( 6 decades) BW: 1 k. Hz – 150 MHz (> 5 decades) M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 12

IPU and AHC – Displacement Characteristics A thin wire forming a coaxial line was displaced diagonally across the pick-up aperture. The measurement was done with a network analyzer: signal was applied to the wire and hybrid signals were observed. M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 13

IPU – Longitudinal Coupling Impedance reference § The pick-up was inserted into a 50 coaxial line (again the wire method) § The signal drop along the pick-up was evaluated by measuring the S 21 scattering transmission coefficient § As a reference was measured the same setup with the pick-up replaced by an equivalent length of a tube (to be independent of the setup) M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 14

IPU – Time Domain Reflectometry Measurements M. Gasior, CERN § The wire method with the 50 coaxial setup § A fast step was applied to the coaxial line and the reflection was observed § The electrode diameter step is visible only for components of lower frequency. Higher frequency components do not see the step since they flow over the titanium low resistance coating An Inductive Pick-up for Beam Position and Current Measurement 15

IPU and AHC – Beam tests in the CTF 2 IPU AHC - CH 2 M. Gasior, CERN H - CH 3 V - CH 4 § Electron beam of one 1 n. C , 5 ps. RMS bunch § The signals have the rise time of about 2 ns (one division) An Inductive Pick-up for Beam Position and Current Measurement 16

Conclusions § An inductive pick-up and a dedicated active hybrid circuit were designed for the drive beam linac of the CTF 3 § They allow to measure beam position with a bandwidth of 5 decades and absolute beam current over 6 decades § The chain IPU-AHC can be tested and calibrated in place with precise current pulses, applied to calibration turns of the IPU transformers § Neither the pick-up nor the AHC contain adjustable elements § The pick-up longitudinal coupling impedance is limited to about 10 in the GHz range Very many thanks to J. Belleman, J. Durand, J. L. Gonzalez, L. Søby, J. P. Potier, Y. Cuvet and J. L. Chouvet http: //www. cern. ch/gasior/pap/dipac 2003. ppt M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 17

Thank you for your attention http: //www. cern. ch/gasior/pap/dipac 2003. ppt M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 18

Emergency slide – the parameter table M. Gasior, CERN An Inductive Pick-up for Beam Position and Current Measurement 19