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Precision Beam Monitors for COSY Jülich

Precision Beam Monitors for COSY Jülich. | Dr. Helmut Soltner. Precision Beam Monitors for COSY Jülich. ● Analysis of present beam position monitors (BPM) ● Suggestion of alternative beam current monitors ● Alternative beam position monitor ● Outlook.

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Precision Beam Monitors for COSY Jülich

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  1. Precision Beam Monitorsfor COSY Jülich | Dr. Helmut Soltner

  2. Precision Beam Monitors for COSY Jülich ● Analysis of present beam position monitors (BPM)● Suggestion of alternative beam current monitors● Alternative beam position monitor● Outlook

  3. Analysis of present beam position monitors (BPM) Beam current monitors Equivalent circuit

  4. „We need an improvement of the beam position monitors to measure smaller beam displacements in the future EDM ring.“ Status:Current beam postion monitors:Established in the 90‘s.Resolution as of today: 0.5 mmGood enough for COSY: „Nobody was interested in higher accuracy till now“

  5. „We need an improvement of the beam position monitors to measure smaller beam displacements in the future EDM ring.“ Analysis of the situation, characterization of the current BPM system:● Preamplifier electronics provides a minimum bandwidth of 10 kHz● Noise measurement with Lock-In amplifer SR 840 (Stanford Research) leads to SV1/2 = 10 nV/√Hz. ● Total voltage noise of 10 nV/√Hz x √10 kHz = 1.2 µV corresponding to about 3.2 µm of displacement resolution

  6. Prerequisites: noise The sensitivity of a sensor is ultimately limited by its internal noise. For electronics: Thermally activated motion of charge carriers in resistors. Nyquist Theorem For 50 Ω

  7. Prerequisites : noise For 50 Ω Noise detrmines the ultimate resolution.

  8. Laboratory setup BPM Lock-In Amplifier Spectrum analyzer

  9. ● Future:Can you tell whether there is a displacement of the beam of 10 nm after one year? ● Specifications for the future system:Make a measurement after one year for one week and say, whether we had a displacement of 10 nm. The beam should not be affected by the measurement (mechanically, electrically)

  10. Suggestion of alternative beam current monitors Proton beam generates the same magnetic field pattern as a current-carrying wire

  11. Proton beam generates the same magnetic field pattern as a current-carrying wire: Flux capture by single winding

  12. Proton beam generates the same magnetic field pattern as a current-carrying wire: Rogowski coil

  13. Proton beam generates the same magnetic field pattern as a current-carrying wire Frequency: f = 750 kHz Number of turns: N = 512 Beam current: I = 0.1 mA Coil cross section: A = π/4 * d2 Permeability constant µ0 = 4*π*10-7 Vs/(Am) Induced voltage Uind = 95 µV

  14. Sensitivity to dispacements of the beam: BEM calculation The induced voltage is practically independent of the beam position.

  15. Sensitivity to inclination of the coil: BEM calculation The induced voltage is practically independent of the coil inclination.

  16. Determination of coil parameters Prerequisites – II : skin effect The current density drops exponentially from the surface Skin depth: λ =1/√(ωμσ)

  17. Determination of coil parameters Prerequisites – II : skin effect The current is concentrated in the surface of the wire. Skin depth: λ =1/√(πωμ0σ) It is no use to choose a wire diameter much larger than the skin depth.

  18. Rogowski coil as an alternative beam current monitoras part of a resonance circuit –The principle of Lock-in amplification Signals with frequencies other than the measuring frequency are rejected.

  19. Prerequisites – II : Lock-In detection

  20. Prerequisites – II : Lock-In detection

  21. Rogowski coil as an alternative beam current monitor as part of a resonance circuit –Design of parameters Inductance of the coil Self capacitance of the coil [pF] Resonant frequency L C Quality factor

  22. Rogowski coil as an alternative beam current monitor as part of a resonance circuit –Design of parameters in MathCad

  23. Rogowski coil as an alternative beam current monitor Vacuum test for the next beam time.

  24. Rogowski coil as an alternative beam position monitor - + Two half torus coils with opposite winding orientation.

  25. Rogowski coil as an alternative beam position monitorBEM Simulation of beam displacement

  26. Rogowski coil as an alternative beam position monitorresonance circuit Q = 50 Uind = 4.7 mV

  27. Outlook: Coupling of Rogowski coil to a SQUID: Superconducting Quantum Interference Device

  28. SQUID principle (Superconducting Quantum Interference Device)

  29. Summary:●The present BPMs can in principle provide a beter sensitivity compared to how they have been operated so far. ●Rogowski coils pepresent an attractive development for comparison and replacement, and may later be coupled to SQUIDs for ultimate sensitivity.

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