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Development of non-intersecting transverse and longitudinal Profile Monitors

Development of non-intersecting transverse and longitudinal Profile Monitors P. Forck, A. Bank, W. Barth, C. Dorn, A. Peters, H. Reeg Gesellschaft f ür Schwerionenforschung, Darmstadt HIPPI Meeting 2005, Oxford Non intersecting methods for:

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Development of non-intersecting transverse and longitudinal Profile Monitors

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  1. Development of non-intersecting transverse and longitudinal Profile Monitors P. Forck, A. Bank, W. Barth, C. Dorn, A. Peters, H. Reeg Gesellschaft für Schwerionenforschung, Darmstadt HIPPI Meeting 2005, Oxford Non intersecting methods for: • Preventing destruction of intersecting material • Parallel observation at different locations • Monitoring of possible time-varying processes • Goal: Same precision as intersecting methods Outline: • Transverse profile monitor by Beam Induced Fluorescence BIF • Bunch Structure Monitor BSM based on residual gas electron spectroscopy • Transmission control by transformers

  2. The UNILAC Facility at GSI Achieved current for U-beam (tpulse = 200 μs) U73+: 2 emA U28+: 5 emA U4+: 16 emA 11.4 MeV/u 1.4 MeV/u Alvarez DTL High Current Injector (RFQ&IH) Single Gap Resonators

  3. Basics of Beam Induced Fluorescence Physics of fluorescence for N2 residual gas: p + N2 p + (N2+)*+ e-  p + N2+ +  + e- • Excitation of residual gas molecules by beam’s energy loss • Decay of N2+ levels generate light, blue light 390 nm <  < 470 nm, lifetime  = 60 ns. Realizations at Los Alamos, CERN, Orsay/Saclay, Uni-Frankfurt, GSI, COSY …. Fluorescence of 200 keV p in N2 (1961) LANL (D. Gilpatrick et al.) p at MeV in 5*10-5 mbar N2 Spectrum confirmed at CERN-PS/SPS from 1 to 450 GeV.

  4. Image Intensifier used at GSI-LINAC Technical realization of image intensifier at GSI: • Photo cathode S20 UV: γ-e- conversion, 15 to 25 % efficiency, 200 nm < λ < 650 nm • Two step MCP (25 mm diameter): 106 fold amplification • P 46 phosphor: e- -γconversion, 300 ns decay, 500 nm < λ < 600 nm • Minifying taper coupling to CCD chip (1/2’’): 7% transmission • Digital camera (Basler A311f): Firewire interface

  5. Test Setup at GSI-LINAC Installation behind Alvarez at 11 MeV/u Compact chamber with 150 mm insertion:

  6. Typical Result at GSI-LINAC Features: • Single photon counting • High resolution (here 0.3 mm/pixel), can easily be matched to application • Low background (sometime larger contribution by neutrons and ) Beam parameters at GSI-LINAC: 4.7 MeV/u Ar10+ beam I=2.5 mA equals to 1011 particles One single macro pulse of 200 s Vacuum pressure: p=10-5 mbar (N2) bump restricted ~1 m,  no influence to beam detected

  7. Application of Beam Induced Fluorescence Special application Variation during the macro pulse detectable: Switching of image intensifier  Exposure window during macro-pulse Signal treatment Statistics offers ‘offline’ optimization statistics  integration time  resolution Beam parameter: Ar10+ at 11 MeV/u with 8 mA

  8. In Preparation: Digital Interface for Firewire Digital camera offers:no loss of data-quality, versatile trigger, variable exposure time CCD-camera: Basler A311f featuring 649x494 pixels, 12 bit, 50 frames/s, IEEE 1394b Iris/MCP-gain variation: Remote controlled iris by local, ethernet based DAC Readout:HUB  optical fiber  real-time controller running RT-LabVIEW (NI) Status: DAQ in preliminary design phase DAQ System: LabVIEW Software:

  9. Novel Device for non-intersecting Bunch Shape Measurement Bunch-Shape seldom measured ! Scheme for novel device: • Secondary electrons for residual gas • Acceleration by electric field • Target localization by apertures and electro-static analyzer (Δy = 0.2 to 2 mm, Δz=0.2 to 1 mm) • rf-resonator as ‘time-to-space’ converter same as intersecting method (INR-Moscow) • Readout Ø70 mm MCP + Phosphor + CCD • Measurement done within one macro-pulse (not yet achieved due to back-ground)

  10. Realization for Bunch Shape Monitor at UNILAC E-field and the energy-analyzer: Installation for beam based tests:

  11. First Results from Bunch Shape Measurement at UNILAC Time information carried by the residual gas e- is transferred to spatial differences: Features: Single electron detection  Recorded within few macro-pulses Resolution better 50 ps = 20@108MHz Pressure bump required • Back-ground should be suppressed Beam parameters: Ni14+ at 11.4 MeV/u I=1.5 mA, 200 μs macro pulse Average: 8 macro pulses Pressure p=2*10-6 mbar Deflector power P=15 W

  12. First Application from Bunch Shape Measurement Variation of buncher: • Bunch shape was determined, influeneced by buncher • Pick-up: No measurable influence • Emittance determination possible Beam parameters: Ni14+ at 11.4 MeV/u I=2 emA, 200 μs macro pulse Average: 4 macro pulses Pressure p=10-5 mbar

  13. Beam Space Charge Contribution The residual gas e- are influenced by beam’s E-field in addition to the monitor E-field  Simulation of influence for different currents: Simulation method: e- trajectory calc. inside beam pipe & linear optics for energy analyzer Simulation parameter: Ekin= 11.4 MeV/u Parabolic bunch shape ∓0.5 ns longitudinal root points ∓5 mm transversal root points Variation of current (as for Ni14+ ) Simulation result:  stronger influence as for standard method, but still acceptable

  14. Dynamic Transmission control at UNILAC Variation of maximal loss via software input: 8 different input thresholds  8 different macro-pulse duration by electric chopper in front of RFQ • Save protection of equipment. FPGA-electronics: ACCT  V/f-converter  Up/down-counter: 1st ACCT ↑, 2nd ↓  Digital comparator  chopper ACCT clamping Integration window ACCT signal 40 μs/div

  15. Conclusion and Outlook Beam Induced Fluorescence BIF: First prototype in operation for ‘single photon counting’, usable during UNILAC operation Data acquisition in design phase (responsible engineer just hired) More investigation with high current required possible problems: broadening by space charge field, two-step excitation…. Non-intersecting Bunch Shape Monitor: Prove-of-principle performed, resolution lower than 50 ps = 20 @ 108 MHz Improvements for back-ground suppression in preparation beam test necessary Calculations and measurements of signal deformation due to beam space charge required Device in experimental condition  engineering design for operation required Dynamic Transmission control: System design finished Hardware in operation Improvements of operation control required

  16. Comparison for different Gases at p Source (Saclay) Choice of fluorescence gas: • High fluorescence yield at optical wave-length • Short lifetime of excited level • Good vacuum pumping Results:  Profile is independent of gas Care: • Long lifetime (N2+: 60 ns)  broadening by beam space charge • Light emitted by primary ions e.g. p + N2 H* + N2+ (only important for Ekin<1 MeV) • At large N2 density (p>10-3 mbar): Two-step processes e.g. N2+ e- N2* + e- possible Example: Ion source100 keV, 100 mA protons P. Ausset et al. (Orsay/Saclay) N2,Ne Ar,Kr Xe Profiles from different gasses

  17. Non-intercepting Profile Measurement based on Energy Loss Standard monitors: SEM-Grid, Wire-Scanner, Scintillation Screen, OTR-Screen… Disadvantage: intercepting, problems for time-varying processes Non-intercepting profile measurement: • Large beam power can destroy the material • Synchrotron: Monitoring during full cycle • LINAC: Monitoring at different locations, variation during the macro-pulse Physics:electronic stopping power Bethe-Bloch formula: - dE/dx = const · Zt ρt/At · Zp2 · 1/β2 · [ ln(const ·γ2β2/I) – β2] M. Plum et al.: p in N2 at CERN-PS cross section α dE/dx pc [GeV] ~ 1/Ekin (for Ekin> 1GeV nearly constant) Target e--density Strong dependence on projectile charge • Profile determination from ionization and excitation of residual gas.

  18. Technical Realization Possibilities for BIF Single MCP: - lower 103-fold amp. + higher resolution Example: CERN-SPS (160 μm/pix), R. Jung et al. Double MCP: +single photon, 106-fold amp. -resolution limited (MCP-channels) Example: GSI-LINAC (300 μm/pixel) Photo-cathode: Only for required wavelength interval to avoid dark currents, e.g. S20UV: 200<λ<650 nm  dark rate 500 e-/cm2/s, S25red:300<λ<900 nm  30000 e-/cm2/s Phosphor: Fast decay ↔ lower sensitivity e.g. P47: τ = 0.1 μs, P43: τ = 1000 μs IP43~ 4 · IP47 Problem: Radiation hardness of CCD camera

  19. BIF at Synchrotrons Example: CERN SPS and PSB,PS (R. Jung, M. Plum et al.) Photon yield scales like Bethe-Bloch energy loss ΔEd for p with 100 MeV < E kin < 450 GeV Method: fluorescence decay by ~5 ns long bunches Comparison to wire scanner at SPS

  20. Realization of Bunch Shape Monitor at UNILAC

  21. Standard Bunch Shape Determination Standard intersecting method developed by INR-Moscow (A. Feschenko, P. Ostrumov et al.):  Insertion of a 0. 1 mm wire at 10 kV  Emission of e- within < 0.1 ps  Acceleration toward 1mm slit  Rf-deflector as time-to-space converter  Detection with Slit+Cup or MCP  Resolution better 1o or 10 ps

  22. Dynamic Transmission control at UNILAC Verification for transmission control: Artificial beam loss by quadrupole variation  chopper window decrease 40 μs/div

  23. High Current Transmission control at UNILAC FPGA

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