Longitudinal Beam Diagnostics with the LBS Line 17. November 2009 Linac4 Beam Coordination Committee Meeting Thomas Hermanns Thomas Hermanns 17. November Geographical Overview LT.BHZ20 LTB.BHZ40 Transfer Line Linac4 and Dump Line LBE Line LBS Line LBE Line LBS Line (1)(2) (3) Slit (1) Spectrometer Magnet (2) SEM Grid (3) Beam Dump Thomas Hermanns 17. November Introduction LBS line: Diagnostics line close to PS Booster injection point Measurement of the Linac4 beam energy and energy spread Correlation between beam energy and vertical beam position induced by spectrometer magnet Subject of this presentation (1) Proposal for a spectrometer line for Linac4 operation (2) Physical performance of the proposed line (3) List of requirements and functional specifications for LBS line upgrade Thomas Hermanns 17. November Energy Distribution (behind slit) MeV dEdE160.6 keV E kin (min.)158.9 MeV E kin (max.)159.5 MeV Thomas Hermanns 17. November Experimental Principle Experimental quantity: Fitted vertical spatial particle distribution on SEM grid Maximum Value Mean beam energy (from calibration function) Beam Size Energy/Momentum spread Install SEM grid at position where beta-function has a local minimum Reduce vertical emittance by vertical slit Analyze particles by strong magnet with large bending angle (high dispersion) Local dispersion function from simulations Thomas Hermanns 17. November Simulation Tools Definition of line layout with envelope code (Trace 3-D) Position of slit, spectrometer magnet, and SEM grid Parameters of spectrometer magnet Proposal for a LBS line layout Implementation of the LBS line layout in particle tracking code (Path) Single particle tracking through line Create output particle distribution at SEM grid position to analyze Simulation of measurements errors Data evaluation with analysis package (ROOT) Physical performance and functional specifications Thomas Hermanns 17. November Proposed Optical Parameters Slit Position: 4089mm behind LTB.BHZ40 Aperture: 148mm (horizontal) 1mm (vertical) Length: 200mm (absorption length of H - -ions at 160 MeV in carbon: 85mm) Spectrometer Magnet Position: 6286mm behind slit exit Radius: 1500mm (B=1.27T) Bending Angle: 54 Edge angles: 10 SEM grid Position: 4139mm from mid-point of magnet Wire clearance: 0.75mm (energy resolution 57 keV) About 20% of all incident particle arrive at SEM grid (I 13mA) Thomas Hermanns 17. November Simulation Results Correlation factor: -99.7% Determination of maximum value (Wire-)binned projection on spatial axis to fit 2 nd order polynomial Current per wire: few A to several 10 A Lower limit 5.5 nA time-differentiated readout seems possible at MHz-rate Correlation for Nominal EnergySEM Grid Simulation and Data Fit dE/dy 82 keV/mm dE per wire keV Thomas Hermanns 17. November Results for Mean Energy Shift manually energy within 1MeV Linear Correlation between fitted position and central energy value Energy shifts determine vertical length of SEM grid Thomas Hermanns 17. November Results for Energy Spread (reference value keV) Validity of approximation Ratio of total beam size to beam size for virtual beam with dp/p=0: = Perturbation less than 1% Reconstructed Energy Spread Reconstructed157.9 keV Deviation-1.7% Thomas Hermanns 17. November Uncertainties Alignment errors Slit, magnet and SEM grid displaced by 1mm Manufacturing errors Magnet edge angles: 0.5 Vertical slit aperture: 5% (equivalent to 50m) Spectrometer B-field: 0.1% Variation of vertical slit width Variation of slit length Variation of input parameters at LTB.BHZ40 Thomas Hermanns 17. November Mean Energy (reference value MeV) Maximum position shifted by... ... error on fit parameter ... systematic error due to deviations from nominal line design Intrinsic Error: Energy spread on one wire due to finite vertical slit width Mean Position Nominal Fit mm Sys. Error mm Total Error Mean Energy (with dE/dy 82 keV/mm) Absolute 8.4 keV (fit) keV (sys.) keV (intrinsic) Relative 1.8 10 -3 Thomas Hermanns 17. November Beam Size and Vertical Dispersion (reference value keV) Beam Size Statistical error of beam size measurement Systematic error due to deviation from nominal line design Vertical Dispersion Value Systematic error due to deviation from nominal line design Total Error Dispersion Absolute0.6 keV (sys.) Relative 0.4 Total Error Beam Size Absolute 2.7 keV (stat.) 0.9 keV (sys.) Relative 1.8 10 -2 Thomas Hermanns 17. November Error on Energy Spread (reference value keV) Total error on energy spread Error on beam size and dispersion Intrinsic Error: Energy spread on one wire due to finite vertical slit width Total Error Energy Spread Absolute 2.9 keV (Beam Size) 0.6 keV (Dispersion) keV (intrinsic) Relative 8.3 Example for Gaussian distributions with energy width 14 keV and energy difference 57 keV Thomas Hermanns 17. November Perturbation Coefficient (reference value ) Systematic error due to deviation from optimal design Perturbation still remains below 1% if error is included Difference between energy spread neglecting and respecting well below other sources of errors dE ( = 0) dE (