X-Ray Diagnostics for the LCLS Jan. 19-20, 2004 UCLA.
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X-Ray Diagnostics for the LCLS Jan. 19-20, 2004 UCLA
General Assumptions (See CDR) Undulators Fixed in Position –Exception: Small motion for alignment Fixed Gap Undulators Permanent Magnet Quads Cavity BPMs following each undulator and prior to the 1 st Full suite of diagnostics every third undulator
Current Thinking Use NdFeB –Radiation Damage Issue Real benefit of Sm 2 Co 17 still no known Must determine acceptable losses APS is doing this for operational reasons 7 Additional undulators planned for use in regular maintenance schedule –Temperature Compensation Sm 2 Co 17 slightly more than a factor of 2 better. Not enough.
Current Thinking K Adjustment/Control Strategy Cant (mrad) Horizontal alignment accuracy (mm) B eff /B eff over 10 mm Range of hort. motion (mm) for B eff /B eff = ±1.5x10 -3 (±5.5x10 -4 ) b Incremental thickness (mm) of mech. shims 20.503.0x10 -3 ±5.0 (±1.8)0.010 30.334.5x10 -3 ±3.3 (±1.2)0.015 40.256.0x10 -3 ±2.5 (±0.9)0.020 a All calculations were made according to a tolerance of 1.5x10 -4 and a total range of 1.5x10 -3 ( 20 Gauss) for B eff /B eff. Spacer thickness steps were chosen to allow full compensation at half travel of the total range of motion. b The range of horizontal motion listed in the parentheses corresponds to ±1°C temperature compensation. To allow for temperature compensation of ±1°C the additional range of motion listed in parentheses should be provided.
Undulator segment tolerances ParameterSpecified Value Trajectory excursion (both planes) 2 m Radiation amplitude deviation2% Phase slippage between undulators10° a Vertical positioning error 50 m a Total allowed phase slippage including all errors. The error in the effective magnetic field Beff, totally dominates the contributions.
Calculated gain length and increase in saturation length using a random uniform distribution of K values from one undulator to the next with end-phase corrections applied for the LCLS beam parameters. a K/K Gain length (m) b Increase in sat. length (m) c ±3.5x10 -4 6.46 * - ±7.0x10 -4 6.50~ 1.7 m ±10.0x10 -4 6.60~ 3.4 m a Normalized beam emittance was 1.5 mm-mrad, beam energy spread 2.1x10 -4, FODO lattice strength 0.112 m -1, and peak current 3.5 kA. Other parameters same as in Table 1. b The gain length was derived over the next-to-last super period of six undulators. c The increase in saturation length was estimated near 100 m by determining how much additional distance was needed to reach the same level of ln|J| 2. * Same value as for K/K = 0.
Current Thinking Undulator System Fully Installed on day 1 Start at 800 eV –Why?
UNDULATOR 3420 627 11528 mm Horizontal Steering Coil Vertical Steering Coil Beam Position Monitor 852 X-Ray Diagnostics Quadrupoles Cell structure of the LCLS Undulator Line 33 Undulators ~ 130-m Overall Length Pioneering Science and Technology Office of Science U.S. Department of Energy
PRIOR WORK FOR INTRA-UNDULATOR DIAGNOSTICS (CDR April 2002) Electron Beam Diagnostics (Section 8.11, Glenn Decker and Alex Lumpkin) Table 8.9 Undulator electron beam diagnostics Type QuantityLocationBXY Notes *Beam position monitor48All stationsCavity / Button combo OTR imaging diagnostic13Every third stationThin aluminum foil screen Wire scanners4Upstream of Undulator segments *Cherenkov Detectors33All stationsFused silica / PMT combo *Current Monitors2Upstream/downstream of undulator Toroid transformer * Non-intercepting X-ray Diagnostics (Section 8.13, Efim Gluskin and Petre Ilinski) On-axis diagnostics Diamond (111), 4 – 9 keV, cooled silicon PIN diode. Off-axis diagnostics Hole crystal, 2 = 90 , CCD detector.
Issues Quad Fixed to the Undulator –Has implications on using the cant for tuning Requires separate motion Tunnel Temperature Control –Would like better than +/- 0.2 Degrees C. Supports will probably need this or better 800 eV –Makes life very difficult for the x-ray diagnostics –Would prefer to start a > 2 KeV
Issues Motion Capability –We need some for K tuning but… –Do we need the ability to completely remove the undulators? Aside: 0.1 G deflects the 14 GeV beam by ~1.5 um in 3.7 m. High Power Damage –Can we even make a diagnostic that is both useful and can handle the power densities of the FEL?
Issues Radiation Damage –We will use NdFeB –We must protect the undulator from radiation This has implications on intraundulator interceptive diagnostics Canted Poles –BBA There will be some arbitrary offset and anle through the undulator How does this impact the K tuning?