LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

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L C L S C O N C E P T U A L D E S I G N R E P O R T and by the phasing through the adjacent end sections of the two undulator segments. The physical break length is of course set when the undulator line is constructed. The phasing through the end sections can be adjusted by applying phase shims near the ends of the undulator segment or by introducing a small gap change at the end of the undulator segment. The latter technique has the advantage that the phasing can be adjusted during the actual operation of the FEL, using the FEL output as feedback. It would allow phase error accumulation to be avoided through the whole beamline. 8.3.3 Requirements for Measurement Facility on LCLS Site The existing measurement facility at APS has adequate resolution and reproducibility for the measurement and tuning of undulator segments for the LCLS project. However, the shipment of tuned undulator segments from Argonne to SLAC may affect the magnetic quality of the undulator segments so they no longer meet the demanding magnetic field quality and stability requirements. For example, a gap change of just over a micrometer may introduce 10° phase slippage. To meet these demanding magnetic requirements, very rigid and reliable construction of the device is necessary. Also, the final tuning of phase slippage should be done by phase tuning at the ends of undulator segments after delivery of the devices to the LCLS site. It is necessary to have the same undulator measurement systems at SLAC as at APS. (A Helmholtz-coil system to measure individual magnet blocks is probably not necessary, however.) In addition, a pulsed wire system for finding the center of a quadrupole within the required tolerance (< 50 µm) will be acquired. 8.4 Measurement and Sorting of Magnet Blocks 8.4.1 Characterization of Magnet Blocks with Helmholtz Coils The requirements for the LCLS undulator are demanding. To help ensure that these requirements can be met, tight tolerances must be imposed on the magnetic properties of the permanent magnet blocks to be used in the undulator segments. In addition to requiring that the magnets be strong (a remanence Br of 1.2 T is specified for the NdFeB permanent magnet blocks), they are also required to be uniform. Each individual magnet block is required to have a total magnetic moment that is within ±1% of the average total moment, where the average is taken over the entire population of magnet blocks. The direction of the total magnetic moment vector is also required to lie within 2° of the mechanical axis of the magnet block. These requirements are checked by measurements made using a system of Helmholtz coils. The vendor measures the magnet blocks when they are manufactured, and the blocks must be measured again by the manufacturer of the undulator magnetic structure. Those measurements are then used in sorting algorithms in order to minimize the effect of errors. The Helmholtz coil measurement system uses a servomotor to rotate the magnet that is held at the center between a pair of coils. A fast 16-bit ADC board is used to measure the signal from the coils on the fly as the magnet is rotated. Typically 2000 points per turn are recorded. A digital integration in software gives the flux of the magnet block at each point during the rotation. 8-16 ♦ U N D U L A T O R
L C L S C O N C E P T U A L D E S I G N R E P O R T This gives the orientation of the magnetic moment in one plane; to determine the angle in the perpendicular plane requires that the magnet block be turned by 90° and the measurement repeated. This by 90° repositioning are done manually. The data file for each magnet block is analyzed to determine the total magnetic moment and its projections along the mechanical axes of the block. A set of 500 magnets has been received for use in building a prototype LCLS undulator segment. Their field uniformity exceeds the specification. The vendor’s Helmholtz coil measurements for those blocks show that the total moment on each magnet block lies within ±0.5% of the average total moment of all the blocks. The magnet blocks have effectively no transverse (x) component to their magnetic moment. They have a systematic vertical (y) component to the magnetic moment, however, and the angle of magnetization is 1.0 ±0.3° from the mechanical axis of the magnet. The magnets are symmetric so that they can be installed in the prototype in either of two orientations, i.e., with the vertical component of the magnetic moment up or down. This will allow the direction of the vertical magnetic moment to be chosen when the magnetic structure is assembled. Some of the magnets have also been measured with the APS Helmholtz coil system. These measurements show excellent agreement with the vendor’s measurements. The rms difference was ±0.06% for the first 35 magnet blocks to be measured. Figure 8.3 Schematic drawing of the half-period measurement fixture. A pole (shown in red) is on either side of the central magnet (shown in blue), on both top and bottom. 8.4.2 Characterization of Magnet Blocks with Half-Period Fixture The LCLS magnets were measured using a specially designed fixture based on the half- period-model of the device. This fixture consists of 4 poles and two magnets as shown in Figure 8.3. U N D U L A T O R ♦ 8-17
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Linac Coherent Light Source (LCLS)
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L C L S C O N C E P T U A L D E S I
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Preface This Conceptual Design Repo
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Table of Contents 1 Executive Summa
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6. Two experiment halls L C L S C O
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2.7.1.7 Conventional Facilities L C
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3 TECHNICAL SYNOPSIS Scientific Bas
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5 TECHNICAL SYNOPSIS FEL Parameters
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and the total peak beam power L C L
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5.4.2.2 Case II - High Charge Limit
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∆P ∆I sat pl / P / I sat pk L C
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5.9 Summary L C L S C O N C E P T U
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6 Injector TECHNICAL SYNOPSIS The i
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εn,x (µm) 4 3 2 1 4-2001 8560A95
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Quantum Yield (electrons/photon) 10
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Bz (T) 0.3 0.2 0.1 1-2002 8560A92 L
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Master Clock 9.917 MHz x8 x6 x6 Df
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1-2002 8560A198 Linac Center Line L
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B z (kG) 3 2 1 4-2001 8560A91 L C L
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γε x,y (µm) 3 2 1 0 3-2001 8560A
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γεx,y (µm) yn 10 0 -10 -10 0 10
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σ γ /γ 0 (percent) ∆N/N 0.02 0
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5 0 -5 5 0 -5 5 0 -5 L C L S C O N
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Table 6.5 PARMELA Output Parameters
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gama x (micro.m) 3 2 1 0 0 L C L S
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∆E/E 0 (%) ∆N/N 0 -1 -2 0.02 0
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〈∆E/E 0 〉 /% I pk /I pk0 0.1
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β (m) 35 30 25 20 15 10 5 0 K21_1B
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β (m) 60 50 40 30 20 10 0 L C L S
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economic reasons. L C L S C O N C E
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Page 268 and 269: Phase [deg. S-band] L C L S C O N C
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8.10.4 Conclusion L C L S C O N C E
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x θ j > 0 L C L S C O N C E P T U
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Quad ∆X/µm Quad ∆Y/µm −500
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∆X/µm ∆Y/µm L C L S C O N C E
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8.13.2 Undulator Cell Structure L C
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9.2 Layout and Optics 9.2.1 Experim
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Fast Valve L C L S C O N C E P T U
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0.01 10 -4 10 -6 10 -8 10 -10 10 -1
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Table 9.5 Mirror requirements L C L
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Refractive Focusing System L C L S
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Pulse Split/Delay L C L S C O N C E
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Figure 9.20 LCLS Ion Chamber L C L
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9.4.3.2 Pulse Length L C L S C O N
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9.4.3.6 Divergence L C L S C O N C
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10 Conventional Facilities TECHNICA
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1-2002 8560A198 Linac Center Line L
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Figure 10.6 Near hall floor plan 10
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11 Controls TECHNICAL SYNOPSIS The
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11.5.3 Motion Controls L C L S C O
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12.1 Procedural Overview L C L S C
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13 Environment, Safety and Health a
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Table 13-1 Hazard Identification an
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13.1 Ionizing Radiation The design
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Table 13-2 Minimum Training Require
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13.10 SLAC References L C L S C O N
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L C L S D E S I G N S T U D Y R E P
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15 TECHNICAL SYNOPSIS Work Breakdow
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A A.1 FEL-Physics A.1.1 Performance
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A.2 Photo-Injector A.2.1 Gun-Laser
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A.2.3.2 Electron Beam L C L S C O N
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A.2.4.7 Vacuum L C L S C O N C E P
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A.3.8 DL-2 A.3.8.1 Subsystem L C L
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A.4 Undulator A.4.1 Undulator A.4.1
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B Control Points B.1 Injector Contr
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C Glossary ACO Anneaux Collisions O
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