BFW Results Heinz-Dieter Nuhn – LCLS Undulator Group Leader June 9, 2009
LCLS Undulator Components Vacuum Chamber and Support BFW Segment Quadrupole Cam Shaft Movers WPM BPM Horizontal SlidesNot visible Manual Adjustments Sand-Filled, Thermally IsolatedFixed Supports HLS
Beam Finder Wire Location on Girder Beam Finder Wire Housing Undulator Segment Beam Direction Vacuum Chamber
BFW Assembly (Body Sectioned) Potentiometer (Out Position) Electrical Connectors (Down Position) Internal Return Spring (Expanded Position) Internal Kinematic Stop Plates (Open Position) Pneumatic Solenoid Valve (Cylinder Vent Position) Lower Limit Switch (Actuated Position) Bellows Seal (Compressed Position) Wire card (Down Position) (Inactive Mode) BEAM Assembly model courtesy: J. Bailey, ANL
BFW Card X-wire end point: 39.614 mm Beam center: 40 mm Gap between beam and X-wire: 0.386 mm Material: Macor Thickness: 3/16” (4.8 mm) Coating: Kovar Full Stroke: 25.4 mm Y-wire end point: 37.014 mm Beam center: 37.2 mm Gap between beam and Y-wire: 0.186 mm Beam in OUT Position Beam in IN Position Beam travels out of slide plane
BFW Card Wiring: Tooling Micrometer stage BFW Card Rods for hanging BFW wire with weights Card holder ‘Carbon wire & weight’ Copper Tabs • Wires soldered to copper tabs • Wires from copper tabs connect to BFW feedthrough • Feedthrough to be grounded and RF shielded Courtesy: C. Field, Y.Sung
BFW Wires X-Wire Nominal Beam Axisin IN Position Wire Radius 34 - 40 µm Y-Wire Note: Wires are fixed!Beam scanning will be achieved through girder motion. Card Out Direction (½ stroke length shown)
BFW Functions BFW ReplacementVacuum Chamber Wires A misaligned undulator will not steer the beam. It will just radiate at the wrong wavelength.The BFW allows the misalignment to be detected. (also allows beam size measurements) BFW Undulator Quad Girder Beam Direction Planned Applications • Loose End Alignment • Beam Profile Scanning
Location of BFW Detectors • 40 Detectors are used for BFW readout • 33 PEP-II style radiator/PMT units: one after each BFW device • 5 ANL Beam loss monitors: next to PEP-II devices on girders 1, 9, 17, 25, 33. • 2 Beam loss fibers: BLF U01-U16 covering upstream girder, BLFU 17-U33 covering downstream girders • Wire charge diagnostics is not installed
Scan Procedure Incorporated in Matlab GUI • Start matlab gui BFWscan_gui • Choose girders (1-33), X-wire or Y-wire, scan range, and scan step sizeFor instance • Girder: 1 - 33 • Wire: ‘X’ and ‘Y’ • Range: -250 microns to +250 microns • Step size: 50 microns. • When started, the gui will then for each selected girder • Move the girder cams to place the upstream girder end to the beginning of the scan range relative to the estimated collision point.(Motion is pivoted at the quadrupole) • Move the wire card to “IN” position (while beam stopper is inserted) • Take measurements from the 8 detectors, add the results to the graphs and go on to the next location.When done, return the girder to the position at which it was started. • Move the wire card to “OUT” position. • Move the girder back to its standard location. • The gui will stop the beam upstream of the undulator line during wire card insertion/extraction and during motion to the next position.
Scan with BFW11 Y-Wire ANL BLM 33 BLF:U01-U16 BLF:U17-U33 ANL BLM 25 PEP-II BLM17 PEP-II BLM25 Dump Cerenkov Dump Scintillator Expected Collision Position
DMP Cerenkov Detector Amplitudes Noise levels is due to coarse step size of 50 microns. 20 microns steps ize scans are planned for the near future.
BLF 17-33 Responses Girder Range Covered by Fiber
FEL Scattering on BFW wire Fringes indicate transverse coherence
Summary • The 33 Beam Finder Wire (BFW) devices in the undulator system are working very well. • They enable monitoring of several parameters • Loose-end alignment • Beam sizes, i.e. betatron matching • BLM calibration • Transverse FEL coherence. • Radiation levels produced by the scans are much lower than originally estimated allowing unrestricted use. • Use has so far been restricted to higher electron beam energies due to the possibility of wire damage when interacting with the lowest energy FEL beam.