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The present CEBAF Wien Spin Manipulator:

The present CEBAF Wien Spin Manipulator: Designed for 100kV beam and max rotation +/- 110 degrees Adaptation of SLAC design (how different?) X turn coil wrapped around iron pole pieces, field mapped to max current 10Amps Electrode power supplies+/- 15kV, max field gradient X MV/m

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The present CEBAF Wien Spin Manipulator:

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  1. The present CEBAF Wien Spin Manipulator: • Designed for 100kV beam and max rotation +/- 110 degrees • Adaptation of SLAC design (how different?) • X turn coil wrapped around iron pole pieces, field mapped to max current 10Amps • Electrode power supplies+/- 15kV, max field gradient X MV/m • Nickel field clamps at entrance and exit, with 1cm aperture • Beam grows in X-dimension at angles > 50 degrees. Significant loss at A1/A2 • “peanut” quads intended to focus beam in X-dimension, installed during G0 to improve transmission through A1/A2. Behavior of quads not so good. Namely, empirical determination of “good” quad settings, does not provide a meaningful relationship between Current and Wien Angle. Said differently: First quad doesn’t seem to do much, Second quad operates at same value regardless of (large) Wien angle. • Note, despite focusing issues, we have operated at large Wien angles many times, and for extended periods of time. But obtaining good transmission takes tweaking. • Emittancevs Wien angle constant (good) M. Poelker, J. Grames, Y. Wang, HAPPEx Collaboration Mtg., 7/23/08

  2. HAPPEx needs another “slow sign flip”, to complement the insertablehalfwave plate. OK • The Wien filter approach seems reasonable, provided beam optics does not change considerably between the two states • Does the present Wien Spin Manipulator meet our requirements? NO • HAPPEx needs spin angles +45degrees and -135degrees. -135 degrees outside present Wien’s range (not enough B, magnet would run too hot), and… • We suspect we would have very different beam optics for these two angles. The Wien quads do not adequately correct beam “blow up” at large angles (>+/- 50degrees) .

  3. Related: • Space is tight in the 100kV beamline • Beamline must be baked when vented: a difficult task • We need a new Wien angle for our 200kV gun. Install summer 2009? • We have a spare identical Wien at the Source Lab: Magnet has been mapped, need to shape the electrodes to match the B field

  4. Solution#1 • Extend the range of the present Wien Spin Manipulator • More B: increase current from 10Amps to 13.5Amps (pick a value). Cooling issue? New magnet with more turns? • More E: need 24kV differential. Our +/- 15kV power supplies are adequate. But have we operated at this high voltage? Do we suffer field emission or breakdown? • Build better quad magnets, to ensure good transmission through apertures A1 and A2 at large Wien angle (i.e., same beam envelope) • Beam should be centered in quads – not the case right now • Pros/Cons/Issues • Cheapest, quickest, easiest fix. Beamline stays the same. • Must answer quad question: what’s wrong with our quads, can we make and mount new ones that actually focus in X at large angle? • Modeling, would be nice to appreciate nature of today’s problems • Use spare Wien to check operation at new E and B values, e.g., 13.5Amps, 30kV differential. Can install at Test Cave

  5. Solution#2 • Design/Build new and better Wien Spin Manipulator, +/-180 degree rotation at 100kV beam energy • More B: longer Wien, more turns • More E: longer Wien, electropolish and high pressure rinse our electrodes, to operate reliably at higher gradient • Build better quad magnets, to ensure good transmission through apertures A1 and A2 at large Wien angle (i.e., same beam envelope across entire Wien operating range) • Include appropriate space on beamline for these new quad magnets (i.e., not viewer crosses). Want quads centered on beam. • The new Wien should also provide +/- 90 degree rotation at 200kV beam energy (i.e., our intended new gun voltage) • Pros/Cons/Issues • An essential part of 200kV gun program • Need modeling expertise: new Wien, new quads and new beamline • Takes a long time to design and build, need a long downtime to install

  6. Solution#3 (Joe’s idea) • Two Wien Spin Manipulators of present design, in series • First Wien operates at 90 degrees, with a downstream counterwound solenoid pair to provide 180 degree flip. Solenoid pair rotates spin but provides the same focusing for the two states, therefore we should maintain same optics • Second Wien provides additional rotation as dictated by machine energy conditions, for example HAPPEx needs +45 degree rotation. • The slow flip requires only the First Wein be changed between +/-90, the Second Wein stays the same • Still need new quads… • Pros/Cons/Issues • A clever idea, we have two Wien filters in-house • Designing new solenoids likely easier than designing new Wien filter but still need modeling expertise: compare/contrast performance using one Wien, and to build new beamline. Is there enough room between gun and chopper for extra Wien? • Not as much stuff to build, but need a long downtime to install

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