1. January 8, 2005Mike Hildreth – ILC-MDI Workshop A BPM-Based Energy Spectrometer Technical Considerations & Plans for the End Station A Test Beam Mike Hildreth University of Notre Dame

2. January 8, 2005Mike Hildreth – ILC-MDI Workshop A few words of Motivation: Overall measurement precision is set by the expected statistical and systematic errors of “benchmark” measurements of m top, m higgs : –require  E beam /E beam ~ 100-200 ppm –(LEP2 achieved ~170 ppm with a combination of techniques) For an “Upstream” spectrometer, the only way we have been able to devise a measurement which produces this accuracy and does ~nothing to the beam is a BPM-Based spectrometer, à la LEP: ~As built in LEP: 1998-2000 Spectrometer Magnet Ancillary Magnet  = 1.9 mrad 0m10m 2.5cm BPMs

3. January 8, 2005Mike Hildreth – ILC-MDI Workshop This Talk… Design Considerations for an ILC version of this technique –Constrained by allowed emittance growth from SR –Constrained by available real estate in BDS, overall size –Those constraints determine needed BPM resolution/stability –Other issues drive systematic errors, diagnostics –Must be robust, invisible to luminosity End Station A Beam Test Program (T474) –Goals –ESA Layout –Time scale for various tests

4. January 8, 2005Mike Hildreth – ILC-MDI Workshop Measurement Strategy I “Pure Displacement” Incoming Beam B1: kick outB4: kick in Central BPM measures offset, offset difference between ±B (cancel some systematic errors) all magnets run to ±B Outer BPMs required to constrain beam trajectory

5. January 8, 2005Mike Hildreth – ILC-MDI Workshop Measurement Strategy II “Pure Angle” all magnets run to ±B Internal BPMs measure trajectory and offset Both schemes require BPMs moving through large excursions (~1cm) Incoming Beam

6. January 8, 2005Mike Hildreth – ILC-MDI WorkshopHybrid Incoming Beam Mantra: “Redundancy is good”

7. January 8, 2005Mike Hildreth – ILC-MDI Workshop Design Decision Diagram Required BPM Resolution Chicane Length Chicane Optics (  ) d  /ds from SR Bend Radius Bend Length  (  Bd ) Mechanical Stability Beam angle jitter Betatron jitter  (bunch charge) Energy jitter Major Design parameter External constraint External input E bunch or ?

8. January 8, 2005Mike Hildreth – ILC-MDI Workshop Emittance Growth in Chicane Primary consideration: radiation at high dispersion point –one can limit emittance growth by having long soft bends, especially where the dispersion is large –smaller dispersion is better for emittance growth, bad for required BPM resolution –increasing  makes required BPM measurements harder Allowed emittance growth plus magnet build-ability determine the allowed maximum bend angle –to be optimized bend radius local  function dispersion

9. January 8, 2005Mike Hildreth – ILC-MDI Workshop Magnetic Field Measurements LEP Technique (NMR+Hall probes) yielded  B/B ~ 2×10 -5 To constrain overall trajectory (betatron, angle jitter), we have to measure/instrument all four dipoles –radiation damage issues If we are going to switch magnet polarities, probably want Super- Conducting Dipoles so that residual field is zero at B=0 –can minimize dependence on B=0 field by measuring at ±B, but it is a powerful constraint on some systematics  keep that option

10. January 8, 2005Mike Hildreth – ILC-MDI Workshop Mechanical Stability Issues Stability requirements determined by overall BPM resolution needed Mechanical support structure must be designed to limit vibration, and with minimal thermal expansion properties –how to cool? Custom temperature regulation needed... Stability must be monitored, for example: –local positions determined by optical encoders on BPM movers –global constraint on relative motion provided by stretched wire system at LEP, stretched wire was good to 130 nm (short) to 200 nm (long)

11. January 8, 2005Mike Hildreth – ILC-MDI Workshop Monitoring Mechanical Stability Other options: Feedback Seismograph ~ 0.5 nm sensitivity up to 100 seconds can use multiple setups to get differential motion over large distances STS-2 Optical Anchor Interferometer based alignment monitoring (LiCAS) Local motion referenced to global straight line CCD BPM Local motion measurement Long-distance reference line Interferometer heads

12. January 8, 2005Mike Hildreth – ILC-MDI Workshop BPM Movers Need precise (< 100 nm) long-throw movers capable of holding BPM assemblies FFTB Movers: May be able to piggy-back on mover designs for other BDS components, with small mods for increased performance

13. January 8, 2005Mike Hildreth – ILC-MDI WorkshopOptics First pass of optics in BDS done by PT last year –We probably want more dispersion, and slightly longer length to relax constraints on BPM resolution

14. January 8, 2005Mike Hildreth – ILC-MDI Workshop Strawman Spectrometer Design Slightly longer than original (~55 m) Bends are different (optimized for small d  /ds) More dispersion (5mm peak) Would like to put this in a BDS location with ~constant (small)  x,  y –(to be negotiated) Ray Arnold

15. January 8, 2005Mike Hildreth – ILC-MDI Workshop End Station A Test Beam Program ESA provides “ILC-like” beam in “realistic” conditions: –Can always tweak jitter parameters to make things worse –Can “simulate” beamstrahlung pair production by using radiators

16. January 8, 2005Mike Hildreth – ILC-MDI Workshop End Station A Facilities

17. January 8, 2005Mike Hildreth – ILC-MDI Workshop concrete shielding ESA Beamline Components Existing RF BPMs can be used for stability, resolution tests Beamline components scavenged from SPEAR, other SLAC surplus Nano-BPMs

18. January 8, 2005Mike Hildreth – ILC-MDI Workshop T-474 Testbeam Proposal Collaborators: Notre Dame, Berkeley, UCL, Cambridge, SLAC Proposal submitted in June 2004 Goals: –Establish a BPM system with electrical and mechanical stability at the 100 nanometer level sanity test for various components in “real” environment –Eventually: Test energy measurement precision to verify feasibility of 100-200ppm measurement error cross check with T-475 (synchrotron stripe experiment) and spin precession in the A line UK institutions able to make substantial contributions in terms of people and M&S funds (from EuroTeV)

19. January 8, 2005Mike Hildreth – ILC-MDI Workshop T-474 Experimental Layout Three RF BPMs and associated electronics moved from the Linac to ESA SPEAR girder also in ESA Additional two RF BPMs will be used to monitor electrical stability, can also be used for Collimator Wakefield studies BPM testing using alcove BPMs already underway by Berkeley group moveable stage BPMs Girder

20. January 8, 2005Mike Hildreth – ILC-MDI Workshop T-474 Run Plans 1.October/November? 2005: Establish Necessary Infrastructure Set up bunch-length measurements Set up wire scanner for emittance measurements Set up BPMs establish DAQ test for stability initial performance tests Some mechanical stability monitoring STS-2 Seismometer(s) 2.Late FY06/Early FY07? Install correctors before/after BPM girder to mimic spectrometer More advanced mechanical stability New BPM electronics? 3.Future Move towards full spectrometer demonstration project (still evolving)

21. January 8, 2005Mike Hildreth – ILC-MDI WorkshopConclusions Spectrometer CDR well underway –Thanks to Ray Arnold –Design advancing many parameters to consider built-in redundancy will be key –need optics design soon to make headway on technical requirements for Spectrometer components “Trust, but Verify” –Beam Tests are critical for these systems tolerances are very tight, many surprises are possible