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CLIC luminosity monitoring/re-tuning using beamstrahlung “?”

CLIC luminosity monitoring/re-tuning using beamstrahlung “?”. 1. Beamstrahlung etc. – from D. Schulte 2. Conceptual design of a CLIC post-collision beam-line (“spent beam”) – from A. Ferrari 3. How could one measure beamstrahlung photons - ideas from E. Bravin

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CLIC luminosity monitoring/re-tuning using beamstrahlung “?”

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  1. CLIC luminosity monitoring/re-tuning using beamstrahlung “?” 1. Beamstrahlung etc. – from D. Schulte 2. Conceptual design of a CLIC post-collision beam-line (“spent beam”) – from A. Ferrari 3. How could one measure beamstrahlung photons - ideas from E. Bravin 4. Possible layout, background, open questions

  2. 1. Beamstrahlung etc. – from D. Schulte

  3. luminosity tuning: performed in BDS, using laser wires etc. ... a tedious, long procedure ... luminosity monitoring and re-tuning: ILC uses incoherent pairs – CLIC has problem: many coherent pairs

  4. -> keep track of luminosity … "fast" signal needed (there will be changes of beam position, angle, waist …) … and correct for these changes -> possible signal: beamstrahlung

  5. beamstrahlung photons: energies: from <1 GeV to <1.5 TeV (max. at > 1 TeV) rate: 2.4 photons per electron (positron) in beam, i.e. 1E+10 photons per bunch x 311 bunches 3E+12 photons per 207 ns pulse (repetition rate 50 Hz) angular distribution: ± 50 mrad (full width) (2005 parameters) NB. all numbers for nominal collision parameters !

  6. 3.

  7. 20 mrad crossing angle – horizontal plane beam separation in the horizontal plane [m] distance from IP [m] H

  8. V distance from IP [m] 4 extraction magnets (- 3.2 mrad) 4 “C” magnets (+ 3.2 mrad) vertical displacement for 1.5 GeV beam [m] beam dump 16 quadrupoles (huge aperture !)

  9. V distance from IP [m] somewhere around here... ? 4 extraction magnets (- 3.2 mrad) 4 “C” magnets (+ 3.2 mrad) vertical displacement for 1.5 GeV beam [m] wrong sign particle diagnositcs / dump E > 200 GeV

  10. A. Ferrari, CLIC note 704

  11. 3. How could one measure beamstrahlung photons - ideas from E. Bravin (18 July 2007 meeting) 3E+12 photons in 207 ns, E up to 1.5 TeV  better use a “thin” detector – “fast” (get information on the number of photons, can not get information on their energy) basic principle: converter + OTR monitor g -> e+e- (optical transition radiation) question: layout, backgrounds, etc. etc.

  12. typical OTR monitor arrangements: e.g. “intensity” and profile e.g. “intensity” only CCD optics PM polished tube works at >10E+11 part. good pos. resolution (+ size of beam) “rad. hard” cameras exist... very slow almost “single counting”; very fast (< 1 ns) “radiation hard” sensitive to “direct hits” ATTENTION: No absolute calibration for the intensity !!

  13. one of the “standard” OTR systems at CERN (different screens for different beam intensities)

  14. Pair Production (nuclear field)in 1 mm graphite (0.005 Xo ) 4.4 E+9 part. Signal B.G. pair production probability 1.8 E+9 part. photon energy [MeV]

  15. 4. Possible layout, background, open questions > 130 m

  16. A. Ferrari, CLIC note 704

  17. top view < 1.5 TeV . . . . . > 200 GeV view through last C-magnet in beam direction (dimension in cm, from CLIC Note 704)

  18. side view last C-magnet

  19. background No. 1: synchrotron radiation photons pair production -> < 50 MeV particles solution (?): 10-3 Tm magnetic field (-> 15 mrad at 20 MeV) (if possible, sweep l.e. particles in H-plane, observe OTR light in V-plane) use “small” OTR screen at 5 m from converter (e.g. diameter 30 mm OTR screen) background No. 2: scattered electrons/positrons of all kinds -> to be studied background No. 3: neutrons (stay far away from IP and from dumps) -> to be studied

  20. side view field 10-3 Tm last C-magnet z=100 m z=95 m

  21. open questions: ->strength of C-magnets (separation beamstrahlung from particles > 100 mm (?)) -> investigate beamstrahlung distribution for variousnon-perfect conditions(e.g. Fig. 20 in CLIC note 704) -> introduce “realistic” monitor into simulations (?) and test the “tuning knobs” + everything overlooked or forgotten !

  22. 5. Summary The option of using beamstrahlung photons for “fast” feedback and luminosity tuning at CLIC appears still valid. The technique using a converter plus OTR has several interesting features (e.g. change converter thickness for lower intensity running, different options for OTR detection, etc. etc.). Assuming that CLIC-Note 704 is the reference design for the post-collision beamlines, the location at about 100 m from the interaction point could be reasonable. “... affaire à suivre ...”

  23. extraction magnet (“window-frame”) C - magnet A. Ferrari, CLIC note 704

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