1. Large Angle Beamstrahlung Radiation Monitor Mikhail Dubrovin, Ivan Avrutsky, Giovanni Bonvicini, David Cinabro, Mike West Wayne State University July 14, 2003 ALC Workshop @ Cornell University, Ithaca, NY

2. Outline ● Basic principles of the large angle radiation monitor ● First prototype of the detector for CESR and results of the experiment ● ¼ of the full scale prototype of the BR detector for CESR-c and status of its installation ● Summary

3. Motivations for Large Angle Beamstrahlung Monitor ➢ Physical motivations were discussed in numerous publications and preprints, i.e. G. Bonvicini, J. Welch, NIM 418, 223,1998; CBN 98-12, etc. ➢ The idea is to exploit a large angle (comparing to ~1  beamstrahlung radiation from the beam-beam scattering at I.P. for monitoring of the beam quality parameters. ● In the short magnet approximation the radiation signal from the beam on beam scattering is expected in the IR range, 850-1200nm, 100% polarized (with factorized spec. & polar.) ● VIS or NIR ranges can be used for background subtraction. ➢ Notes on detector and optics design, simulation: CBN 98-12; CBN 98-26 PR E59, 4584, 1999; + conference presentations.

4. Degrees of freedom at beam-beam scattering ● 7 d.o.f. Are important for luminosity tuning ● Radiating power, its spectral-angular distribution and polarization also depend on these d.o.f. ● We may measure the photon yield for two polarizations for both beams at two  angle

5. Expected BR signal for beam-beam misplacements

6. The Program of Experimental Study ● Stage 1: Radiation Profile Monitor ➢ Exp:Feb.2002- Feb.2003 ➢ Use it for alignment of equipment ➢ Estimation of the rates in VIS/NIR/IR spectrum ➢ Search for the signal from beam-beam scattering ➢ Observe the expected profile of radiation ● Stage 2: ¼ of the full scale Beamstrahlung Monitor ➢ Exp:Aug.2003-June 2004 ➢ Proof of principle optics, detector and experiment ➢ Alignment of equipment ➢ Study of the photon yield features for IR and VIS ranges and two polarization at fixed angular location ● Stage 3: Full scale BM @ 4 angular locations

7. Scheme of Radiation Profile Monitor ● Results (see next slides): ✔ Alignment ✔ Estimation of rates for radiation in VIS, NIR ranges (IR PMT requers T < -30C) ✔ We have observed an expected profile from SR ✔ First attempt to see the radiation from beam- beam scattering @ NIR range

8. Radiation Profile Monitor @ CESR

9. Electro-mechanics of the Radiation Profile Monitor Moving slit Stepping motor Position sensitive potentiometer

10. VIS PMT, E(beam)=1.8 GeV

11. VIS-PMT, E(beam)=3.7GeV I+=5mA I-=170mA I+/I-=128/107mA

12. NIR-PMT with filter E(beam)=4.2GeV @HEP

13. ¼ of Beamstrahlung Radiation Monitor ● PBS – Polarizing Beam Splitter (Glan-Laser, Calcite) ● BS – Beam Splitter ● M – Mirror ● HM – Hot Mirror ● IR/VIS PMT – Hamamatsu Photo- multipliers R316-02/ R6095

14. BR Detector at CESR ● All parts and optics are in hands ● IR/VIS PMT-s have been tested ● BR Detector will be installed at CESR by the end of July 2003 ● Then we plan an alignment & physics shifts depending on status of CESR-c

15. Summary ● Beamstrahlung radiation looks very attractive for beam quality monitoring. ● Preliminary calculations shows the feasibility of the large angle BR detector. ● First prototype had been tested and shows an expected profile of the background radiation from I.P. Region in VIS and NIR ranges. ● ¼ of full scale prototype is going to be installed @CESR in July 2003 for experiments with BR.