Large Angle BeamstrahlungRadiation Monitor

Mikhail Dubrovin,Ivan Avrutsky, Giovanni Bonvicini,

David Cinabro, Mike WestWayne State University

July 14, 2003 ALC Workshop @ Cornell University, Ithaca, NY

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

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.

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 twoangle

Expected BR signalfor beam-beam misplacements

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

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

Radiation Profile Monitor @ CESR

Electro-mechanics of the Radiation Profile Monitor

Moving slit

Stepping motor

Position sensitive potentiometer

VIS PMT, E(beam)=1.8 GeV

VIS-PMT, E(beam)=3.7GeV

I+=5mA

I-=170mA

I+/I-=128/107mA

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

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

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

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.