A First Look at Synchrotron Radiation Backgrounds in Panta’s 4.3 m L * FF.

1. A First Look at Synchrotron Radiation Backgrounds in Panta’s 4.3 m L* FF. • With all the interest in the new FF it is important to begin to understand • background implications, • collimation implications, • how collimation scales with energy (specific request from PT). • This is just a first look, and is not a complete study. LC Beam Delivery Meeting, Stan Hertzbach

2. WORKING ASSUMPTIONS, Etc. • SR from tail will determine collimation. • The tail is represented by a Gaussian with  = 10 mrad (vs. ~20 rad for the nominal beam). • The tail contains 0.1% of the particles in the beam. • Numbers have been calculated for 109 electrons, approximately a bunch train. (1010 x 95 x 10-3) • No SR photons should have a direct path to the detector beam pipe, especially near the vertex detector. • Note that, for clarity, SR fans are drawn from trajectories on only one side of the beam line. LC Beam Delivery Meeting, Stan Hertzbach

3. Synchrotron radiation fans from QD0 and QF1 in Panta’s 4.3 m L* FF. • Limit set by 10 mm beam pipe aperture at IP. • Trajectories at the IP must be limited to ~300 rad in the horizontal plane and to ~1200 rad in the vertical plane. • Because the beam pipe is round, the limit is smaller than 300 rad x 1200 rad. • The Be ring mask at R=1.26 cm and 55 cm < |z| < 65 cm is a problem for SR. LC Beam Delivery Meeting, Stan Hertzbach

4. Synchrotron radiation fans from QD0 and QF1 in Panta’s 4.3 m L* FF. • Limit set by Be Ring Mask. • If this mask is ignored in collimation then: For ECM= 250 GeV, 1.4x108 ’s with <E> = ~370 keV hit Be mask, 1.5x107 ’s with E > 1 MeV. • Trajectories at the IP must be limited to ~160 rad in the horizontal plane. • Because the beam pipe is round, the limit is smaller than 160 rad x 1200 rad. LC Beam Delivery Meeting, Stan Hertzbach

5. SR from distant quads passes through IP apertures in vertical plane. • Bends direct SR in horizontal plane away from IP . • Some SR from QD2 reaches IP M1 masking in the horizontal plane. QD2 is 150 m from IP, and it should be possible to mask this. • SR from bends has not been looked at recently. LC Beam Delivery Meeting, Stan Hertzbach

6. How Does Collimation Scale With Energy? • SR energy scale is proportional to E2B, or to E3 if B is scaled with E. • The number of SR photons per electron is proportional to , or to E. • Because we are not interested in the lowest energy photons, our problem scales slightly more rapidly with energy than the above. • HOWEVER, the SR fans are independent of energy. • COLLIMATION (in IP angle) IS INDEPENDENT OF ENERGY. • As a measure of the scaling with energy, look at the SR hitting the beam pipe in the horizontal plane if the angular divergence is 310 rad x 120 rad. • 300 rad was OK in horizontal plane. • 1200 rad was OK in vertical, so 310 rad x 120 rad is just a horizontal stripe. LC Beam Delivery Meeting, Stan Hertzbach

7. SR on 10 mm Beam Pipe if Horizontal Collimation is 310 rad. • Ecm = 1 TeV 3.8x105 <E> = 22 MeV • Ecm = 500 GeV 1.8x105 <E> = 3.0 MeV • Ecm = 350 GeV 1.2x105 <E> = 1.1 MeV • Ecm = 250 GeV 0.8x105 <E> = 0.4 MeV (9x103 have E > 1 MeV) • If horizontal collimation allows 320 rad, then Ecm = 250 GeV 12.3x105 <E> = 0.4 MeV (156x103 have E > 1 MeV) • Similarly the number of photons and their energy grows rapidly if one looks at R = 9 mm instead of the 10 mm beam pipe.Ecm = 250 GeV 87.3x105 <E> = 0.4 MeV (106 have E > 1 MeV) LC Beam Delivery Meeting, Stan Hertzbach

8. CAVEATS and SUMMARY • The collimation limits were calculated in the limit of vertical and horizontal “ribbons” of beam. • The vertical and horizontal collimation limits required for the synchrotron radiation to pass through a round aperture will be smaller. • Plots of synchrotron radiation fans have been calculated with  set to 10 rad, but this is just a scaling variable, NOT the beam . • In general, synchrotron radiation from the 4.3m L* final focus does not appear significantly different from the case of the CD-1 final focus. • This final focus has been used to make the argument that the required collimation, in terms of the total IP divergence angle, is likely to be independent of energy. • It was pointed out during the meeting that only the down-beam half of the Be ring mask is required, and the SR on this half may be OK. LC Beam Delivery Meeting, Stan Hertzbach