Length of the beam delivery system?

The plots mentioned in the text can be found here.

NLC 2000 system consists of short final focus (500 m long), skew correction and diagnostics (200 m), and collimation section (1600 m). See attached optics plots 1+2 .

For CLIC at 3 TeV we have a baseline odd-dispersion optics with a length of 3.3 km. See attached optics plot 3. It achieves about 80% of the ideal luminosity. It includes 4 locations with beta functions and dispersion sufficiently high for collimator survival (B. Jeanneret, J. Pancin S. Fartoukh), and thus it offers the possibility to incorporate betatron collimation. For every 104-105 electrons lost, 1 Bethe-Heitler muon will reach the detector (H.-J. Schreiber). This number may be further increased by a factor 10-100 using muon toroids.

Since we were not yet successful in designing a short alternative final focus ourselves (see attached optics plot 4), we copied the short NLC system and started to adjust it to our parameters. At the moment this system is about 500 m long (see attached optics plot 5), and it achieves 50% of the ideal luminosity. The performance can almost certainly be improved further. There likely is only 1 location where a collimator may survive beam impact.

We believe that we need a separate section for energy collimation. Scaling from the NLC design, T. Risselada found that a minimum length of 2 km is required for collimator survival and that a 4-km long section gives acceptable emittance growth. Perhaps one could take half of this system, if the second stage of absorbers can be made part of the final focus.

The dedicated NLC betatron collimation is 600 m long, and its length will increase for our parameters, to about 1 km. We may need it in option (2) below.

We decided to consider the following two scenarios:

  1. conventional odd-dispersion final focus including betatron collimation [3.3 km] + half of the energy collimation [2 km] + diagnostics section [200 m] => total length per side = 5.5 km, which could become 7.5 km if fully separate energy collimation is necessary
  2. short final focus w/o collimation plus diagnostics section [1 km] + 2 stages of energy collimation [4 km] + betatron collimation [1 km] =>total length per side = 6 km.

The lengths are quite comparable, slightly above 5 km per side. We set 10 km per side as our target value.