The chicane magnets were introduced with their design arc lengths of 320,752,512mm, and the deflection angles have been adjusted accordingely to 2.362,7.348,4.986deg in order to close the orbit bump from the chicane. However, this will cause tiny spurious dispersion of about 1mm around the ring, since the magnets are not short. Furthermore, the measured effective field lengthes of 273,713,483mm differ from the ideal arc lengths, which will affect the closure of the orbit bump. Since details of the fringe fields are not included in the model, the final values of the magnet currents eventually have to be ontained empirically from orbit correction.
The chicane affects emittance, energy loss per turn, momentum compaction factor and circumference of the machine (compare table below with F6T data). The circumference increase of 7.3mm requires a change of the radio frequency by -13kHz. For more information see SLS-TME-TA-2003-0223 (PDF)
Like already done for F6T, the local tune variation over the 5L straight was established: With constraints for betas and alfas at the ends of 5L, the quadrupoles QLG-04/05, QLH-04/05 and QFT-1/2 are varied to adjust both tunes within a range of +/-0.06. Parabolic fits to the matching results give for each quads five parameters to set its current for a local tune change dQx, dQy:
dI = A*dQx + B*dQy + C*dQx2 + D*dQx*dQy + E*dQy2
This plot (PS) shows the quadrupole currents as function of tune shifts (top to bottom: data, fit, difference), and the coefficients are given in the snap file. (Basically, the tuning could include QFT3 for maintaining alpha_y=0 in the radiator center, but this would allow only a small tuning range.)
This optics will be used for startup of FEMTO in April 2006.
| Circumference [m] | 288.0073 |
| Working Point Qx / Qy | 20.43 / 8.72 |
| Natural chromaticities | -67.3 / -21.0 |
| Corrected chromaticities | +5 / +5 |
| Momentum compaction factor | 6.05E-4 |
| Horizontal emittance at 2.4 GeV [nm rad] | 5.59 |
| rms relative energy spread at 2.4 GeV | 8.57E-4 |
| Energy loss per turn (no IDs) [keV] | 540 (incl. Femto U19) |
| Short straight: Beta_x / Beta_y / Disp [m] | 1.38 / 1.00 / 0.00 |
| Medium straight: Beta_x / Beta_y / Disp [m] | 2.26 / 2.50 / 0.00 |
| Long straight: Beta_x / Beta_y / Disp [m] | 4.52 / 5.00 / 0.00 |
| FEMTO radiator: Beta_x / Beta_y / Disp [m] | 8.71 / 0.52 / 0.00 (alfa_x = -2) |
| Maximum values: Beta_x / Beta_y / Disp [m] | 23.1 / 23.7 / 0.35 |
F6CWO snap file for upload to control system, also includes current settings for the chicane magnets.
F6CWO Lattice file composed from database as input for TRACY.
F6CWO listing of beta functions (TRACY).