HIPPI yearly meeting, sep28-sep30 2005 Beam dynamics in LINAC4 Edgar Sargsyan , Jean-Baptiste Lallement Alessandra Lombardi HIPPI yearly meeting, sep28-sep30 2005

contents Changes to the layout and impact on the beam dynamics End-to-end simulations Open questions

Layout

Change # 1 : DTL-RF field Field ramp : 1.5 to 3.0 MV/m Phase law : -42 to -25 Constant field at 3.3 Mv/m in tank1 ; 3.5 MV/m in tank2,3 Phase law : -30 to -20

Effects of change # 1 Shorter DTL (13.4 vs 16.6m) 27 drift tubes in tank1 (vs. 41) Same beam dynamics Increased sensitivity to RF errors but tolerable same longitudinal acceptance

Change#2-DTL focusing FD focusing instead of FFDD Smaller beam radius Less sensitive to errors Less halo development Higher integrated gradient (70% more gradient for 20% less radius)

Effect of change # 2

Today’s focusing law FFDD in tank1 limited by the max quadrupole length (45mm) in a 3 MeV 352 MHz drift tube and the max gradient achievable by ITEP PMQ. FDFD afterwards Study ongoing to evaluate the effect of leaving a 3 meter section FFDD in a 70 m machine with FD everywhere…..

Change # 3 –accel phase Phase at -20 degrees also for CCDTL and SCL 5 meters shorter CCDTL, same length SCL

Sensitivity to errors Tracking the centre of the beam through the DTL-CCDTL-SCL with a field and phase errors of 0.5% and 0.5deg r.m.s. Results of 100 runs. No feedback correction Energy and phase jitter are limited to 5 degrees and 250 keV r.m.s. By Matteo Pasini

End-to-end : 4D waterbag RFQ input beam: Nparticles=50000 I=70 mA Win=95 keV ΔW/W=0.5 % (rms) Distribution=4D WB εx=0.25 π mm-mrad (norm. rms) εy=0.25 π mm-mrad (norm. rms)

End-to-end : gaussian RFQ input beam: Nparticles=50000 I=70 mA Win=95 keV ΔW/W=0.5 % (rms) Distribution=gaussian εx=0.25 π mm-mrad (norm. rms) εy=0.25 π mm-mrad (norm. rms)

End-to-end : 40 mA RFQ input beam: Nparticles=50000 I=40 mA Win=95 keV ΔW/W=0.5 % (rms) Distribution=4D WB εx=0.25 π mm-mrad (norm. rms) εy=0.25 π mm-mrad (norm. rms)

Conclusion Changes to the design of the DTL have a positive impact on the layout and little effect on the beam dynamics A current of 70 mA, present baseline of the LINAC4, is at the limit of the acceptance of the chopper line and some re-matching is needed.