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

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

3. Layout

4. 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

5. 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

6. 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)

7. Effect of change # 2

8. 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…..

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

10. 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

11. 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)

12. 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)

14. 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)

15. 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.