Update on injection studies of LHC beams from Linac4 V. Forte (BE/ABP-HSC) Acknowledgements: J. Abelleira, C. Bracco, E. Benedetto, S. Hancock, M. Kowalska LIU-PSB Injection Meeting - 06/10/2015

Outline 2 options of multi-turn injection Brightness curves RMS emittances evolution

2 options of simulated multi-turn injection Transverse painting (injection at x=-35 mm and y= 3 mm) + KSW modulation for betatron mismatch On-axis (injection at x=-35 mm and y= 0 mm) + constant KSW until multi-turn is over ZOOM No undershoot to mm considered in the next simulations on-axis (does not matter for LHC beams, which are small)

2 options of multi-turn injection Transverse painting emittance at I=3.42e12 p. at (Qx,Qy)=(4.43, 4.6) ~1.2 ~0.6

Brightness curves after 10e3 turns The “infamous” Giovanni’s tables (EDMS – )

Brightness curves after 10e3 turns On-axis simulations for the nominal working point for two initial bunch lengths (47% and 61% chopping factors)

Brightness curves after 10e3 turns Moving the working point up-right to (4.43, 4.60) -> gain in brightness

Brightness curves after 10e3 turns Comparison with Elena’s results (IPAC15 – THPF088) for 61% chopping factor (optimal choice)

A deeper look… On-axis vs. transverse painting (61% chopping factor) -> tr. painting gives worst results in the first 10e3 turns (~10 ms). These cases will be analysed from now on…

550 ns 570 ns 603 ns 600 ns Longitudinal profiles after 10e3 turns  p/p= 1.35e-3 Matched area = 1.27eVs The matched area is computed as the area of the iso-Hamiltonian (without s.c.) starting from the maximum bunch phase (obtained through a foot-tangent algorithm). S. Hancock suggestion: use RMS bunch length which is sort of bunch shape-independent

Longitudinal profiles after 10e3 turns The current profiles of 609 ns – 403 keV rms are similar to the solutions adopted by Elena et al. in IPAC15- THPF088. There, the initial emittance of 1.17 eVs leads to slightly longer bunches Current (initial 1.1 eVs rectangle area) – after turns Elena (initial 1.17 eVs rectangle area) – after 7000 turns ~620 ns ~600 ns

Longitudinal profiles after 10e3 turns The current profiles of 609 ns – 403 keV rms are similar to the solutions adopted by Elena et al. in IPAC15- THPF088. There, the initial emittance of 1.17 eVs leads to 620 ns bunches after ~7 ms. The second option of creating a very long bunch of 1.48 eVs initial area is attractive (very high brightness) but risky, because leads to fill 94% of the acceptance with already some losses at the edges… Current (initial 1.1 eVs rectangle area) – after turns Elena (initial 1.48 eVs rectangle area) – after 7000 turns ~600 ns – 1.27 eVs ~680 ns – 1.6 eVs This solution gives better results in terms of brightness but it is very close to the acceptance (the bunch occupies 94% of the bucket area)

A deeper look… The two best cases will be now analysed in more detail These cases will be analysed from now on…

RMS emittances vs. Intensity…

On-axis or transverse painting? The transverse painting preserves the shape of the distribution (it starts from higher emittances!) The on-axis solution is completely dominated by space charge but could be a bet! On-axis after 10e3 turns Transv. Painting after 10e3 turns Halo

On-axis or transverse painting? The transverse painting permits a “controlled” initial blow-up through the betatron mismatch The on-axis solution is completely dominated by space charge Going to absurd -> extrapolated constant linear growth induced by the vertical integer resonance. But in 40 ms from injection   increases of 27% -> 27% less s.c. tune shift!

On-axis or transverse painting? The on-axis solution, after 10 ms, has smaller emittance and 0.59,0.73 s.c. tune shift The transverse painting solution, after 10 ms, has bigger emittance, leading to 0.50,0.57 s.c. tune shift, and almost a steady state situation in rms emittance On-axis at 3.421e12 p. Transverse painting at 3.421e12 p.

Summary and next steps Long term (10 ms) multi-turn injection simulations have been performed for the CERN PSB with PTC-Orbit The multi-turn injection scheme has been implemented without energy modulations using Elena’s inputs. In particular: Quadrupolar errors at the chicane magnets + Eddy currents + Compensation QDE3, QDE14 (time varying) Beta-beating (mostly in vertical) corrected Excitation of half-integer corrected Excitation of the integer line Foil scattering Brightness curves have been simulated for different cases (on-axis and transverse painting injection, different working points and bunch lengths). They still confirm a brightness increase bigger than a factor 2. This margin is useful because these simulations don’t take into account other error sources (like distributed quadrupolar field errors and misalignments). A longitudinal injection scheme at 403 keV rms (optimal from IPAC15 MOPJE042) and 609 ns injected per turn (60.9% chopping factor) has been chosen as optimal at 40 mA unchopped from the Linac4, as it guarantees a matched area of ~1.3 eVs (75% of total acceptance) and 600 ns bunch length over 10 ms A different matched area method has been implemented (S. Hancock-like). Bigger chopping factors (at this energy spread) can lead to longitudinal losses even if beneficial for space charge blow up reduction (IPAC15 – THPF088) The on-axis injections: - have dynamics which are completely dependent on space charge (very small initial emittances). - show good agreement with the previous results by E. Benedetto et al. ( IPAC15 – THPF088). - Option to not be discarded for commissioning because give always better brightness than the transverse painting, but not yet steady state in 10 ms (risk of transverse halo formation!). The transverse painting injections - show a quick suppression of the tune spread to be far from the integer resonances. - preserve the single particle profiles.

Appendix

Scan with working point E. Benedetto (SC meeting 19/3/15)