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Recent LCLS injector studies & plans

Recent LCLS injector studies & plans. Feng Zhou Thank Brachmann, Decker, Ding, Huang, Loos, Raubenheimer, Turner et al for the contributions March 6, 2013. C ontents. Collimator as an aperture to reduce emittance New applications of a collimator located in BCs:

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Recent LCLS injector studies & plans

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  1. Recent LCLS injector studies & plans Feng Zhou Thank Brachmann, Decker, Ding, Huang, Loos, Raubenheimer, Turner et al for the contributions March 6, 2013

  2. Contents • Collimator as an aperture to reduce emittance • New applications of a collimator located in BCs: • For slice emittancemeasurements • Trace back OTR2 emittance issue • Shorter x-ray FEL production (planning) • Thoughts of future R&D programs at ASTA and LCLS injector

  3. Collimator used to reduce emittance • Placed collimator in a non-dispersion area: to collimate  beam size • Expected 40% emittance reduction with one circular collimator • Collimator wakefield is of the major concern 40% reduction

  4. Observed wake effect for a smaller gap • Analytical shows circular collimator has much lower wake effect than the flat one (Bane/Stupakov) • Wake simulation for flat and circular collimator is underway (Li/Xiao) • Design/fabricate a circular collimator and test it at the LCLS injector CY14 IF simulations confirm the circular one to be good. x~250um (Aug2, 2012) x~130um (Sep26, 2012)

  5. Collimator used to measure slice emittance Chirped beam Chirped beam length 11mm

  6. BC1 emittance vs. collimator gap • Evaluate side effects: space charge (x/y), collimator wakefield (x, y?), CSR and dispersion (x) • Model/data show negligible collimator wake effect (Bane) • Y-data/model show negligible space charge effect • X-dispersion slightly leaks out • Can y-emittance represent BC1 slice emittance?

  7. Dependence of X-band cavity offset? • Slice emittance is independence of X-band cavity transverse offset – easier to understand.

  8. BC1 slice x/y emittances (150pC) • BC1 slice y-emittance is ~0.45um with routine laser profile. • BC1 slice x-emittance is slightly larger due to the leaked-out dispersion • How to compare with LCLS injector OTR2 emittance?

  9. OTR2/WS2 emittance comparison (150pC) • During routine operation, what is the LCLS injector realistic emittance? • OTR2 vs. WS2, LH chicane ON vs. OFF

  10. Area counts comparison (OTR2/WS2) • Obviously, notable lights from the LH chicane are added to the OTR2 profile, which make OTR2 emittance data deviate from the reality.

  11. OTR2 slice emittance comparisons • OTR2 slice emittance with chicane-off is similar to BC1 slice emittance – data from routine operation (150pC)

  12. During our taking data More typical laser for operations Deep Science Mining for Matter

  13. Discussions on OTR2/BC1 emittances • OTR2 emittance with LH chicane-on under-estimates the injector emittance: • Additional lights from the LH chicane modify the OTR2 beam profiles • OTR2 with LH chicane-on may not provide absolute emittance value, but the emittance trend • Bunch length with LH chicane-on is 10% shorter than chicane-off – probably the additional lights impact the data. • With a routine laser profile, slice emittance at OTR2/WS2 and BC1 is ~0.45um for 150pC; • Plan to measure 250pC. • BC1 collimator used to measure slice emittance has been validated – the technique is reliable to measure slice beam. • BC2 slice emittance measurements (planning)

  14. Shorter x-ray FEL production (planning) Collimator gap Final bunch length after the chicane (collimator out) Rms beam size at the collimator To compare with slotted foil (BC2): better or cleaner FEL background? Plan to do MD. Lanfa helps us to check simulations

  15. Possible to reduce LCLS emittance • Lengthen laser pulse to reduce space charge and use smaller laser size: improved slice emittance but projected emittance may be slightly worse (RF emittance). • September 2011 data: different laser pulse length (2.4-4.4ps) but with same laser size on the cathode (250pC) September 2011 data

  16. Further test at LCLS injector with longer laser pulse (CY14) • Simulations show that slice emittance is reduced by 30% with 7ps laser pulse with laser size of 0.8mm, against current 3ps with optimum 1mm of laser size (250pC) – may be tested CY14 Projected emittance simulations

  17. Thoughts of ASTA R&D programs • Robust laser cleaning (very near-term, CY13) • Upgrade RF gun & laser for 360Hz operations • Address gun heating issues for 360Hz • Upgrade laser for 360Hz operation, and MOD/klystron • Develop a load-lock system and higher QE (>5%) cathodes (e.g., Cs2Te): • May reduce thermal emittance to zero • Operate cathode with 360Hz and/or multi-bunch operations • Significantly simplify laser systems (remove 4-pass MPA) • Greatly improve laser profiles thus the emittance and µBI • Great benefit for FACET-II 3-5nC RF gun operation They are fully aligned with future LCLS demands

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