LCLS-II physics meeting 3/25/2015 Injector layouts Injector RF coupler correction w/ a weak quad Feng Zhou LCLS-II physics meeting 3/25/2015

This is a team work … Tor/JohnS – initiated the layout work for me Dowell – develop theory on the RF coupler correction with quad Z. Li showed me about his early work on quad correction for RF couplers Vivoli (FNAL), Christos P (LBL), Adam (Cornell) and me – simulations and crosscheck with different codes Chad (LBL) – understand the solenoid and benchmark ImpactT etc Bruce (Cornell) – provided drawings Henry – made layouts drawings …

Concerns for the baseline layout Some emittance concerns Aperture concerns: smaller physical apertures at SOL/BPM Baseline layout SOL1 SOL2

Baseline layout: emittance concerns Emittance increases from CDR layout to baseline layout due to the increased drift between SOL2 and CM Have to turn off both Cav2 and Cav3 to get 0.6 um emittance otherwise the emittance is >0.8um (300pC) Beam size at the Cav1 coupler is large, causing ~30% emittance growth without coupler correction (300 pC)

Baseline layout: aperture concerns (300 pC) z (m) half aperture h (mm) rms beam size x (mm) h/x SOL01 0.306 14.3 5.47 2.6 valve1 0.481 20.0 5.25 3.8 XC01 0.566 15.0 5.15 2.9 YC01 BPM01 0.629 4.7 3.2 BUN01 0.895 23.8 3.97 6.0 XC02 1.029 25.5 3.57 7.1 YC02 7.2 Laser injection 1.179 11.1 3.4 3.3 IM01 1.324 13.5 3.35 4.0 YAG01 1.468 19.1 3.34 5.7 XC03 1.55 3.37 7.0 YC03 SOL02 1.689 3.39 4.2 BPM02 1.931 2.78 5.4 XC04 1.94 2.76 YC04 valve2 2.079 2.48 8.1

E-beam size at SOL1 2.5cm close to physical aperture 2.8cm

Proposed beamline modifications New proposal Baseline layout Use Cornell SOL/BPM package (7 cm rather than 3cm of physical aperture) Move SOL2 upstream Shorten drift between SOL2 and CM SOL1 (Cornell) SOL2 (Cornell) SOL1 (Apex) SOL2 (Apex)

Solenoid: Apex vs. Cornell Use same layout: only replace the solenoids It looks not matter using apex or Cornell solenoids in term of emittance, but they have different apertures: Cornell 7 cm of physical aperture Apex 2.8 cm of physical aperture SOL1/SOL2 Emittance (um) Cornell/Cornell 0.565 Apex/Apex 0.595 300pC

Aperture comparison (300 pC) h/x w/ proposed layout w/ baseline layout w/ Cornell demonstrated injector SOL1 6.1 2.6 5.4 BPM1 3.2 5.0 x/y correctors 2.9 SOL2 9 4.2 4.5 BPM2 4.7 Laser injection Easy to make larger 3.3

Emittance comparison (300 pC) Proposed layout Baseline layout Best operating mode (both Cav2 and Cav3 off) 0.56 um (10% reduction from baseline layout) 0.62um Mode with one cavity failure (turn on cav2 or cav3 due to one of 4th to 8th cavity failure) 0.63-0.65um 0.8-0.85um Emittance growth (due to the cav1 coupler) 10% 30% With 1D cavity field With 3D cavity field including coupler Note all of my simulations in this talk use conservative cathode/laser parameters: 1) 1um/mm of thermal emittance, and 2) spatial uniform laser profile

Tracking with RF couplers w/o correction 300pC Cav1 Baseline layout: emittance growth 30% New layout: emittance growth 10%

RF coupler correction – quad ‘stigmator’ RF coupler of Cav1 has strong effect on the emittance growth (300 pC): RF coupler corrections Standard corrections (FNAL) Simple and inexpensive but effective method – dc quad ‘stigmator’; motivated by the work: Z. Li Ph. D thesis and D. Dowell LCLS-II tech. note

Quad stigmator principle RF coupler kick: Corrections with skew quad: Dowell, LCLS-II tech. note

Quad correction for RF couplers @ 300 pC (baseline layout) Integrated strength 3Gs with 0.2 rad of rotation in front of CM The emittance growth caused by the RF couplers is almost completely corrected with a weak quad

Summary New proposed layout has advantages: RF coupler effect can be almost completely corrected with a weak quad in front of CM Proposed layout baseline layout Best operating mode (both Cav2 and Cav3 off) 0.56 um 0.62um Mode with one cavity failure (one of 4th to 8th cavity) 0.63-0.65um 0.8-0.85um Emittance growth due to RF couplers (w/o correction) 10% 30% Half apertures/rms-beam-size 6 2.6 - 3

This is a team work … Tor/JohnS – initiated the layout work for me Dowell – develop theory on the RF coupler correction with quad Z. Li showed me about his early work on quad correction for RF couplers Vivoli (FNAL), Christos P (LBL), Adam (Cornell) and me – simulations and crosscheck with different codes Chad (LBL) – understand the solenoid and benchmark ImpactT etc Bruce (Cornell) – provided drawings Henry – made layouts drawings …