CeC during Run 19

1. CeC during Run 19 Vladimir N Litvinenko July 9, 2019 RHIC Machine/Experiment Meeting

2. Goals • Demonstrate generation of electron beam with beam parameters satisfying or exceeding requirements for CeC demonstration experiment * minimal goal • Demonstrate control of newly discovered Plasma-Cascade Instability (PCI) and develop means of its suppression in the ballistic compression beam-lines

3. Optimized plan • Establish level of power generated by electron beam with natural (Poisson) noise: use long trains with very low charge per bunch, smooth lattice (need to simulate) and modest compression (to fit within exhaust pipe of the dipole chamber) • Explore averaging at the scope (1 & 10 Hz) • Lock-in amplifier • Define sensitivity and noise level • Use lattices with good compression to 50-100 A peak current and relaxed transverse focusing (supported by simulations with Impact T) 1.5 nC– developed • Establish level of IR detector signals generated by compressed bunches as function of - continued • Bunching voltage and phase; • Focusing lattice and laser beam size at the cathode • Measure time structure of the electron beam: compare measurements in dogleg with simulations – in the partially done – will check when finished optimization • Measure lowest level of the IR signal for e-beam with 50-100 A and calculate the noise level – in progress • Options, if time permits: • Use transition radiation from Cu mirror • Measure noise level in bunch used during imprint studies

4. Progress – week 2 • We established three compression settings – both in simulations and RF set-ups – with 50 A, 75 A and 100 A peak current in the e-beam for 1.5 nC bunches generated by 375 psec laser pulses • We started exploration of the parameter space – finished with scan of bunching voltage, started studies of the lattice influence • We established with a good level of confidence the baseline level of radiation (e.g. resulted from Poison statistical shot noise). Rechecked this level after modification of the IR detector location and shielding (see next point) • A garage with two new photocathodes was installed this Monday (maintenance day) as well as IR detector was moved into an additional shielding made of a lead-bricks. • X-ray background was reduced by additional factor ~ 3-5. • We continue measurements with this low back-ground.

5. New IR diagnostics CVD diamond window 45o dipole magnet Sol 5 Sol 3 Sol 1 Sol 2 Sol 6 Sol 4 3 quads IR detector 704 MHz SRF linac Added lead shielding Profile monitor 2 500 MHz cavities Profile monitor 1 Added lead shielding

6. Couple of graphs: baseline Measured signal <V*cos>~ -105 V/C; <V*sin>~ 100 V/C; Abs(V )=145 V/C.

7. Couple of graphs: couple of dependencies (preliminary) Regular Run 18 lattice 75 A peak current V/C V/μC I, A Bunching voltage setting, kV 75 A peak current – optimizing LEBT lattice V/μC I, A

8. Instead of conclusions • We are making steady progress towards establishing reliable measurements. The best achieved level of noise power in the beam is ~ 4-6 times above baseline (preliminary) • It is very easy to make noise power 10,000 and more above the baseline level by changing focusing of the beam or forcing an over-bunching – it can be easy seeing on a scope since signal is huge. A lot of THz radiation power –m ay be of interest to folks at light source • Plan to continue our studies till the end of the run, including Monday (a LEReC dedicated day). Main concerns are: • APEX with continuous changes of energy – orbit of CeC 1.75 MeV beam will change a lot • Our cathode is at the limit of generating 1.5 nC – will need an short access to put new cathode in a day or two

10. Predicted evolution of the 26.5 GeV/u ion bunch profile in RHIC 40 mins of PCA CeC e-bunch with normal (Poisson) shot noise Initial bunch shapes Witness bunch in 40 mins e-bunch with 225-fold increase noise power e-bunch with 225-fold increase noise power Simulated longitudinal profiles of 26.5 GeV ion bunches in RHIC. Black – initial profile, red – witness (non-interacting) bunch after 40 minutes. Profiles of interacting bunches after 40-minutes in PCA-based CeC for various levels of white noise amplitude in the electron beam: dark blue – nominal statistical shot noise, magenta – 10 fold, light blue – 15 fold and green – 30 fold - higher than the statistical level. Cooling will occur if electron beam has micro-bunching with power (e.g. BM radiation power) less than 225-fold of spontaneous (shot noise) radiation

11. Layout 0.724 m

12. Time line & status • March 13 – this experimental program was approved • March 14 – April 30 (3 maintenances/accesses to RHIC) • Repairs and preparation for operating CeC accelerator (cathode manipulator, CsK2Sb photocathode, LiHe system, PPS, RF maintenance/check-out…) • Modification to the accelerator/dogleg section vacuum system • Installation of diamond CVD window and IR diagnostics at new location • April 30 - CeC accelerator ready for operation in pulsed mode • May 1 - ASSRC Meeting – stop of CeC accelerator operation • only SRF gun was allowed to operate, main dipole PS locked-out, accelerator can no be tuned • May 16 - ASSRC memo allowing temporarily to operate at 0.1 μA (10 pulses) level, pending tests and modification of MPS • June 3 – Tests and modification of MPS are implemented • June 4 -21 accelerator tune-up started, IR diagnostics is tested (limited to 10 pulses) –we did everything possible and waited for permission to operate at 5,000 pulses • June 21 -ASSRC memo allowing to operate at 2.5 μA level, pending modification of MPS and controls (expected to be done today, June 25) • We have 20 days to complete the experiment