3 5 Ge V Xband linac for primary

3. 5 Ge. V X-band linac for primary electron beam facility at CERN Alexej Grudiev, (CERN) for Y. Dutheil (CERN), T. Åkesson (Lund University), L. Evans (CERN), S. Stapnes (CERN), Y. Papaphilippou (CERN), and the working group PBC-acc-e-beams@cern. ch , CERN, Switzerland HG 2018, Shanghai, June 2018 https: //arxiv. org/abs/1805. 12379 2

Outline • • Light Dark Matter e. Xperiment (LDMX) Electron complex • • • Linac SPS Extraction Beam structure Example of user groups for the CERN primary electron beam facility Conclusion 3

Light Dark Metter e. Xperiment Search for dark photons 4

Electron complex 3. 5 Ge. V Linac Acceleration to in SPS Extraction 5

Electron complex 3. 5 Ge. V Linac 6

Linac parameters • 0. 1 Ge. V S-band injector • 3. 4 Ge. V X-band linac • • modulator kl kl 2 x 50 MW p c High gradient CLIC technology 13 RF units to get 3. 4 Ge. V in ~70 m e~5. 3 m Possible parameters Energy spread (uncorrelated*) <1 Me. V Bunch charge 52 p. C Bunch length ~5 ps Norm. trans emittance ~10 um N bunches in one train 40 Train length 200 ns Rep. rate 50/100 Hz RF DESIGN OF THE X -BAND LINAC FOR THE EUPRAXIA@SPARC_ LAB PROJECT M. Diomede Et al. , IPAC 18 7

Layout e-linac to SPS (single bunch => multi bunch) Based on the initial desing for Eu. SPARC (Frascati) parameters Cell R’/Q~95 MOhm/m Q ~ 6500 comments <a> [mm] 3. 2 d [mm] 2. 5 Ls [mm] 500 Qe 21400 vg/c [%] 2. 5 – 0. 77 Tf [ns] 121 R’_PC [MΩ/m] 350 Number of bunches S-band Injector 100 Me. V Layout of one RF unit =G 2/(Pkl/L) Single bunch Multi bunch 1 40 Bunch spacing [ns] X-band linac 3. 4 Ge. V 13 RF units kl p c kl Energy gain: Single bunch: 336 Me. V Multibunch 200 ns: 264 Me. V 5 Pulse length [ns] 121 325 Active gradient: G [MV/m] 84 66 N structures 104 Total active length: Lt [m] 52 52 Energy gain: Vt [Me. V] 4368 3432 Total klystron power: Pt [MW] 1056 1000 N klystrons 26 26 On crest, No losses in WG Active gradient for multibunch: Tp = 325 ns => 200 ns bunch train 2 x 40 MWx 1. 6 us + CLIC pulse compression ~3 => 240 MWx 325 ns => 30 MW/AS => Gacc = 66 MV/m

Transverse Long-range wakes Scan Q vs bunch charge Q = 5000; Bunch spacing = 5 ns Strong effect of detuning 1 st cell 60 th cell a [mm] 3. 636 2. 764 d [mm] 2 2 Amplitude [V/p. C/mm/m] 117. 1 168. 2 Frequency [GHz] 16. 08 17. 03 A. Latina “GOOD” is < 2 Undamped: Q ~ 5000; Max charge = 300 p. C

Linac • • • Flexible bunch pattern provided by photo-injector 5 ns, 10 ns, … 40 ns bunch spacing High repetition rate • 200 ns trains at 100 Hz To be installed in the available transfer tunnels TT 4, in line with the SPS 10

Transfer tunnel, TT 60, from the Linac into the SPS Injection into the SPS Bunch to bucket injection in the 200 MHz SPS longitudinal RF structure. Total of 75 trains of 40 bunches 3000 bunches 1012 electrons in the ring 11

SPS RF system • • Acceleration to 16 Ge. V can safely be achieved Existing 200 MHz cavities from LEP era to be re-installed • • • Voltage for 5 min quantum lifetime Energy loss per turn (Me. V) Courtesy J. Jowett Need 10 MV for 16 Ge. V electrons (12 + 1) 200 MHz Standing Wave Cavities [1 MV per cavity] available Space is available to install them 5 ns, 10 ns, … 40 ns longitudinal structure is imposed by the available cavities Trains of 200 ns (linac) separated by 100 ns gaps (injections kicker) [1] Talk by A. Grudiev and E. Montesinos, SPS RF for eupdate, March 1 st 2018, CERN indico. cern. ch/event/703049/ 12

Slow extraction to experiments Extraction 05/08/2018 Primary electron beam facility at CERN 13

Slow extraction principle, in frequency space • Spread in oscillation frequency within the beam follows • • • Transverse distribution Longitudinal distribution in presence of chromatic lattice Position of the resonant condition is set by the machine Quantum excitation constantly diffuse the particles, hence frequencies, within the beam Electrostatic The extraction rate can be controlled by Septum changing the position of the resonant condition Resonant condition extraction diffusion Tune (frequency) Extraction rate 14

Structure of extracted beam Beam in the SPS up to 40 bunches with 5 ns spacing Gap of 100 ns with 0. 5 m injection kicker Energy 200 ns ~1 s Beam on target 0 s • 10 s 20 s 30 s Flexibility • • 100 ns Bunch spacing 5 ns, 10 ns, … 40 ns Average electrons per bunch can be chosen from <1 to anything Transverse beam spot on target from very small up to hundred cm 2 This flexibility can deliver the needs of LDMX • • Phase 1 : 1014 electrons Phase 2 : 1016 electrons 15

In addition • • After this beam has been delivered there is still a lot of electrons in the SPS These can quickly be dumped into a separate beam line 1012 electrons within 25μs, possibly up to 4 times more • Beam in the SPS … Energy ~1 s Beam dumped Beam on target 0 s 10 s 20 s 30 s If there would be a high priority the dump can be repeated every 2 s 16

Example of user groups for the CERN primary electron beam facility Physics • LDMX • Other hidden sector experiments, incl. dump-type experiments using available higher intensity • Nuclear physics Accelerator physics : • CLIC: Linac goes a long way towards a natural next step for use of technology (collaborate with INFN and others also using technology for X-band linacs in coming years) • Plasma studies with electrons • Use electron (3. 5 Ge. V) beam as driver and/or probe – study by AWAKE WG Positron production (interesting for LC and plasma) and studies with positrons (plasma) General acc. R&D as in CLEAR today (https: //clear. web. cern. ch) • • • Plasma-lenses, impedance, high grad, medical, training, instrumentation, THz, ESA irrad. General Linear Collider related studies • • Example: damped beam for final focus studies (beyond ATF 2) …. . in all cases we have representatives in e-SPS WG …. 17

Conclusion • Based on previous usage of the CERN accelerator complex, and building on the accelerator R&D for CLIC an electron beam facility would be a natural next step • No show-stoppers have been found when exploring this option • This facility could deliver the beam needed for the LDMX program, deliver electrons to an electron beam dump experiment, and opens for a wide range of accelerator research and development studies with relevance for CERN 18

Thank you 19