APEX description, status and plans John Corlett for the APEX team Lawrence Berkeley National Laboratory 1

Motivation Tomorrow’s x-ray laser sources ~ microseconds ~ attoseconds to femtoseconds Intense pulses at high rep rate ≲ millijoule Coherent X-rays with high repetition rate, unprecedented average brightness, and ultrafast pulses

Approach CW superconducting linac, laser heater, bunch compressor High-brightness, high rep-rate gun and injector Beam spreader Array of independent FELs X-ray beamlines and endstations High average power electron beam distributed to an array of FELs from high rep- rate injector and CW SCRF linac

Repetition rate 1 MHz Charge per bunch from ~10 pC to ~1 nC Emittance <10 -6 mm-mrad (normalized) Electric field at the cathode ≥~10 MV/m (space charge emission limit) Beam energy at the gun exit ≥~500 keV (space charge control) Bunch length ~100 fs to ~10 ps for handling space charge effects, and for allowing different modes of operation Compatible with magnetic field control within the gun (emittance exchange and compensation) Torr vacuum capability (cathode lifetime) Accommodates a variety of cathode materials High reliability for user operations Injector design goals – APEX gun The gun is the most challenging component LBNL approach uses a CW VHF cavity

Frequency 187 MHz Operation mode CW Gap voltage 750 kV Field at the cathode 19 MV/m Q0Q Shunt impedance 6.5 M  RF Power 90 kW Stored energy 2.3 J Peak surface field 24 MV/m Peak wall power density 25 W/cm 2 Accelerating gap 4 cm Diameter/Length 70/35 cm Operating pressure < Torr APEX gun VHF cavity operates in CW mode Low power density on cavity walls High conductance vacuum slots High gradient at cathode

Injector design and beam dynamics – multiobjective genetic optimization Gun Buncher Projected normalized emittance (m-rad, 100%) RMS bunch length (m) 300 pC

APEX stages Diagnostics systems in collaboration with Cornell CLASSSE Accelerating cavities in collaboration with ANL AWA Phase I: Beam characterization at gun energy (750 keV) Phase 0: Gun and photocathod e tests Planning for final installation in 2013 Phase-II: Beam characterization at 15–30 MeV 6-D brightness measurements

Phase 0 scope: Demonstration of the RF performance at full repetition rate. Demonstration of the RF performance at full repetition rate. Vacuum performance demonstration. Vacuum performance demonstration. Dark current characterization. Dark current characterization. High QE cathode physics High QE cathode physics (QE and lifetime measurements) Under commissioning Phase I scope: (Phase 0 + extended diagnostics) High QE cathode physics High QE cathode physics (Intrinsic emittance measurements) Diagnostics systems tests. Diagnostics systems tests. Low energy beam characterization Low energy beam characterization Planned operation in fall 2012 Phase 0 Phase I 8 APEX stages – 0, I

APEX Phase II layout Phase II scope: Demonstration of the brightness performance at ~ 30 MeV at low repetition rate* Demonstration of the brightness performance at ~ 30 MeV at low repetition rate* (*Shielding limited) Planning for operation in late APEX stages – II

Tuning mechanism principle tested Torr achieved with 1 (out of 20) NEG pump and no bake Successful low power RF test APEX Description Status & Plans (J. Corlett) 10 Gun cold-test and installation

APEX gun: high-brightness MHz electron source APEX cavity is successfully RF conditioned

APEX in the Beam Test Facility

APEX Activity and Plans F. Sannibale Yb fiber photocathode drive laser 1 MHz reprate Yb fiber laser LLNL/UCB/LBNL collaboration

High QE Good lifetime at mBar Low transverse momentum Photocathode materials R&D K 2 CsSb: 6% QE at 532 nm 0.36 microns / mm rms  n >> 1 week lifetime

PEA Semiconductor: Alkali Antimonides CsK 2 Sb, (developed at LBNL) - <~ps pulse capability - reactive; requires ~ Torr pressure - high QE > 1% - requires green/blue light (eg. 2 nd harm. Nd:YVO4 = 532nm) - for nC, 1 MHz reprate, ~ 1 W of IR required PEA Semiconductor: Cesium Telluride Cs 2 Te (In collaboration with INFN-LASA) - <~ps pulse capability - relatively robust and un-reactive (operates at ~ Torr) - successfully tested in NC RF and SRF guns - high QE > 1% - photo-emits in the UV ~250 nm (3 rd or 4 th harm. conversion from IR) - for 1 MHz reprate, 1 nC, ~ 10 W 1060nm required FLASH INFN-LASA APEX Description Status & Plans (J. Corlett) Cathodes successfully developed at INFN/LASA and delivered to LBNL Cathodes under development at LBNL (H. Padmore’s group) Promising lifetime and intrinsic emittance results (Cornell and LBNL) Transfer chamber to VHF gun in preparation Collaboration with BNL for diamond amplifier testing 15 Photocathodes

Modified version of the FLASH plug for reduced field emission. Not tested yet! Status of the APEX Project F. Sannibale Flexibility for testing different photocathode materials The APEX Project at LBNL (J. Corlett) Adapted version of the INFN/PITZ/DESY load-lock system 16 Cathode mount & vacuum load-lock

Acceptance test completed at LBNL, fully operational Acceptance test completed at LBNL, fully operational The 120 kW CW 187 MHz RF amplifier required to operate the VHF gun has been manufactured by ETM Electromatic The 120 kW CW 187 MHz RF amplifier required to operate the VHF gun has been manufactured by ETM Electromatic APEX Activity and Plans (J. Corlett) APEX Description Status & Plans (J. Corlett) 17 VHF amplifier

APEX Activity and Plans (J. Corlett) APEX Description Status & Plans (J. Corlett) Single RF source: 1.3 GHz, 25 MW pulsed at 10 Hz with 10  s pulse LINAC: 3 accel. sections. AWA/ANL type Buncher cavity: Buncher cavity: LBNL design Deflecting cavity: Deflecting cavity: Modified Cornell Type Modified Cornell Type RF Distribution System 18 APEX phase-II RF distribution

APEX Activity and Plans (J. Corlett) APEX Description Status & Plans (J. Corlett) The solenoid cure worked! Minimal length, NTi coated and water cooled. Alternative approach 19 Coaxial feed multipacting cure

At Dec. 15, 2011 integrated < 120 hours of conditioning. At Dec. 15, 2011 integrated < 120 hours of conditioning. December 15: CW mode at nominal power ran for 12,5 hours without faults Results reconfirmed the day after (> 24 hours no fault) Power stability ~2x10 -3 APEX Activity and Plans (J. Corlett) APEX Description Status & Plans (J. Corlett) Gun RF conditioning started on November 7, 2011 Pulsed 20 RF conditioning completed

Measurements performed in CW mode on a coaxial Faraday cup right downstream the beam pipe exit APEX Description Status & Plans (J. Corlett) 21 Dark current follows Fowler-Nordheim dependence on the E field At the nominal field (19.5 MV/m) the present value is ~ 8  A Expected to decrease when the beamline is installed and vacuum bake completed Dark current

APEX Description Status & Plans (J. Corlett) 22 Measurements performed with a Dycor 2000 RGA system 1 NEG pump out of 20 activated, 1 ion pump, 2 turbo pumps; no bake H2H2 He O HO HO 2 N N2N2 O2O2 Ar CO 2 C C Vacuum performance

APEX Description Status & Plans (J. Corlett) 23 We have two “regimes”: cold cavity in the first ~ 30 min where the copper is going to temperature; warm when the copper temperature stabilizes T S1 T S2 T C2 TCTC Thermal effects on frequency

The APEX injector is being commissioned Designed for high-brightness electron beam at MHz repetition rate VHF cavity Flexibility in photocathode materials Progress: VHF cavity is RF conditioned Initial characterization of dark current and tuning Cathodes under development Plans: Photoemission experiments to start soon Phases I and II add diagnostics, bunching, acceleration Plan to complete construction and begin final beam characterization in 2013 Summary – APEX R&D program

F. Sannibale, B. Bailey, K. Baptiste, J. Byrd, M. Chin, D. Colomb, J. Corlett, C. Cork, S. De Santis, S. Dimaggio, L. Doolittle, J. Doyle, J. Feng, D. Filippetto, G. Huang, H. Huang, T. Kramasz, S. Kwiatkowski, R. Lellinger, W. E. Norum, H. Padmore, C. Papadopoulos, G. Penn, C. Pogue, G. Portmann, J. Qiang, D. Garcia Quintas, J. Staples, T. Vecchione, M. Venturini, M. Vinco, W. Wan, R. Wells, M. Zolotorev, F. Zucca, … 25 A team effort