July LEReC Review July 2014 Low Energy RHIC electron Cooling Sergey Belomestnykh SRF and RF systems

July Outline Scope Parameters Major Procurements Relocated equipment –used/borrowed/repurposed –Moved to make space Equipment installation location and conventional facilities requirements Timeline Risk list Summary 2

July Scope 704 MHz SRF photoemission gun providing a 1.6 to 2.0 MeV beam of electrons – requires some modification for LEReC. 130 kW CW RF system for the SRF gun – new high power RF amplifier. 704 MHz 5-cell SRF cavity operating at a voltage up to 0.9 MV for energy spread correction – relocated from R&D ERL. 20 kW CW RF system for the 5-cell cavity – shared with the CeC PoP linac. 2.1 GHz warm cavity operating at a voltage up to 460 kV cavity for further correction of the energy spread – new design. 20 kW CW RF system for the warm cavity – new RF system. 3

July Location in LEReC MHz SRF gun 704 MHz 5-cell SRF cavity 2.1 GHz 7-cell warm cavity

July SRF Photoemission Electron Gun 5  The 704 MHz ½-cell SRF gun with an independently cooled (by helium gas) demountable cathode stalk uses a multi- alkali photocathode.  A quarter wave RF choke-joint supports the photocathode stalk and has triangular grooves for suppression of multipacting.  Two Fundamental Power Couplers (FPCs) are designed to deliver up to 1 MW of RF power. Will need only 100 kW for LEReC.  The gun’s Qext will have to be adjusted from 5.5e4 to 4.1e5. This will be accomplished with 3-stub waveguide transformers.  A high-temperature superconducting solenoid is located inside the cryomodule.  Frequency tuning range is 1 MHz (1 mm of cavity deformation).  HOM damping is provided by an external beamline ferrite load with a ceramic break. Cathode isolation Valve Cathode installation cart Beam line isolation valve Top cover with facilities feedthrough Cavity assembly Internal Helium dewar Adjustable supports Magnetic and thermal shielding HOM Ferrite Vacuum vessel Power Couplers (2) Insulating Vacuum Port HTS solenoid

July SRF Gun Parameters 6 RF frequency703.6 MHz Cavity active length8.5 cm (0.4 cell) Maximum energy gain2.0 MeV Maximum field at the cathode26.7 MV/m E acc at 2 MV23.5 MV/m Installed RF power120 kW R/Q96.2 Ohm Geometry factor112.7 Ohm Cavity operating temperature2 K Cathode operating temperature80 K Cathode RF losses (80 K) at 2.0 MV226 W Q ext 4.1x10 5 Required RF power100 kW Installed RF power130 kW More details on the SRF gun performance in “Commissioning Program of the 704 MHz SRF gun” by Wencan Xu

July Major Procurements for the SRF Gun Two 65 kW CW RF amplifiers Circulators, RF loads, transmission line components LLRF New cathode 3-stub WG transformers 7 More details on high power RF and LLRF in “Power amplifiers and low-level RF” by A. Zaltsman

July Relocated Equipment The SRF gun cryomodule and the cathode insertion setup will be relocated from the R&D ERL to IP2 8

July Location in LEReC MHz SRF gun

July cell SRF Cavity 10  Fundamental mode resonates at MHz.  Large (24 cm dia.) beam tubes allow all HOMs to propagate toward room- temperature ferrite HOM dampers.  The cutoff frequency of beam pipes is 790 MHz, while the first dipole mode is at 810 MHz.  50 kW CW fundamental power coupler of the SNS type with water cooled RF window.  First horizontal test was in March of Several more tests were carried out after that.  Mechanical tuner has 112 kHz tuning range, piezo provides 9 kHz fast tuning.  In CW operation the cavity is quench- limited to 11.5 MV/m due to to the AlMg 3 seal located between the NbTi and stainless steel flanges on one of the beam pipes (on the FPC side). The cavity performance is more than sufficient for LEReC.  The cavity is used to “de-chirp” energy spread along the bunch.

July cell Cavity Parameters 11 Frequency703.6 MHz No. of cells5 Geometry Factor225 Ohm R/Q404 Ohm E pk /E acc 1.97 B pk /E acc 5.78 mT/(MV/m) Length152 cm Beam pipe diameter24 cm Cavity voltage900 kV Q ext 2x10 7 Required RF power1 kW Installed RF power20 kW

July Major Procurements for the 5-cell Cavity RF transmission line components to connect the cavity to the 20 kW CW RF amplifier installed for CeC PoP 12 More details on high power RF and LLRF in “Power amplifiers and low-level RF” by A. Zaltsman

July Relocated Equipment The 5-cell cryomodule will be relocated from the R&D ERL to IP2 13

July Location in LEReC MHz 5-cell SRF cavity

July GHz Warm Cavity 15  The third harmonic cavity is used to “fine-tune” the beam energy spread.  This is a 7-cell copper structure with magnetic coupling between cells.  The cavity is designed for an accelerating voltage up to 460 kV.  The dissipated power at this voltage will be 15.7 kW.  We plan to use a CEBAF-type RF window modified from 1.5 GHz to 2.1 GHz.  There will be two plunger-type frequency tuners operating in parallel.  Two ion pumps will be maintaining the cavity vacuum and one small pump will be located near the RF window.  The RF design is nearly complete as well as preliminary mechanical design.  Next step: ANSYS analysis (mechanical stresses & thermal).

July GHz Cavity Parameters 16 Frequency2.11 GHz No. of cells7 R sh 13.6 MOhm R/Q1.207 kOhm Cavity voltage460 kV Required RF power15.7 kW Installed RF power20 kW Regular Cell End Cell

July Major Procurements for the 7-cell Cavity Cavity Fundamental power coupler 20 kW CW klystron amplifier WR430 components, circulator, RF load LLRF 17 More details on high power RF and LLRF in “Power amplifiers and low-level RF” by A. Zaltsman

July Location in LEReC GHz 7-cell warm cavity

July Timeline FY2014: finish detailed design of the 2.1 GHz cavity; commissioning of the SRF gun in pulsed/low current mode FY2015: engineering design reviews, place orders for the 2.1 GHz cavity, FPC, RF amplifiers, other RF components; commissioning of the SRF gun in pulsed/low current mode; SRF gun modification for CW operation FY2016: receive and inspect components; high-current commissioning of the SRF gun and 5-cell cavity in CW mode (bldg. 912) FY2017: install in IP2, commissioning FY2018: commissioning with RHIC beams and low energy Au operation 19

July Risk list Low risk –SRF Gun Cathode lifetime, as determined by ERL testing, is lower than design specification. Likelihood: U. Mitigation: Cathode insertion system will have to be redesigned to allow the loading and remote changing of multiple cathodes for efficient RHIC operations. This load lock assembly must be designed to Torr vacuum. Expiration: 4QFY15. 20

July Summary There will be three SRF/RF systems in LEReC: 704 MHz SRF gun and 5-cell cavity, and 2.1 GHz 7-cell warm cavity. The SRF gun commissioning with high beam currents in CW mode will have to be completed in bldg. 912: new cathodes; improved cathode cooling; new HTS solenoid leads. The gun’s FPC coupling will be modified using 3-stub waveguide transformers. The 5-cell cavity is ready for LEReC, just needs to be relocated. The new 7-cell third harmonic cavity operating at 2.1 GHz has its RF design complete. Mechanical design is in progress. The cavity will be straightforward to manufacture and there is a number of companies who can do this (AES, CPI, RI, Niowave, etc.). It also can be fabricated in collaboration with a national lab, e.g. SLAC. 21