STATUS OF THE NC BUNCHING RFQ (Sub-task: SC-RFQ) Antonio Palmieri INFN-LNL

General considerations 3D details End cells RF coupler Preliminary thermo-structural analysis Sensitivity to perturbations: tuning system Next Steps

Basic choice for the buncher RFQ: Four vane structure Optimization of power consumption Experience in design of High power four-vane RFQ structures (TRASCO RFQ) No need to use brazing joints for the rated power level Cost effectiveness Feasibility of a 88 MHz four-vane RFQ being demonstrated at higher power level (SPIRAL2) Frequency88 MHz Voltage kV Q19800 Mean aperture R mm Length5.077 m Dissipated power/meter 29 kW Max power density19 W/cm 2 Current density on the joint (max) 38 A/cm

RF DESIGN OF THE TRANSVERSE SECTION FOR 88 MHz WITH NEW BEAM DYNAMICS SPECS R0R0R0R0 3.4 mm  V iv 40.4 kV L m ( m (0.53 λ ) h mm h2 50 mm t 20 mm H 313 mm R 30 mm fq MHz fd MHz U J/m Q0Q0Q0Q PdPdPdPd ~10kW( * ) E sup 18 MV/m H max 960 A/m (*) 20 % margin

Jmax=9.8 A/cm (on the joint) Power and current densities pdmax=0.12 W/cm 2

EURISOL TASK 6 CERN 28/11/06 RF DESIGN OF THE END-CELL Main goals: Ensure a matched termination for the RFQ transmission line (f end-cell ≈ f RFQ ) Check the power density Check the current density on the joint Tool used: HFSS v.8.5 and v /8 of RFQ sim. length=L/2=1m ~100k mesh tethraedra With such dimensions f end-cell =87.866MHz (f RFQ = MHz)

EURISOL TASK 6 CERN 28/11/06 pmax= ~2.W/cm 2 Power density distribution in the end-cell region Current density distribution in the end-cell region J(on the joint)= 25 A/cm

CONSIDERATIONS ABOUT THE RF COUPLER In order to feed the RFQ a single water-cooled loop could be used. An estimation of the coupling area required could be given by calculating the coupling coefficient With H=1000 A/m, P diss =10kW R 0 =50 Ω, the area required in order to have critical coupling (β=1) is about 14 cm 2. 3” 1/8 coaxial line Ceramic seal Water-cooled Loop (1 cm diameter)

HFSS SIMULATIONS positioning of the coupler: in the middle of the first meter Dissipative S 11 parameter simulation on ¼ RFQ L=50 cm Power handling exstimation: assuming H=2500 A/m in the vicinity of the loop, the power density is about 0.78 W/cm2 and the power dissipated in the loop is 24 W 10kW input power 10kW input power

PRELIMINARY THERMO-STRUCTURAL ASSESSMENTS Cooling channels arrangements: Thermal loads from HFSS simulations Channel radii = 15mm (vanes), 10 mm (bulk) Water velocity= 2.5 m/s (vanes), 2 m/s (bulk) Water temperature at the inlet = 20°C ANSYS simulations : temperature and deformation fields

Temperature distribution The maximum ΔT is found in the end-cell undercut and is equal to +4.6°C

Deformation profile The maximum transverse displacement is equal to 0.01 mm (ΔR 0 max ≈ 0.01 mm) The maximum longitudinal displacement is equal to 0.3 mm and is located in the end-cell undercut Modulus of displacement Transverse displacement Longitudinal displacement

Comments  R0 =0.298   =0.201 The associated frequency variation due to transverse displacement is 84 kHz The frequency sensitivity with vanes inlet water temperature is about 20 kHz/°C Closed loop regulation with 0.1±0.2 °C precision feasible The 0.3 mm deformed vane end provokes a variation of the quadrupole frequency by about 30 kHz Different cooling channels arrangements are to be studied: i.e. series connection of neighbouring vanes cooling channels

EURISOL TASK 6 CERN 28/11/06 TUNING SYSTEM OF THE RFQ The favorable L/ ratio makes not necessary the usage of segmented structure with coupling cells (the frequency of the 1 st upper quad. Mode lies 28 MHz higher) at least up to a length of about 4±5 m. The dipole stabilizers appear not to be necessary (the dipole frequency lies more than 2 MHz apart from fq) The non-uniformities can be only corrected with standard slug tuners The estimation of the tuning capability of such tuners can be performed with the Slater formula In our case  f~N*0.75 kHz for a=50mm. Therefore if we use 16 tuners (2tuners/quadrant*meter)  h≈10 mm permits to match the 88 MHz. Proposed tuners location: at z=30 cm, z=70cm, z=130 cm, z=170cm a=tuner radius  h= tuner penetration U=stored energy N=number of tuners

Case of one electrode transversally displaced of 0.05 mm in all RFQ length: Δf ~ 100 kHz dipole contents of 0.4% TUNING SYSTEM OF THE RFQ (cont’d): Example of tuning By moving the tuners of the quadrants adjacent to the electrode of 1 cm the frequency shifts and the perturbating dipole component are recovered

Partial Comparison table Parameter EURISOL NC four vane (bunching) EURISOL four rods tandem (bunching+acceleration) Frequency88 MHz A/q8.5<9.52 Input energy2.35 keV/u Output Energy37.1 keV/u460 keV/u Voltage43.3 kV60 kV Q17700~8000 Mean aperture R mm4.3 mm Length2 m3.87m+3.95m Dissipated power/meter5 kW33 kW Max power density2 W/cm 2 2.5W/cm 2

Next Step Proposals for a comparison table Beam dynamics issues: T, e T & e L growth (start-to-end) RF structure issues: previous table and eqivalent numbers for the SC-RFQs (PIAVE-like at 88 MHz) Mains power Cost Technical challenges...