BARC’s CW Power Coupler at 325 MHz for IIFC Rajesh Kumar BARC alternate mail id:

BARC’s CW Power Coupler at 325 MHz for IIFC Overview of RF Coupler development at BARC Existing Coupler designs for LEHIPA cavities at BARC RF Design of a Coaxial Coupler at 325 MHz Conclusions

Overview of RF Coupler development at BARC Design choices Side iris coupled End iris coupled Loop coupling Probe coupling Loop coupling with stand alone RF window with planar (disc type) RF window integrated to assembly with planar (disc type) or cylindrical RF window integrated to assembly Wave guide type Coaxial Type Waveguide-coax

Overview of RF Coupler development at BARC Couplers under development at BARC Coaxial loop type coupler- 50 kW CW, 350 MHz ( 2 Nos. required) Waveguide type iris couplers- 250 Kw CW, MHz ( 10 Nos. required)

Specifications of waveguide Couplers for LEHIPA Couplers to be rated for 250 kW-CW, MHz Return loss for these couplers should be better than 30 dB in different operating conditions Min. frequency shift to cavity frequency ( less than 1 MHz ) Flexibility of coupling coefficient variation

6 RF Simulations for Coupling Coefficient Half Height WR2300 waveguide is reduced to small cross-section on the RFQ Ridge loading is used to maintain the same cut-off and impedance match Power handling: 250 kW CW, Total estimated heat loss: 3 kW r l1 a b 190 mm 35mm Gap=1.55 mm a= mm b= mm l1=90mm r=5mm

7 Coupling coefficient adjustments β = Qo/Qext Ref. J.Gao, Nuclear Instr. and Meth. A-309(1991) p l 2 2l 1 a b e o = (1- l 2 2 /l 1 2 ) 1/2 Coupling can be increased by increasing the iris length!

8 Quarter-wave match with stepped section Ref.- High Power RF Coupler development for LEHIPA- Rajesh Kumar et.al. Indian Particle Accelerator Conference-InPac 2009

9 Magnetic field distribution inside the coupler

10 Electric field distribution inside the coupler

11 ComponentPower level- CW E max field ( kV/cm) H max field ( A/m) Loss WR-2300 WG250 kW kW/ 100 ft WG- Coupler for LEHIPA RFQ cavity 250 kW kW (2 ft) Rigid- 1 5/8” Coax50 kW kW/ 100 ft Coax-Coupler for RFQ cavity of deutron accelerator 50 kW54000 ( in loop region) 1 kW (2 ft) Comparison of Electric and Magentic field levels inside couplers

Front view end view 3 D Model of waveguide couplers for RFQ Cavity Ridge waveguide couplers with reduced dimensional tolerance requirements also being developed in collaboration with Indian Institute of Technology (IIT) Bombay Dimensional tolerances: microns in end gap region

13 l w a b l =200 mm w = 40 mm a = mm b = mm Drift Tube Linac (DTL)cavity Waveguide coupler for DTL cavities

Waveguide couplers for LEHIPA-Summary 14 Coupler- Cavity Incoming WG Dimensions at cavity end (mm) Length (mm) RF Power (KW) Cu Loss (KW) Type of proposed cooling Material of fabrication WG/ RFQ- LEHIPA WR-2300 a=584.2, b= W1=90, W1’=50, H1’= 35 H1= Water jacket SS plated with Cu WG/DTL- LEHIPA WR-2300 a=584.2, b= W1= 220 H1= Water jacket SS plated with Cu Coaxial/ 400 keV RFQ 6-1/8” Rigid Coax 48 OD Water tubes + air ETP/OFE Cu + Alumina tubes

15 Total Power Requirement of 400 keV RFQ accelerator at BARC is 80 kW-CW at 350 MHz. E field in cavity High vacuum Components 50 kW, 350 MHz Tetrode Amplifier DC Matched load Circulator Existing Coaxial Coupler scheme for 400 keV BARC RFQ Coupler1 50 kW,350 MHz Coupler Two coaxial couplers will be fed by two 50 kW Tetrode amplifiers.

16 50 kW CW 350 MHz Coaxial Coupler schematic for 400 keV BARC RFQ Cu gasket Cavity flange Shorted stub Rotation possibility without changing the flange location and axis 61/8” line from Input 61/8” to 15/8” tapered transition

17 50 kW coaxial coupler assembly 6 1/8" to 1 5/8" tapered transition 1 5/8" Quarter wave shorted stub High purity alumina coaxial window Loop part shorting inner and outer conductors Total Heat loss estimated: 1.2 Kw Max. Temp. after cooling: 90 deg.C RF Simulation Model of Coaxial Coupler Ref- RF Design of High Power Couplers for ADS- Rajesh Kumar et.al. Indian Particle Accelerator Conference-InPac Mumbai-2006 RF Design of Coaxial Coupler

18 Salient features of Coaxial Coupler design for BARC RFQ Variable Coupling by loop rotation ( off- line) Limited tuning possible during cold testing by shorted stub water cooling through shorted stub integrated disc type window

19 RF Design of Coaxial Coupler for BARC RFQ RF Simulation Model of Coaxial Coupler in CST Microwave Studio

20 Variation of minimum return loss frequency with stub length

Thermo structural analysis of Coaxial Coupler Heat transfer coeff. (h) =15000 W/m 2 K Inlet coolant temp = 16 0 C Max. deformation = 64 microns Ref- Thermo-structural analysis of 400 keV deuteron RFQ components Piyush Jain, S.V.L.S Rao, Rajesh Kumar, P.K Nema, P. Singh Asian Particle Accelerator Conference-APAC RRCAT Indore -2007

P one-point is proportional to (fd) 4 Z P two-point is proportional to (fd) 4 Z 2 Multipacting analysis of Coaxial Coupler f in GHz, d is OD in mm, Z is Characteristic impedance in Ohm SW Multipacting barriers for 1 5/8” line (350 MHz) : 150W to 5 Kw SW Multipacting barriers for 6 1/8” line (350 MHz) : 42 kW onwards P TW = 4* P SW 1 5/8” line TW Mode: 600 W to 20 kW 6 1/8” line TW mode: 168 kW onwards Ref- Analysis of multipacting in Coaxial lines, E. Somersalo et.al PAC-1995

23 Fabrication and RF measurement status 50kW peak, 350 MHz Pulsed power Coaxial Coupler Coaxial Coupler’s coupling measurement

24 Fabrication and RF measurement status contd. Coaxial disc type alumina window prototype 50 kW Coaxial coupler assembly parts

25 Schematic of coupler conditioning set-up Klystron Circulator DC Window Two Couplers Load/Cavity VSG Load Ref. & Fwd Vacuum Coupler Vacuum Load/C Power Port/signal (optional) Arc Arc detectors Temperature detectors Vacuum signal Forward & Ref. power Arcing signal

26 Test cavity for coupler conditioning 6 1/8”- 3 1/8” -1 5/8”- N Type Transition developed by IPR for characterizing Coaxial couplers RF Cavity developed for Coaxial Coupler Conditioning

27 RF Design of 325 MHz Coaxial Coupler for IIFC contd. Salient features of LEHIPA Coupler Conflat Flange Size: 82.3 mm Port ID: 50 mm Coax: 1 5/8” Port depth: 72.3 mm Coupling type: Loop Coupler length: 450 mm approx. Cooling: DM water Rating: 50 kW, CW 350 MHz Proposed modifications in LEHIPA Coupler for IIFC Conflat Flange Size: 82.3 mm ( to be decided ) Port ID: 50 mm ( to be decided ) Coax: 1 5/8” Port depth: 72.3 mm ( to be decided ) Coupling type: Loop/ Probe Coupler length: 450 mm approx. Cooling: DM water Rating: 50 kW, CW 325 MHz?

28 For 325 MHz operation, increasing the stub length from mm to mm will give required return loss minima at 325 MHz. RF Design of 325 MHz Coaxial Coupler for IIFC contd.

29 Return loss variation with stub length RF Design of 325 MHz Coaxial Coupler for IIFC contd.

30 Return loss variation with stub length RF Design of 325 MHz Coaxial Coupler for IIFC contd.

31 Research activities on variable coupling It is proposed to change the coupling by iris rotation Prototype S band cavity and rotation type RF Coupler made and tested at low power. Author’s Recent publications : 1.Rajesh Kumar, ‘A Novel Method for variable coupling using iris rotation in RF Couplers’, Nuclear Instruments and Methods in Physics Research-A, Vol. 600, Issue 3,11 March 2009, pp ) 2.Rajesh Kumar,G.N Singh, P Singh ‘Development of a 350 MHz quarter wave resonator for power coupler testing’, IEEE Applied Electromagnetics Conference- AEMC 2009 doi: /AEMC High Power RF Coupler development for LEHIPA- Rajesh Kumar et.al. Indian Particle Accelerator Conference-InPac 2009

32 Conclusions BARC’s coaxial coupler design can be adapted for Project X under IIFC Data related to power requirements, allowable port sizes and cavity of Project X are needed to finalize the detailed design

33 Thank You