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PXIE RFQ Derun Li Lawrence Berkeley National Laboratory PXIE Program Review January 16-17, 2013.

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Presentation on theme: "PXIE RFQ Derun Li Lawrence Berkeley National Laboratory PXIE Program Review January 16-17, 2013."— Presentation transcript:

1 PXIE RFQ Derun Li Lawrence Berkeley National Laboratory PXIE Program Review January 16-17, 2013

2 Outline PXIE RFQ: 162.5 MHz Normal Conducting CW RFQ (5 mA) –Beam dynamics –RF EM and structure design studies –Engineering design, thermal and structure analyses Primary Technical Challenges –CW operation: thermal management –Fabrication (tests): Tools and fixtures, brazing and fabrication techniques Progress to Date –Beam dynamics –RFQ engineering design, fabrication tests and fabrication plan Major Milestones PXIE Review, Derun Li2

3 PXIE RFQ Design Beam dynamics design Meet the design requirements in intensity, emittance growth, LEBT matching to RFQ (TWISS parameters) and good transmissions –Low vane tip-tip voltage (60 kV) while maintaining good beam dynamics Lower CW RF power requirement and easier thermal management RFQ RF structure design –RF simulations in collaboration with Fermilab (3D CST MWS) Mode separation (pi-rods) Cut-backs (including radial matcher in entrance) at both ends Field perturbation due to pi-mode rods, tuners, cut-backs Tuner location and sensitivity RF coupler (collaboration with Fermilab) –Engineering and mechanical design Thermal management and mechanical structure Vacuum and water cooling system 3 PXIE Review, Derun Li

4 Primary Technical Challenges CW Operation –Effective thermal management of CW RFQ structure Low CW RF power while maintain good beam dynamics design (lower vane tip-tip voltage) Design and fabrication of cooling schemes/passages to control the temperature rise and thermal stress of the RFQ structure Fabrication & fabrication tests –Brazing test Brazing clamp design Distortion after brazing –Former cutter –Gun-drill of water cooling passages –Fabrication of vane with modulations –A half length module (IMP) PXIE Review, Derun Li4

5 PROGRESS TO DATE PXIE Review, Derun Li5

6 PXIE RFQ Design Requirements ParametersPXIEUnit Ion Type H- Output Energy 2.1MeV Duty factor 100% Frequency 162.5MHz Beam current 5 (nominal); 1-10mA Transverse Emittance < 0.25 (norm. rms)  mm-mrad Longitudinal Emittance 0.8-1.0keV-nsec Input energy 30kV Emittance Growth 10% Transmission 95% TWISS Parameter  sLess than 1.5 6 PXIE Review, Derun Li

7 Beam Dynamics Design at I = 5 mA Beam distribution derived from ion source emittance measurements; Transmission: 99.9 % at 5 mA; Transverse output emittance: 0.15 pi mm-mrad Longitudinal emittance: 0.7 keV-nsec Current (mA) 7 PXIE Review, Derun Li The design is frozen since early 2012. Transmission (%)

8 Beam Dynamics Design Beam Dynamics Design (cont’d) ParametersValueUnit Vane Tip Voltage 60kV RFQ Length 4.45m Transmission 99.8% Transverse Emittance 0.15  mm- mrad Longitudinal Emittance 0.70 keV- nsec TWISS Parameters  x,  y 0.187 -0.088 Minimum longitudinal r 1.029cm Max. modulation index m 2.3 Total # of cells 208 8 PXIE Review, Derun Li Transverse Emittance vs I Longitudinal Emittance vs I

9 PXIE Review, Derun Li9 Ellipse parameters at cell 208: alpha beta Emit,u,rms Emit,n,rms cm/rad cm-mrad cm-mrad x: 0.1867 23.0494 0.2159 0.01452 y: -0.0878 11.8954 0.2170 0.01459 deg/MeV MeV-deg MeV-deg z: 0.0430 989.4600 0.0410 0.04097 Percent of beam within rms multiples for each phase plane: 1rms 2rms 3rms 4rms 5rms 6rms 7rms 8rms 9rms 10rms x: 41.9 66.3 79.9 87.1 91.4 94.1 95.9 97.1 97.9 98.4 y: 41.8 66.4 79.9 87.1 91.5 94.0 95.7 97.0 97.8 98.5 z: 48.2 71.4 83.8 88.7 91.2 93.1 94.7 95.9 96.9 97.6 The design is frozen since early 2012.

10 Error Analysis PXIE Review, Derun Li10 Beam parameters at the end of the RFQ are modeled as a function of –Input matching conditions as a function of input Twiss parameters –Input current –Input centroid offset created during transition of LEBT chopper –Flat gradient errors –Gradient tilts –Halo content for 100,000 particles –Periodic field oscillation due to the 20 tuners in each quadrant –20 linacs with random errors along the structure –All simulations use a particle distribution based on the measured emittance distribution –All but the 20 tuner errors simulated with PARMTEQM; the tuner error with a modified Version of PARMTEQ that allows arbitrary field variations. Very robust beam dynamics design, large field errors results in small emittance growth

11 Comparison with the SNS RFQ Design PXIE Review, Derun Li11 No sharp inflection points along structure where the beam must meet criteria of proper bunch shape, space charge density, etc. Most of the length is devoted to acceleration.

12 EM (RF) simulation studies and design (Fermilab) Structure design (engineering): modules, structure layout, pi-mode rods, tuners, water cooling paths, probes, vacuum pump ports, support brackets, cut-backs RFQ Structure Design RF design complete Engineering design complete Detailed thermal analysis and mechanical design complete Fabrication drawings complete Feb. 2013 12 PXIE Review, Derun Li

13 RF Simulation and Structure Design Collaboration with Fermilab –2D SUPERFISH simulations Frequency (cross-section), RF power density Parameterized 2D model –3D CST MWS simulations Mode stabilization schemes VCR versus PI-mode stabilization rods Field perturbation due to rods, tuner, … Power dissipation (3D) Thermal calculations –RFQ termination Cut-back and radial matcher at entrance Cut-back at exit –Tuners L1L1 L2L2 RVRV RWRW L max Θ2Θ2 r0r0 r T = ρr 0 Θ1Θ1 L1L1 13 PXIE Review, Derun Li

14 14 PXIE Review, Derun Li

15 3D RF Simulation Results (G. Romanov) ParametersPXIE-TUnits Frequency162.493MHz Frequency of dipole mode181.99MHz Q factor14660 Q factor drop due to everything-14.7% Power loss per cut-back (In/Out)336/392watts Max power loss density at cut-back7.9 W/cm 2 Total power loss74.6kW H (1/2 of the inner width of the RFQ)172.73mm 15 The model includes: Pi-mode stabilization rods Radial matcher and two terminations Tuners PXIE Review, Derun Li

16 Perturbation from Pi-rod Stabilization ParametersPXIEUnit Frequency162.486MHz Quad. frequency shift due to Pi-mode rods-5.56MHz Q factor15333 Q factor drop due Pi-mod e rods-9.65% Power loss per Pi-mode rod188Watts Dipole mode frequency179.6MHz Dipole mode shift22.1MHz Field perturbation at x=y=5 mm0.3% H171.44 (176.59)mm 16 PXIE Review, Derun Li

17 RFQ Termination Design 17 PXIE Review, Derun Li

18 Tuner Studies 20 tuners/module: 80 in total Simulations conducted in a structure period Codes used: CST MWS and ANSYS 18 ParametersPXIE-TUnit Frequency162.495MHz Frequency shift due to tuners1.334MHz Q factor16115 Q factor drop due tuners-4.1% Power loss per tuner60.6Watts Tuning sensitivity16.7kHz/mm Nominal tuner intrusion20Mm H177.84mm PXIE Review, Derun Li

19 RF Coupler Design (S. Kazakov) Two coaxial couplers Multipacting exists in the coupler  Simulations show the HV bias can effectively suppress the multipacting on coupler region RF design complete Thermal and stress analysis in progress Prototyping and high power test this year Identical RF port dimensions with the IMP RFQ – IMP RFQ coupler (similar to MICE and APEX coupler) can be as a backup design PXIE Review, Derun Li19 APEX coupler

20 Summary of RF Power Requirements* 20 SectionTotal, kWPer unit, W Walls29.84- Vanes, 4 units31.337825 Input cut-backs, 4 units1.34336 Output cut-backs, 4 units1.57392 Pi-mode rods, 32 units5.6175 Tuners, 80 units4.8560.6 Sub-total74.6 Beam power at 5 mA10.5 Total85.1 *Based on 3D RF simulation results. PXIE Review, Derun Li

21 Module 1 Module 2 Module 3 Module 4 RFQ Structure (Mechanical) Design Summary of the PXIE RFQ design: o RFQ: 4.45 meters long consists of four modules; o 32 Pi-mode stabilization rods; o 2 RF power couplers; o 80 slug-tuners (20 per module); o 48 RF probes. 21 PXIE Review, Derun Li

22 RFQ Design Approach Development of the PXIE RFQ design based on past LBNL experience Use proven, low risk techniques from the SNS RFQ design –Four vane copper-to-copper braze –Fly cut modulated vane tips –Brazed, water cooled pi-mode rods –Low profile, bolted module joints –Removable fixed slug tuners 22 PXIE Review, Derun Li

23 PXIE RFQ Module Design Features Each module consists of four separately machined vanes Gun drilled vane and outer wall cooling passages Precision ground mating surfaces High reliability copper-to-copper braze forms cavity module 20 fixed slug tuners/module 8 pi-mode stabilizing rods per module 12 field sensing loops per module RF power feed through two loop couplers Two vacuum pumping ports per module Separate wall and vane cooling circuits provides active tuning capability Sealing provided by RF and O-ring seals at bolted joints 23 PXIE Review, Derun Li

24 Mechanical Analyses Numerous engineering analyses carried for design validation Cavity body thermal analysis using ANSYS to calculate RF field, power dissipation density, compared well with SUPERFISH output Stress analysis using converted ANSYS thermal model Water temperature tuning analysis using a separate ANSYS model Calculation of area properties for body stiffness analysis 24 PXIE Review, Derun Li

25 Frequency Tuning Analysis 25 The RFQ cavity resonant frequency can be shifted by altering the cooling water temperature (dynamic tuning): walls and vanes, independently. Wider tuning range can be achieved by varying only the vane water temp. Displacements from the structural analysis are used in an ANSYS RF model to predict tuning performance Analysis results:  200 kHz tuning range possible PXIE Frequency ShiftShift Overall (kHz/ o C)-2.80 Vane (kHz/ o C)-16.70 Wall (kHz/ o C)13.90 % Error3.8% Wall channels Vane channels PXIE Review, Derun Li

26 RFQ Cooling System Each module has 12 cooling channels (8 wall, 4 vane) 12 mm diameter channels flow 0.26 l/s at 2.29 m/s velocity – Reynolds number is 25,900 (turbulent flow) – Maximum flow to prevent Cu erosion is 4.57 m/s – Lower flow rate used to reduce chiller size Total system flow: 8.3 l/s wall, 4.1 l/s vane – Nominal water temperature rise is 1.9 o C – Commercial closed-loop chillers that meet system requirements are readily available – Two units needed (one for vanes, one for walls) Small flow in pi-mode rods (.04 l/s each) necessary to limit axial thermal stresses 26 Commercial chiller example PXIE Review, Derun Li

27 RFQ Vacuum System 27  Primary gas loads are: module joint and tuner O-rings, cavity wall out-gassing and gas from LEBT  RFQ body has 8 vacuum ports (2 per module)  Vacuum could be achieved by four 8” Turbo-pumps (two per RFQ side)  Additional 4 vacuum ports are blanked off  Cavity walls only need to be detergent cleaned (no baking)  Viton O-ring seals are to be pre-baked and ungreased PXIE Review, Derun Li

28 Fabrication Test 28 PXIE Review, Derun Li Vane cutting tool test: –Profile cutter, 2 prototypes in development. –Copper bar, quantity 4, 16mmx75mmx1125mm at LBNL –Work can start immediately (8 weeks of work) Full length vane test: –Horizontal vane, quantity 1, copper –Machining can start as soon as the material arrives. –Need to contact & schedule a gun drilling shop for the cooling passages (6 weeks of work) Braze test –SS material at LBNL, no copper material yet –Need to schedule with the braze company Fabrication copper to arrive end of Feb. 2013

29 Summary and Major Milestones Engineering design and analysis of the PXIE RFQ complete –The PXIE and IMP RFQ’s designs are nearly identical and are being carried largely out in parallel, beneficial to both RFQ designs PXIE RFQ design review was held in April 2012 at LBNL Fabrication tests are under way at LBNL –Tests at LBNL to be complete by April 2013 –Equivalent tests are far along at IMP, Lanzhou, China Final fabrication/design drawings –To be complete by Feb. 2013 Complete the first brazed RFQ module –April 2014 Completed RFQ assembly to arrive at FNAL –Low power RF measurements, RFQ tuning, water cooling manifold, RFQ support and assembly –Ready for RFQ commissioning in August 2014 (RF power and water cooling connection) 29 PXIE Review, Derun Li

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