PXIE RFQ Progress John Staples, LBNL 10-12 April 2012 Collaboration - PowerPoint PPT Presentation

PXIE RFQ Progress John Staples, LBNL 10-12 April 2012 Collaboration Meeting, LBNL

Summary LBNL is tasked with the design of RFQs for both FNAL (PXIE) and IMP (Lanzhou) These two CW RFQs are very similar The beam dynamics and structure design have been converging to nearly a single design, differing only in details of beam parameters. The mechanical design is compatible with available manufacturing techniques in both China and the USA. E-beam welding is used only on the ends of the gun-drilled water passages. Both projects are on an accelerated schedule The beam dynamics design for PXIE and for IMP is complete

From Steve Holmes, September 2011

RFQ Parameter List PXIE IMP Input energy 30 35 keV Output energy 2.1 2.1 MeV Frequency 162.5 162.5 MHz DC Current 5-15 5-20 mA Vane-vane voltage 60 65 kV Vane Length 444.6 416.2 cm RF Power 100 110 kW Beam Power 10.5 21 kW Duty Factor 100 100 percent Transverse emittance <0.15 mm-mrad, rms, normalized Longitudinal emittance <1.0 keV-nsec

What's New? The beam dynamics design is frozen for both machines At FNAL's request, an exit radial matcher has been added to reduce the divergence of the output beam Transmission >99% to 10 mA Transverse emittance <0.15 pi mm-mrad to 10 mA Longitudinal emittance <0.25 pi mm-mrad (<.78 keV-deg) to 10 mA Vane length is 443.0 cm, cavity length 444.66 cm Error analysis of the structure and of the beam dynamics implications carried out LEBT chopper design integrated with the transverse acceptance of the RFQ Detailed MWS simulations of the structure (G. Romanov, FNAL) carried out

Design Highlights Constant cross-section of structure along entire length constant transverse vane radius: only one form cutter profile needed The minimum longitudinal vanetip radius = 1.03 cm: easy design of cutter Four modules, joined with butt joints Each module assembled with brazes: no electron-beam welding, except to close the ends of the gun-bored water channels. No complex brazing operations: (No Glidcop in structure) Wall power density less than 0.7 Watts/cm 2 CW (SNS was 1.7 at 6% duty factor) Pi-mode stabilizers offer very large mode separation and field stability against machining errors. 32 stabilizers used: 4 pairs/module. Mode separation, quadrupole to dipole frequency is 17.5 MHz. Length only 2.4 free-space wavelengths long (SNS was over 5 wavelengths) 80 tuners, 48 sensing loops, two drive ports

Beam Dynamics Simulations Beam load derived from ion source emittance measurements: halo present Capture is 99.81% of 5 mA input beam Transverse output emittance 0.15 pi mm-mr Longitudinal emittance 0.68 keV-nsec Simulation using 100,000 particles, 5 mA

Input and Output phase space plots, 100,000 particles. Input phase space derived from emittance measurement, include all ion source halo. Exit radial matcher reduces output beam maximum divergence. Beam at a waist.

Output Phase Space Distributions, x-y and phi-E, 100,000 particles

Vane Dimensions, Exit Radial Matcher Exit beam nearly at a waist. Last few cells of RFQ

Error Analyses 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 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.

Output Emittance vs. Input Current Optimized input current is 5 mA. Other current values use same input match. Re-matching at other currents may result in lower output emittance, so this represents the worst case away from nominal. The transverse input emittance is 0.011 pi cm-mrad, normalized, rms, derived from emittance scans of the ion source. Output longitudinal emittance at 5 mA is 0.68 keV-nsec. x, y, z output normalized emittance vs Input Current 0.050 0.045 0.040 normalized emittance (cm-mrad, rms) 0.035 0.030 x-emitt y-emitt 0.025 z-emitt 0.020 0.015 0.010 0.005 0.000 0 2 4 6 8 10 12 14 16 Input Current (mA)

Transverse Particle Distribution 1.0E+04 1.0E+03 Transverse Particle Distribution Fraction 1.0E+02 100,000 particles 1.0E+01 2-gaussian fit 1.0E+00 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 x (cm) 25% 0.5 mm rms gaussian + 2 gaussians and original spectrum 75% 0.74 mm rms gaussian Transverse Particle Distribution 1.0E+04 1.0E+03 1.0E+02 1.0E+01 Fraction 1.0E+00 1.0E-01 1.0E-02 1.0E-03 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 x (cm) fitted spectrum

Longitudinal Energy Distribution Longitudinal Energy Distribution 1.0E+05 1.0E+04 100,000 particles 1.0E+03 Fraction 3-gaussian fit 1.0E+02 1.0E+01 71.5%, 2.5 keV rms spread + 1.0E+00 2.06 2.08 2.10 2.12 2.14 2.16 2.18 2.20 2.22 28.0% 8.5 keV rms spread + KE (MeV) 0.5% 20 keV rms spread 3 gaussians and the original spectrum The 20 keV component has a Longitudinal Energy Distribution very large error bar, as it includes 1.0E+05 only a few particles. 1.0E+04 1.0E+03 1.0E+02 Fraction 1.0E+01 1.0E+00 1.0E-01 1.0E-02 2.06 2.08 2.10 2.12 2.14 2.16 2.18 2.20 2.22 KE (MeV) The fitted spectrum

Independent Parameter: Output Longitudinal vs input Transverse Emittance Transverse input emittance. 1 0.9 0.8 0.7 0.6 keV-nsec 0.5 Output longitudinal 0.4 emittance as a function 0.3 of transverse input 0.2 0.1 emittance. 0 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022 0.024 0.026 cm-mrad Output vs Input transverse emittance Output transverse 0.030 emittance as a function 0.025 of transverse input 0.020 emittance. cm-mrad 0.015 17% transverse emittance 0.010 growth for input emittance 0.005 of 0.15 mm-mrad. 0.000 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022 0.024 0.026 cm-mrad

% Transverse emittance growth vs input Twiss alpha Independent Parameter: 60 Input Twiss alpha Percent Transverse Emittance Growth 50 40 30 Output transverse and 20 longitudinal emittance as a function of mismatch 10 of Twiss parameter alpha 0 at RFQ entrance. 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Twiss Alpha Nominal value of alpha is 1.6. Longitudinal Output Emittancs vs. input Twiss alpha 5 mA input current. 0.85 Longitudinal Emittance (keV-nsec) 0.8 0.75 0.7 0.65 0.6 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Twiss Alpha

Independent Parameter: Output Longitudinal Emittance vs Twiss beta 1.2 Input Twiss beta 1 0.8 keV-nsec 0.6 Output transverse and 0.4 longitudinal emittance as a function of mismatch 0.2 of Twiss parameter beta 0 3 4 5 6 7 8 9 10 at RFQ entrance. cm Nominal value of beta is 7 cm. % emittance growth vs input Twiss beta 70 5 mA input current. 60 50 40 30 20 10 0 3 4 5 6 7 8 9 10

Scan of Output Emittance vs. Input Twiss Parameters The output emittances are minimized for the nominal value of the input Twiss parameters. Transmission is greater than 99% for all cases. 5 x 5 scan of input Twiss parameters Nominal input match: Alpha = 1.6 Beta = 0.07 m (7 cm) Scan beta from 0.05 to 0.09 meters Scan alpha from 1.2 to 2.0

Output Beam Parameters vs. RFQ Field Errors Errors Considered Flat-field gradient error Field tilt error, field held constant at entrance Field tilt error, field held constant at exit Field ripple error from the tuners PARMTEQM can only simulate the first three: the field ripple is simulated with another version of parmteq with arbitrary field error.

Fractional emittance variation vs. field gradient Independent Parameter: 1.4 Flat field gradient 1.3 ex, ey, ez deviation from nominal 1.2 1.1 1.0 0.9 0.8 0.7 Output emittance and deviation from nominal 0.6 0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 2.13 MeV output energy Fraction of nominal gradient as a function of flat gradient error. Output Energy Deviation (MeV) vs gradient 0.005 0.000 -0.005 -0.010 MeV -0.015 -0.020 -0.025 -0.030 0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 Overall gradient fraction of nominal

Independent Parameter: Fractional emittance variation vs. field tilt 1.2 Overall field tilt 1.1 ex,ey,ez deviation from nominal 1.0 0.9 Effect on output emittance and deviation from nominal 0.8 output energy as a function 0.7 of field tilt error, pivoting around zero field error in 0.6 -8 -6 -4 -2 0 2 4 6 8 the center of the RFQ. Field tilt (%), each end from center Change of output energy (MeV) vs tilt 0.006 0.004 0.002 Energy deviation in MeV 0.000 -0.002 -0.004 -0.006 -0.008 -0.010 -0.012 -8 -6 -4 -2 0 2 4 6 8 Field tilt (%), each end from center