MEBT Emittance Scanner Calibration L Prost et al

MEBT Emittance Scanner Calibration L. Prost, et. al PIP-II Technical Meeting 14 February 2017

Outline • • Beamline configuration, scanner specs Position calibration Angular calibration A word on errors/uncertainties – Slits widths, space charge 2 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

MEBT beamline • Emittance scanner installed downstream of the first MEBT section – 2 quad doublets with BPMs, 1 scraper assembly, 1 bunching cavity – Followed by another scraper assembly and a toroid – Horizontal direction 3 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Scanner specs/key design parameters Parameter Value Front slit width, d 1 0. 2 mm Rear slit width, d 2 0. 2 mm Electric plate length, Lp 300 mm Slit-to-slit distance, Ls 320 mm Geometric gap, g 5. 51 mm Saw-tooth plate depth, d 0. 356 mm Max. electric plate voltage, V/2 Beam kinetic energy Nominal* Max. pulse length Signal dynamic range 1 k. V 2. 1 Me. V 20 ms 103 * At the nominal beam size of 2 mm (rms) Limit beam power to < 8 W/mm 2 4 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Position calibration V. Scarpine, A. Saewert, D. Slimmer, M. Alvarez • Move emittance scanner head with Labview GUI • Check encoder readbacks against measurements with a micrometer attached to the scanner head – Closed-loop • Excellent linearity 5 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Position calibration (cont’) V. Scarpine, A. Saewert, D. Slimmer, M. Alvarez • For requested displacements of 0. 25 mm to 5 mm, the displacement error is 0± 0. 018 mm (rms) – Independent of the direction of motion – Error maybe dominated by micrometer readings accuracy (10 microns) 6 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Angular calibration • In the measurements of the x-x’ phase-space, the angular coordinate is determined by the voltage applied across the plates according to: q. U ≡ ion energy Le ≡ effective length of the plates ge ≡ effective gap between the plates Note in this definition, the plates’ voltages are +V/2 and –V/2 • Le and ge are not exactly the geometric values – Fringe field effect • Electrostatic field simulations can lead to Le and ge – Independent in-situ calibration of the ratio Le / ge 7 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Initial calibration • With the increased length of the deflecting plates and the smaller gap (w. r. t. the LEBT emittance scanner), fringe field effects are greatly reduced ⇒ Le = Lp and ge = g + d for initial calibration • Simulations (electrostatic + single particle tracking) with SAM in agreement to within 5% Front-slit -500 V +500 V Particle initial parameters: 2. 1 Me. V, 6 mrad 8 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

In-situ calibration methodology • Steer the beam with a corrector upstream of the emittance scanner (in free space) – In phase space, the beam’s centroid displacements in X and X’ are geometrically related Nuclear Instruments and Methods in Physics Research A 815 (2016) 7– 17 Ld ≡ Distance between the corrector and the front slit of the emittance scanner – Method used/established for the LEBT emittance scanner Data from LEBT emittance scanner calibration 9 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Nominal settings limitations • 5 m. A, 20 ms chopper, 10 Hz, “file #1506” (i. e. nominal) • As opposed to the calibration of the LEBT emittance scanner, the range available for steering is limited • Need solution that allows moving the beam without cutting out part of the phase space • Kick beam upstream en = 0. 241 mm mrad (1% cut) Dx’ max. range = ± 12 mrad X’, mrad – In addition, M 10 corrector is very close to the scanner – But possible motion is limited by aperture restrictions X, mm 01/09/17 – 11: 27 (M 10 CXI = 0) 10 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

– Settings such that the waist of the beam is near the entrance slit – Longer baseline reduces errors en = 0. 227 mm mrad (1% cut) X’, mrad Beamline settings • 5 m. A, 20 ms chopped pulse, 10 Hz • Second doublet off, bunching cavity off, kick with M 00 corrector (01/17/17) 01/17/17 – 10: 12 (M 00 CXI = 0) X, mm M 00 corrector Smallest apertures Emittance scanner (horizontal direction in actual beamline) 11 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Calibration result with 1/17/17 data set • 1% cut, ‘end’ of pulse Ld_m = 1/1. 0457 = 0. 9563 m Standard error, s. Ld_m = 0. 002 m 5 ‘good’ data points out of 8 +10 mrad -10 mrad M 00 CXI = +2 A 12 L. Prost, et. al | MEBT Emittance Scanner Calibration M 00 CXI = 0 A 02/14/2017 M 00 CXI = -1 A

Comparison with the expected distance Ld • Mechanical center of correctors → Slit = 1030. 5 mm – Actual ‘center of mass’ for the field in the corrector with quads installed is shifted (downstream) by 77 mm – Ld = 1030. 5 – 77 = 953. 5 mm Less than 0. 3% difference !! – To be compared with Ld_m = 956. 3 mm Angular calibration of the emittance scanner is correct 13 L. Prost, et. al | MEBT Emittance Scanner Calibration Much less than other possible sources of error 02/14/2017

Space charge effect • Increase of the beamlet height between 1 st and 2 nd slit due to defocusing from space charge (flat, constant-density beam without thermal expansion): L , defined on Slide 4; s Nuclear Instruments and Methods in Physics Research A 815 (2016) 7– 17; Eq. (7) PIP 2 IT typical beam perveance, Pb, in MEBT (5 m. A, 2. 1 Me. V) = 1. 6× 10 -6 m. A/V 3/2 with sx = 2. 5 mm Ibl ≡ beamlet current ~1% increase Completely negligible 14 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Slits widths effect • Assuming Gaussian beam: ‘m’ ≡ measured ‘t’ ≡ true R. D'Arcy, A. Shemyakin, Calculation of the effect of slit size on emittance measurements made by a two-slit scanner, ar. Xiv: 1503. 06055 [physics. acc-ph]. Ls, d 1, d 2 defined on Slide 4; a, b are the Twiss parameters Typically 4 -5% effect Example: Quad scan (1/11/17) e. g. : for the data here, on average, it’s a 4. 4% effect When the slit width correction is applied, the reported emittance is independent of the focusing settings 15 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Discussion of errors/uncertainties • Position uncertainty from measurements: ± 0. 018 mm (rms) • Deflecting voltage accuracy: ± 0. 5 V (rms) ← Negligible • Calibration factor w. r. t. formula on Slide 7 i. e. Ld_m/Ld = 1. 01 ± 0. 01 – Consistent with simulations • ‘Statistical’ uncertainty: standard deviation < 5% – Limited data – Note that we also know that the beam parameters drift in the LEBT • Not clear how it affects beam parameters downstream, but could artificially increase perceived measurements spread 16 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Effect of steering • Relatively large variations of b and emittance when steering (1/17/17) – Signal integral varies < 0. 5% ⇒ No scraping – Focusing effect from correctors ? Standard deviation ~ 12% Each measurement 45 min apart (‘initial’ settings) 17 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017

Summary • Angular calibration of the MEBT emittance scanner is good – Cross-checks with BPM and scraper data agree well with expectations (not shown here) • Systematic errors: – Calibration: < 1% – Slits widths effect: - 4 -5% • Statistical fluctuations: ~3% – For a limited data set with varying steering and focusing in MEBT Some data and analyses in PXIE MEBTShifts2017_01_09_Emit_Scanner PXIE MEBTShifts2017_01_17_AM And PXIE MEBTShifts2017_01_11_AM 18 L. Prost, et. al | MEBT Emittance Scanner Calibration 02/14/2017