PIP-II R&D Program PXIE Ion source and LEBT Lionel Prost PIP-II Machine Advisory Committee Meeting 15-17 March 2016 Outline Performance requirements Conceptual design Status Additions/changes since P2MAC 2015 Operation highlights Dipole bending magnet status Summary & Plan 2 Lionel Prost | 2016 P2MAC 3/15/2016 Performance requirements Ion Source (IS) capable of delivering 10 mA (5 mA, nominal) DC, H- at 30 keV to the Low Energy Beam Transport section Low Energy Beam Transport (LEBT) capable of creating pulses over a wide range of duty factors via a chopper Prevents beam propagation downstream when fault condition is identified (Machine Protection) Includes beam current diagnostics Kinetic energy stability Beam current stability [for frequencies > 1 Hz (ripples)] 0.5% rms 5% Output transverse emittance over 1-5 mA current range < 0.18 mm mrad Single pulse flat top Maximum pulse frequency 3
Lionel Prost | 2016 P2MAC 1 msec - DC 60 Hz 3/15/2016 Ion source & LEBT PIP-II conceptual design Two ion sources Maximize beam availability Repair/service/install one without interrupting operation of the other Good vacuum near RFQ to help achieve high reliability Chopping far from RFQ No direct line of sight from the IS to RFQ 4 Lionel Prost | 2016 P2MAC RFQ 3/15/2016 PXIE Ion Source and LEBT Commercial ion source D-Pace, Inc. Current transformer T. Hamerla Gate valve DCCT 3 solenoids Bending dipole
Part of Personnel Protection System Diagnostics Ion Source Beam current monitors Emittance scanner Electrostatic chopper One of the kicker plates is the beam absorber 5 Lionel Prost | 2016 P2MAC Chopper Port for emittance scanner Solenoids Possibility of partially unneutralized transport Main scheme Possibility of scraping the beam at various locations 3/15/2016 P2MAC 2015 status Demonstrated up to 10 mA, DC and pulse 1-60 Hz pulses Twiss parameters close to those needed for the RFQ Solutions for both maximum neutralization and partial neutralization transport schemes Stabilization loops to deal with source variability IS arc current stabilization, beam current regulation loop
Ion Source 6 Lionel Prost | 2016 P2MAC Vacuum valve DCCT Faraday cup Toroid Emittance scanner Chopper 3/15/2016 Since P2MAC 2015 Continued beam measurements and analyses Focused on readiness for RFQ commissioning Beam profiles/sizes, phase space, neutralization Moved emittance scanner to the IS vacuum box T. Hamerla Pencil beam aperture Permanent location Comparisons with simulations Regular aperture
Installed LEBT scraper Water-cooled, electrically-isolated copper paddle with 2 round apertures and a D-shaped aperture D-shaped aperture Bending dipole magnet (and vacuum chamber) designed and under fabrication Shutdown for RFQ installation IS cleaning/maintenance 7 Lionel Prost | 2016 P2MAC 3/15/2016 Current beam line configuration All components except for the bending dipole magnet have been installed and commissioned Beam stop will be removed when installing the dipole Added components since last P2MAC Emittance scanner LEBT scraper assembly Toroid Beam stop Collimator DCCT Ion Source Vacuum valve
RFQ Chopper T. Hamerla 8 Lionel Prost | 2016 P2MAC Solenoid #1 Solenoid #2 Solenoid #3 3/15/2016 Operation readiness for RFQ commissioning Two complications with direct consequences on operation Near term/temporary: MEBT diagnostics will not be quite ready when starting to Evolution of the Twiss parameters and emittance commission with beam at the exit of the ion source during a long run LEBT diagnostics as the b primary input to MPS Long term: The beam parameters have shown 0.01 mm mrad/div 1 unit/div a slow variations over the 0.5 m/div course of several hours Normalized of operation and from emittance (rms) day-to-day Envelope variations at the entrance of the RFQ 9
Lionel Prost | 2016 P2MAC 47 hours 3/15/2016 LEBT scraper functions Large round aperture LEBT/RFQ Interface flange T. Hamerla Protects RFQ vanes Beam size stabilization Machine Protection System input Pencil beam aperture T. Hamerla, R. Andrews, D. Snee Regular aperture Small round aperture Pencil beam D-shaped aperture D-shaped aperture Beam size measurements Max transmission 10 Lionel Prost | 2016 P2MAC
3/15/2016 LEBT scraper in use Use LEBT scraper current read back to monitor possible variations of the beam condition &zkickerstart structure zkickerend Beam envelope stabilization Regulate solenoid #3 current to keep beam loss on the scraper constant 2s beam envelope Constant beam size zkickerstart zkickerend outmost z kickerstart z kickerend particle Large round aperture has been sized to let the beam with the proper Twiss functions go through with <1% loss on the scraper Machine Protection System LEBT scraper aperture RFQ vanes Iscraper Set limits on LEBT scraper losses signals pulse width and amplitude Beam deflected onto the absorber upstream of Solenoid #3 when pulse violates limits 11
Lionel Prost | 2016 P2MAC 3/15/2016 MPS Configuration to-date Primary beam inhibit LEBT Chopper (~ 150 ns delay + 110 ns rise time + propagation) Secondary beam inhibit IS HV bias supply 125 MHz digitizer - 30 MHz carrier output( arbitrary) monitors scraper beam loss and beam pulse width thresholds to drive Permit line to LEBT chopper General purpose FPGA Board 64 inputs expandable to 162 32 outputs 405 MHz max for registered logic RFQ Status A. Warner CHOPPER HV Status Timing Triggers LEBT SCRAPER Mode verify Serial data CHOPPER Permit MPS LOGIC - PERMIT SYSTEM OK/not OK CHOPPER mode ctl HV INHIBIT 30 MHz
12 Lionel Prost | 2016 P2MAC Modulator Extractor Source HV Supply 30 MHz Toroid/DCCT RING PU etc. LEBT CHOPPER LEBT Scraper threshold Vacuum Beam Stop 3/15/2016 IS phase space measurements and beam steering s = 4.2 mm Beam phase space measurements at e = 0.12 mm mrad 1% cut above background the exit of the ion source rms mrad Up-to-date beam parameter inputs for simulations Position and angle bumps at the LEBT scraper
~5% for position ~10% for angle Within measurements errors Dx meas., mm Correctors in solenoidal field model for calibration Accuracy: 3.7 mA in DCCT DC J-P. Carneiro, B. Hanna AllisonScan-2015-07-13_14-57 mm 6 y = 0.9733x - 0.198 R = 0.9999 4 2 0 -2 -4 -6 Tuning with RFQ -6 -4 -2 0 2
4 Dx calc., mm Center the beam in LEBT scraper hole, then change the angle without changing the position to maximize transmission 13 Lionel Prost | 2016 P2MAC 3/15/2016 6 Phase space measurements at the end of the beam line Solenoid #3 scans -2 190 Multiple data sets a at the Allison scanner Beam envelope stabilization proof-of-principle Same settings but initially different Twiss 170 160 200 210 -4 Partially un-neutralized transport is the main scheme
180 150 220 -6 5.5 mA, 1.5 ms IS pulse, chopped down to 50 ms, 60 Hz 230 -8 240 -10 240 250 -12 260 -14 1 parameters a few amps adjustment on Solenoid #3 to correct 1.5 2 2.5 3 3.5
4 First measurement 20 40 60 80 Study 100 Linear (Study) 120 140 160 -2 DISol3 = 8 A -3 -4 y = -0.0586x - 1.422 R = 0.9857 -5 a -6 -7 -8 -9 Initial measurement
-10 -11 -12 14 Lionel Prost | 2016 P2MAC 4.5 b at the Allison scanner, m Same focusing y = -0.064x - 1.1915 settings R = 0.9929for all data points b, cm 3/15/2016 180 Beam transmission through 1st solenoid Based on phase space integrals, for nominal IS settings and 5 mA measured by the DCCT, ~30% of the beam is lost at the IS vacuum chamber exit aperture PIC simulations that include the beam line aperture profile show fairly good agreement Modified beam line design to move this uncontrolled loss to EID #1 Allows measuring the J-P. Carneiro amount of beam being scraped off Possibility to change EID #1 aperture Beam current vs. Extraction voltage Installation of the modified beam line at the same time as a dipole magnet 15
Lionel Prost | 2016 P2MAC 3/15/2016 Comparison with PIC simulations Agreement between measurements and simulations depends mostly on the assumption of the neutralization pattern Dedicated measurements indicate 70-80% neutralization upstream of the chopper No good measurement downstream + it will be different with the RFQ (i.e. no potential well due to diagnostics) Solenoid #3 scan, 50 ms chopped beam, 5.5 mA Envelope simulation for 5 mA. Initial conditions obtained from phase space measurements at the exit of the IS. Data points Aperture 3.6 3 3 Outmost particle cm 2.4 2 1.8 1.2 1s envelope 1
J-P. Carneiro 0.6 0 0 100 Neutralized 16 Lionel Prost | 2016 P2MAC 200 z, cm 0 Un-neutralized 3/15/2016 Bending dipole magnet and vacuum chamber Designs completed in Fall 2015 V. Kashikhin Dipole magnet: Air cooled Removable pole tips Vacuum chamber: Water-cooled, electrically- isolated beam absorbers W. Robotham S. Krave T. Hamerla
R. Andrews D. Snee Construction close to completion Magnet built by Technical Division 17 Lionel Prost | 2016 P2MAC 3/15/2016 LEBT performance summary Up to 10 mA, DC and pulsed (up to 60 Hz) Low uncontrolled beam loss (<2%) beyond IS vacuum chamber exit aperture IS vacuum chamber aperture restriction to be corrected Uninterrupted operation for > 48 hours Average filament lifetime > 300 hours (max up to 800 hours) Twiss parameters appropriate for RFQ commissioning Drift of the beam Twiss parameters corrected via adjustments to Solenoid #3 current (automated) Beam lost on the LEBT scraper as a diagnostic of the beam size variations Optics solutions for different transport schemes (see backup slides) at 5 mA Measured emittance within specs 18 Lionel Prost | 2016 P2MAC 3/15/2016 LEBT performance summary (cont) Accurate beam steering at the entrance of the RFQ Position & angle Machine Protection Scheme under development Beam loss on LEBT scraper as the main input for unexpected changes to the beam conditions
Timing and amplitude LEBT kicker for fast response Secondary action: turn off IS HV To be complemented with turning off the IS modulator in the future More diagnostics at the exit of the RFQ will be included Ring pickup Expected to become the primary input 19 Lionel Prost | 2016 P2MAC 3/15/2016 Plan Support RFQ (and MEBT) commissioning Safe start with pencil beam first, 20 ms max. pulse length Ensures that there are always beam losses on the LEBT scraper whatever the focusing solution is Pulse length limit protection using the LEBT scraper signal Switch to normal aperture and beam size regulation MPS primary signal from MEBT diagnostics as soon as ready Tune beam line Complete dipole construction Measure magnetic field Compare with model Possibly modify pole tips/shimming Installation this summer Assumes that the beam coming out of the RFQ is sufficiently characterized 20 Lionel Prost | 2016 P2MAC 3/15/2016 Additional slides
21 Lionel Prost | 2016 P2MAC 3/15/2016 Proton Improvement Plan II Injector Experiment (PXIE) PIP-II is designed as a CW linac, operated initially in pulsed mode PXIE is part of the R&D program, which addresses the risks associated with the front-end of PIP-II Nominal regime is CW Needs to work in pulsed mode for commissioning and for Booster injection scheme 30 keV 2.1 MeV LEBT RFQ MEBT 22 Lionel Prost | 2016 P2MAC 10 MeV 25 MeV HWR SSR1 HEBT 3/15/2016 Maximum vs. partial neutralization transport schemes Beam potential profile along the beam line tailored by means of biasing electrodes (located in solenoids #1 and #2, a.k.a. EID #1 & #2), the kicker plate and/or an additional electrode downstream (EID #3 or LEBT scraper) Maximum neutralization: EID #1 @ +50V, EID #2 and kicker plate grounded, EID #3 or LEBT scraper @ +50V Partial neutralization: EID #1 & #2 @ +50 V, kicker plate at -300 V, EID #3 or LEBT scraper positively biased or grounded Zero current
Full current 3 2.5 2 3 410 3 310 3 210 1 3 0 100 200 z, cm 510 z kickerend 3 410 2 3
310 1.5 3 210 1 3 110 0.5 0 100 200 z, cm 23 0 3 z kickerstart x y Bz 2.5 0 Lionel Prost | 2016 P2MAC For illustration
only 110 0.5 3 2.5 sigma envelopes, cm 510 z kickerend 1.5 0 Complete neutralization transport z kickerstart x y Neutralization Bz Bz, G Partial neutralization scheme 2.5 sigma envelopes, cm 3 3/15/2016 0
Bz, G Space-charge enhanced configuration (i.e. partial neutralization scheme) Positive biasing of electrically isolated diaphragms to contain ions 5 ms Clearing field at the chopper Ion source extractor voltage -300 V Vacuum downstream of 1 ms Chopper voltage solenoid #2: low 10-7 torr 3 ms Chopped beam 0 kV -5 kV Ion clearing +40 V Ions trap Approximate location of RFQ 1st vane +40 V -300 V 24 Lionel Prost | 2016 P2MAC
3/15/2016 Configuration without ion clearing (i.e. maximum neutralization scheme Positive biasing of electrically isolated diaphragms 5 ms No DC offset at the kicker Ion source extractor plate voltage 1 ms Chopper Chopped beam voltage 0 kV -5 kV 3 ms +40 V Ions trap Approximate location of RFQ 1st vane +40 V Grounded 25 Lionel Prost | 2016 P2MAC 3/15/2016 Beam scraping before solenoid #1 When Solenoid #1 was first installed, losses were observed on the bellows
Added a bellows shield Unknown amount (a priori) With emittance scanner relocated in the IS vacuum chamber, one can use the phase space integral as a measurement of the beam current being extracted Phase space integral vs. beam current calibration from measurements downstream 26 Lionel Prost | 2016 P2MAC 3/15/2016
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