PIP-II Injector Test s Low Energy Beam Transport: Commissioning and Selected Measurements

Transcription

1 PIP-II Injector Test s Low Energy Beam Transport: Commissioning and Selected Measurements A. Shemyakin 1, M. Alvarez 1, R. Andrews 1, J.-P. Carneiro 1, A. Chen 1, R. D Arcy 2, B. Hanna 1, L. Prost 1, V. Scarpine 1, C. Wiesner 3 1 Fermilab, Batavia, IL 60510, USA 2 DESY,Hamburg, Germany 3 IAP, Goethe University, Frankfurt am Main, Germany NIBS 16 FriO7 16 September 2016

2 Outline Introduction: PIP-II and PI-Test PI-Test LEBT LEBT commissioning Secondary particles production Summary 2 A.Shemyakin PI-Test LEBT

3 Future of Fermilab accelerator complex: PIP-II Linac: 400 MeV H- 15 Hz, 25 ma, 30 µs 700 GeV to NOvA 30 GeV GeV to muon experiments PIP-II: 800 MeV H- 2 ma CW Proton Improvement Plan second stage = PIP-II, a program of upgrades for the Fermilab accelerator complex to allow >1 GeV for LBNF, 10s 8 GeV for SBN at the same time a path toward >2 GeV + up to 100 MeV for Mu2e + room for future experiments Centered around a new SRF CW 800 MeV linac 3

4 PI-Test PIP-II Injector Test (PI-Test, or PIP2IT, formerly PXIE): accelerator to test the concept of PIP-II front end 30 kev 2.1 MeV 10 MeV 25 MeV LEBT RFQ MEBT HWR SSR1 HEBT Goals (partial list) 40 m, ~25 MeV Reliable operation with 2 ma CW, 25 MeV H- beam to dump Bunch-by-bunch selection in the MEBT Leaves 2 ma from initially 2 5 ma true CW MHz beam 4

5 LEBT parameters and scheme Parameter Value Unit Kinetic energy 30 kev Nominal/Maximum beam current, DC 5/10 ma Output transverse emittance over 2-5 ma < 0.18 µm current range Typical pressure ~10-6 Torr Chopping frequency, max 60 Hz Pulse length µs Ion Source Solenoid #1 Solenoid #2 Solenoid #3 Neutralized section Chopper Potential barrier RFQ Un-neutralized section Goal: good vacuum in RFQ Ion Source #1 Ion Source #2 Solenoid #1-1 3 solenoids + bend Dipole Solenoid #1-2 Solenoid #2 Solenoid #3 Chopper PIP-II LEBT with two ion sources. Only one will be used at PI-Test. The bend will be installed in Fall 16. Full neutralization upstream Sol#2 and zero downstream Chopper between solenoids #2 and #3 5

6 LEBT components in straight configuration Turbo pump Solenoid #1 Solenoid #2 Solenoid #3 Scrapers Toroid Emittance EID #1 EID #2 EID #3 EID #4 scanner EID #5 DCCT Faraday cup Ion Source assembly Turbo pumps (2) Chopper assembly (w/ turbo pump) Vertical scraper assembly (w/ interface flange to RFQ) Non-cesiated, TRIUMF-type (filament) 15-mA DC, 30 kev H - volume-cusp ion source from D-Pace. Added modulator to the extraction electrode Several configurations (mainly diagnostics location) Chopper: upper plate as absorber. 60 Hz, µs Dipole correctors in all solenoids Z, m 6

7 Diagnostics Turbo pump Solenoid #1 Solenoid #2 Solenoid #3 Scrapers Toroid Emittance EID #1 EID #2 EID #3 EID #4 scanner EID #5 DCCT Faraday cup Ion Source assembly Turbo pumps (2) Chopper assembly (w/ turbo pump) Vertical scraper assembly (w/ interface flange to RFQ) Beam current: DCCT, toroid (ACCT), Faraday Cup, EIDs Beam profile: scans with dipole correctors; scrapers LEBT scraper (permanent) Temporary scrapers Allison type emittance scanner In several locations Z, m Horizontal beam size measurements with temporary scraper. (a) - current measured from the scraper plate as a function of the scraper position; (b) density projection on the horizontal axis reconstructed as a derivative of the data in (a) over position. The data are recorded 1 ms from the front of a 1.5 ms modulator pulse.

8 Allison scanner Water-cooled Allison-type scanner Location of proton beam Region for analysis of neutrals modified version from previous LBNL/SNS designs Emittance measurement uncertainty is estimated to be <5% Heavily used in many applications, e.g. Calibration of elements Analysis of fast neutrals and protons created by stripping Phase portrait recorded near the ion source at the beam current (at the LEBT exit) of 10 ma. H- and proton beam profiles. R. D Arcy et. al., NIM-A 815, 7-17 (2016) 8

9 Optics simulations PIC simulations, mainly with TRACK Issues: quality of initial distribution; level of neutralization Reasonable agreement with measurements Symbols- rms beam size measured with different instruments along the beam line. Red line- simulations. The blue contourvacuum chamber aperture. The beam current out of the LEBT is 5 ma. 9

10 Commissioning Goals Stable operation understand the optics optimize parameters for RFQ injection prepare for operation of future sections downstream Several configuration, different mainly by diagnostics location Mainly pulsed mode; DC for dedicated studies only i.e. 5 ma, 60 Hz, 1.5 ms from ion source, 50 µs after chopper To minimize chances for catastrophic failures 10

11 Commissioning results Up to 10 ma (DC and pulsed) is delivered to the end of LEBT At 5 ma, Twiss parameters to match into RFQ, and optimized settings, emittance is 0.13 µm (rms, norm.) the scheme with partial neutralization works Vacuum at the LEBT exit is < Torr in all modes 20% of beam is scraped in the Sol#1 and upstream Transmission between the ion source box and DCCT. Green crosses -beam currents recovered from the Allison scanner s phase space portrait integrals. Blue diamonds -beam currents measured by the DCCT and EID #1. Red curve -TRACK simulations. Ion source settings are optimized for 5 ma in the LEBT. 11

12 RFQ matching Twiss parameters measured at the end of the LEBT when varying the current of solenoid #3. Beam current is 4.5 ma and 0.5 ma. Sampling is at the end of a 1 msec pulse chopped out of a 2 msec pulse from the ion source. The emittance measured at the target beta-function is 0.13 µm for the 4.5 ma and 0.11 µm for the 0.5 ma. Emittance and Twiss parameters were measured with the emittance scanner located at the end of the LEBT ~20 cm downstream of the virtual location of the RFQ vanes Target (α=1.6 and β=0.07 m) was propagated in TRACK through 20 cm At target β, α mismatch ~20% 12

13 Stability and stabilization loops Day-to-day and in-shift drifts Current: ~10%; Origin is unclear Current stabilization loop Adjust extractor electrode voltage to keep the beam current within 1% Beam size stabilization loop Insert the LEBT scraper to scrape part of the beam Adjust Sol #3 to keep the scraper current constant Tested successfully but not with the RFQ Drift of the beam parameters during a continuous run of a DC beam. Top: beam current and emittance. Bottom: Twiss parameters at the end of the LEBT. The discontinuity on the beam current trace is the result from a trip. 13

14 Correctors calibration Dipole correctors are inside the solenoids Change of a corrector current kicks the beam in both planes 3D model of solenoid + correctors was simulated; 3D fields transferred to TRACK for typical solenoid fields, the beam shift along corrector s direction is 10-30% lower than with the solenoid off Procedures were developed for independent shift and angle adjustments Testing of procedures for a horizontal shift (left) and an angle variation (right). 14

15 Secondary ions IS ground electrode EID#1 (40V) EID#2 (40V) e current absorber plate (0V) LEBT Scraper (50V) H 2+ ions H beam, 5 ma kicker plate (-300V) sum of H 2+ and e current EID= Electrically Isolated Diaphragm Secondary ions flux from upstream of EID#2 is suppressed when calculated voltage on axis is zero =>neutralization upstream is close to full. Red EID#2 at +100V, blue- at ground. 15

16 Fast neutrals and protons Electron stripping in H- collisions with gas Double: protons. Follow the same envelope as H-. Can be accelerated through RFQ and downstream. ~0.5% Measured with Allison scanner at the end of LEBT Single: fast neutrals. Fly ballistically, following H- trajectories upstream of Sol #1. ~10% near ion source, <0.1% at RFQ Estimated with Allison scanner (near ion source) by comparing signals with suppressor electrode voltage at -100V and at ground Measured calorimetrically in a short configuration H- beam passed through an EID EID temperature growth rate is proportional to current * pressure Ground electrode 31.9 cm 34 cm Bergoz MPCT-S-175 ( cm 48 cm EID cm Faraday Cup 16

17 RFQ commissioning and plans Present configuration of PI-Test: LEBT + RFQ + short MEBT MHz CW RFQ designed and manufactured by LBNL Reliable in pulse mode; partially commissioned in CW MEBT: 2 quad doublets, bunching cavity, diagnostics Magnets are made by BARC, India Beam to the dump on the first try RFQ transmission is 98% ±3% at 5 ma; 10 ma to the dump Max average current 0.2 ma 10 Hz, 4 ms, 5 ma Limitations: radiation, RFQ Hope to see CW beam in Fall 16 Plans: Full-length MEBT in 2017 SRF in

18 Summary The PI-Test LEBT is successfully commissioned to its nominal parameters in its initial, straight configuration in both pulsed and DC modes For optimum tuning, the emittance measured is 0.13 µm Pressure at the LEBT exit is Torr in all modes Beam scraping ~20% for 5 ma beam current Scheme with partial neutralization works Flow of neutralizing ions is controlled by EID#2 voltage Production of fast neutrals and protons was due to electron detachment on the residual gas agrees with estimations ~0.5% of the beam is converted into the fast protons flux of neutrals at the end of LEBT is < 0.1% 18