Front end, linac upgrade, and commissioning of J-PARC. Y. Liu KEK/J-PARC, Japan

KEK Front end, linac upgrade, and commissioning of J-PARC j-parc Y. Liu KEK/J-PARC, Japan ICFA mini-workshop on Beam Commissioning for High Intensity Accelerators Dongguan, China, June 8-10, 2015

Outlines J-PARC Overview J-PARC linac upgrade scheme 181 400MeV, Jan. 2014 15/25mA 30/50mA, Oct. 2014 } for RCS output 1MW J-PARC frontend Typical Procedures for J-PARC linac commissioning J-PARC commissioning for energy upgrade J-PARC commissioning for intensity upgrade Conclusion and Discussions

J-PARC Facility Layout at Tokai, JAEA Site Materials and Life Science Experimental Facility (MLF) 3-GeV Rapid-Cycling Synchrotron, RCS (Circumference 350m) Hadron Experimental Facility ADS: Accelerator Driven Nuclear Waste Transmutation System (in the 2 nd phase) Linac (181 -> 400MeV) (330m) Neutrino Experimental Facility Main Ring Synchrotron, MR (30-50 GeV) (Circumference 1600m) Multi-Purpose Facility Joint Project between KEK and JAEA

J-PARC Linac Layout and Upgrade Scheme 181/190MeV 400MeV: installation in 2013 Summer, accomplished in Jan., 2014 15/30mA 30/50mA: on-line in 2014 Summer, accomplished in Oct. 2014 J-PARC linac consists of 50-keV negative hydrogen ion source New ion source 3-MeV RFQ RFQ3 50-MeV DTL (Drift Tube Linac) SDTL (Separate-type DTL) 181-MeV 190MeV 400 MeV ACS (Annular Coupled Structure Linac) 90-deg dump 100-deg dump RCS injection Injection section 2 nd Arc Front-end (7 m) DTL (27 m) SDTL(+SDTL16) (84 m) MEBT2 (+ 2 new bunchers) Newly installed ACS section Collimator section 1 st Arc 30-deg dump 3 MeV 50 MeV 181 MeV 50mA 190MeV Front-end = IS + LEBT+ RFQ + MEBT (109 m) 400MeV 0-deg dump 50m

Overview of J-PARC linac and Upgrade Brief scaling-laws Linac 15mA RCS 0.3MW output Linac 50mA RCS 1MW output (50mA, 400MeV) same Laslett tune shift at RCS as (15mA, 181MeV) J-PARC linac apply equi-partitioning (EP) condition for baseline lattice

J-PARC Linac Energy Upgrade: Hardware 190 400MeV with ACS (Annular-ring Coupled Structure), a kind of of coupled cavity linac (CCL) proposed by Kageyama, Yamazaki, KEK 21 + 2 bunchers + 2 debunchers Axial symmetry with: Negligibly small transverse kick Smooth surface Mechanical stability The shunt impedance~ 40MΩ/m*L Satisfies the J-PARC operation with a duty factor of 3%, potential of 15%

Frontend Upgrade IS Sol1 Sol2 RFQ 33 >60mA Filament RF Cs free Cs needed RFQ1 RFQ3 New chopper w/ Larger aperture Larger kick angle New scrapers Tandem scraping

J-PARC Linac Current Upgrade: Hardware 30mA 50mA with new front-end (IS+RFQ3) Filament (LaB 6 ) RF-driven Cs free Cs needed

J-PARC RF IS and Its Test-bench

RFIS_#2 Beam Emittance @50keV 33mA ε norm.rms 60mA ε norm.rms

J-PARC RFQs

RFQ3 Fabrication Tuner Assembling Dimension accuracy +/- 0.03 mm after brazing.

At test-stand Apr. 2013 High power test started May 2013 Beam test started Feb. 2014 50mA test Jun. 2014 Long run test done RFQ3 Milestones Cryopumpx3 Ion pump x4 Fixed tuner Jul. 2014 RFQIII transported to the tunnel Alignment of the new front end Longitudinal alignment RFQ3 is longer, LEBT moved to upstream Vertical alignment Due to the earthquake, 0.2 mrad vertical bend between the RFQ1 and the MEBT1. The new RFQ and the LEBT were aligned parallel to the MEBT1 beam axis. Horizontal alignment For the proton removal at the MEBT1, the LEBT/RFQ and the first two QMs in MEBT1 are aligned off-center position horizontally. NEG pump NEG pump Input coupler Verification of tank level with transmission scan

RFQ3 Measurement at Test-stand Measurement Simulation

Typical Procedures for J-PARC linac commissioning LEBT tuning 2d scan for (2) solenoids 2d scan for steering magnets (h. and v. ) 1d scan for IS HV RFQ transmission scan (for verification of tank level) } maximize RFQ transmission MEBT1 tuning Bunchers phase scan; based on simulation WSM measurement Chopper tuning, scraper conditioning Orbit correction } trial and error for DTL output ε Phase scan For setting of DTL, SDTL, ACS, bunchers and debunchers amplitude and phase Need phase scan data and application, lattice settings and timing for phase scan Use low current to avoid wake field of pass-by idle cavities between ToF monitors 5~10mA Transverse matching Injection tuning Inj. orbit, energy, momentum spread, Twiss

Monitors used in J-PARC linac FCT: fast current transformer, for energy measurement BLM: beam loss monitor SCT: slow current transformer, for current BPM: beam position monitor WSM: wire scanner for beam profile BSM (bunch shape monitor): Necessary for 3D matching SDTL-ACS (324 972MHz) But absent during energy upgrade (Dec. 2013~Jan. 2014) Vacuum problem since online test at MEBT2/ACS since 2012 Worries for affecting newly installed ACS Try solving with offline baking One of three installed in MEBT2 for intensity upgrade (Sep. ~Oct. 2014)

J-PARC linac Matching Scheme 7 sections with transverse measurement in J-PARC linac -- 5 with transverse matching --1 with 3D matching (now 2D) BSM: still not fully ready Match with MEBT2-B1, B2 + Q07~10 (or Q09~12) BSM#1 WSM#1 BSM#2 MEBT2-ACS matching section WSM#2 BSM#3 WSM#3 WSM#4 100-deg dump INJ WSM No Matching L3BT-SCRY WSM+ Matching 90-deg dump To RCS DB2 ACS01 ACS02 ACS03 ACS04 MEBT2 ACS IS WSM Matching Not available WSM+ Matching WSM+ BSM+ 3D Matching L3BD0 WSM+ Matching L3BT-ARC WSM+ Matching 30-deg dump RFQ DTL SDTL ACS LEBT MEBT1 MEBT2 DB1 0-deg dump

ACS phase scan and wake Short ToF pair ACS#i phase scan Long ToF pair wake wake wake wake ACS#i ACS#i+1 ACS#i+2 Powered Idle Idle FCT: Fast Current Transformer for ToF measurement for phase scan ~12kW wake or 0.5MeV beam energy loss at 25mA per tank 5mA for ACS phase scan 5~10mA for DTL and SDTL

Beam Loss Study: Residual Radiation Doses at MEBT2 and ACS Trend along ACS ACS Residual Radiation after one week 15mA*400MeV 1 BLM data 2 3 4 Beam ACS tank A Q1 Q2 3 4 ACS tank B Q1 Q2 1 2 Slope with increasing z / energy Same tendency for BLM data High at section between tank B-A, lower at A-B 3 4 is below 50μSv/h, significant difference, why?

Scheme and main progresses of energy upgrade: Major Tasks/Steps Establishment of 181MeV And monitor check Establishment of 400MeV Phase scan of S16, ACS accel. cavities, bunchers and debunchers at 5mA Fine tunings, matching Preparation for user operation at 15mA High power study at 25mA To achieve Acceptable beam loss along linac and beam line Acceptable orbit, center energy, energy jitter and emittance for RCS injection

Scheme and main progresses of 400MeV upgrade: Milestones (1/3)

Scheme and main progresses of 400MeV upgrade: Milestones (2/3)

Scheme and main progresses of 400MeV upgrade: Milestones (3/3) Linac Part of Energy Upgrade & Study accomplished in 27 days During Run 50/51

DB2 W(MeV) 400MeV Upgrade Accomplished: Jan. 2014 Energy measurement with ToF 405 400 395 385 3750 120 240 360 ACS21 phase (deg) y 1) TOF (time of flight) Resolution of phase detector is 1 degree/20-period 2) Orbit at dispersion section Resolution of BPM is 0.1 mm/2.5mm x ΔW/W < 0.8% 30-deg dump ACS Arc section Energy verification with dispersion measurement ACS20 ACS21 FCT1 FCT2 DB1 BPM1 BPM2 0-deg dump

Emittance Growth and Halo: Lesson learnt 400MeV/15mA user operation and 400MeV/25mA beam test were established with acceptable beam loss/ residue radiation doses But, emittance growth and beam halo were observed after ACS Halo recognition From measured profiles we get rms as well as sigma from fit with Gaussian; Sigma beam core; rms includes halo Reason for halo after ACS Imperfect matching at MEBT2-ACS due to absence of BSM Other reasons? Inconsistencies between modeling and reality, No longitudinal measurement Emittance growth at MEBT1 Imperfect matching at MEBT1 Unknown longitudinal mismatch in DTL-SDTL After the readiness of linac setting for 25mA on Jan.24, an improved second lattice accomplished on Jan. 26, and studied until Jan. 29. The setting is based on applying Results from transverse measurement and matching at SDTL Ideal longitudinal match between DTL and SDTL

Emittance Growth and Halo Studies: Halo found at downstream of ACS r rms r sig. SDTL,50MeV,25mA 2014.1.23 ACS;191MeV 25mA 2014.1.23 r rms > r sig. 400MeV,25mA 2014.1.23 Comparison 181MeV,25mA 2013.4.14 Similar phenomena also found in previous high power test at 181MeV, now stronger Note the changing of correlation of profiles in rms and sigma! Significant increase of halo after ACS

Emittance Growth and Halo Studies: the Worst Case Profile in y direction at L3BT-ARC section: 5σ~1.2mm; 5rms~1.7mm, parameter 1, Jan.24

Emittance Growth and Halo Studies: Improvement Profile in y direction at L3BT-ARC section: 5σ~1.2mm; 5rms~1.5mm, parameter 2, Jan.26

Emittance Growth and Halo Studies: An Improved Setting for 25mA x-plane Increase from design Improvement 10~20% collimation y-plane Emittance is reduced by 10~20% in y direction at L3BT No improvement in x direction; Halo significantly mitigated but still exist Significant change of the correlation between rms and sigma rms emittance increases in consistency with beam halo formation Beam core (sigma emittance) becomes slim

Emittance Growth and Halo Studies: lessons learnt Halo found in downstream of ACS Imperfect matching at MEBT2-ACS due to absent of BSM, improvement expected after re-installation in coming summer shutdown Other reasons? Inconsistencies between modeling and reality, No longitudinal measurement in upstream (too) Emittance growth at MEBT1 Longitudinal mismatch in DTL-SDTL Imperfect matching at MEBT1 After the readiness of linac setting for 25mA on Jan.24, an improved second lattice accomplished on Jan. 26, and studied until Jan. 29. The setting is based on applying Results from transverse measurement and matching at SDTL And with assumption of small longitudinal mismatch between DTL and SDTL Further improvement requires more efforts for consistency between theoretical model and reality

Outlines J-PARC Overview J-PARC linac upgrade scheme 181 400MeV, Jan. 2014 15/25mA 30/50mA, Oct. 2014 J-PARC frontend J-PARC commissioning for energy upgrade J-PARC commissioning for intensity upgrade Conclusion and Discussions } for RCS output 1MW

Scheme and main progresses of intensity upgrade: Major Tasks/Steps Preparation in the summer shutdown (commissioning related) Replacement of front-end: IS + RFQ Upgrade of MEBT1 New chopper cavities Tandem scraper Installation of one bunch shaper monitor. Replacement of signal wires of WSMs to thin one to sustain 50 ma beam. Commissioning tasks/steps Achievement of 400 MeV acceleration Tuning of 30 ma beam for user operation Tuning of 50 ma beam for a high power test To achieve for 30mA operation and 50mA beam study Acceptable beam loss along linac and beam line Acceptable orbit, center energy, energy jitter and emittance for RCS injection

Scheme and main progresses of 50mA upgrade: Milestones (1/2)

Scheme and main progresses of 50mA upgrade: Milestones (2/2) Intensity upgrade successfully accomplished with 5 ma (7 days) tuning for 400 MeV establishment and monitor check, 30 ma (5.5 days) and 50 ma (3.5 days) preparations

First Lesson in Intensity Upgrade: Init. Twiss The linac lattice was prepared based on RFQ3 simulation verified by offline measurements But the transmission of first beam in the commissioning is poor Online Q3-WSM#2 scan helped to find the right MEBT1 starting beam parameters MEBT1 start match to DTL MEBT1 WSM#2 - - - - w/ simu 30mA - - - - w/ simu 50mA w/ fit 30mA w/ fit 50mA

First Lesson in Intensity Upgrade: BEAMI (cont.)

Beam phase shaking observed by BSM DATA: BSM1_2014-11-28_05-02-25 Caused by RF; other effects

J-PARC linac output emittance improvements after intensity upgrade

Conclusions and Overlook Accomplishments of energy and intensity upgrades A recent example of commissioning; Ready for RCS 1MW output and demonstrated User operation at 300, 400, 500kW,, 1MW (2016) Encouraging Improvements Beam loss mitigation, emittance

Lessons and further Discussions Monitors/applications/procedures: basic and optional Basic? Transmission measurement, phase scan, (transverse) matching, orbit, Optional? BSM at MEBT1 (RFQ-DTL) could be helpful Offline vs. online measurements Besides well-planned offline measurements, online systematic measurements might still be needed Beam loss esp. for H- linac Dark current (RF IS) IBSt, intra-beam stripping Dr. Maruta Beam loss localization Identification of halo Keys for improvements: fight against ambiguities and mistakes More beam study time, accumulations of measurements

Thank you