Laser Based Diagnostics for Measuring H - Beam Parameters

Transcription

1 Laser Based Diagnostics for Measuring H - Beam Parameters Yun Liu on behalf of Beam Instrumentation Group Research Accelerator Division Spallation Neutron Source Oak Ridge National Laboratory

2 OUTLINE Overview of laser based H - beam diagnostics SCL laser wire profile monitor HEBT laser emittance scanner MEBT laser bunch shape monitor Commissioning experience Conclusion 2 Managed by UT-Battelle

3 Non-invasive Beam Profile Diagnostics at SNS Injection Ring Extraction Ion Source 2.5 MeV 87 MeV 186 MeV 387 MeV 1 GeV MEBT DTL CCL SRF, β=0.61 SRF, β=0.81 HEBT RTBT Liquid Hg Target 3 Managed by UT-Battelle

4 Non-invasive Beam Profile Diagnostics at SNS 1 MEBT Laser Bunch Shape Monitor 2 SCL Laser Wire Profile Monitor 3 HEBT Laser Emittance Scanner Injection Ring Extraction Ion Source MeV 87 MeV 186 MeV 387 MeV 1 GeV 4 HEBT MEBT Electron Scanners (WEOCN2) DTL CCL SRF, β=0.61 SRF, β=0.81 RTBT Liquid Hg Target Mode-lock Laser Q-Switch Laser 4 Managed by UT-Battelle

5 Non-invasive Beam Profile Diagnostics at SNS 1 MEBT Laser Bunch Shape Monitor 2 SCL Laser Wire Profile Monitor 3 HEBT Laser Emittance Scanner Injection Ring Extraction Ion Source MeV 87 MeV 186 MeV 387 MeV 1 GeV 4 HEBT MEBT Electron Scanners (WEOCN2) DTL CCL SRF, β=0.61 SRF, β=0.81 RTBT Liquid Hg Target Mode-lock Laser Q-Switch Laser 5 Managed by UT-Battelle

6 Photo-ionization Physics behind Laser Based Ion Beam Diagnostics H - Photo-ionization hν H 0 S H 0 N e Electron Collector 6 Managed by UT-Battelle

7 Laser Wire Profile Monitor Laser Y-scan Deflector H 0 electron H - y z Faraday Cup 7 Managed by UT-Battelle

8 Layout of the SNS Laser Wire Profile Monitors LR Laser room Camera 4 LW from 200 MeV Laser wire station Mirror 4 LW from 450 MeV 32 Cryomodule number Power meter 1 LW at 1 GeV ~250 m 225 m 140 m 20 m Ring Nd:YAG Laser 1064 nm Hz 1 J MEBT DTL CCL SCL 8 Managed by UT-Battelle Target Liu et al, NIMA 612 (2010)

9 Laser Wire Station (design) 9 Managed by UT-Battelle

10 Laser Wire Station (implementation) Optics H-scan V- scan Ion Beam 10 Managed by UT-Battelle Liu et al, NIMA 612 (2010)

11 Laser Wire Station (implementation) Correction magnet Collection magnet 11 Managed by UT-Battelle Liu et al, NIMA 612 (2010)

12 1-MW H - Profiles Measured by Laser Wire at SCL Amplitude (arb. unit) Liu et al, Appl. Opt. 49 (2011) Horizontal Vertical X(Y) (20mm/div) 12 Managed by UT-Battelle

13 1-MW H - Profiles Measured by Laser Wire at SCL Measurement time window 13 Managed by UT-Battelle

14 Sigma_X Sigma_Y Magnet Setting Sigma_ X Sigma_ Y Distance SCL Mag QH SCL LW SCL Mag QV HEBT WS SCL Mag QH HEBT WS HEBT_Mag QV HEBT_Mag QH Beam Size (mm) Distance (m) Signal Horizontal Profile HEBT HEBT SCL Position (mm) Signal HEBT WS2 HEBT WS1 SCL LW32 Vertical Profile HEBT WS HEBT WS1 0.4 SCL LW Position (mm) 14 Managed by UT-Battelle Work performed by Y. Zhang and Y. Liu

15 Effects of Laser Pulse Energy mj 1 Amplitude (V) (a) 225 mj 150 mj Amplitude (V) (b) mj X (mm) Y (mm) Laser pulse energy (mj) σ H (mm) σ V (mm) C H (mm) C V (mm) A H (V) A V (V) Managed by UT-Battelle

16 Effects of Ion Beam Position 3 3 Measured Beam Size (mm) σ V σ H Measured Beam Size (mm) σ V σ H Horizontal Beam Shift (mm) Vertical Beam Shift (mm) 32 Measured Beam Center (mm) C H C V Measured Beam Center (mm) C H C V Managed by UT-Battelle Horizontal Beam Shift (mm) Vertical Beam Shift (mm) Liu et al, Appl. Opt. 49 (2011)

17 HEBT Laser Emittance Scanner (design) 17 Managed by UT-Battelle

18 HEBT Laser Emittance Scanner (design) φ50 um Ti wire 18 Managed by UT-Battelle 1064nm/200mJ laser pulse

19 HEBT Laser Emittance Scanner (implementation) Laser Slit Wire Scanner 19 Managed by UT-Battelle

20 Laser Emittance Measurement Step 1: H - H 0 + e - with Laser Wire Step 2: H 0 p + + e - with Wire Scanner Wire Position (mm) Wire Position (mm) Detector Output (arb. unit) Detector Output (arb. unit) Slit Position (mm) Slit Position (mm) 20 Managed by UT-Battelle

21 Emittance Measurement Measured emittance: ~ 0.2 mm mrad Signal-to-noise ratio will be improved through optimization of signal amplification and wire scanner scheme. 21 Managed by UT-Battelle

22 Laser Bunch Shape Monitor: a laser probed sampling oscilloscope Laser pulses ~100 ps H - pulses time 22 Managed by UT-Battelle

23 Mode-Locked Ti:Sapphire Laser 300 Pulse Width Autocorrelation ps Delay (ps) Timing jitter ~1 ps Repetition rate: 80.5 MHz (5 th subharmonic of the accelerator clock) 23 Managed by UT-Battelle

24 Laser Interception Site 24 Managed by UT-Battelle

25 Preliminary Measurement using Mode-Locked Laser and MCP at 2.5MeV Electron detector signal [a.u.] RMS size: ~ 110 ps Saeed, Proc. EPAC 2006, p Laser phase offset Experiments are ongoing to investigate fiber transmission Damage threshold Launch efficiency Output beam quality Pulse jitter Pulse width broadening 25 Managed by UT-Battelle

26 Effects of Radiation All optics related components are enclosed within ¼ thick stainless steel boxes Hardware Radiation Hardened Laser (Big Sky U1064-HN) Distance from beam line Laser head (~ 1 ) Driver (>20 ) Findings Laser driver was damaged within 1-2 days. Not clear about head. Optics stepper motors motorized flippers ~ 1 No damage found Picomotor actuators > 5 Open-loop (ν8301) is OK. Close-loop (ν8310) encoder was damaged Optical power meter heads (Ophir L50(150A)) Gigabit Ethernet cameras (Prosilica GE640) 26 Managed by UT-Battelle > 5 No damage found > 5 1 of 4 was damaged Liu et al, Appl. Opt. 49 (2011)

27 Laser Beam Pointing Instabilities CAM05_PosY Power Meter Position (200 m from laser) 8 Position (mm) Power (W) Laser Power Time (sec) 27 Managed by UT-Battelle

28 Laser Beam Position Stabilization with Feedback Control Feedback off piezo-driven mirror beam sampler target driver ε(t) laser delay time t d controller δ(t) error signal generation image sensor y(t) set point Feedback on yt () = xt () + gε ( t t ), ε () t = λε ( t t ) + kδ (), t δ () t = Y yt (). T d d ± m 28 Managed by UT-Battelle Hardin et al, Opt. Express 19 (2011)

29 Longitudinal Scan of Beam Train with Laser Wire 1 st mini-pulse Mini-pulse #1 #750 #26 #16 #38 Laser-beam interaction location (unit: sub-rev turn, ~30 ns) 29 Managed by UT-Battelle

30 Profiles at Different Mini-Pulses Mini-pulse # 30 Managed by UT-Battelle Horizontal Vertical X(Y) (10mm/div)

31 Profiles within a Single Mini-Pulse Liu et al, Proc. IPAC 2010, p Managed by UT-Battelle Delay time 5 ns 10 ns 15 ns 20 ns 25 ns 30 ns 35 ns 40 ns 45 ns 50 ns 55 ns 60 ns 65 ns 70 ns 75 ns 80 ns 100 ns 300 ns Horizontal Vertical X(Y) (10mm/div)

32 Summary Three different types of laser based diagnostics have been developed at SNS for measuring H - beam parameters World-first large scale, operational laser wire system has been implemented at SNS-SCL. Profile measurement has been conducted on 1 MW, neutron production beam. Laser emittance scanner has been commissioned at SNS HEBT. Laser based bunch shape monitor is being developed at SNS MEBT. Laser based ion beam diagnostics at accelerator facilities is reliable and realistic and can provide novel capabilities. More laser based diagnostics are expected as a result of applying fast-growing laser technology. 32 Managed by UT-Battelle