Laser Based Diagnostics for Measuring H - Beam Parameters

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

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

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

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 4 2.5 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 1 2 3 Mode-lock Laser Q-Switch Laser 4 Managed by UT-Battelle

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 4 2.5 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 1 2 3 Mode-lock Laser Q-Switch Laser 5 Managed by UT-Battelle

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

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

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 1 2 3 4 5 12 13 14 15 17 32 ~250 m 225 m 140 m 20 m Ring Nd:YAG Laser 1064 nm 10 ns @ 30 Hz 1 J MEBT DTL CCL SCL 8 Managed by UT-Battelle Target Liu et al, NIMA 612 (2010) 241 253

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

Laser Wire Station (implementation) Optics H-scan V- scan Ion Beam 10 Managed by UT-Battelle Liu et al, NIMA 612 (2010) 241 253

Laser Wire Station (implementation) Correction magnet Collection magnet 11 Managed by UT-Battelle Liu et al, NIMA 612 (2010) 241 253

1-MW H - Profiles Measured by Laser Wire at SCL Amplitude (arb. unit) Liu et al, Appl. Opt. 49 (2011) 6816-6823 Horizontal Vertical X(Y) (20mm/div) 12 Managed by UT-Battelle

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

Sigma_X Sigma_Y Magnet Setting Sigma_ X Sigma_ Y Distance SCL Mag QH32 0.1 SCL LW 32 2.64 2.49 326.841 SCL Mag QV32 0.1 HEBT WS1 5.94 2.67 336.2245 SCL Mag QH33 0.1 HEBT WS2 7.13 2.88 340.1351 HEBT_Mag QV01 0.2 HEBT_Mag QH02 0.1 Beam Size (mm) 8 7 6 5 4 3 2 1 0 325 330 335 340 345 Distance (m) Signal Horizontal Profile 2 1.8 1.6 HEBT 1.4 1.2 1 HEBT 0.8 0.6 0.4 SCL 0.2 0-30 -20-10 0 10 20 30 Position (mm) Signal HEBT WS2 HEBT WS1 SCL LW32 Vertical Profile 2 1.8 1.6 1.4 1.2 1 HEBT WS2 0.8 0.6 HEBT WS1 0.4 SCL LW32 0.2 0-20 -10 0 10 20 Position (mm) 14 Managed by UT-Battelle Work performed by Y. Zhang and Y. Liu

Effects of Laser Pulse Energy 1.2 1.2 1 300 mj 1 Amplitude (V) 0.8 0.6 (a) 225 mj 150 mj Amplitude (V) 0.8 0.6 (b) 0.4 75 mj 0.4 0.2 0.2 0 0 5 10 15 20 25 30 35 40 0 0 5 10 15 20 25 30 35 40 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) 75 2.4 3.2 19.8 23.0 0.38 0.36 150 2.4 3.2 19.8 23.1 0.71 0.62 225 2.4 3.3 19.8 23.1 0.95 0.92 300 2.4 3.2 19.8 23.0 1.14 1.18 15 Managed by UT-Battelle

Effects of Ion Beam Position 3 3 Measured Beam Size (mm) 2.5 2 1.5 1 σ V σ H Measured Beam Size (mm) 2.5 2 1.5 1 σ V σ H 0.5 0.5 0-6 -4-2 0 2 4 6 Horizontal Beam Shift (mm) 32 0-6 -4-2 0 2 4 6 Vertical Beam Shift (mm) 32 Measured Beam Center (mm) 30 28 26 24 22 C H C V Measured Beam Center (mm) 30 28 26 24 22 C H C V 20 20 18-6 -4-2 0 2 4 6 16 Managed by UT-Battelle Horizontal Beam Shift (mm) 18-6 -4-2 0 2 4 6 Vertical Beam Shift (mm) Liu et al, Appl. Opt. 49 (2011) 6816-6823

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

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

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

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) 0 1 2 3 4 5 6 7 8 9 10 Detector Output (arb. unit) 0 1 2 3 4 5 6 7 8 9 10 20 22 24 26 28 30 32 34 Slit Position (mm) 20 22 24 26 28 30 32 34 36 38 40 Slit Position (mm) 20 Managed by UT-Battelle

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

Laser Bunch Shape Monitor: a laser probed sampling oscilloscope Laser pulses 1 2 3 11 ~100 ps H - pulses time 22 Managed by UT-Battelle

Mode-Locked Ti:Sapphire Laser 300 Pulse Width Autocorrelation 250 200 150 100 2.5 ps 50 0-6 -4-2 0 2 4 6 Delay (ps) Timing jitter ~1 ps Repetition rate: 80.5 MHz (5 th subharmonic of the accelerator clock) 23 Managed by UT-Battelle

Laser Interception Site 24 Managed by UT-Battelle

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. 3161-3163. 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

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) 6816-6823

Laser Beam Pointing Instabilities CAM05_PosY Power Meter 01 80 10 60 Position (200 m from laser) 8 Position (mm) 40 20 6 4 Power (W) Laser Power 0 2-20 0 0 100 200 300 400 500 600 Time (sec) 27 Managed by UT-Battelle

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 ±1.25 mm @ 250 m 28 Managed by UT-Battelle Hardin et al, Opt. Express 19 (2011) 2874-2885.

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

Profiles at Different Mini-Pulses Mini-pulse # 30 Managed by UT-Battelle 500 300 100 30 20 10 2 1 Horizontal Vertical X(Y) (10mm/div)

Profiles within a Single Mini-Pulse Liu et al, Proc. IPAC 2010, p. 1221-1223. 31 Managed by UT-Battelle 10 20 40 30 50 60 70 300 100 80 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)

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