Beam Halo Monitoring using Optical Diagnostics Hao Zhang University of Maryland/University of Liverpool/Cockcroft Institute

Outline Introduction Motivation to Study Beam Halo Method Adaptive Method Using Digital Micro-mirror Device Experiment University of Maryland Electron Ring (UMER) JLAB FEL Injection of SPEAR3 storage ring 2

Beam Halo has many negative effects  Nuclear Activation of The Transport Channel  Emittance Growth  Emission of Secondary Electrons  Increasing Noise in The Detectors Halo Picture credit: Kishek, Stratakis Motivation for Beam Halo Studies 3 Halo can be regarded as small fraction of particles out a well defined beam core.

Solutions: 1) Passive spatial filtering, e.g. solar corography applied to beam imaging by T. Mitsuhashi of KEK DR = achieved 2) Spectra-Cam CID, DR ~ 10 6 measured with laser by J. Egberts, C. Welsch, T. Lefevre and E. Bravin 3) Adaptive Mask based on Digital Micromirror Array; DR ~ 10 5 measured with laser and 8 bit CCD camera by Egberts, Welsch Problems: 1) Need High Dynamic Range ( DR > ) 2) Core Saturation with conventional CCD’s: blooming, possible damage 3) Diffraction and scattering associated with high core intensity contaminate halo 4) Adaptability when the beam core shape change. Imaging Halos 4

Digital Micro-mirror arrayDevice * Micro-mirror architecture: 12 0 *DLP TM Texas Instruments Inc Mirror size: um x um Resolution: 1024 X 768 pixels

Computer Mirror Source Halo Light Core Light DMD Camera Sensor L3 L4 L1 L2 Computer Camera Sensor L3 Mirror Source L1 DMD L2 L4 Image 2 Image 1 Mask Adaptive Method for Halo Measurement 6 32mm

Quadrupole Screen Energy (keV)10 Pulse width (ns)100 Repetitive rate (Hz)20-60 Beam current (mA)0.6, 6, 21,80 UMER Experiment 7

Testing filtering ability of DMD 8 Beam on, DMD all onBeam on, DMD all off 32mm Average readout of the core region

Integration Frames: Dynamic Range Test of DMD with intense beam and circular mask* 9 Integration Frames: 32mm

Circular Mask Data line profile mm

x y (a) (b) IQIQ %I Q 66.3%I Q 49.7%I Q Quadrupole Current 32mm Demonstration of Adaptive Masking on UMER 11

Bending Magnet Energy135 MeV Macro pulse width:1 ms Repetitive rate:60 Hz Micro-pulse repetition rate :4.68 MHz Charge:60 pc/micro pulse Halo Experiment with OSR in JLab FEL 12 Beam pipe

1 1.2 s No mask X y 4 mm Integration Time s 1.5 s 4 s 80 s Mask Level Masking OSR Image of JLAB FEL Beam s

Measurement of Dynamic Range for OSR DMD System Normalized Counts pixel

DMA/DMD Configuration M=4 M=1 M=0.14

More Details… Mechanical Shutter (5ms) Diffraction pattern 1000x1000 DMD Filter wheel f=+125mm f=+100mm, 2” dia Scheinflug angle

9.6m M1=0.138 M2=3.55 DMD M3=1 M = M1*M2*M3 = m f=+2m f=+125mm f=+100mm Aperture & Cold finger 24° PiMax Filter wheel OSR Source Injector READOUT GateInjected beam Stored beam SPEAR3 Data acquisition BTS

PSF measurement of the stored beam  2 ms shutter mode  Increase the mask size by changing the intensity threshold level  ND filter from ND =5 to ND = 0 ND 5 ND 4 ND 3 ND 2 ND 1 ND 0 Mask 18 mm No Mask

Injected beam with presence of stored beam with different currents (a)(b) 6.11mA3.05mA1.52mA0.42mA Current /bunch Stored beam Injected beam 18 mm

Three matching condition by altering the quads in the BTS

Evolution of Beam centroid and beam size

Conclusion Applied a adaptive optics to detect small image signals from either beam halo or Injected beam compared with beam core or stored beam. Achieve a high dynamic range with this method.

Discussion How can we apply this method to other existing machines? What is the limitation of dynamic range? For Proton machine, since the beam is destructive, are there any usable screens?