A DIGITAL MICROMIRROR ARRAY BASED BEAM HALO MONITOR
A DIGITAL MICRO-MIRROR ARRAY -BASED BEAM HALO MONITOR Blaine Lomberg University of Liverpool and The Cockcroft Institute 3 rd OPAC Topical Workshop on Beam Diagnostics 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 1
Layout q Aims q Basic principles q. Design and development q. Halo Monitor operation q. Software control q. Masking Algorithm q. Preliminary Results q. Summary 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 2
Aims To demonstrate the operation of an optimized, programmable light filtering device and use it as a adaptable optical mask that employs a digital micro-mirror array to produce an image of the halo of a beam with an enhanced dynamic range. • “Beam Halo” is associated with many negative effects for high Intensity Beams: – Particle losses lead to nuclear activation, • Increase in secondary emission, space-charge. • Damage of the surrounding vacuum chamber. • Using the monitor to observe the number of particles in the tail region of the beam distribution – and minimise particles at large radii (nσ: n=3 -4 ) from beam core. – What makes this monitor so special ? – HDR can be extended easily • Provide knowledge on beam losses which originate in the low-density halo that extend far from the beam core 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 3
Basic Principles Define Beam Halo: Beam Losses associated with a small fraction of particles surrounding a dense beam core. Difference between “tail” and “halo” (Beam losses? ) Knowledge about the structure of halo Depend: beam distribution or halo mechanism Define it either by “geometrical characteristic” or “nature of mechanism”* Formation due to specific halo Mechanisms** Provide understanding and“Halo possible control/prevention *(ICFA Workshop 03”, Long Island 2003) 08/03/2021 **(ICFA Workshop “Halo and Scraping”, Wisconsin 1999) B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 4
Design and Development § 1920 x 1080 array Al micro-mirror [ Discovery 4100] §USB Interface (0. 95” Chipset ) § DMD dimensions 14. 4 x 10. 8 mm § high-speed port 64 -bit @ 400 MHz for data transfer 10. 8 um 08/03/2021 § up to 23. 148 full array mirror patterns / sec (48 GBs) B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 5
HALO MONITOR OPERATION 48 o Rough Halo 4σ Beam Spot 24 o B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 08/03/2021 6
Compensations 1. DMD micro-mirrors have three possible states: - all floating, flat state ( no power) - two independent assignable + or - 12 0 states (power on) 2. Rotation axis along diagonal of each micro-mirror, i. e. at 45 degrees wrt to HD-DMD row or column - rays imaged onto the DMA plane are reflected with different optical path lengths at twice the angle of incidence 3. Diffraction effects: array acts like a 2 D grating producing diffraction patterns 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 7
Scheimpflug Angle Path length difference generated by DMD tilted mirror Reflected Beam Lens 24 o Target 12 o Image on DMD Incident Beam 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria DMD Mirror Pixel 8
Software Control 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 9
Calibration/Correction The selection of 8 reference points 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 10
Masking Algorithm Adaptive light filtering for masking any beam shape 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 11
Coordinate Transformations Information transfer from CCD to DMD Define area Set mask limit or size 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 12
Priliminary results DR with CCD only DR~>10 -2 (i. e. ~400) Extended with HD-DMD 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 13
HD-DMD Filtering Ability Beam on, DMA all off 1 mm Beam on, DMA all on CCD exposure time=15 ms, gain=1 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 14
Comparison of Images DMA all on (with Scheimplug compensation) DMA all floating (no compensation) I = 20 k counts INormal = 5 k counts Texposure=15 ms , Gain=1 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria Texposure=15 ms , Gain=1 15
1. 5 mm Laser spot image (colour corresponds to pixel value) Masked(Smoothed image ) 1 D distributions; Fitted to the equation Full profile Vertical (95% confidence bounds) a = 1. 045 (1. 037, 1. 052) b = 0. 09277 (0. 09229, 0. 09326) c = 0. 07938 (0. 07869, 0. 08007) Horizontal (95% confidence bounds) a = 1. 041 (1. 035, 1. . 047) b = 0. 1314 (0. 1311, 0. 1317) c = 0. 05562 (0. 05524, 0. 056) 08/03/2021 Masked profile Goodness of fit: SSE: 0. 464 R-square: 0. 9867 Adjusted R-square: 0. 9867 RMSE: 0. 01942 Goodness of fit: SSE: 0. 3539 R-square: 0. 9893 Adjusted R-square: 0. 9893 RMSE: 0. 01478 Vertical (95% confidence bounds) a = 0. 2466 (0. 239, 0. 2542) b = 0. 08099 (0. 07766, 0. 08432) c = 0. 1315 (0. 1268, 0. 1362) Horizontal (95% confidence bounds) a = 0. 2366 (0. 2298, 0. 2433) b = 0. 125 (0. 1229, 0. 1272) c = 0. 09309 (0. 09003, 0. 09616) B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria Goodness of fit: SSE: 0. 7308 R-square: 0. 7682 Adjusted R-square: 0. 7678 RMSE: 0. 02436 Goodness of fit: SSE: 0. 7007 R-square: 0. 7675 Adjusted R-square: 0. 7673 RMSE: 0. 02079 16
Top Level masking From a geometrical perspective: Define the halo as the area that contains all particles outside the Gaussian shaped beam core. To increase DR, mask needs to be larger and then exposure time B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam extended. 08/03/2021 Halo Talk- Vienna, Austria 17
Overflow (error) Signs of charge overflow and could allow using the DMD to characterize a whole range of sensors. 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 18
Summary The method is versatile and adaptable to any accelerator High or low intensity, energy or any particle species Preliminary Results Limitations on dynamic range Adaptive mask method developed and use to measure halo of laser High dynamic range measured (~ 10 -4) Good filtering ~10 -4 Beam intensity Screen property: efficiency, saturation, light filters Scattered light Possible solution in accelerator higher intensity beam (LHC) More efficient screen, e. g. YAG, or use of OSR, OUR etc. improve optics (large aperture optics, Lyot stops) 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 19
Future Work Gas-jet monitor measurements at Cockcroft Institute Other prospects Study halo propagation in the BSRT at CERN Experiments at the ALICE facility at Daresbury Labs 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 20
Thank you Acknowledgements: This work is supported by the European Union under contract PITN-GA-2011 -289485 and by STFC under the Cockcroft Institute Core Grant No. ST/G 008248/1. 08/03/2021 B. Lomberg-3 rd OPAC Topical Workshop on Beam Diagnostics: Beam Halo Talk- Vienna, Austria 21
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