Beam Profile Monitor for Spot-Scanning System Yoshimasa YUASA

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 2 Beam Energy – MeV Current –3nA (PMRC, Tsukuba) Repetition –250Hz (up to 1kHz) Scanning speed –4msec (up to 1msec) Beam spot size –1cm*1cm at isocenter Irradiation area –20cm*20cm at isocenter 200mm 10mm

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 3 Requirements Inexpensive Sensitive area –20cm*20cm Spatial resolution –1mm = 10 divisions of beam size Fast DAQ speed –Every bunch measurement –below 4msec/spot Charge resolution –1% 200mm 10mm 1mm

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 4 Idea for our Monitor Wire… –Resolution is good for spatial and charge. –Speed is limited by a decay time It is not so fast as a few msec. –Electronics is complicated. Very expensive; a few ten million yen Scintillation… my favorite one –Wire to Fiber Fiber size is mm square and circle. Decay time is so fast as a few nsec. –Photomultiplire tube to Image sensor Electronics is simple. It become inexpensive. A scanning speed of the sensor is a order of MHz. Fast DAQ taking is possible.

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 5 Monitor Driver Circuit Image Sensor Data Processing Unit DAQ-PC Plastic Scintillation Fiber

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 6 Scintillating Fiber Enough spatial resolution !!! Suitable fiber : 3HF 1mm(square) Kuraray –Specification –Shape and Size Square and Round –Size 0.2 mm (min.) - 2 mm (max.) L=10cm, 30cm, 100cm, 300cm

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 7 Image Sensor and Utilities HAMAMATSU –NMOS linear image sensor : S Large Sensitive Area !!! 20 pixels for 1mm Fiber Tolerance of height : 1.5mm

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 8 Image Sensor and Utilities HAMAMATSU –Driver circuit : C7884 Fast sequence speed !!! Alternate measurement of background and correct event

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 9 Image Sensor and Utilities HAMAMATSU –Data processing unit to convert video signals from the driver circuit into digital signal and transfer them to a PC Parallel drive and Large memory !!! Store the information in beam on-time and flush it in beam off-time

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 10 Feasibility Study Spread by multiple scattering Radiation durability Resolution of charge Signal to Noise

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 11 Spread by Fiber Multiple Scattering Distance to the isocenter < 300mm = Spread size < 1mm

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 12 Energy Loss in Fiber Bethe-Bloch For an estimation of radiation durability For an estimation of light yield

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 13 Radiation Durability of Fiber Irradiating dose –Proton beam : 80MeV, 3nA –Plastic density : 1g/cm 3 –Scanning repetition : 10*10 pixels / 1scan 10 pixels

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 14 Radiation Durability of Fiber Experiment: 60 Co gamma-ray to Kuraray-3HF fiber –K.Hara., et.al., NIMA411(1998)31 “Radiation hardness and mechanical durability of Kuraray optical fibers” –Irradiating time 68 hours = 5% loss of light yield Not serious!!!

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 15 Light Yield from Fiber A number of generated photon for a fiber A number of photon at the end of fiber –Solid Angle : 20deg –Attenuation : 4m A power of emitted light at the end of fiber Beam size Fiber width 1mm (fiber) 1mm t (fiber) 10mm (beam) 150MeV protonFiber thickness Scintillating photon 3nA, 1kHz (a small bunch)

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 16 I/O in Image Sensor and Utilities Sensor Driver Circuit DAQ-unit Sensitivity Irradiated area Gain ADC Resolution Saturation Voltage Charge Voltage Digital Driver circuit DAQ-unit Sensor 1% charge resolution = 1Digit

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 17 Signal/Noise Signal –150MeV * 3nA(1kHz) Noise –Dark current –Switching noise Signal/Noise per bunch Good S/N !!!

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 18 Simulation Event generation Beam energy : 150MeV Beam intensity : 2*10 7 (particle/bunch) Beam size : 10mm(sigma) Fiber : 1mm(sqr.) Fixed dE : keV/mm Fixed Acceptance : 5% Scintillation light : 530nm Sensor sensitivity : 0.2 (C/J)

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 19 Simulation I/O in sensor and utilities ADC :2 12 /10 (Digit/V) Gain : 0.3 (V/pC)

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 20 Simulation Reconstruction Sensor pitch : 50 (micro-m) Fiber pitch : 1 (mm) Good reconstruction !!!

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 21 Cost Estimation $ 3 million !?

2004/02/16BPM for Spot Scanning System, Yoshimasa YUASA 22 Conclusion Beam profile and intensity monitor is designed. –Scintillating fiber and image sensor Specifications of this monitor are described as followings; –Inexpensive : $ 3 million –Fast speed : 500Hz It is faster than the beam repetition, 250Hz A background and correct event can be measured alternately. –Enough spatial resolution : 1mm = 10 divisions of beam size It is determined by a scintillating fiber size –Enough charge resolution : 1% –Everywhere installation The beam detection is not affected by magnetic and electric field.