Beam Profile Monitor for Spot-Scanning System

1. Beam Profile Monitorfor Spot-Scanning System Yoshimasa YUASA

2. 10mm 200mm 200mm Beam • Energy • 80 - 150MeV • 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 10mm BPM for Spot Scanning System, Yoshimasa YUASA

3. 10mm 1mm 1 2 3 4 5 6 7 8 9 10 200mm 200mm 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% 10mm BPM 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 0.2 - 2 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. BPM for Spot Scanning System, Yoshimasa YUASA

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

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

7. Image Sensor and Utilities • HAMAMATSU • NMOS linear image sensor : S3901-1024 Large Sensitive Area !!! 20 pixels for 1mm Fiber Tolerance of height : 1.5mm BPM 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 BPM 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 BPM for Spot Scanning System, Yoshimasa YUASA

10. Feasibility Study • Spread by multiple scattering • Radiation durability • Resolution of charge • Signal to Noise BPM for Spot Scanning System, Yoshimasa YUASA

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

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

13. 10 pixels 10 pixels Radiation Durability of Fiber • Irradiating dose • Proton beam : 80MeV, 3nA • Plastic density : 1g/cm3 • Scanning repetition : 10*10 pixels / 1scan BPM for Spot Scanning System, Yoshimasa YUASA

14. Radiation Durability of Fiber • Experiment: 60Co 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!!! BPM for Spot Scanning System, Yoshimasa YUASA

15. 150MeV proton Fiber thickness Scintillating photon Beam size 3nA, 1kHz (a small bunch) 1mmt (fiber) Fiber width 10mm (beam) 1mm (fiber) 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 BPM for Spot Scanning System, Yoshimasa YUASA

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

18. Simulation • Event generation Beam energy : 150MeV Beam intensity : 2*107 (particle/bunch) Beam size : 10mm(sigma) Fiber : 1mm(sqr.) Fixed dE : 572.4 keV/mm Fixed Acceptance : 5% Scintillation light : 530nm Sensor sensitivity : 0.2 (C/J) BPM for Spot Scanning System, Yoshimasa YUASA

19. Simulation • I/O in sensor and utilities ADC :212/10 (Digit/V) Gain : 0.3 (V/pC) BPM for Spot Scanning System, Yoshimasa YUASA

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

21. Cost • Estimation \ 4 million !? BPM 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. BPM for Spot Scanning System, Yoshimasa YUASA