Beam Diagnostics for High Intensity Proton Accelerators

1. Beam Diagnostics for High Intensity Proton Accelerators T. Toyama KEK OverView Current Monitor Beam Position Monitor Beam Loss Monitor Profile Monitor Summary

2. OverView Main patrs of a particle accelerator: Accelerating = RF cavity Steering, Trapping = Magnet Making the environment = Vacuum chamber Observing the beam = Beam diagnostic Controling the beam = Control system

3. Aims Measuring impotant beam paramters: Intensity, energy, emittance, … Proving, keeping and improving machine performance: Beam position, beam loss, beam profile, tune, … Beam is a “very sensitive device”! Principles Electromagnetic ~ nearly nondestructive except wake fields Interaction between a beam and matterials Passive / active

4. Example: J-PARC LINAC transverse size ~ a few mm

5. ℓ~80-20 m ℓ~100-80 m 50GeV MR injection 3GeV RCS injection extraction ~15 mm extraction ~44 mm ~38 mm ~62 mm Example: J-PARC Rings

6. Beam and environment

7. Current Monitor (CT) Example: KEK 12 GeV PS Main Ring Vert. Exciter BPM BPM

8. Profile monitors KEK-PS 20MeV Linac

9. Special requirements for high intensity proton accelerators Protecting diagnostic tools form radiation Selection of proper matterials: metals, ceramics, polyimide, … No, or least amplifiers in the accelerator tunnel semiconductors shoud be avoided to use in the tunnel / in a “sub-tunnel” Beam loss is a big issue ---> observed only by loss monitors ! Machine safety Radiation environment Hands-on maintainance, easy maintainance Coupling impedance Design criteria

10. Current Monitor Current Transformers Purpose: monitoring beam intensity Precision: <1% deteriorated by lower, and higher cut off frequencies magnetic core saturation noise Usually categolized as AC CT AC CT with Hereward Feedback DC CT

11. AC Current Transformer Principle

12. AC Current Transformer Frequency response (calculated) Step response (calculated) Magnetic field in the core: cancelled on the working freq. DC fields remain!

13. AC Current Transformer Example: KEK-PS 500 MeV BT Ceramic gap Shield (electrostatic, magnetostatic, electromagnetic) In-situ calibration winding

14. AC Current Transformer Notch at 22.4 MHz was measured Beam measurement at the KEK-PS 500MeV beam transport line

15. AC CT with Hereward Feedback Principle Original Hereward feedback is using an operational amplifier. The mehod using a feedback winding can be regarded as an extension of Hereward idea. Original work was done by R. Yamada, JJAP 1 (1962) 92.

16. Frequency response Carefull treatment of the feedbackloop necessary Magnetic field in the core Almost DC component is relevant Calculated frequency response

17. Compensation of sag extending lower cut-off frequency Zero reset every acceleration cycle Normalization by fRF NB=IB/ fRF In-situ calibration Additional winding

18. Number of protons measured by the Feed-back CT Beam for the neutron user Beam for the MR KEK-PS 500 MeV Booster V: 4x1011p/div, H: 5 ms/div Slow-extracted beam Number of protons measured by the Feed-back CT Magnetic field KEK-PS 12 GeV Main Ring V: 2x1012p/div, H: 200 ms/div

19. DC CT Principle Modulation-> saturation field Modulator/demodulator

20. DC CT Principle combination of the modulator/demodulator DCCT and the Hereward CT

21. DC CT Reducing a modulation ripple component Parallel feedback DCCT Series feedback DCCT K. Unser (CERN) S. Hiramatsu (KEK)

22. DC CT Chamber (KEKB)

23. DC CT Parallel feedback DCCT Frequency response

24. Wall Current Monitor Principle

25. Wall Current Monitor Practice Ceramic gap Resister for high frequency application Example: KEK-PS (IB~0.8 A in average) total resistance = 1W For hcurrent application -> smaller resistance More than 1 GHz possible with HOM damper

26. Beam Position Monitor Surface charge induced by the beam a line charge / charge density=l(r, f) <- beam a perfectly conducting cylindrical pipe The electric field of the line charge and its image Expanding by r, and put x=rcosf y=rsinf

27. Beam Position Monitor 2 monopole intensity dipole position size quadrupole sextupole … higher

28. Beam Position Monitor 2 Position x, y:

29. Beam Position Monitor 2 Size sx, sy:

30. Beam Position Monitor Pick-up Electrostatic PU Magnetic loop coupler Resistive PU Stripline etc.

31. ESM (ElectroStatic Monitor) Frequency response

32. Beam Position Monitor z Verious electrodes shapes position response aq Linear Linear Noninear

33. Beam Position Monitor Which position response is the best? For small-size beams: nonlinearity no problem proton linac e+, e storage rings, etc. we can use mapping data For large-size beams: nonlinearity problem !

34. Diagonal-cut ESM BPM for the J-PARC 50 GeV MR

35. Diagonal-cut ESM

36. Diagonal-cut ESM Position response Calibration with a wire

37. ESM (ElectroStatic Monitor) Frequency response ( coupling between electrodes )

38. Parallel-cut ESM Frequency response Calibration with a wire KEK-PS MR New BPM Position response Red: Measured with a wire Black: Fit of the data: -15 - 15 mm

39. Stripline (directional coupler) Principle

40. 60 MeV Test Linac BPM before the upper half of the Q magnet is set Stripline used for short bunchs 1 ns/div 50 mV/div Beam current 8 mA

41. Signal processing Analog processing synchronized detection amplitude-to-phase conversion processing log-ratio processing ….. Digital processing ADC 14 bit/ 105 MSPS FPGA / DSP

42. AM/PM processing (J-PARC linac BPM) 324 MHz • R&D • balancing att. and phases between two channels • dynamic range of limiters

43. Digital processing by FPGA (J-PARC 50 GeV MR) ADC: 80 MSP / 14 bit COD --- FFT, peak detect @fRF, and (L-R)/(L+R) single bunch position --- peak - bottom ⇨ Test at the KEK-PS 12GeV MR

44. Beam Loss Monitor Beam loss Scintillator Ionization / proportional chamber ⇨ ⇨ secondary particles enegy loss in matterials ⇨ exciting, or ionizing the atoms and/or molecules ⇨ scintillation, electrons, ions Example of ionization Bethe-Bloch formula Detection is usually in “current mode”. Too many particles for “counting”

45. fast response < 50 ns very large gain radiation damage <1-2 years Scintillator loss monitors scintillators liquid plastic phototubes KEK-PS Linac S.Lee et al. and T. Kawakubo et al.

46. no gain (x1) fit to higher energy > GeV/c slow response ~ 1 ms negligible radiation damage Ionization chamber KEK-PS free- air ionization chamber H. Nakagaw at al., NIM 174 (1980) 401.

47. Rise time vs. HV Signal vs. loss amount Signal vs kinetic energy Ionization chamber KEK-PS free- air ionization chamber

48. Ionization chamber KEK-PS MR Loss distribution around the ring

49. Ionization chamber

50. gain ~ 100 - 1000 fast response ~ 1 ms Proportional chamber radiation damage pure Ar … no damage Ar + CH4/CO2 … gain degraded scintilation proportional chamber S.Lee et al. and H. Someya et al.