1. Applications of psec TOF in proton and heavy-ion accelerators Peter Ostroumov Pico-Sec Timing Hardware Workshop November 18, 2005

2. Outline • TOF measurements in accelerators • Rare Isotope Accelerator Facility • Accelerated bunched beam velocity (energy) measurements based on induced rf signals • Bunch time profile measurements with resolution ~10 picoseconds based on streak camera • Improvement of time resolution of the existing BLD • Bunch time structure measurements using X-rays • High resolution is obtained by using streak cameras • Examples of TOF technique application in nuclear physics experiments at ATLAS: mass and nuclear charge identification of radioactive ions using gas-filled magnet

3. TOF systems • High-power (hundreds of kilowatts) accelerators such as RIA driver linac • Require high-precision control of beam energy • Maintain short bunches (~40-100 picoseconds) • Beams of rare isotopes must be analyzed by detecting individual particles. Fast time measurements (~20 picoseconds resolution) are necessary to control bunched beam quality • Absolute energy measurements based on TOF system • Required for many experiments • Non-destructive, cheap compared to magnet • Well suited for beam velocities <0.5c • Very high accuracy can be obtained • Wide range of beam currents starting from ~0.3 nA (~1010 particles/sec) can be analyzed

4. Absolute energy measurement using resonant TOF system SCR SCR Power Amplifier Power Amplifier VCX VCX SCR SCR Clock Clock Power Amplifier Power Amplifier Limiter Limiter VCX VCX Attenuator Attenuator Phase Shifter Phase Shifter Preamplifier Preamplifier Detector Detector Attenuator Attenuator RF Control Module RF Control Module _ _ Aerror Aerror 20dB 20dB 40dB 40dB REF REF + + RF Control Module RF Control Module FIG. 4. SCR low-field operation simplified diagram. FIG. 4. SCR low-field operation simplified diagram. FIG. 3. Simplified RF diagram of ATLAS super conducting resonator in accelerating mode. FIG. 3. Simplified RF diagram of ATLAS super conducting resonator in accelerating mode. Clock Clock 48.505 MHz FEE FEE FEE f=48.505-48.500 = 5 kHz Phase meter Beam frequency = 48.500 MHz Resonator frequency =48.500 MHz

5. Absolute energy measurement using resonant TOF system

6. Absolute energy measurement using resonant TOF system • Precision of TOF measurements: • Signal – noise ratio • Phase jitter due to vibration, some thermal effects • Major contribution –beam phase jitter Phase advance over 9 m – 5400 deg of 48.5 MHz Phase meter precision ~ 0.2 deg TOF=300 nsec • Accuracy of beam energy measurements: • Additional effect is the distance between the detectors • Typical number is E/E=210-4

7. High accuracy is achieved by using • Chain of bunches, signal is integrated in the resonator (msec); • Mixing of two frequencies in the resonator helps to avoid extra noise that can be accumulated in external circuits • The bunch phase at 48.5 MHz is directly translated to 5 kHz and minimizes phase meter errors • Front End Electronics • Amplitude detection • Narrow band-pass filter (5 kHz) • AGC (automatic gain control) amplifier

8. Bunch Length detector Ion beam j I( ) j , Z I(X) X Secondary electrons U t arg 1 2 3 1-tangstin target wire, 2-collimator, 3-plates of the rf deflector, 4-MCP, 5-phosphor screen, 6-CCD camera,. 4 5 6

9. Electron beam trajectories with no RF applied (streak camera)

10. Electron beam image on the phosphor with no RF applied Focused electron beam profile Resolution is ~15 pixels Bunch width = 10 deg at 97 MHz=290 picoseconds 15 pixels corresponds to ~10 picoseconds resolution

11. RF on, bunch image

12. Bunch time profile • 58 Ni bunch profile (a) inferred from scintillator signal (b).

13. Time resolution • The time required for the emission of secondary electrons • The time difference, due to the different arrival times of the secondary electrons originating from different points of the wire, at the rf deflector • The contribution to the detector resolution from the angular and energy distributions of the secondary electrons • The time of flight of the electrons through the electrostatic field of the plates. • Finally the RF voltage and rf phase jitter is a very important factor in determining the time resolution of the detector.

14. Improvement of time resolution of the existing BLD • Reduce both the entrance and exit slits size down to ~0.2 mm; • Use single electron mode of measurements. In the single electron mode the problem associated with the finite size of the SE beam will be minimized. • Reduce the diameter of the wire to ~0.03 mm; • Increase the voltage applied to the wire up to 15 kV; • Increase the rf voltage to have large sweeping amplitude on the exit slit; • Improve electron beam optics to obtain more isochronous trajectories; • Improve phase jitter of the rf deflector by introducing an external RF synthesized signal generator with a high stability.

15. Heavy-ion bunch time structure using X-rays Focusing spectrograph for picosecond time resolution of ion beam (adapted from [1]) Streak camera BEAM [1] O.N. Rosmej et al. 30th EPS Conference on Contr. Fusion and Plasma Phys., St. Petersburg, 7-11 July 2003 ECA Vol. 27A, O-1.9C

16. Typical streak camera being used at electron synchrotrons Time resolution of streak cameras can be less than 1 picosecond

17. Heavy-ion bunch time structure using X-rays (proposal) • Ions penetrate the thin target ( 0.1-0.2 mm) and undergo multiple collisions with target atoms. • Excitation of bound electrons followed by radiative decay gives rise to projectile and target radiation. Decay time ~10 femtosec • Focusing specrograph with spatial resolution provides high spectral and spatial resolution of the K-shell spectra. • Streak camera measures the temporal structure of the beam with picosecond resolution.

18. ATLAS Layout

19. Mass and nuclear charge identification using gas-filled spectrograph • Difficulty: • The masses are very close • The same q/m, velocity

20. TOF for mass and charge identification

21. Time-of-Flight Measurement with the Storage Ring in the Isochronous Mode (Milan Matos’ presentation)

22. Time-of-Flight Spectrum

23. Conclusion • Time resolution of 3-5 picoseconds is required to tune and operate high-power heavy-ion linacs • So far the technique remains complex and expensive to provide high resolution • TOF is a common technique for identification of mass and nuclear charge of rare isotopes. Currently several large facilities are being constructed worldwide to produce beams of exotic nuclei. • High resolution MCPs can help to reduce the cost of storage rings or spectrographs in future rare isotope accelerator facilities