1. Beam based measurements
3rd September BND school Dieter Prasuhn

2. Outline: What can be measured
Lattice properties
Closed orbit
Betatron tunes
Chromaticity
gtransition
Properties of the beam
Beam intensity
Beam profile
Momentum spread
Time structure
3. September 2015
Dieter Prasuhn

3. Lattice properties

4. Closed Orbit measurements
What is the origin of closed orbit deviations?
How to measure closed orbit?
Why to measure and correct CO deviations?
3. September 2015
Dieter Prasuhn

5. The origin of closed orbit deviations
Beampipe
focussing
defocussing
Quadrupoles
3. September 2015
Dieter Prasuhn

6. The center of mass of the beam
Beampipe
focussing
defocussing
Quadrupoles
3. September 2015
Dieter Prasuhn

7. One quadrupole is misaligned
Beampipe
focussing
defocussing
Quadrupoles
3. September 2015
Dieter Prasuhn

8. How to measure the closed orbit
Make use of the image current of the beam induced in the outer vacuum pipe
3. September 2015
Dieter Prasuhn

9. Beam Position Monitors (Button type):
mainly used in electron synchrotrons, electron storage rings and light sources etc.
3. September 2015
Dieter Prasuhn

10. Beam Position Monitors (capacitive pick-ups):
mainly used in hadron synchrotrons and storage rings D S
3. September 2015
Dieter Prasuhn

11. Why do we measure (and correct) the closed orbit?
The centered beam has more space in the vacuum chamber
Quadrupole changes will not change the beam position
The beam - target overlap can be optimized
3. September 2015
Dieter Prasuhn

12. Optimizing the Luminosity
Counting rate of the experiment
Closed orbit bump
Beam Intensity
3. September 2015
Dieter Prasuhn

13. Betatron tunes We follow 1 particle through the accelerator
3. September 2015
Dieter Prasuhn

14. Betatron tunes We follow many particles through the accelerator
3. September 2015
Dieter Prasuhn

15. The motion of each particle seen at one position follows the phase space ellipse:
The betatron tune is the number of oscillations on the phase ellipse during one revolution in the storage ring
3. September 2015
Dieter Prasuhn

16. Magnet errors generate angle kicksx` x
3. September 2015
Dieter Prasuhn

17. Betatron resonances q = integerx x`
q = integer
shows the effect of emittance growth and beam loss
3. September 2015
Dieter Prasuhn

18. Resonances occur, if In general: l*qx + m*qy = n
q = integer 1st order resonance
2*q = integer 2nd order resonance
3*q = integer 3rd order resonance
qx + qy = integer 2nd order sum resonance
qx - qy = integer 2nd order difference resonance
In general:
l*qx + m*qy = n
3. September 2015
Dieter Prasuhn

19. The resonance plot
l*qx + m*qy = n
3. September 2015
Dieter Prasuhn

20. How to measure a tune x` x Beam path BPM Stripline unit
D signal of BPM
RF-output
Spectrum analyzer x x`
Beam path
3. September 2015
Dieter Prasuhn

21. Frequency spectrum of the PU signal
Deuterons
pc = 970 MeV
f0 = kHz
= 0.459
Qx = 3.65
Qy = 3.56
Since fractional tune q > 0.5:
f+ = (2+q)f0
f- = (2-q)f0
f+ = (1+q)f0 f0
2f0
3f0
4f0
5f0
horizontal
Result with f- = (2-q)f0
and f+ = (1+q)f0:
revolution frequency f- + f+ = 3f0
fractional tune q = f+/f0 - 1
vertical
Measured with BPM09
Green and red curves: stored spectra when cavity is ON to make revolution frequency visible
Courtesy: Hans Stockhorst
3. September 2015
Dieter Prasuhn

22. Chromaticity
x =

23. For Correction: Sextupoles
3. September 2015
Dieter Prasuhn

24. How to measure the chromaticity
The width of the betatron side bands depend on x and dp/p
q = q0 + x dp/p
3. September 2015
Dieter Prasuhn

25. or with electron cooled beam
Change the voltage of the electron beam
The energy of the proton beam follows
Measure the new tune
3. September 2015
Dieter Prasuhn

26. g transition (momentum compaction factor)
Beam particles have different momenta
Different momenta result in different velocities
and different paths and path lengths
Momentum spread leads to frequency spread =h
3. September 2015
Dieter Prasuhn

27. How to measure gtransition
Switch off the RF to measure the free revolution frequency
Now introduce a change in B-field (corresponding to a momentum change)
Measure the new revolution frequency due to the new orbit length
The change of frequency due to magnetic field is proportional to the g2transition
3. September 2015
Dieter Prasuhn

28. 3. September 2015
Dieter Prasuhn

29. with electron cooler Have de-bunched beam
Change the electron cooler voltage
Measure the shift in the longitudinal Schottky spectrum
3. September 2015
Dieter Prasuhn

30. Why do we measure gtransition
If g=gtransition bunched beams become unstable
Stochastic cooling needs „mixing“ (Hans Stockhorst). Mixing is defined by the difference of g and gtransition.
3. September 2015
Dieter Prasuhn

31. And for experiments: to measure the target thickness
Mean energy loss leads to a frequency shift
3. September 2015
Dieter Prasuhn

32. Result
3. September 2015
Dieter Prasuhn

33. Beam properties

34. Beam Intensity Beam current transformer I = Ncirc * f0 * Z*e
Charged particles circulating with a frequency f0 in storage ring are seen as a winding of a tranformer.
The current I measured in a 2nd winding is proportional to the number of circulating particles Ncirc
I = Ncirc * f0 * Z*e
3. September 2015
Dieter Prasuhn

35. One example of BCT
Beam
3. September 2015
Dieter Prasuhn

36. One picture of the BCT signal
Experiment counting rate
BCT signal
3. September 2015
Dieter Prasuhn

37. Beam Profile Monitors Thin fibers are moved quickly through the beam
Seconary electrons emitted from the target are measured as function of the fiber position
Disadvantage: destructive measurement
3. September 2015
Dieter Prasuhn

38. Ionisation Beam Profile Monitor
Advantage: non-destructive measurement
3. September 2015
Dieter Prasuhn

39. The IPM at COSY
3. September 2015
Dieter Prasuhn

40. Beam profile measured with the IPM
Beam profile before and after cooling
3. September 2015
Dieter Prasuhn

41. Momentum spread
For experiments often the momentum resolution is of big interest
= h
3. September 2015
Dieter Prasuhn

42. Measure gtransition or h
Measure the width of the longitudinal Schottky spectrum
3. September 2015
Dieter Prasuhn

43. Time structure of the beam
Makroscopic time structure
Defined by the cycle of the accelerator
3. September 2015
Dieter Prasuhn

44. Microscopic structure due to bunching
A de-bunched beam delivers a quasi DC-beam
In LINACS, Colliders, electron accelerators and in hadron machines with internal target bunching is mandatory.
Experiments will directly show the time structure of the beam
3. September 2015
Dieter Prasuhn

45. Different Bunch signals
Pure sinusoidal voltage on an integer harmonic of the revolution frequency
Colliders and synchrotron light sources work on high harmonics
Medium energy hadron accelerators work at low harmonics
At COSY usually h=1 is used for acceleration
3. September 2015
Dieter Prasuhn

46. Bunch signals during electron cooling
3. September 2015
Dieter Prasuhn

47. Barrier bucket
Advantage: homogenious beam intensity in the bucket, short time without beam
3. September 2015
Dieter Prasuhn

48. Summary
Introduction to some measurements of lattice parameters and beam parameters
Exercises are planned during the afternoon excursion
3. September 2015
Dieter Prasuhn

49. Outlook: The afternoon excursion
We prepared three demonstration objects:
COSY control room
Magnetic field measurements
RF-cavity measurements
Walk around COSY
3. September 2015
Dieter Prasuhn

50. Map of Forschungszentrum Jülich
Institute for Nuclear Research
COSY
COSY test hall
Main gate
„face control“
3. September 2015
Dieter Prasuhn

51. Thank you for your attention
and
enjoy the excursion
3. September 2015
Dieter Prasuhn