Beam based measurements 3rd September 2015 BND school Dieter Prasuhn

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

Lattice properties

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Frequency spectrum of the PU signal Deuterons pc = 970 MeV f0 = 570.6 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

Chromaticity   x =

For Correction: Sextupoles 3. September 2015 Dieter Prasuhn

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

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

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

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

3. September 2015 Dieter Prasuhn

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

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

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

Result 3. September 2015 Dieter Prasuhn

Beam properties

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

One example of BCT Beam 3. September 2015 Dieter Prasuhn

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

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

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

The IPM at COSY 3. September 2015 Dieter Prasuhn

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

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

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

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

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

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

Bunch signals during electron cooling 3. September 2015 Dieter Prasuhn

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

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

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

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

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