Storage ring optics characterization

1
Storage ring optics characterization the basics

• Beam Diagnostics
• DCCT
• Strip lines
• BPMs
• Scrapers
• Synchrotron light monitors
• Loss monitors
• Measuring tunes, b, h, chromaticity, a?

2
Photon factory DCCT
T. Honda et al., EPAC98
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SPEAR3 DCCT
TOROID
image current
TOROID
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DCCT (or PCT) circuit
Bergoz PCT
7 kHz
14 kHz
Nonlinear ferrite core
beam
J.A. Hinkson, LBNL
The DC bias current is adjusted to remove the 2nd
harmonic (14 kHz) response of toroid. The beam
current is proportional to the DC bias current.
Ferrite core Xsection
Simplified circuit, K. Unser, 1992
5
Beam position monitors
Electron BPM buttons sample electric fields
striplines couple to electric and magnetic
fields. Examples of photon BPMs
Copper fluorescence bpm
Split ion chamber
Tungsten blade monitor
6
Loss monitors
Bergoz
Kuske measurements made with scintillator and
photo multiplier.
Kuske et al., PAC01.
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Beam size measurements Scrapers
Synchrotron light monitors
8
Beam frequencies
Beam frequencies Importance, global measure of
optics. First measurements made of
ring. Instabilities
If you have a single bunch with charge q in a
storage ring with a revolution time T0, the
signal on an oscilloscope looks like
where Im assuming a zero-length bunch. A
spectrum analyzer would see the Fourier transform
of this,
w0
T0
Time
Frequency
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frequency (1/sl)
For SPEAR3, c/sl 67 GHz.
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Betatron tune
Integer and ½ integer ambiguities
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Synchrotron tune
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Measured spectra
HLS tune meas., Sun et al. PAC01
Courtesy J. Byrd
Multibunch spectra, instabilities, Sebek, Friday.
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More on spectrum
Turn by turn measurements, FFT, NAFF, betatron
phase (Tuesday) Nonlinear dynamics (tune vs.
amplitude tune vs. closed orbit
Thursday) Impedance measurements (Friday) Beta
function measurements Chromaticity
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Beta function measurement
DnubetaKL/4pi Measurement issues Keep orbit
constant Hysteresis Saturation Sometimes cannot
vary individual quadrupoles
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SPEAR b-function correction
before
after
Courtesy Heinz-Dieter Nuhn
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Other b measurements
Fit response matrix Mij sqrt(), Y. Chung et
al., PAC93 Derive from betatron phase
measurements (Tuesday lecture) Beam size
measurement
Minty and Spence, PAC95
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Dispersion
Dispersion is the change in closed orbit with a
change in electron energy. The energy can be
changed by shifting the rf frequency.
(a momentum compaction)
So the dispersion can be measured by measuring
the change in closed orbit with rf frequency.
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Dispersion
X-Ray Ring h indicates large Kx errors
Dispersion distortion can come from quadrupole or
dipole errors.
Vertical dispersion gives a measure of vertical
bending errors or skew gradient errors in a
storage ring.
PEPII hx and hy measurement
Uli Wienands
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Chromaticity
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Momentum compaction