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Submitted on 1 Jan 1985
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INFLUENCE OF BETATRON OSCILLATIONS ON
THE PROTON BEAM POLARI ZATION
A. Nakach
To cite this version:
A. Nakach.
INFLUENCE OF BETATRON OSCILLATIONS ON THE PROTON BEAM
POLARI
ZATION.
Journal
de
Physique
Colloques,
1985,
46
(C2),
pp.C2-655-C2-656.
�10.1051/jphyscol:1985281�. �jpa-00224600�
JOURNAL DE PHYSIQUE
Colloque C2, supplément au n°2, Tome 46, février 1985 page C2-655
INFLUENCE OF BETATRON OSCILLATIONS ON THE PROTON BEAM POLARIZATION*
A. Nakach
LaboTatoive National Saturne, CEN-Saclay, 91191 G-if-sur-Yvette, France RESUME
On a étudié à SATURNE, l'influence sur la polarisation d'un faisceau de protons, à la traversée de deux résonances "intrinsèques" G = vz et G = 8 - v , de l'ampli-tude des oscillations bétatron verticales. L'amplil'ampli-tude maximum est contrôlée par une déformation des trajectoires poussant le faisceau sur une cible, à l'injection, en-traînant une perte. Ces deux résonances, étudiées à 1,2 GeV et 1,45 GeV, sont très fortes et capables de renverser le spin des particules de grande amplitude mais pas de celles composant le coeur. Après les deux traversées, on trouve effectivement une polarisation supérieure à celle mesurée après une seule traversée.
ABSTRACT
The influence of the vertical betatron amplitude on the depolarization of the proton beam when crossing tha two consecutive intrinsic resonances 7G = v and 7G = 8 - v with adiabatic spin flip has been studied at SATURNE II. The maximum Betatron amplitude was controlled by vertical beam displacement after injection and a beam scraper in fixed position. The effective polarization of the extracted beam was measured at 0.88 GeV (below the first resonance),at 1.20 GeV (after crossing the first resonance and at 1.45 GeV (after crossing both resonances)(Figure 1). These resonances are due to the main quadrupoles of the ring. The results are consistent with adiabatic flip of only the peripheral part of the beam, not the core.
The measurement presented here is part of SATURNE II machine study of depolarization phenomena occuring during acceleration of the polarized proton beam. The aim is detailed understanding of resonant depolarization mechanisms in order to minimize polarization losses up to full energy of the accelerator.
The influence of the vertical betatron oscillation amplitudes on the polarization when crossing the two consecutive intrinsic resonances 7G = v and 7G - 8 - v with adiabatic spin flip has been studied. The maximum betatron amplitude was controlled by vertical beam displacement after injection and a beam scraper in fixed position. The effective polarization of the extracted beam was measured at 0.88 GeV (below the first resonance) at 1.20 GeV (between the two resonances) and at 1.45 GeV after crossing both resonances. Both resonances are due to the main quadrupoles of the ring.
The effective beam polarization was measured by extracting the beam onto the "Nucleon-Nucleon" beam line polarimeter [l]. The initial polarization at 0.88 GeV was carefully optimized for full beam intensity, i.e. for full betatron oscillation. The measured value was P = 0.9004 ± 0.0063. At this energy, the beam polarization was found to be independent of the maximum betatron oscillation, as shown on Figure 1, curve a (crosses).
Next, the beam was extracted at i.20 GeV, above the intrinsic resonance 7G = v . The maximum polarization at full betatron amplitude (full beam intensity) was P = 0.725 ± 0.005 and the polarization was found to decrease strongly when the oscillation amplitude was reduced (P . = 0.300 ± 0.005 , curve b ) .
m m
Finally, the beam was extracted at 1.45 GeV after crossing successively both the 7G = c and 7G = 8 - c resonances. The beam polarization at this energy is always larger,i.e. closer to the initial value at 0.88 GeV. Furthermore, reducing the maximum betatron
amplitu-in collaboration with the N-N Group, DPhPE and DPhN-ME, CEN-Saclay, France
C2-656 JOURNAL DE PHYSIQUE
de has definitely less Pffect on the polarization which decreases from P = 0.789
*
0.004 to P.
t 0.50 (curvec).max mln
Independence of the beam polarization on the betatron amplitudes at energies below the
yG = v resonance at 2 0.92 GeV was confirmed by an additional measurement at 0.725 GeV (curveZa, solid points). The results at 0.88 and 0.725 GsV confirm that the polarimeter response is independent of the beam intensity in the range considered here.
We Observe that the effective bem. polarization (a) increases after crossing the second resonance instead of continuing to decrease and (b) shows differentdepenaence on the maxi- mum betatron amplitude at the different eneroies: below the first resonance it is independent of the betatron amplitude, between the resonances it is strongiy decreasing when the amplitude is reduced while above the second resonance it shows weaker dependence. All of these observations are consistent with adiabatic spin flip only for the peripheral part of the beam whereas the core is not flipping in this type of resonances.
INCREASING VERTICAL BETATRON AMPLITUDE
-
+
0.880
GeV
0.7
25
GeV
n0.120
GeV
o
0.145
GeV
lo9
Protons
/Burst
Pl.g.1 Porarization of the extracted beam as a function cf the circulating beam i.ntensity. Maximum intensity correspsnds to fur; betatron oscillation ampiitude. Reduces ictensities corresponc: to reduction of the maximum betakron amplitude by vertical beam displacement and beam scraper. Curves a, b an2. c show the polarization below, between and above the two resonances, respectively.
REFERENCE
