History: Spin Physics with EDDA
April 1996
In April 1996
polarized protons had been accelerated in COSY
accelerator ring for the first time.
As a fast diagnostic tool for polarization development
at COSY the internal EDDA experiment could be abused as polarimeter.
Possible methods of determining the polarization of COSY synchrotron beam
by the means of the EDDA detector
are
- proton proton elastic scattering,
- proton proton inclusive scattering with a choosable inelastivity cut,
- proton carbon inclusive scattering,
- proton CH2 inclusive scattering.
It had been possible to measure beam polarization during
beam acceleration.
Up to a beam momentum of 800 MeV/c
a beam polarization greater than zero has been observed.
One depolarizing imperfection resonance at 463 MeV/c has been crossed succesfully.
Another intrinsic resonance at 828 MeV/c depolarized
the recirculating proton beam (see filled dots in figure below).
Beam polarization has been deduced from proton carbon inclusive scattering from a poly-propylene
fibre target (diameter: 4x5 mu).
December 1996
In December 1996 a non-zero polarization of COSY proton beam could be traced
up to beam momenta above 2000 MeV/c
crossing at least three imperfection and six intrinsic resonances.
(see filled dots in figure below).
Beam polarization has been deduced from proton proton inclusive scattering
from a poly-propylene
fibre target
(diameter: 4x5 mu)
with reference to proton proton elastic kinematics.
An additional flattop measurent at 1455 MeV/c reconfirmed
our pp inclusive result at the given beam momentum (see figure below).
Elastic analysis of proton proton scattering yields a beam polarization similar
to the one elastically deduced.
Crossing depolarizing resonances
The following figure shows non-zero polarization observed up to beam momenta
above 2000 MeV/c.
All plotted errors are purely statistical (and hence PRELIMINARY!).
Systematical errors are still subject to extensive investigation!
Download PS-version of this plot? (restricted access) >
This figure is not meant to testify the currently reachable maximum of polarization
of a proton beam stored in COSY but to demonstrate the feasibilty of crossing
the above mentioned depolarizing resonances.
So far, the maximum polarization observed in COSY is 80% at 800 MeV/c.
Since the data displayed in open dots and filled dots were taken with different machine settings,
they do not have to match (concerning the absolute polarization value).
Conservation of polarization in COSY
Example:
conservation by spin-flip at imperfection resonance "2"
(463 MeV/c)
-
Steerer distortion (April 1996)
Flipping the spin by means of a steerer distortion has been utilized to optimize partial conservation of beam polarization while crossing depolarizing resonances.
Using this spin-flip technique it was possible to increase
beam polarization from about 0.4 to 0.8 after crossing the imperfection resonance at 463 MeV/c (108 MeV kinetic energy).
Partial snake (April 1996)
Instead of stimulating a spin-flip utilizing a steerer distortion, additional efforts had been made to achieve a possibly more complete spin-flip by the means of a partial snake.
Comparably to the above mentioned steerer method, it was possible to increase
beam polarization from about 0.4 to 0.8 after crossing the imperfection resonance at 463 MeV/c.
There is no visible further amelioration when raising
the power supply of the partial snake from 50% to 100% of maximum power. Even the lower power satisfies the need of a total spin-flip.
Questions, complaints, comments etc. to E. Weise:
weise@iskp.uni-bonn.de