12 research outputs found
Spin Coherence Time studies for the storage ring EDM search
This thesis is part of the feasibility studies for a search for an Electric
Dipole Moment (EDM) of charged particles in a storage ring. The evidence
for a non-vanishing EDM at the sensitivity of present or planned experiments
would clearly prove the existence of new CP violating meachanisms
beyond the Standard Model. The proposed solution to measure the EDM
of charged particles is the use of a storage ring where the polarized charged
particle beam can be kept circulating while interacting with a radial electric
field. Starting with a longitudinally polarized beam, the EDM signal
would be detected as a polarization precession starting from the horizontal
plane and rotating toward the vertical direction. A long horizontal polarization
lifetime, called spin coherence time, is required since it represents
the time available to observe the EDM signal. In order to have a sensitivity
about 10â29 e·cm to the deuteron EDM, the spin coherence time should
reach 1000 s while the measurement of a vertical polarization change should
detect angles as small as micro-radians.
The aim of this work is the analysis of the mechanisms which control
the spin coherence time in a storage ring. The measurements presented
here were made at the COSY (COoler SYnchrotron) ring located at the
Forschungszentrum-Jšulich GmbH (Germany).
There are two set of measurements presented in this thesis: the first is a
study of a spin resonance induced by a radio-frequency (rf) solenoid and the
second shows the results from the first direct measurement of the horizontal
polarization as a function of time.
The first experiment sought to estimate the spin coherence time by measuring
the width of a deuteron spin resonance induced by an rf-solenoid.
Since the width of the resonance depends on the spin tune spread and thus
on particle momentum distribution, each mechanism that can change the
particle velocity in the beam could contribute to the spin tune spread. In
particular, these mechanisms are betatron oscillations related to the beam
emittance and synchrotron oscillations that are present only in a bunched
beam.
The experiment consisted in the measurement of the vertical polarization
measurements with the rf-solenoid running at fixed frequency on and
off resonance, for both uncooled and cooled bunched beam. In order to
interpret the data, a simple âno-latticeâ model was developed based on two
rotation matrices for the spin precession about the vertical axis and the
solenoid kick about the longitudinal axis; synchrotron oscillations were included
as simple harmonic motion. The model demonstrated that the effect
of synchrotron oscillations on the induced spin resonance were large enough
to hide any dependence on emittance.
The second experiment was the direct measurement of the horizontal
polarization as a function of time. This task was accomplished through
the development of a dedicated data acquisition system synchronized with
the revolution frequency of the beam. By changing the horizontal beam
emittance with a white noise electric field, the measurements gave the first
experimental evidence of a dependence of the spin coherence time on the
horizontal beam size. The dependence is due to the path lengthening introduced
by betatron oscillations which forces the particles to go faster in order
to respect the isochronous condition in a bunched beam. A possible method
to correct for emittance effects is to use sextupole magnets. In fact the field
varies as the square of the radius from the center and provides an adjustment
to the particle orbit to remove the term driving the spin tune change.
It has been demonstrated that for a particular value of sextupole strength
the contribution from the horizontal emittance was canceled, reaching a
spin coherence time of a hundred seconds
Synchrotron oscillation effects on an rf-solenoid spin resonance
New measurements are reported for the time dependence of the vertical polarization of a 0: 97 GeV/c deuteron beam circulating in a storage ring and perturbed by an rf solenoid. The storage ring is the cooler synchrotron (COSY) located at the Forschungszentrum Julich. The beam polarization was measured continuously using a 1.5 cm thick carbon target located at the edge of the circulating deuteron beam and the scintillators of the EDDA detector. An rf solenoid mounted on the ring was used to generate fields at and near the frequency of the 1 - G gamma spin resonance. Measurements were made of the vertical beam polarization as a function of time with the operation of the rf solenoid in either fixed or continuously variable frequency mode. Using rf-solenoid strengths as large as 2.66 x 10(-5) revolutions/turn, slow oscillations (similar to 1 Hz) were observed in the vertical beam polarization. When the circulating beam was continuously electron cooled, these oscillations completely reversed the polarization and showed no sign of diminishing in amplitude. But for the uncooled beam, the oscillation amplitude was damped to nearly zero within a few seconds. A simple spin-tracking model without the details of the COSY ring lattice was successful in reproducing these oscillations and demonstrating the sensitivity of the damping to the magnitude of the synchrotron motion of the beam particles. The model demonstrates that the characteristic features of measurements made in the presence of large synchrotron oscillations are distinct from the features of such measurements when made off resonance. These data were collected in preparation for a study of the spin coherence time, a beam property that needs to become long to enable a search for an electric dipole moment using a storage ring
Performance Evaluation of Linac4 During the Reliability Run
Linac4 will replace Linac2 as the first element in the CERN proton injector chain from 2020 onwards, following the second LHC long shutdown (LS2). With more than three times higher energy and number of compo-nents than Linac2, beam availability is one of the main challenges of Linac4. Intended as a smooth transition from commissioning to operation, a Linac4 Reliability Run was started in July 2017 and is foreseen to last until mid-May 2018. The goal is to achieve the target availability of 95 %. This implies consolidated routine operation and identification of recurring problems. This paper introduces the schedule and operational aspects of the Linac4 Reliability Run, including the developed tools and methods for availability tracking. The paper also summarizes the lessons learned during the first period of the Linac4 Reliability Run with respect to fault tracking and provides an in-depth analysis of the failure modes and observed availability
Comparison of Different Transverse Emittance Measurement Techniques in the Proton Synchrotron Booster
The measurement of the transverse emittance in an accelerator is a crucial parameter to evaluate the performance of the machine and to understand beam dynamics processes. In recent years, controlling and understanding the emittance became particularly relevant in the Proton Synchrotron Booster (PSB) at CERN as part of the LHC Injectors Upgrade (LIU). The LIU project is a necessary step to achieve the goals of the High-Luminosity LHC project. In this framework, an accurate and reliable emittance measurement of high brightness beams is mandatory to study the brightness reach of the LHC injectors. In the PSB there are two main instruments available for emittance measurements: wire scanners and secondary-emission (SEM) grids. In this paper emittance measurements performed during the 2017 physics run with these two systems are compared, taking into account various systematic error sources
Commissioning of the Beam Instrumentation for the Half Sector Test in Linac4 with a 160 MeV Hâ» Beam
In the framework of the LHC Injector Upgrade (LIU) project, the Proton Synchrotron Booster (PSB) will be extensively modified during the Long Shutdown 2 (LS2, 2019-2020) at CERN [1]. This includes a new injector, Linac4, which will provide a 160 MeV Hâ» beam and a complete new injection section for the PSB composed essentially of a chicane and a stripping foil system. The equivalent of half of this new injection chicane, so-called Half-Sector Test (HST), was tempo-rarily installed in the Linac4 transfer line to evaluate the performance of the novel beam instrumentation, such as, stripping foils, monitoring screens, beam cur-rent transformers, Hâ°/Hâ» monitor and dump, beam loss monitors, and beam position monitors. The results of the instrumentation commissioning of the HST are presented in this paper
Commissioning of the Stripping Foil Units for the Upgrade of the PSB Hâ» Injection System
The PSB will be extensively upgraded during the next long shutdown of the CERN accelerator complex, to double the brightness of the stored beams. The existing multi-turn injection will be replaced by a charge exchange system designed for the 160 MeV hydrogen ions provided by Linac4. Part of the injection equipment has been temporarily installed along the Linac4-to-PSB transfer line and tested with beam. This allowed to gain experience with the system, test the related diagnostics and benchmark calculations with measurements. An additional permanent stripping foil test stand is also installed right after the Linac and will be used to characterise new foils for possible future applications. The main outcomes, issues and applied or planned mitigations are presented for both installations
Beam Instrumentation for the CERN LINAC4 and PSB Half Sector Test
The construction, installation and initial commissioning of CERN's LINAC4 was completed in 2016 with Hâ» ions successfully accelerated to its top energy of 160 MeV. The accelerator is equipped with a large number of beam diagnostic systems that are essential to monitor, control and optimize the beam parameters. A general overview of the installed systems and their functional specifications will be followed by a summary of the most relevant results. This includes transverse profile monitors (wire scanners, wire grids and a laser profile monitor), beam position and phase monitors (whose ToF measurements were essential for adjusting RF cavity parameters), beam loss monitors, beam current transformers and longitudinal beam shape monitors. This contribution will also cover the beam instrumentation for the so-called PSB Half Sector Test, which has been temporarily installed in the LINAC4 transfer line to study Hâ» stripping efficiency. At this facility it was possible to test the new Hâ°/Hâ» beam current monitor, designed to monitor the stripping efficiency and an essential element of the beam interlock system when the LINAC4 is connected to the PSB in 2019
Commissioning and Results of the Half-Sector Test Installation with 160 MeV Hâ» beam from Linac4
During the Long Shutdown 2 (LS2) at CERN in 2019/20, the Proton Synchrotron Booster (PSB) will undergo a profound upgrade in the framework of the LHC Injector Upgrade (LIU) project involving also the connection to the new Linac4 injector. The 160 MeV Linac4 H' injection entails a complete replacement of the PSB injection section, including a stripping foil system, injection chicane, an Hâ°/H' dump and novel beam instrumentation. The equivalent of half of this new injection chicane was temporarily installed in the Linac4 transfer line to evaluate the performance of the equipment and prepare controls, interlocks and applications for the connection. Outcomes of this so-called Half-Sector Test (HST) are presented in this paper
Machine Development Studies in the CERN PS Booster, in 2016
The paper presents the outstanding studies performed in 2016 in preparation of the PS Booster upgrade, within the LHC Injector Upgrade project (LIU), to provide twice higher brightness and intensity to the High-Luminosity LHC. Major changes include the increase of injection and extraction energy, the implementation of a Hâ» charge-exchange injection system, the replacement of the present Main Power Supply and the deployment of a new RF system (and related Low-Level), based on the Finemet technology. Although the major improvements will be visible only after the upgrade, the present machine can already benefit of the work done, in terms of better brightness, transmission and improved reproducibility of the present operational beams. Studies address the space-charge limitations at low energy, for which a detailed optics model is needed and for which mitigation measurements are under study, and the blow-up reduction at injection in the downstream machine, for which the beams need careful preparation and transmission. Moreover they address the requirements and the reliability of new beam instrumentation and hardware that is being installed in view of LIU