29 research outputs found
Phase locking the spin precession in a storage ring
This letter reports the successful use of feedback from a spin polarization
measurement to the revolution frequency of a 0.97 GeV/ bunched and polarized
deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control
both the precession rate ( kHz) and the phase of the horizontal
polarization component. Real time synchronization with a radio frequency (rf)
solenoid made possible the rotation of the polarization out of the horizontal
plane, yielding a demonstration of the feedback method to manipulate the
polarization. In particular, the rotation rate shows a sinusoidal function of
the horizontal polarization phase (relative to the rf solenoid), which was
controlled to within a one standard deviation range of rad. The
minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753
kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a
requirement for the use of storage rings to look for an intrinsic electric
dipole moment of charged particles
Collective oscillations of a stored deuteron beam close to the quantum limit
We investigated coherent betatron oscillations of a deuteron beam in the
storage ring COSY, excited by a detuned radio-frequency Wien filter. These beam
oscillations were detected by conventional beam position monitors, read out
with lock-in amplifiers. The response of the stored beam to the detuned Wien
filter was modelled using the ring lattice and time-dependent 3D field maps of
the radio-frequency Wien filter. The influence of uncertain system parameters
related to manufacturing tolerances and electronics was investigated using the
polynomial chaos expansion. With the currently available apparatus, we show
that oscillation amplitudes down to \SI{1}{\micro \meter} can be detected.
Future measurements of the electric dipole moment of protons will, however,
require control of the relative position of counter-propagating beams in the
sub-picometer range. Since the stored beam can be considered as a rarefied gas
of uncorrelated particles, we moreover demonstrate that the amplitudes of the
zero-point betatron oscillations of individual particles are within a factor of
10 of the Heisenberg uncertainty limit. As a consequence of this, we conclude
that quantum mechanics does not preclude the control of the beam centroids to
sub-picometer accuracy. The smallest Lorentz force exerted on a single particle
that we have been able to determine is \SI{10}{aN}.Comment: 38 pages, 16 figure
First Search for Axion-Like Particles in a Storage Ring Using a Polarized Deuteron Beam
Based on the notion that the local dark-matter field of axions or axion-like
particles (ALPs) in our Galaxy induces oscillating couplings to the spins of
nucleons and nuclei (via the electric dipole moment of the latter and/or the
paramagnetic axion-wind effect), we performed the first experiment to search
for ALPs using a storage ring. For that purpose, we used an in-plane polarized
deuteron beam stored at the Cooler Synchrotron COSY, scanning momenta near 970
MeV/c. This entailed a scan of the spin precession frequency. At resonance
between the spin precession frequency of deuterons and the ALP-induced EDM
oscillation frequency there will be an accumulation of the polarization
component out of the ring plane. Since the axion frequency is unknown, the
momentum of the beam and consequently the spin precession frequency were ramped
to search for a vertical polarization change that would occur when the
resonance is crossed. At COSY, four beam bunches with different polarization
directions were used to make sure that no resonance was missed because of the
unknown relative phase between the polarization precession and the axion/ALP
field. A frequency window of 1.5-kHz width around the spin precession frequency
of 121 kHz was scanned. We describe the experimental procedure and a test of
the methodology with the help of a radiofrequency Wien filter located on the
COSY ring. No ALP resonance was observed. As a consequence an upper limit of
the oscillating EDM component of the deuteron as well as its axion coupling
constants are provided.Comment: 25 pages, 24 figures, 7 tables, 67 reference
Intraperitoneal drain placement and outcomes after elective colorectal surgery: international matched, prospective, cohort study
Despite current guidelines, intraperitoneal drain placement after elective colorectal surgery remains widespread. Drains were not associated with earlier detection of intraperitoneal collections, but were associated with prolonged hospital stay and increased risk of surgical-site infections.Background Many surgeons routinely place intraperitoneal drains after elective colorectal surgery. However, enhanced recovery after surgery guidelines recommend against their routine use owing to a lack of clear clinical benefit. This study aimed to describe international variation in intraperitoneal drain placement and the safety of this practice. Methods COMPASS (COMPlicAted intra-abdominal collectionS after colorectal Surgery) was a prospective, international, cohort study which enrolled consecutive adults undergoing elective colorectal surgery (February to March 2020). The primary outcome was the rate of intraperitoneal drain placement. Secondary outcomes included: rate and time to diagnosis of postoperative intraperitoneal collections; rate of surgical site infections (SSIs); time to discharge; and 30-day major postoperative complications (Clavien-Dindo grade at least III). After propensity score matching, multivariable logistic regression and Cox proportional hazards regression were used to estimate the independent association of the secondary outcomes with drain placement. Results Overall, 1805 patients from 22 countries were included (798 women, 44.2 per cent; median age 67.0 years). The drain insertion rate was 51.9 per cent (937 patients). After matching, drains were not associated with reduced rates (odds ratio (OR) 1.33, 95 per cent c.i. 0.79 to 2.23; P = 0.287) or earlier detection (hazard ratio (HR) 0.87, 0.33 to 2.31; P = 0.780) of collections. Although not associated with worse major postoperative complications (OR 1.09, 0.68 to 1.75; P = 0.709), drains were associated with delayed hospital discharge (HR 0.58, 0.52 to 0.66; P < 0.001) and an increased risk of SSIs (OR 2.47, 1.50 to 4.05; P < 0.001). Conclusion Intraperitoneal drain placement after elective colorectal surgery is not associated with earlier detection of postoperative collections, but prolongs hospital stay and increases SSI risk
Conceptualization, design and simulation of a hybrid antenna system as a simultaneous RF hyperthermia applicator at 600 MHz and RF coil for Magnetic Resonance Imaging at 3 Tesla
This paper presents the conceptualization, design and simulation of a hybrid multi-frequency antenna system for Radio Frequency (RF) hyperthermia and Magnetic Resonance Imaging (MRI) applications with ultra-sharp hotspot. Two different bowtie antenna arrays have been designed, simulated and integrated. The first antenna array is designed as an RF coil for MR imaging. It is optimized to generate a highly homogeneous transmit B⃗ 1 + field and is intended for 3 T MRI systems. This corresponds to a frequency of 128 MHz. The second array aims to induce heat by accumulating the electromagnetic energy at one location thereby forming a hotspot. The operating frequency of the second system is 600 MHz. The computed homogeneity of the B 1 + field generated by the imaging antennas shows similar values compared to a birdcage coil at the same frequency. The size of the hotspot generated by the heating subsystem was 26 × 26 × 93 mm 3 . The heating produced by the MR imaging antennas was negligible, compared to the RF hyperthermia applicator