The Radio Frequency Quadrupole (RFQ) is a linear accelerator that focuses, bunches, and accelerates a continuous input of charged particles while preserving the beam emittance. This paper focuses on ...the study of the transverse acceptance of an RFQ and how this concept can be used in the design of frontend structures. A simple and fast system to qualify a source and low energy transfer line has been developed in terms of the number of particles delivered in the RFQ acceptance. Multi-particle simulation results show a dependence of the RFQ transverse acceptance on the particle phase in the radio frequency period. The usually referred-to acceptance value is, in fact, just an average value over the 360° phase range, whereas a modulation has been found between more and less favorable phase values, with different patterns depending on the specific structure. We use as a study case three RFQs designed and operated at CERN to investigate such correlations.
During operation, the radio-frequency quadrupole (RFQ) of the LINAC4 at CERN is exposed to high electric fields, which can lead to vacuum breakdown. It is also subject to beam loss, which can cause ...surface modification, including blistering, which can result in reduced electric field holding and an increased breakdown rate. First, experiments to study the high-voltage conditioning process and electrical breakdown statistics have been conducted using pulsed high-voltage DC systems in order to identify materials with high electric field handling capability and robustness to low-energy irradiation. In this paper, we discuss the results obtained for the different materials tested. To complement these, an investigation of their metallurgical properties using advanced microscopic techniques was done to observe and characterize the different materials and to compare results before and after irradiation and breakdown testing.
In the years 2009–2013 the Large Hadron Collider (LHC) has been operated with the top beam energies of 3.5 and 4 TeV per proton (from 2012) instead of the nominal 7 TeV. The currents in the ...superconducting magnets were reduced accordingly. To date only seventeen beam-induced quenches have occurred; eight of them during specially designed quench tests, the others during injection. There has not been a single beam-induced quench during normal collider operation with stored beam. The conditions, however, are expected to become much more challenging after the long LHC shutdown. The magnets will be operating at near nominal currents, and in the presence of high energy and high intensity beams with a stored energy of up to 362 MJ per beam. In this paper we summarize our efforts to understand the quench levels of LHC superconducting magnets. We describe beam-loss events and dedicated experiments with beam, as well as the simulation methods used to reproduce the observable signals. The simulated energy deposition in the coils is compared to the quench levels predicted by electrothermal models, thus allowing one to validate and improve the models which are used to set beam-dump thresholds on beam-loss monitors for run 2.
The effect of double frequency heating on the performance of the CERN GTS-LHC 14.5 GHz Electron Cyclotron Resonance (ECR) ion source in afterglow mode is reported. The source of the secondary ...microwave frequency was operated both in pulsed and continuous wave (CW) modes within the range of 12–18 GHz. The results demonstrate that the addition of the secondary frequency can significantly impact the extracted beam currents and the temporal stability of the beam during the afterglow discharge. For example, up to a factor of 2.6 increase was achieved for Pb20835+ and a factor of 3.1 for Pb20837+ compared to single frequency afterglow currents. It is shown that these effects are dependent on the choice of the secondary frequency with respect to the primary one and on the temporal synchronization between the two microwave sources. Overall, the results provide new insight into the afterglow discharge supporting the prevailing understanding of the physical processes behind the phenomenon.
The collimation efficiency for Pb82+208 ion beams in the LHC is predicted to be lower than requirements. Nuclear fragmentation and electromagnetic dissociation in the primary collimators create ...fragments with a wide range of Z/A ratios, which are not intercepted by the secondary collimators but lost where the dispersion has grown sufficiently large. In this article we present measurements and simulations of loss patterns generated by a prototype LHC collimator in the CERN SPS. Measurements were performed at two different energies and angles of the collimator. We also compare with proton loss maps and find a qualitative difference between Pb82+208 ions and protons, with the maximum loss rate observed at different places in the ring. This behavior was predicted by simulations and provides a valuable benchmark of our understanding of ion beam losses caused by collimation.
An association between hyperinsulinemia and hypertension has been suggested by epidemiological surveys. To assess whether this association is independent of the presence of other hyperinsulinemic ...states, such as obesity and glucose intolerance, we measured the insulin response to oral glucose in a group of middle-aged moderately obese 144 +/- 4% overweight (mean +/- SEM) patients (n = 18) with essential hypertension (174 +/- 5/104 +/- 2 mm Hg) and normal glucose tolerance. Normotensive subjects (n = 17) with normal glucose tolerance, matched for age and degree of overweight, served as the control group. The mean insulin response to glucose was twice as high in the hypertensive patients (25.8 +/- 0.2 mU/ml X 2 h) as in the normotensive subjects (11.3 +/- 0.2; P less than 0.001), yet the glucose incremental area was 3-fold higher in the former (10.9 +/- 1.0 g/dl X 2 h) than in the latter (3.5 +/- 0.7; P less than 0.001), thus indicating more severe insulin resistance. In the hypertensive group, systolic blood pressure levels were directly correlated with the 2-h plasma insulin values (r = 0.75; P less than 0.001). Furthermore, the 2-h plasma insulin value and the degree of overweight accounted for 65% of the variation in the systolic blood pressure in a multiple regression model (r = 0.81; P less than 0.001). We conclude that in obesity, the occurrence of hypertension marks the presence of additional hyperinsulinemia and insulin resistance, independent of any impairment of glucose tolerance.
Electroweak asymmetries from SLD Bellodi, G
Nuclear physics. Section B, Proceedings supplement,
06/2002, Letnik:
109, Številka:
2
Journal Article
We present a summary of the results on electroweak asymmetries performed by the SLD experiment at the Stanford Linear Collider (SLC). Most of these results are final and are based, unless otherwise ...stated, on the full 1993–1998 data set of approximately 550,000 hadronic decays of
Z
0 bosons, produced with an average electron beam polarization of 73%.
Electroweak measurements with heavy quarks at SLD Bellodi, G.
Nuclear physics. B, Proceedings supplement/Nuclear physics. B, Proceedings supplements,
03/2001, Letnik:
93, Številka:
1
Journal Article
Odprti dostop
The SLD detector collected a sample of 550K hadronic events at the
Z
0 peak from
e
+
e
− collisions at the SLC during the 1993 to 1998 period. Polarized electron beams, a small and stable interaction ...point and the excellent performance of the 3-D CCD vertex detector provide a unique environment for precision electroweak tests of the Standard Model. Improved measurements of heavy quark electroweak parameters are presented here.
The present study assessed the prognostic value of hyperglycemia--a common feature in the early phase of acute myocardial infarction (AMI)--in 330 nondiabetic patients. Seventy-nine known diabetics ...and 10 (3%) unknown diabetics--diagnosed before discharge by stable glycosylated hemoglobin greater than 6.9% and by oral glucose tolerance testing--were excluded. Thirty-three (10%) patients died. The mortality rate was higher in women, in patients with anterior AMI, in older patients (greater than 65 years) and in the presence of heart failure. It was highest in patients with cardiogenic shock (24/36 vs 9/294; p less than 0.0001). Admission plasma glucose was significantly higher in nonsurvivors than in survivors (163 +/- 60 vs 114 +/- 36 mg/dl; p less than 0.0001). Mortality rate increased with increasing admission plasma glucose: 3% in normoglycemic patients (less than or equal to 120 mg/dl) versus 15% in patients with borderline plasma glucose (121 to 180 mg/dl) versus 43% in hyperglycemic patients (greater than 180 mg/dl) (p less than 0.0001). Multiple regression (stepwise) analysis identified cardiogenic shock, infarct site and age as the major determinants of mortality, while admission plasma glucose failed to reach full statistical significance (p = 0.067). Hyperglycemia was related to all 3 of these independent prognostic factors; when age and infarct site were accounted for, hyperglycemia was significantly associated with heart failure only and this association was characterized by a remarkable mortality rate. In nondiabetic patients with AMI, hyperglycemia is a correlate of heart failure and, therefore, an important factor of prognosis.
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