5102800
Fermilab electron cooling project: field measurements in the cooling section solenoid
To provide the maximum possible cooling rate for the Recycler Electron Cooling (REC), the cooling section has to be immersed into a high-quality longitudinal magnetic field. Namely, the solenoidal field of 50-150 G should have an integral of the transverse component below 1 G-cm over the whole 20-m cooling section. The transverse field components are measured by a dedicated compass-based sensor, which has been designed and manufactured at Budker INP, Novosibirsk. The paper describes results of the field measurements performed on the cooling section solenoid prototypes as well as the design and the calibration procedure of the sensor.
37574495
Fermilab Electron Cooling project: engineering aspects of cooling section
The Fermilab Electron Cooling project involves interacting a 4.3 MeV, 0.5 A DC electron beam with 8.9 GeV/c antiprotons in the FNAL Recycler Ring. This interaction occurs through a 20-meter long cooling section consisting of 10 solenoid modules. This cooling process would lead to an increase in the Tevatron collider luminosity needed to support the Run IIb parameters. There are several important engineering aspects of this cooling section including: solenoid design, vacuum system design, magnetic shielding, support system, and alignment methods. Details of the engineering issues related to each of these areas will be discussed.
59152543
Successful MeV-range electron beam recirculation
Electron cooling [1] of heavy particle beams with energies of some GeV per nucleon requires high-quality dc electron beams of MeV energies and ampere range currents. The enormous electron beam power dictates that the beam current be returned to the high voltage (HV) terminal which provides the accelerating potential. In this paper we describe the successful recirculation of a dc electron beam at energies 1-1.4 MeV and currents in excess of 300 mA with typical relative losses of 1-2·10. Currents of 200 mA were maintained for the periods of one hour (typical) without a single breakdown, 300 mA for 20 minutes.
55310480
A 1500 MHz niobium cavity made of electropolished half-cells
A 1500 MHz niobium cavity has been fabricated with two half-cells, which are pre-electropolished with a very simple and compact system. In this paper, we present half-cell electropolishing, cavity fabrication and first test results.
118934519
A pathway to SRF niobium cavities processing simplification and quality factor improvement via elimination of the post-annealing chemical treatment
We investigate the effect of high temperature treatments followed by only high-pressure water rinse (HPR) of superconducting radio frequency (SRF) niobium cavities. The objective is to provide a cost effective alternative to the typical cavity processing sequence, by eliminating the material removal step post furnace treatment while preserving or improving the RF performance. The studies have been conducted in the temperature range 800-1000C for different conditions of the starting substrate: large grain and fine grain, electro-polished (EP) and centrifugal barrel polished (CBP) to mirror finish. An interesting effect of the grain size on the performances is found. Cavity results and samples characterization show that furnace contaminants cause poor cavity performance, and a practical solution is found to prevent surface contamination. Extraordinary values of residual resistances ~ 1 nOhm and below are then consistently achieved for the contamination-free cavities. These results lead to a more cost-effective processing and improved RF performance, and, in conjunction with CBP, open a potential pathway to acid-free processing.
67812767
Improved Performance of JLab 7-Cell Cavities by Electropolishing
The great majority of experience in niobium SRF cavity processing at Jefferson Lab is with BCP etching. This has been used on CEBAF cavities and others totalling over 600 in number. With improved process quality control, field emission is now largely controlled and other factors limit performance. All of the prototype cavities developed for the 12 GeV upgrade, although meeting minimum requirements, have demonstrated a Q-drop in the 17?23 MV/m range that is not remedied by 120 C bake. Most of these cavities received >250 micron removal by BCP etch. Two of these cavities have been electropolished using the protocol under development within ILC R&D activities. The first such cavity was transformed from Q = 3×109 at 17 MV/m to quench from 1×1010 at 35 MV/m. The details of this and subsequent electropolished JLab 7-cell cavities will be reported.
5587472
Role of mesons in the electromagnetic form factors of the nucleon
The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q 2 behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q 2 or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as “charge distributions,” nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment‐theory comparisons.