Carlo Pagani

Flow of a Rarefied Gas past an Axisymmetric Body. II. Case of a Sphere

The drag exerted by the flow on a sphere is explicitly calculated by using the relation between the drag and a certain functional. A comparison of the results with the experimental data of Millikan gives excellent agreement.

Comparison of kinetic theory analyses of linearized heat transfer between parallel plates

Abstract Linearized heat transfer between two parallel plates is considered for inverse Knudsen numbers ranging from 0 to 10. The Bhatnagar, Gross and Krook model is used and transformed into a couple of integral equations for density and temperature. These equations are solved numerically. Besides a variational calculation of the solution is made by introducing simple trial functions in a suitable variational principle. The results obtained for the heat flux through the two methods are compared and found in strict agreement (discrepancy less than 0·5 per cent). For the limiting case of the half-space problem, the temperature jump coefficient is evaluated both by a numerical and a variational procedure. The latter gives a value differing by about 0·5 per cent from the value given by the former procedure and of about 1 per cent from the value previously obtained by Welander. Comparisons are made with the results of the non-linear analysis of Willis, the linearized four moment solution and Takaos experimental data.

Influence of the accommodation coefficient on the heat transfer in a rarefied gas

Abstract Linearized heat transfer between parallel plates and concentric cylinders is considered for inverse Knudsen numbers ranging from 0 to 10, and arbitrary accommodation coefficients. The Bhatnagar, Gross and Krook model is used and transformed into a system of integral equations. These equations are solved by a variational method, previously applied to simpler situations. Comparisons are made with experimental results and previously available calculations.

Study of thermal radiation shields for the ILC cryomodule

The main linacs of the International Linear Collider are composed of 1824 cryomodules. As part of the R&D on the cryomodule, simplifications of the design were considered to reduce the construction and installation costs, including the possibility of removing a portion of the 5 K thermal shield. For this investigation the heat load measurements of a 6 meter cryomodule with and without the 5 K shield were performed, and used to determine emissivity coefficients. A thermal model of a full cryomodule was then created, and the heat loads of the cryomodule with the full set of the 5 K shield and without the lower 5 K shield were calculated with these parameters. By using a modified cooling scheme for the high temperature thermal shielding, we showed that the heat loads at 2 K between two models are substantially equivalent, and indeed, the thermal model without the 5 K lower shield requires 2% less work from the refrigerator.

Improved design of the ILC blade-tuner for large scale production

The ILC superconducting linacs ask for the use of a compact and cost effective tuner design with no interference with the cavity end group area. The integration of the piezo-assisted fast tuning option made the Blade-Tuner, successfully tested at DESY on the superstructures, the most viable candidate to be included into the ILC BCD. In the perspective of large scale production and on the basis of the experience acquired so far, two alternative prototypes have been recently designed and built. They mainly differ for the materials adopted (titanium or stainless steel) and have been optimized to minimize material and construction cost, while fulfilling the reviewed performances required for the high gradient cavity operation up to 35 MV/m or even higher. In this paper we discuss the rationales that brought us to the current solutions, together with a critical comparison of the two systems behavior and cost.

Improvement of the Blade Tuner Design for Superconducting RF Cavities

As of today, no complete technological solution exists for a cold tuning system fulfilling the requirements envisaged for the International Linear Collider, based on the superconducting RF technology. We present here the design improvements for the blade tuner, a coaxial device, which can provide both the slow structure tuning and the fast tuning capabilities needed for Lorentz Force Detuning (LFD) compensation and microphonics stabilization (by means of the integration with a piezoelectric system). The system has been originally built by INFN and installed and tested at DESY on the superstructures, since it is located around the cavity helium vessel and does not require longitudinal clearance. Its design here is parametrically reviewed in terms of the requirements for higher accelerating fields and of the mechanical integration with a piezoelectric based system for the LFD and microphonics compensation.

High QE photocathodes performance during operation at FLASH / PITZ photoinjectors

Since 1998, the DESY photoinjectors at FLASH and PITZ routinely use high quantum efficiency (QE) photocathodes produced at LASA (INFN-Milano). To further understand the photocathode behavior during beam operation, photocathode QE measurements have been performed at different operating conditions in both photoinjectors. The analysis of these measurements will be used to improve the photocathode preparation procedures and deepen our understanding of the photocathode properties. An important goal is to further increase their lifetime and to preserve a high beam quality during the operation in the RF gun of the photoinjector.

Overview of ILC

I will review the history of the linear colliders since the original Tigner proposal of 1965, passing through the great success of the TESLA Collaboration and TTF, up to the current Global Design Effort, aiming at its realization.

The VHF-Gun, the LBNL High-Brightness Electron Photo-Injector for MHz-Class Repetition-Rate Applications

Science needs are pushing the development of MHz-class repetition-rate linac-based facilities generating high-brightness electron beams. The successful lower repetition-rate RF gun schemes cannot be scaled up to MHz rates. At LBNL, we developed the VHF-Gun, a room-temperature RF gun designed for CW operation and high-brightness beam performance.

Update on Third Harmonic XFEL Activities at INFN LASA

After the successful installation and beam operation of the first batch of 3.9 GHz cavities into the XFEL Third Harmonic Injector Module, ten more cavities have been tested and delivered to DESY to be assembled into a spare cryomodule. In this paper, we report on the activities related to the cavities fabrication, treatment and vertical testing at INFN LASA.