Paolo Pierini

Niobium cavity development for the high-energy linac of the Rare Isotope Accelerator

This paper will cover the design of a 6-cell /spl beta//sub g/ = 0.47 cavity for the Rare Isotope Accelerator, as well as the fabrication and RF testing of single-cell prototypes. Single-cell prototypes were chosen as a first step, as they provide a quick and inexpensive way to find out whether the desired field level and Q can be reached, and to check for problems with multipacting. An accelerating gradient of 8 MV/m was chosen as a goal for the /spl beta//sub g/ = 0.47 cavity.

CONSTRUCTION, COMMISSIONING AND CRYOGENIC PERFORMANCES OF THE FIRST TESLA TEST FACILITY (TTF) CRYOMODULE.

A principal goal of the ongoing TESLA superconducting linac project is the production of affordable cryostats that still meet stringent requirements for alignment, vibration and heat leak. Each cryostat contains 8 superconducting RF cavities cooled to 1.8 K, a quadrupole magnet package cooled to 4.5 K, thermal shields cooled to 70 K and 4.5 K, active and passive magnetic shielding, cryogenic service pipes and all associated instrumentation. The axes of the 8 cavities must be aligned to the ideal beam axis to within ± 0.5 mm and those of the quadrupoles to within ± 0.1 mm. Additionally, the vertical mid plane of the quadrupole package must be aligned to the vertical direction to ± 0.1 mrad. These alignments must remain fixed after cool down and during operation. The cryostat must be designed so that there are no resonant vibration modes near the 10 Hz operating frequency of the accelerator. Although dynamic loads associated with the operation of the RF and the beam dominate the heat load, reasonable efforts to reduce the static heat leak into the cryostat are necessary.

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.

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.

A multigrid-based beam dynamics code for high current proton linacs

A beam dynamics code has been developed for the design assessment of a superconducting high current proton linac for the ENEA/INFN TRASCO Project (intended for nuclear waste transmutation in a subcritical reactor). The code deals with the dynamics of a moderate energy (above tens of MeV) and high current proton beam in a beamline composed of elliptical superconducting cavities and quadrupoles. A 3D Poisson solver based on multigrid techniques has been chosen for the space charge calculations. The simulation results for the reference linac design, with particular care to emittance growth and halo generation, are reported.

Design of the Thermal Shields for the New Improved Version of the TESLA Test Facility (TTF) Cryostat

One of the principal goals of the ongoing TTF project is to produce prototype low cost and reliable cryomodules meeting the stringent requirements for TESLA. The first cryomodule was assembled and tested at DESY. The experience gained during the design and the commissioning suggested new solutions to improving the technical design.

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.

COOLDOWN SYMULATIONS FOR TESLA TEST FACILITY (TTF) CRYOSTATS

The first TTF cryostat has been tested in June 1997 and monitored to study the deformations produced during the cool-down procedure. A numerical study of the thermal shields of the cryostat has been carried out with finite element analysis simulations. The results allowed to understand the effect of the cooldown on the TTF cryostat.