Paolo Michelato

A simple apparatus for measuring the energy spectra of mass-selected light particles, using the power law technique

Abstract The present paper describes a two-module analog device for particle identification and spectra acquisition, using the power law technique with a counter telescope.

A Monte-Carlo simulation of low energy photoelectron scattering in Cs2Te

The quantitative description of low kinetic energy photoelectron emission in semiconductors is still an open question. In this article a model is developed to simulate the photoexcitation and transport of low kinetic energy electrons in Cs2Te. The statistical extension of the model, by Monte Carlo trajectory calculations, gives photon energy dependent quantum yields in agreement with experimental data. This is regarded as evidence that for near threshold photoemission in Cs2Te the dominant scattering mechanism is electron-phonon, while the mean energy scattering energy loss is 5 meV and the electron mean free path is 3 nm. The spatial distribution and the time response (0.4 ps) of the photoemitted electrons are estimated.

DAG, a digital-to-analog generator of coincident pulse pairs

Abstract This paper discusses the simulation of analog signals from a nuclear radiation detector telescope. This goal is reached by means of a generator that reads 39 pairs of digital data punched on a paper tape and presents, as output, the corresponding analog pulses at a frequency variable up to 60 kHz.

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.

CARE activities on superconducting RF cavities at INFN Milano

The SC RF group at INFN Milano-LASA is involved both in the TESLA/TTF collaboration and in the research and design activity on superconducting cavities for proton accelerators. Among these activities, some are supported by the European community within the CARE project. In the framework of the JRASRF collaboration we are developing a coaxial blade tuner for ILC (International Linear Collider) cavities, integrated with piezoelectric actuators for the compensation of the Lorenz force detuning and microphonics perturbation. Another activity, regarding the improved component design on SC technology, based on the information retrieving about the status of art on ancillaries and experience of various laboratories involved in SCRF, has started in our laboratory. Finally, in the framework of the HIPPI collaboration, we are testing two low beta superconducting cavities, built for the Italian TRASCO project, to verify the possibility to use them for pulsed operation. All these activities will be described here, together with the main results and the future perspectives.

Use of non evaporable getter pumps to ensure long term performances of high quantum efficiency photocathodes

High quantum efficiency photocathodes are routinely used as laser triggered emitters in the advanced high brightness electron sources based on radio frequency guns. The sensitivity of “semiconductor” type photocathodes to vacuum levels and gas composition requires special care during preparation and handling. This paper will discuss the results obtained using a novel pumping approach based on coupling a 20 l s−1 sputter ion getter pump with a CapaciTorr® D100 non evaporable getter (NEG) pump. A pressure of 8⋅10−8 Pa was achieved using only a sputter ion pump after a 6 day bake-out. With the addition of a NEG pump, a pressure of 2⋅10−9 Pa was achieved after a 2 day bake-out. These pressure values were maintained without power due to the ability of the NEG to pump gases by chemical reaction. Long term monitoring of cathodes quantum efficiencies was also carried out at different photon wavelengths for more than two years, showing no degradation of the photoemissive film properties.

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.

High pressure rinsing system comparison

High pressure rinsing (HPR) is a key process for the surface preparation of high field superconducting cavities. A portable apparatus for the water jet characterization, based on the transferred momentum between the water jet and a load cell, has been used in different laboratories. This apparatus allows collecting quantitative parameters that characterize the HPR water jet. In this paper, we present a quantitative comparison of the different water jets produced by various nozzles routinely used in different laboratories for the HPR process.

First energy spectra obtained with a time-of-flight (TOF) electron spectrometer on Cs/sub 2/Te photocathodes

The first electron energy spectra obtained from a Cs/sub 2/Te photocathode using a time-of-flight (TOF) spectrometer are presented and discussed in this paper. The high-resolution angle resolved TOF electron spectrometer has been developed at INFN Milano-LASA (theoretical resolution: 2 meV at 5 eV). The system has been designed for the investigation of the electron beam thermal emittance that is a key parameter for future generation FEL based high brilliance photon sources. The excitation light source is a short pulse solid-state Nd:glass laser (4/sup th/ harmonic, /spl tau/=400 fs, /spl lambda/=264 nm). In this paper the spectrometer is presented together with first measurements on different metals and Cs/sub 2/Te.

NON-LINEARITY OBSERVED IN THE DIRECT SUB-PS PHOTOEMISSION REGIME IN MO

The total charge emitted from a polycrystalline Mo surface by 500 fs-264 nm laser pulses has been measured. Though a one-photon photoelectric effect is expected, a non-linear increase of the photoelectric yield was observed as a function of laser peak intensity, confirming earlier observations on Au, W and Zr. The threshold intensity for this non-linearity is 2 between 0.1 and 0.2 GW/ cm . The linear and non-linear regimes were clearly discerned in the experimental data. The non-equilibrium heating of the conduction electrons is considered as the cause of the observed non-linear behaviour.