CLIC Post-Collision Diagnostics

We discuss non-conventional diagnostics for the beam line between the interaction point and the beam dump of CLIC. The main focus is put on the beamstrahlung monitor, but also other systems such as a coherent pair monitor, tail monitors, and interferometric beam dump thermometer are considered

Effects of rf breakdown on the beam in the Compact Linear Collider prototype accelerator structure

Understanding the effects of RF breakdown in high-gradient accelerator structures on the accelerated beam is an extremely relevant aspect in the development of the Compact Linear Collider (CLIC) and is one of the main issues addressed at the Two-beam Test Stand at the CLIC Test Facility 3 at CERN. During a RF breakdown large electro-magnetic fields are generated and produce parasitic magnetic fields which interact with the accelerated beam affecting its orbit and energy. We discuss here measurements of such effects observed on an electron beam accelerated in a CLIC prototype structure. Measurements of the trajectory of bunch-trains on a nanosecond time-scale showed fast changes in correspondence of breakdown which we compare with measurements of the relative beam spots on a scintillating screen. We identify different breakdown scenarios for which we offer an explanation based also on measurements of the power at the input and output ports of the accelerator structure. Finally we present the distribution of the magnitude of the observed changes in the beam orbit and we discuss its correlation with RF power and breakdown location in the accelerator structure.Comment: 10 pages, 8 figures. We replace the previous version of the article with this one, in which we extend our discussion on the experimental set-up and on the interpretation of our measurements, on the basis of the inputs received during the review process for publication on Phys. Rev. Special Topics - Accelerators and Beams. The essence of our conclusions remain unchange

Conceptual Design of a Vacuum Window at the Exit of the CLIC Post-Collision Line

In this paper, we present a design of the window between the accelerator vacuum and the beam dump at the end of the CLIC post-collision line. We propose to use a thick (1.5 cm) layer of carbon-carbon composite, with a thin (0.2 mm) leak-tight foil. The energy deposition and the temperature increase due to the beam impact, as well as the stress levels in the window, are estimated and we show that Aluminium is the most suitable material for the thin foil. At the beam impact, the temperature increase after the passage of a CLIC bunch train is of the order of 1 K and the subsequent (cyclic) thermal stress remains smaller than 1 MPa. As for the (static) mechanical stress, it is about 4 MPa in the beam impact region, and it goes up to 15 MPa near the lateral edges of the window. Still, these constraints are more relaxed than for the LHC dump window

Controlling Self-Bunching in Ion-Storage Rings

Abstract. We discuss a feedback system to cure self-bunching instabilities in high intensity storage rings that operate with coasting beams. Such a system consists of a high-bandwidth pickup, a very fast digital FIR filter based on programmable logic chips, and a kicker magnet. We discuss design parameters and limitations of such a system under realistic constraints such as digitization in time and signal amplitude

Enhancement of the Curie temperature in GaMnAs/InGaMnAs superlattices

We report on an enhancement of the Curie temperature in GaMnAs/InGaMnAs superlattices grown by low-temperature molecular beam epitaxy, which is due to thin InGaMnAs or InGaAs films embedded into the GaMnAs layers. The pronounced increase of the Curie temperature is strongly correlated to the In concentration in the embedded layers. Curie temperatures up to 110 K are observed in such structures compared to 60 K in GaMnAs single layers grown under the same conditions. A further increase in T$_C$ up to 130 K can be achieved using post-growth annealing at temperatures near the growth temperature. Pronounced thickness fringes in the high resolution X-ray diffraction spectra indicate good crystalline quality and sharp interfaces in the structures.Comment: 4 pages, 4 figures, submitted to Appl. Phys. Let

Characterization of deep impurities in semiconductors by terahertz tunneling ionization

Tunneling ionization in high frequency fields as well as in static fields is suggested as a method for the characterization of deep impurities in semiconductors. It is shown that an analysis of the field and temperature dependences of the ionization probability allows to obtain defect parameters like the charge of the impurity, tunneling times, the Huang–Rhys parameter, the difference between optical and thermal binding energy, and the basic structure of the defect adiabatic potentials. Compared to static fields, high frequency electric fields in the terahertz-range offer various advantages, as they can be applied contactlessly and homogeneously even to bulk samples using the intense radiation of a high power pulsed far-infrared laser. Furthermore, impurity ionization with terahertz radiation can be detected as photoconductive signal with a very high sensitivity in a wide range of electric field strengths

FAST COOLING TIME MEASUREMENTS IN CELSIUS USING A THIRD GENERATION MOBILE PHONE SIGNAL PROCESSING DEVICE

Abstract We present hardware to measure longitudinal cooling times of electron cooled ion beams in CELSIUS. The measurements are performed by an a fast ADC and a AD6620 receiver signal processor evaluation board that we interfaced to a Linux PC. The specialized signal processors are developed for third generation mobile phone systems and consist of several digital mixing, filtering, and downsampling stages. We describe the measurements and the hardware that allows us to record and analyze high resolution spectra at very high update rates