CERN, Geneva
The UA9 experiment was installed in the CERN-SPS in March '09 in view of investigating crystal assisted collimation in coasting mode. Inside a vacuum vessel, two 2 mm long silicon crystals, bent by about 150 microradians are mounted on accurate goniometers, and a small 10mm long tungsten target is used to compare the effect of crystals with that of a standard scatterer. A moveable 60 cm long block of tungsten is located downstream at about 90 degrees phase advance to intercept the deflected beam. Scintillators, gas GEMs and beam loss monitors measure nuclear loss rates induced by the interaction of the halo beam in the crystal itself. A Roman pot is installed in the path of the deflected particles in between the crystal and the collimator, equipped with a Medipix detector to reconstruct the transverse spot of the impinging beam. Finally UA9 takes advantage of an LHC-collimator prototype installed close to the Roman pot to help in setting the beam conditions and to reveal in a destructive manner the deflected beam shape. This paper describes in details the hardware installed, and the procedures developed to set-up and detect the channeling conditions.
INFN-Roma, Roma
CERN, Geneva
JINR, Dubna, Moscow Region
We present a detailed analysis of the beam loss data collected at the SPS during the 2009 machine developments devoted to test crystal collimation. Scintillator counters and Gas electron multiplier detectors were installed in special points to detect the effect of inelastic interaction of protons with the crystals in various orientation with respect to the beam. Clear correlations of the counting rates with the crystal positions and orientation were detected during the data-taking and were crucial to put the crystal in optimal channeling position. For one of the crystal the pattern of losses showed evidence of several planar and axial channeling conditions.
CERN, Geneva
IHEP Protvino, Protvino, Moscow Region
TRIUMF, Vancouver
The LHC has two dedicated cleaning insertions: IR3 for momentum cleaning and IR7 for betatron cleaning. The collimation system has been specified and built with tight mechanical tolerances (e.g. jaw flatness ~ 40 μm) and is designed to achieve a high accuracy and reproducibility of the jaw positions. The practically achievable cleaning efficiency of the present Phase-I system depends on the precision of the jaw centering around the beam, the accuracy of the gap size and the jaw parallelism against the beam. The reproducibility and stability of the system is important to avoid the frequent repetition of beam based alignment which is currently a lengthy procedure. Within this paper we describe the method used for the beam based alignment of the LHC collimation system, its achieved accuracy and stability and its performance at 450GeV.
CERN, Geneva
The high charge PHIN photo injector is studied at CERN as an electron source for the CLIC Test Facility (CTF3) drive beam as an alternative to the present thermionic gun. The objective of PHIN is to demonstrate the feasibility of a laser-based electron source for CLIC. The photo injector operates with a 2.5 cell, 3 GHz RF gun using a Cs2Te photocathode illuminated by UV laser pulses generated by amplifying and frequency quadrupling the signal from a Nd:YLF oscillator running at 1.5GHz. The challenge is to generate a beam structure of 1908μbunches with 2.33nC perμbunch at 1.5GHz leading to a high integrated train charge of 4446nC and nominal beam energy of 5.5MeV with current stability below 1%. In the present test stand, a segmented beam dump has been implemented allowing a time resolved measurement of the energy and energy spread of the electron beam. In this paper we report and discuss the measured transverse and longitudinal beam parameters for both the full and time gated train of bunches, and the obtained photocathode quantum efficiency. Laser pointing and amplitude stability results are discussed taking into account correlation between laser and electron beam.
CERN, Geneva
JINR, Dubna, Moscow Region
A number of tests were performed by the UA9 Collaboration* in the North area of the SPS in view of investigating crystal-particles interactions for future application in hadron colliders. The rate of nuclear reactions was measured with 400 GeV proton beams directed into a silicon bent crystal. In this way the background induced by the crystal itself either in amorphous or in channeling orientation was revealed. The results provide fundamental information to put in perspective the use of silicon crystals to assist halo collimation in hadron colliders, whilst minimizing the induced loss. Crystals made of Germanium were also investigated in view of the expected increase of the collimation efficiency respect to silicon. Finally, crystals were tested in axial orientation and with incoming particles of negative charge. The collected results are presented in details.
* http://greybook.cern.ch/programmes/experiments/UA9.html