Tests of A Roman Pot Prototype for the Totem Experiment

Abstract

The TOTEM collaboration has developed and tested the first prototype of its Roman Pots to be operated in the LHC. TOTEM Roman Pots contain stacks of silicon detectors with strips oriented in two orthogonal directions. To measure proton scattering angles of a few microradians, the detectors will approach the beam centre to a distance of 10 σ + 0.5 mm (= 1.3 mm). Dead space near the detector edge is minimised by using two novel "edgeless" detector technologies. The silicon detectors are used both for precise track reconstruction and for triggering. The first full-sized prototypes of both detector technologies as well as their read-out electronics have been developed, built and operated. The tests took place in the proton beam-line of the SPS accelerator ring. In addition, the pot's shielding against electromagnetic interference and the longitudinal beam coupling impedance have been measured with the wire method. ROMAN POTS FOR THE TOTEM EXPERIMENT AT LHCThe LHC experiment TOTEM [1] is designed for measuring the elastic pp scattering cross-section, the total pp cross-section and diffractive processes. These physics objectives require the detection of leading protons with scattering angles of a few µrad, which is accomplished with a Roman Pot ("RP") system having stations at 147 m and 220 m from the interaction point 5 where CMS will be located. Each station is composed of two RP units separated by 2.5 -4 m depending on beam equipment integration constraints. Each RP unit consists of a vacuum chamber equipped with two vertical insertions (top and bottom) and a horizontal one. Each insertion ("pot") contains a package of 10 silicon detectors in a secondary vacuum. The pots can be moved into the primary vacuum of the machine through vacuum bellows. In order to minimize the distance of the detectors from the beam, and to minimize multiple scattering, the wall thickness of the pot is locally reduced to a thin window foil (140 -210 µm).The low impedance budget of the LHC machine (broadband longitudinal impedance limit Z/n ≈ 0.1 Ω) imposes a tight limit on the RPs' beam coupling impedance. Because of the beam's bunch structure and its high intensity, the pick-up noise on the detector electronics caused by electromagnetic leakage is a potential concern and needs to be studied and minimised. THE ROMAN POT PROTOTYPE IN THE SPS BEAMDuring the summer 2004 the TOTEM collaboration has performed tests on a prototype unit made of 2 vertical RPs. The unit has been installed in the LSS5 section of the SPS accelerator at CERN. The motors moving the pots towards the beam, the electronics of the detectors and the cooling system stabilising the temperature of the detectors inside the pots were operated remotely from a temporary control room in a surface building. The upper and lower pots contained each a set of 8 silicon strip detectors with 66 µm pitch, built in two novel technologies allowing for efficiency up to the physical edge [1]. Six of them were read out with analogue APV25 chips and 2 with digital VFAT chips delivering...

Final size planar edgeless silicon detectors for the TOTEM experiment

“…Three different bunch structures were tested in the SPS accelerator: 1 single bunch in the accelerator ring, 4 bunches equally spaced, and 4 equally spaced trains of 4 bunches of 8 × 10 10 270 GeV protons with a revolution period of 23 μs [8].…”

Applications of the tensor pomeron model to exclusive central diffractive meson production

“…Several experimental groups, e.g. COMPASS [26], STAR [27], CDF [28], ALICE [29], ATLAS+ALFA [30], and CMS+TOTEM [31] have potential to make very significant contributions to this program aimed at understanding the spin structure of the soft pomeron.…”

The TOTEM Experiment at the CERN Large Hadron Collider

“…The pot together with the bellow creates a resonant RF cavity for the beam running along the axis of the Roman Pot. Measurements of the beam coupling impedance have been performed in the lab where a metallic wire was strung through the RP [11]. A vector network analyser generated current pulses to simulate the beam and measured the complex transmission coefficient.…”

“…The full operation of a Roman Pot unit prototype, consisting of a vacuum chamber equipped with two vertical insertions, was tested in a coasting beam experiment in the beamline of the SPS accelerator at CERN [11]. Each of the two insertions hosted four pairs of edgeless silicon detectors mounted back to back.…”