CERN, Geneva
The LHC circulating beam current measurement is provided by 8 current transformers, i.e. 2 DC current transformers (DCCT) and 2 fast beam current transformers (FBCT) per ring. This paper presents the DCCT, designed and built at CERN, including the sensor, the electronics and the front-end instrumentation software. The more challenging requirements are the needed resolution, of the order of 1μA rms at 1s average, and the wide dynamic range of the circulating beam intensity from the pilot bunch (8μA) to the ultimate beam (860mA). Another demanding condition is the high level of reliability and availability requested for the operation and machine protection of this highly complex accelerator. The measurement of the first RF captured beam in ring 2 is close to meet the specifications in term of resolution (1.3μA rms at 1s average) and stability over a period of a few hours (drift less than 3μA). Finally elements intended to be installed in the near future are presented.
PSI, Villigen
For the neutron spallation source SINQ at PSI a novel visual monitor (VIMOS) has been devised to guarantee correct beam conditions, triggered at the occasion of irradiating the delicate liquid metal target during the MEGAPIE project. VIMOS is looking directly for the most relevant parameter: it checks whether any point on the target is hotter than allowed. For this purpose the incandescence of a glowing mesh right in front of the beam entrance window is observed by means of dedicated radiation hard optics and suitable cameras. Starting from the initial goal of reliably detecting beam anomalies in a timely manner the scope of the system has been extended to serve as a standard device for beam monitoring and fine tuning of the settings of the proton beam transport lines. Over the course of the five years of continuous reliable operation of this unique system valuable experience has accumulated, which is employed for steady improvements of the device with respect to endurance in the radiation environment, calibration, maintenance, and price. A summary of the operational experience of VIMOS will be reported as well as steps taken towards further upgrades.
MPI-K, Heidelberg
At the Max-Planck-Institute for Nuclear Physics in Heidelberg a cryogenic electrostatic storage ring (CSR) is under construction, which will be a unique facility for low velocity and in many cases also phase-space cooled ion beams. Among others the cooling and storage of molecular ions in their rotational ground state is planned. To meet this demand the ring must provide a very low level of blackbody radiation and a vacuum in the XHV range (10-15 mbar) which is achieved by cryogenic cooling of the ion beam vacuum enclosure to 2-10K. The beam current will be in the range of 1 nA -1 μA. The resulting low signal strengths together with the cold environment put strong demands on the amplifier electronics. We plan to make use of a resonant amplifying system. Using coils made from high purity copper, we expect quality factors of ~1000. The mechanical design has to provide stability of the alignment against thermal shrinking when switching from room temperature operation to cryogenic operation. A prototype pickup has been built in order to test resonant amplification and the mechanical design with a wire. The amplification principle will be tested in the MPI-K’s Test Storage Ring.
MPI-K, Heidelberg
The cryogenic storage ring CSR is a 35 m circumference electrostatic ring, for molecular- and atomic physics experiments at MPI-K Heidelberg. It will operate at pressures down to 10-13 mbar and temperatures <10 K. The beam intensities will be in the range of 1 nA to 1 uA, particle energies are between 20 - 300 keV. An intensity measurement for coasting beams below 1 uA requires magnetic field detection devices, which are much more sensitive than existing DC beam transformers. The highest sensitivity is currently achieved with DC SQUID based cryogenic current comparators (CCCs). At GSI, a prototype of such a CCC was successfully tested in the mid 90’s, reaching a resolution of ~250 pA/Hz1/2. Recently a resolution of 40 pA/Hz1/2 could be achieved under laboratory conditions at Jena University, however, the CCC sensitivity in an accelerator environment depends strongly on efficient shielding and mechanical decoupling. We describe our work on adaptation and improvement of the CCC beam transformer for the CSR. Furthermore a concept for an ionisation profile monitor is discussed, which in addition to low beam intensities, has to cope with extremely low gas densities at 10-13 mbar.
