Presented at the ASC'98 -Applied Superconductivity Conference, Palm Spring, CA, USA, September 1998 We describe the systems for AC loss and magnetic field measurements developed for the LHC superconducting magnets. AC loss measurements are performed using an electric method, while field measurements are performed using either fixed pick-ups or rotating coils. We present results obtained on 1-m long model dipoles, and compare the results of the different methods in terms of average inter-strand resistance. Abstract  We describe the systems for AC loss and magnetic field measurements developed for the LHC superconducting magnets. AC loss measurements are performed using an electric method, while field measurements are performed using either fixed pick-ups or rotating coils. We present results obtained on 1-m long model dipoles, and compare the results of the different methods in terms of average interstrand resistance. Measurement of AC Loss and Magnetic

Abs#mct-Wc have nicusured the magnetic ficld at rnom te~~lperatrirc and at '1.3 K on more than twenty, 1-m long, single aperturc LHC supercanducting dipole modcls. The mugnets rccalurc cithcr : I 5-bl(ick coil gconiclry or the baseline 6-black gcniiictry foreseen for ilic LUC. Cnmptlrisrm I. INTRODUCTrONThe main bcnding dipoles for the Large Hadron Collider (LIIC) must satisfy strict requiIemenis on the magnetic field qunlity in order to achieve the expected bcnni luminosity at collision energy. This translates to tight manufacturing tolcranccs and. requires that all magnets arc systeinatically tested during production and at the reception at CERN [ I ] . The LI-IC dipoles nre manurtcturcd assembling four supcrconducting coils in a support structurc h m c d by laminated collars. Thc cdlared coil assembly is coinplctcd by lati iron yoke and n leak-tight shrinking cylinder of stainless steel. One of h e key paramcters to he controlled during production i s the gcomctry of the coils after assembly in the collars, and in particular thc azinwthal length m of the coil laycrs. This is defined as the length of the aIc hetween the coil inidplone and the surface of thc polc (see Fig. I). This pclraineter dcpcnds mainly on the pole shims between tlic coil and the collars and on the collar deformation during asscmbly. Studies on the magnets at HkliA [2] Here we extend the analysis to a larger number of magnets, featuring different coil gcnmetries and collar materials. As done in 141 we focus on the first allowed harmonics. A good control of the allowed Iiarmonics is very important BS they will produce systematic effects i n the LHC. SERIES OF MAGNETS TESTEDThe series of short models that are being manufactured at CERN within the frame of the R&D program for the LHC main dipoles [5] providcs an ideal tcst-bed for correlation studies. A total of 21, 1-m long, single nperture magnets (the MBSMS series) and S twin aperture magnets (the MBSMT series) havc been produced so far. The main purpose of the short model program is tn cxplmc the influcnce of manuhcturing parametas on the quench perFormance and training behaviour. For this reason the coils of these magnets have bccn collared adjusting .the pole shims to achieve coil compressions spanning a wide range, approximately 20 to 70 MPa after cool-down. Consequently the azimuttial length of the coils after collaring varied from magnet to magnet.This has given a good opportunity to study the dependence of the Cield harmonics on the coil sizc. The magnets considered here are the single aperime models MElSMS4 to MBSMS23 that we group in three families: 0 magnets MBSMS4 through MBSMS13 constitute the first family. They are built using coils with 5 blocks of cables per quadrant (see Fig. 2). assembled into Ai-alloy collars; the coil cross section has been modified as a result of optimization studies that have taken place during the R 8 D program. Magnets MBSMS 15 through MBSMS23 feature the new optimized coil, with 6-cable blocks per quadrant (see again Fig. 2). About half of the...

The field quality of 10 m long LHC dipole models has been measured with short rotating coils to explore its dependence on time and position. Multipoles exhibit a longitudinal periodic variation, with period equal to the twist pitch length. This periodicity is shown here to have at least two components with very different time constants. The amplitude of the component with the shorter time constant, in the range of 100 to 300 s, depends on position and time. Larger amplitudes are measured at early times after a ramp and close to regions with incomplete cable transposition with respect to the non-uniform external field change. As the multipoles periodicity is due to current imbalance in the cables, we attribute the short time scale variations to the presence of space and time decaying boundary induced coupling currents (BICC's) in the cable. An estimate of their value is given.

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Extensive power tests of the LHC dipole magnets required the development of new techniques to study the quench and training behaviour. Magnetic measurements of short and long model dipoles have allowed to understand and quantify the time dependent behaviour of the field quality during the current flat top needed during beam injection. The experience gained is employed for the design of the measuring tools presently under construction for the series measurements of the LHC dipole magnets. The economically important issue of how many magnets have to be measured in the superconducting state is addressed in view of the field quality required for the performance of the LHC.