• M.C.L. Buzio, P. Arpaia, O. Dunkel, D. Giloteaux, G. Golluccio, A.M. Lombardi, F. Mateo Jimenez, S. Ramberger
  CERN, Geneva

Linac 4 is the injector upgrade currently under construction at CERN to improve luminosity and reliability for the whole accelerator chain. This machine will include about 120 high-gradient, 20 mm aperture Halbach-array permanent quadrupoles (PMQ) housed in the Drift Tube tanks, as well as about 80 electromagnetic quadrupoles (EMQ) with power cycles approx. 2 ms long. This paper is concerned with the magnetic measurements carried out at CERN on the first batch of PMQ, including several prototypes from different manufacturers, as well as those done on several spare Linac 2 EMQs reused in Linac 4's 3 MeV test stand. We first describe the test setup, focusing our attention on a prototype test bench based on technology developed for the LHC and able to carry out high-precision harmonic measurements in both continuously-rotating and stepping-coil mode (FAME*). Next we present the results obtained in terms of integral field strength and quality, with special emphasis on the analysis of very fast eddy current transients in the EMQs. Finally, we discuss the expected impact of these findings on the operation of the machine.

* N. R. Brooks et al, "Estimation Of Mechanical Vibration Of The LHC Fast Magnetic Measurement System", IEEE Transactions on Applied Superconductivity, vol. 18, No. 2 , 2008.

• M.C.L. Buzio, L. Bottura, O. Dunkel, L. Fiscarelli, J. Garcia Perez, G. Montenero, E. Todesco, L. Walckiers
  CERN, Geneva
• P. Arpaia
  U. Sannio, Benevento

One of the main requirements for the operation of the Large Hadron Collider at CERN is the correction of the dynamic multipole errors produced in the main magnets*. In particular, integrated sextupole errors in the main dipoles must be kept well below 0.1 units to ensure acceptable chromaticity. The feed-forward control of the LHC is based on the Field Description for the LHC (FiDel), a semi-empirical mathematical model capable of forecasting the magnet's behaviour in order to generate suitable corrector current waveforms. Measurement campaigns were recently undertaken to validate the model making use of a novel fast rotating-coil magnetic measurement system (FAME)**, able to detect superconductor decay and snapback transients with unprecedented accuracy and temporal resolution. In this paper we discuss the test setup and the results obtained both on the test bench and in the actual operation of the accelerator.

* P. Xydi et al, "A Demonstration Experiment For The Forecast Of Magnetic Field … ", EPAC 2008
** N. R. Brooks et al, "Estimation Of Mechanical Vibration Of …", IEEE TAS 2008