SIMPLE CHARACTERIZATION METHOD OF SMALL HIGH GRADIENT PERMANENT MAGNET QUADRUPOLES Concetta Ronsivalle,Luigi Picardi, Monia Vadrucci (ENEA C.R. Frascati, Frascati (Roma)) Fabrizio Ambrosini (“La Sapienza” University, Roma) Abstract The application of quadrupoles with high or ultra-high gradient and small apertures requires a precise control over harmonic components of the field. A simple, fast, low cost measurement method on small size PMQs (Permanent Magnet Quadrupoles) is described. It is based on the same principle of the familiar "rotating coil technique", but in this case, profiting of the small dimensions of the PMQ, it consists in rotating the PMQ itself instead of the coil. In such way a gain on accuracy and measure time is obtained. It has been applied to characterize a set of commercial PMQs with a gradient around 200 T/m and an internal radius of 3.5 mm to be mounted in a SCDTL (Side Coupled Drift Tube Linac) structure for the acceleration of a proton beam from 7 to 12 MeV. This structure has been developed in the framework of the Italian TOP-IMPLART (Intensity Modulated Proton Linear Accelerator for Radiotherapy) Project 1. PMQs for a 3 GHz SCDTL The SCDTL is employed in the medium energy section of the TOP IMPLART proton linear accelerator 2. MEASUREMENT OF THE HARMONIC FIELD IN THE PMQ APERTURE THE TOP-IMPLART ACCELERATOR SCHEME De-mountable PMQs (BJA Magnetics) Side Coupled DTL: Short DTL tanks coupled together by side cavities. The DTLs are short tanks, each having 4 to 6 cells of  length, and the side cavity extends in a space left free on the axis for the accommodation of very short (3.3 cm long, 7 mm i.d.) PMQ (Permanent Magnet Quadrupole) for transverse focusing 3. MEASUREMENTS ANALYSIS AND RESULTS TOP IMPLART MeV SCDTL module The SCDTL (Side coupled Drift tube Linac) structure RFQ+DTL up to 7 MeV (425 MHz) CCL up to 150 MeV (phase-1) MeV (phase-2) ( MHz) 4 SCDTL modules MeV ( MHz) TOP IMPLART PROJECT: The aim of the project (ENEA,ISS,IFO collaboration) is to build a protontherapy linac to be housed in the largest oncological hospital in Rome,IFO. The accelerator section up to 150 MeV (funded by Regione Lazio,Italy) is under reaòization at the Research Centre in Frascati in a 30m long 3 m wide bunker for full proton beam characterization and validation before the relocation to IFO. PMQs mounted in the inter-tank space The PMQ is placed on a lathe where is put in rotation A 9- turns, 40 mm long and 1.4 mm wide coil is placed on the tool rest The PMQ is rotated and the induced voltage on the coil is measured and recorded 11 PMQs have been measured by usimg this quick and precise technique 4. PROTON BEAM TRANSPORT (check of beamline alignment and matching with injector) Effective length=30 mm Max gradient=200 T/m LEBT 4 EMQ MEASUREMENT SET-UP FIRST EXPERIMENTAL TEST: PROPAGATION IN A SHORT DOFO CHANNEL (4 PMQs) SECOND EXPERIMENTAL TEST: PROPAGATION IN THE COMPLETE DOFO-like CHANNEL (9 PMQs) MOUNTED ON THE SCDTL (RF off) Beam spot after 1 PMQ (#1) in position 4 Beam spot after 4 PMQ (#1,2,3,4) Beam spot after 1 PMQ (#2) in position 4 Harmonic content from with n=1 (dipole),n=2 (quadrupole),n=3 (sextupole),n=4 (octupole) Q-pole gradient rom,with T=period, Leff=3 cm, N=9 (number of coil turns),d=1.4 mm (coil width). Rrif=0 Rrif=1 mm,,with Displacement between the magnetic and geometrical axis of the quadrupole  the measured gradient values, that result to agree with the design value within 2%.  negligible content of multipolar components.  the difference between the magnetic and mechanical center for each quadrupole: the values are all well below the specified tolerance of 50 µm. fluorescent target Beam spot at SCDTL (no RF) exit Internal tube diameter=6 mm