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Contents 1 – Collision hazard 2 – Tool handling 3 – Impact on human health

Working Safely with the Magnetic Fields of the Accelerator Magnets Marco Buzio. Contents 1 – Collision hazard 2 – Tool handling 3 – Impact on human health. Collision hazard – what can go wrong. Collision hazard examples.

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Contents 1 – Collision hazard 2 – Tool handling 3 – Impact on human health

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  1. Working Safely with the Magnetic Fieldsof the Accelerator Magnets Marco Buzio Contents 1 – Collision hazard 2 – Tool handling 3 – Impact on human health

  2. Collision hazard – what can go wrong

  3. Collision hazard examples Relatively common accidents in the MRI (Magnetic Resonance Imaging) field. One fatality on record (O2 bottle) Worst case at CERN: LEP’s L3 0.5 T magnet(currently in ALICE)none injured.

  4. Tool handling inside a magnetic field uniform field in the gap tools align to the magnetic field non-magneticCuBe tools B r gradient field in the end regions tools are pulled into the magnetic field in the fringe: B  3 mT for sources  100 mT(Directive 2013/35/EU)

  5. Magnetization of ferromagnetic objects H field (irrotationali.e.H=0) NS inside and outside the material H=Hext+Hd, Hd=-NM Hint closely spaced poles  strong demagnetizing field (e.g. sphere N=1/3) force N S N force S Hext external field Hd Hd demagnetizing field widely spaced poles  little demagnetization (N0) Hd M magnetization B B field (solenoidal i.e.B=0) closed field lines force per unit volume is much stronger on elongated objects

  6. Safety classification of magnetic materials • Non-magnetic and weakly magnetic (r  1-10) • Elements: aluminum, copper, titanium • Bronze, brass, beryllium copper, aluminum bronze • Austenitic + high Ni/Cr/Mo stainless steels e.g. 316 (annealed) • Virtually all polymers and glasses, most ceramics • Strongly magnetic (r  10-5000) • Elements: iron, nickel, cobalt • Low-C (soft) e.g. ARMCO steel • Ferritic (e.g. 409) and martensitic (e.g. 420) stainless steels • Most other steel types • NiFe alloys e.g. permalloy, mumetal (r up to 106) • Ferrites (Mn/Ni/Zn ceramics) • Permanent magnets (Br 1.5 T) • Ferrites, AlNiCo, rare-earth ceramics (NdFeB, SaCo) largemagnetic forces

  7. Radioprotection instrumentation and magnetic fields fixed induced activity monitors may be affected (e.g. ATLAS) → calibrated in situ portable survey meters, electronic dosimeters:impact of B varies by type (e.g. B<50 mT)→ may fail or give inaccurate readings KTT: DGS/RP/SP + Politecnico di Milano are developing field-compatible dosimeters ( 1 T for now)→ 4 prototypes available on demand individual dosimeters = passive sensors → no problem

  8. Interference with welding process example: moderate arc blow (source www.twi.co.uk) • plasma arc- or electron beam-based welding processes are sensitive to local and ambient magnetic field • lower-current methods (e.g. TIG) tend to be most sensitive • problems appear already between 1 and 4 mT: instability, “arc blow” (deflection), molten metal spray  arc welding impossible above 20-40 mT

  9. Improvised current leads • Also related to live magnets: risk of electrical arcs in case of sudden lead disconnection • Energy stored in the inductor E = ½ LI2is released very quickly → risk ofelectrical shockand irreversible damage to the insulation 

  10. Incorrect current lead connection - 1 Accident occurred on a SPS main dipole test bench in bldg. 867, during a 6kA rampup (2012) 6kA copperconnection box MB dipole 6kA current leads fluxmeter

  11. Incorrect current lead connection - 2 bad connection  copper melts  circuit opens  electrical arc  explosion, flame molten Cu freshly broken long-time broken(cause of the fault) fastening bolts

  12. Magnetic field effects on human health • Iron in human blood: 3 g (red cells) 1 g (ferritin) (typ. adult male values)isolated atoms, no ferromagnetic domains  negligible forces • conducting fluid elements  induced currents  magnetic drag flow slows down (7% @ 5T)  small blood pressure increase(3% @ 8T) v = flow speed(max  2-3 m/s in the ascending aorta) E=v × B J =  Eelectric field, induced current B = magnetic field(worst case = horizontal) dF/dA = J  B = magnetic drag force small effects no health hazard of whole-body field immersion B8 T(confirmed by epidemiologic studies in the MRI field)

  13. Interaction of DC fields with implants vascular clips(e.g. aneurysm)  eye implants splinters orthopedic implants plates, screws, rods hearing aidscochlear implants Co-Cr implantsbraces neural/bone stimulators heart valves, pacemakers  infusion pumps IUD needles magnetic anus bullets, shrapnel jewelry, piercings implants may malfunction or dislodge (especially if recent)

  14. Interaction of magnetic fields with pacemakers • Normal pacemaker function: sense electrical cardiac pulses, if needed provide pulses at an appropriate intensity and rate • A reed switch can be magnetically closed from outside to: • - disable pulse sensing and go into fixed-frequency mode (asynchronous pacing) • - go into programming mode • Uncontrolled switch behavior if B > 0.7 mT competitive rhythms  discomfort,arrhythmia, death • AC fields may interfere with pulse detection/generation electronics reed switch external field  magnetization and closure of contacts pacemakers, implantable defibrillators (ICD) etc exposure to B > 0.5 mT is absolutely forbidden field sources > 0.5 mT are ubiquitous (office magnets, electrical components, machinery ….)

  15. Exposure limits at CERN according to IS36.2 heart implant(pacemaker, defibrillator) general public(generic implants) employees(all categories) B  200 mT B  10 mT B  0.5 mT 40 h /week OKconservative limit takes into account potential long-term effects occasionally OKneed authorization ofMedical Service/RSO B > 200 mT

  16. Safety perimeter around magnets 1/r3 decay rate(far field) B(r) r • fringe field radiates from the gap as far as 45 gap lengths (more if the coils are exposed !) • for non-saturated magnets, minor leakage only from the yoke • safety perimeter measured and documented in some cases (e.g. main PS units)

  17. Safety signs WARNING: flashing light + delimitationmagnetic field  0.5 mT bldg. 181 field map showing 0.5 mTand 10 mT boundaries must be exposedand communicated to HSE(this is done in CMS and ATLAS: not possible in TE/MSC labs!) a whole enclosed area can be markedas restricted (authorization needed) bldg. 375 – ISR tunnel

  18. Safety Form OHS 0-0-3 Occupational Hazards (for staff members) • To be compiled at least once a year (MARS interview) or upon function changes • For our typical sources, tick boxes 604 and 605(somewhat unclear formulation, will be updated to separate RF from quasi-DC sources)

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