Forces on MICE magnets in Step IV, commissioning steps J Boehm

Basic layout of magnets in Step IV Three magnets in line and within iron shield (positive return yoke, PRY) Interaction forces between magnets and PRY, and between magnets themselves Only cold magnet bobbins are floating, suspended by tie rods (red), rest is fixed Only the focus coil has read-outs for interaction forces (load cells)

Attractive forces All three magnets powered will give a minimum of attraction forces between magnet suspensions Stresses within bobbins are well contained by their aluminium formers. However, should one magnet quench a severe force unbalance will appear immediately … SSD has its end coil M1 not operational. The force between SSD and FC will be less than between FC and SSU

Maximum forces on magnet suspensions Operation at 4T: Net force on solenoid suspension: 17.5 t Net force on FC suspension: 29 t Visibility of forces: only on load cells on FC !!! Design forces: 50 t Actual forces: See Jaroslaw’s table 4T Example of electro-magnetic attraction vs distance: precise location of bobbins important

Polarity of fields important! Magnetic flux direction needs to be verified. If magnetic forces between magnets are repulsive (as shown above) the attractive force between PRY and solenoid will see the addition of the repulsive force from FC  suspension of solenoid may break

Load and temperature indicators on Focus Coil

Steps for commissioning magnets Maximum force scenario must be considered Reducing risk to magnets makes operation at 3T advisable (interaction force is proportional to I1 X I2 x geometry factor (constant)) Method for establishing forces: Ramp SSU to 3T Slowly ramp FC in solenoid mode and observe load cells and temperatures Load indicators will change due to magnetic attraction Temperature indicators will change due to minimal movements of cold mass in FC: the outer walls of the FC are very tight against the radiation shield and the cold mass