How do they handle energy in magnets at LHC? I'm guessing that when the LHC ramps up to 4000 GeV this means they are increasing the current in the superconducting magnets as RF fields accelerate the beams.  Where does this current go when they ramp down?  Is it dissipated as heat?  Is it fed back into the grid?
P.S.- by 'ramp' I mean the normal increasing/decreasing of the current in the magnet at the beginning and ending of a fill.  It builds gradually (ramps) and decreases gradually.  The whole time the magnet is still superconducting.
 A: This link might enlighten you, also this.

The cryogenic technology chosen for the LHC uses superfluid helium, which has unusually efficient heat transfer properties, allowing kilowatts of refrigeration to be transported over more than a kilometre with a temperature drop of less than 0.1 K. LHC superconducting magnets will sit in a 1.9 K bath of superfluid helium at atmospheric pressure. This bath will be cooled by low pressure liquid helium flowing in heat exchanger tubes threaded along the string of magnets. The LHC cryogenic system is very large as well as very cold. Refrigeration power equivalent to over 140 kW at 4.5 K is distributed around the 27 km ring. To save costs, the four existing LEPII 12 kW, 4.5 K cryoplants will be reused. Their cooling power will be increased by 50% and 1.9 K stages will be added. In all, LHC cryogenics will need 40,000 leak-tight pipe junctions. 12 million litres of liquid nitrogen will be vaporised during the initial cooldown of 31,000 tons of material. The total inventory of liquid helium will be 700,000 litres. 

Unfortunately the FAQ page at the CERN page  is out of order at the moment and cannot be linked. Here is the LHC machine outreach page.
During normal beam dumps there is controlled quenching, using the systems set up for emergency quenching when there are problems with a magnet. Here is a book on LHC like magnet design.
A: "Each dipole magnet is connected to 153 neighbors, and their energy also has to be immediately removed. A switch sends the energy into large resistors, where it heats eight tons of steel to a temperature of 300°C (570°F) in less than two minutes."
There are actually deliberate heaters in the magnet windings. So if a point quench is detected it rapidly heats the whole magnet out of superconducting and the energy is spread evenly.
http://www.symmetrymagazine.org/cms/?pid=1000570
A: I am not familiar with the exact design of the LHC magnets. For 'normal' superconducting magnets the procedure to ramp up or ramp down the field is quite similar: 


*

*You ramp up/down the power supply to match exactly the current that is at the moment in the superconducting magnet. 

*The switch heater is turned on and will create a small portion of the coils that is above the critical temperature. Now you have a large superconducting coil which is shunted by a normal resistor and the power is supplied externally.

*The external supply is ramped up/down to the target field. This can take some time, as the magnet will have a very large inductance and you don't want to heat it up by vortex movement.

*At the target field the switch heater is deactivated, the whole magnet becomes superconducting again. 

*The external power supply is ramped down and shut off.


This is the normal mode of operation, if there is an emergency, i.e. a quench the energy is dissipated rapidly and Martin Beckett's post explains where that energy flows into (in the ideal case, otherwise the magnet can blow up, which happened at CERN earlier).
