On Monday Nov 3rd at around 8:30, the experiment was planning on switching the
polarity of the polarized target magnet. To do this the magnet first needed to
be ramped down. In the process of this ramp down the magnet quenched.
The target operator was ramping down then magnet and was 
requesting to ramp down the magnet at 20A/min. In the power supply of the
magnet is firmware in the power supply CPU that actually controls the ramp 
rate of the magnet. The sweeps rates are  for 78 to 72 amps a rate of 1 amps/min
for 72 to 60 amps a rate of 1.5 amps/min and for 0 to 60 amps a rate of 2 amps/min 
In the top figure "commands.pdf" shows the current
versus time for the . In the bottom figure shows the instanteous ramp rate
which are consist with the ramp rates in the PS manual. The magnet quench when
going below 60amps.

The magnet was cooled down during day and most of swing shift on Monday.
When trying to ramp up the magnet, the following problem was found
"However when we stop ramping with a current of 3.5 A in the magnet 
the Voltage is 4.7 V - much more than we expect from the leads."
It was decide not to keep trying to set field in the magnet and 
investigate more on Tuesday. 

On Tues the status was report as :
**********

Diagnostics on the magnet were performed this evening.

The magnet has in parallel to it's coils, a superconducting switch, used for connecting the magnet to 
the power supply, and diodes, used for current dissipation during a quench. There are test leads 
throughout the coil and diode array. Under normal cold conditions, there should be 
no measurable resistance on these leads, since the coils are superconducting 
and in parallel with these other components. The target group 
was not able to measure any resistance across any of these leads.

While the magnet was energized with a small current, voltage 
measurements were made across these leads. This too, because the wires 
are superconducting, should have been zero--it was not. When the 
switch connecting the power supply to the magnet was turned off, this voltage slowly decayed. 
This seems to be indicative of a broken coil that is resistive. The 
voltage appears while the PS supplies current to the magnet, and ohmic 
heating dissipates the current (and voltage) after the power supply is switched off.

The power supply, as mentioned in Donal's previous post (172392, 11/04/08), 
also indicates an unwanted resistance in the magnet. The Power supply 
is being forced to use more voltage than is normal to supply 
the requested current (indicative of extra resistance). A plot 
of the voltage vs current is attached, and it seems to 
indicate a resistance that is decreasing as current increases.

In order to check that this apparent resistance (about 2 ohms) is coming 
from the magnet, and not the power supply, the PS leads were connected 
to one another, and the PS was ramped up. The expected resistance 
was seen (that 2 ohms was not coming from the supply or leads). Also, the 
supply's output was checked on a scope for irregularities. 
50 mV 60Hz noise was found, but would not have caused the problems we have been seeing.

We will, tomorrow, attempt to slowly ramp the magnet up 
again and watch the current limit. It is hoped that 
the V vs I curve will flatten out enough that we can reach an operational magnetic field strength (2.5 T). 

**************

On Weds. the following report


********************

It is the consensus that the polarized target magnet coil is damaged and must be repairedin order for the experiment to proceed.

Evidently the quench on the morning of November 3 damaged one of the magnet coils, or more exactly 
one of the joints that connects the coils (or sections of coils).

All the tests we have done confirm a resistive element in the 
coil (voltage on the PS even when it is not being ramped, 
greatly increased helium boil off when there is current in 
the magnet, and direct measurements of resistence and voltage at the coil taps).

The cooling of the magnet has stopped and the ancillary systems 
are being disassembled while it warms up. Once the target 
is warmed up it can be removed from the pivot. The coil 
package can then be removed and taken out of the hall.

Oxford Instruments has been contacted about the repair 
and further discussions to clarify the details 
of getting the repair done are in progress.

We will provide updates as they are available.


***********************

On Weds. Nov 5th  measurements were made of the voltage
at I= 0.55A across the taps in the "D" 10 pin seal.
How the taps are connected to the coils is shown in
Fig (magnet-diagram3.pdf).
The measurements are shown in the the attached logbook page.
The large voltage across taps AB and BC and the open resistance
from CD indicdate major problems and the decision was made to warm 
up the magnet to look inside.