Linear current control for solenoid

Hello Everone!!

I have a constant current source with two outputs (3A each) and a helmholtz coil (which are basically two solenoids kept on the same axis) in which a constant magnetic field is generated in response to the current. I want to control the magnetic field in helmholtz coil by controlling the current through both the channels of the current source using arduino mega. I tried with many tutorials using darlington transistors and power MOSFETs. But problem with such circuits is that the control over current is not linear. I want a linear increment in magnetic field with as high resolution as possible (which means high resolution over current). Can someone suggest me some kits or circuits with suitable components (which can handle this much current) to solve this problem…?

Thanks in advance.
Regards
Vyom

http://docs-europe.electrocomponents.com/webdocs/0d88/0900766b80d885f6.pdf

A couple of these to monitor current in each coil then take their output signals as feedback into the arduino.

The issue is providing a true analog output - this requires a DAC chip somewhere.

However firstly we need some information - full details on the constant current source
(model number, link to datasheet etc).

@MarkT

Here is the link for specification for Helmholtz coil as well as power supply.
http://www.sestechno.com/pro1/1f.htm
Please note that I am not allowed to modify the internal circuitry of the power supply. Maximum I can do is to set it to full and use output.

Regards
Vikas

@jackrae

Thanks for your reply. Can you suggest something for controlling the current also?

Regards
Vikas