Quadrupole Computer Controls

• There are 4 quadrupole magnets http://en.wikipedia.org/wiki/Quadrupole_magnet located on our accelerator.

• These magnets and their control power supplies have been upgraded to computer control from the original potentiometer control.
• Each quadrupole magnet has 2 power supplies designated QuadA and QuadB with independent current adjustments.
• A sample computer control window is shown below.

• Ideally, the A and B currents should be equal to focus a symetric beam entering the quadrupole on its center axis.
• The computer control window displays a graph window with QuadA current indicated on the X-Axis and the QuadB current indicated on the Y-Axis.
• The diagonal line is the locus of points A = B for reference.
• The QuadA and QuadB currents are adjusted by moving the bullseye cross hair graphic. The bullseye is initially adjustible in the “Grab” mode.
• The QuadA and QuadB currents are displayed in text under the X axis. The X and Y full scale values are fixed at 50 Amps.
• The Grab mode allows you to set the mouse pointer over the bullseye and while depressing the left mouse button, drag the bullseye to another set of A and B current values. The Grab mode initially is a rather coarse mode mainly used to initially set the quad currents to an approximate value and the quad currents adjust as the bullseye is moved. The Grab mode can be set to a finer resolution by pressing the Fine button and more coarse by pressing the Coarse button. In all but the initial Grab mode the mouse does not need to be on the bullseye. The independent (free form) X and Y movements of the mouse (when the left mouse button is depressed) are translated to steps in QuadA (X) and QuadB (Y) currents. You can continue to make the steps finer by pressing the Fine button and more coarse by continuing to press the Coarse button. The modes cycle through the modes Grab, Med, Fine, ExtraFine. In each of these ranges mouse movements are translated into steps in current for QuadA (X) and QuadB (Y) whenever the left mouse button is pressed.
• After presetting the quad currents to an approximate value using the Grab mode, an initial beam tune of the quadrupole would often be to switch to the mode A=B.
• In the A=B mode, the A current is made equal to the B current and the currents are simultaneously adjusted by moving the mouse left and right with the left mouse button depressed. As the mouse is moved from left to right the currents are increased. As the mouse is moved from right to left, the currents are decreased. This mode will adjust the A and B currents on the A=B line. The sensitivity on this range is fixed and is not changeable with the Fine or Coarse buttons.
• In the dA=dB mode, the dA current (change in A current) is made equal to the dB current and the currents are adjusted by moving the mouse left and right with the left mouse button depressed. As the mouse is moved from left to right the currents are increased. As the mouse is moved from right to left, the currents are decreased. This mode will adjust the A and B currents simultaneously on a line parallel to the A=B line. The sensitivity on this range is fixed and is not changeable with the Fine or Coarse buttons.
• When in the A=B mode or dA=dB mode, pressing the Fine button will result in a free form mode with the sensitivity set to Med.
• When in the A=B mode or dA=dB, pressing the Coarse button will result in a free form mode with the sensitivity set to Grab.
• When the mouse cursor is moved below the X axis and to the left of center Step Mode QuadA allows adjusting the QuadA currents up and down 1 step at a time using the same resolution that the mouse movements were using. Left mouse button steps QuadA current down 1 step and the right mouse button steps the QuadA current up 1 step.
• When the mouse cursor is moved below the X axis and to the right of center Step Mode QuadB allows adjusting the QuadB currents up and down 1 step at a time using the same resolution that the mouse movements were using. Left mouse button steps QuadB current down 1 step and the right mouse button steps the QuadB current up 1 step.
• Momentarily depressing the left mouse button when in the main field of the plot will set the step resolution 1 level finer.
• Momentarily depressing the right mouse button when in the main field of the plot will set the step resolution 1 level more coarse.
• The Save button will save the current values of the QuadA and QuadB currents. These values may be restored using the Rest button. This is very useful when you try to improve beam tuning and find that you have only made things worse. Remember to press the Save button before making changes to a previously good tune of the quad so you can Rest if you find you made things worse.
• Sometimes, when a large step in quad current is attempted too quickly, the power supply currents will start oscillating and will not respond to adjustments of the computer control. If this happens, turn of the quad main power at the quad console, run the quad currents to 0 using the Grab function, then turn the supply back on and reset the currents.

Don Carter 2012/03/21 10:56