Linac RF Summary GUI

Contents

Introduction

The LCLS Linac RF Summary GUI is a Continuously Updating Display (CUD) showing status for each station and subooster from LI21 to LI30. L2 acts as a single energy modulation on the LCLS beam. At the cost of some acceleration, we can also induce an energy spread riding off crest in L2, which is supplemented by the BC2 feedback. L3 also acts as a single, energy modulator that is maintained by the FB31 Feedback. Because the beam is not destined for another bunch compressor, beam in L3 does not typically ride off crest. The bottom of this display shows phasor diagrams representing BC1, BC2 and FB31 feedback states. Press start/stop button to initialize the GUI. Look at the legend for a description of the colors and abbreviations.

BLUE BOX, L2

\ L2 starts at 21-3, after BC1 and ends on 24-6, before BC2 and includes suboosters in LI21,22,23 and 24. All stations are in phase with each other, thus acting like a single, BIG, energy modulator. If fully forward phased (on crest) the ideal energy gain is 4.05Gev, however, if the beam rides the RF wave off crest, it will induce an energy spread while losing some acceleration (energy). This energy spread in the X plane will then manifest itself as a compressed beam in the Z plane after passing through BC2.

• L2 <PDES> is the AVG desired phase of all 4 suboosters.
  
• L2 <PACT> is the AVG actual phase of all 4 suboosters.
  
• The BLACK BOXES under the sector numbers show DES and ACT values for the individual suboosters, top to bottom respectivley. They should be very close or equal to each other. Notice the dynamics during an L2 phase scan.
  
• KLYSTRONS are shown vertically with their ID numbers under each sector.
  

ORANGE BOX, L3

L3 starts at 25-1, after BC2 and ends on 30-8, before DL2, includes suboosters in LI25,26,27,28,29 and 30. All stations are in phase with each other, thus acting like a single, BIG, energy modulator. If fully forward phased (on crest) the ideal energy gain is 9.30 Gev.

• L3 <PDES> is the AVG desired phase of all 6 suboosters.
  
• L3 <PACT> is the AVG actual phase of all 6 suboosters.
  
• The BLACK BOXES under the sector numbers show DES and ACT values for the individual suboosters, top to bottom respectivley. They should be very close or equal to each other. Notice the dynamics during an L3 phase scan.
  
• KLYSTRONS are shown vertically with their ID numbers under each sector.

CYAN BOX, FEEDBACK DISPLAYS

BC1

BC1 phasor diagram representing Energy on the X axis and Chirp on the Y axis.

This phasor diagram shows the feedback state of L1S phase and amplitude in terms of energy and energy spread (bunch length) for beam destined to BC1. Unique to this display, the vector has been normalized to the TARGET running values (phase = -22 degrees and amplitude = 144 MV) meaning a length and an angle of zero in the display corresponds to nominal running conditions for L1S, deviations from these values will increase the vector size or rotate the vector respectively. The horizontal axis quantifies the energy given to the beam as requested by the BC1 energy setpoint (controlled by L1S Amplitude). The vertical axis quantifies the induced energy spread as requested by BC1 Bunch Length Setpoint (controlled by L1S Phase), which will manifest itself as a particular bunch length, once through BC1. A RED vector implies there is no more headroom for the actuators to feedback on the measurements made, given the desired states. GREEN means there is headroom. The scale is from 0 to 10 Mev, any more amplitude is undesired, therefore unnecessary to show on this display. 0 degrees corresponds to Crest or fully forward phased where no chirp is induced. 90 degrees corresponds to a fully compressed beam with no enrgy gain. 180 degrees is fully back phased and 270 degrees is over compressed ?????????

This display shows the devices responsible for BC1 energy and bunch length regulation. Green boxes tag which decivces are being used in this feedback.

BC2

BC2 phasor diagram representing Energy on the X axis and Chirp on the Y axis.

This display is similar to the BC1 display (above), however, the mechanism driving the 2 feedbacks differ from one to the other. The yellow arrows represent the phase for 24-1 and 24-2 (24-3 is a spare klystron for this feedback). The dark blue arrow is the resultant amplitude vector and the cyan arrow is the resultant phase vector. The length of the yellow arrows are proportional to the Amplitude of each station but this parameter is not used in the feedback for BC2 chirp, unlike BC1 and it's use of L1S Amplitude. Rather, 2 stations are used in equal and opposite phase (such that the resultant vector has a single component in the energy plane (X axis)) to achieve energy gain without introducing energy spread. If energy spread is desired for compression in BC2 then the 2 vectors are rotated such that a component in the chirp plane (Y axis) is non zero while keeping a constant phase difference between the 2 yellow arrows. If the 2 yellow arrows are symmetric about the Y axis, then the 2 stations compress the beam with no energy gain. A RED vector implies there is no more headroom for the actuators to feedback on the measurements made, given the desired states. GREEN means there is headroom. The scale from 0 to 500 Mev is the amount of headroom this feedback has to work with. So if more than 2 stations trip off in L2, this feedback will not have enough headroom to compensate, resulting in a red arrow and a lower energy beam then expected.

This display shows the devices responsible for BC2 energy and bunch length regulation. Green boxes tag which decivces are being used in this feedback.

FB31

FB31 phasor diagram representing Energy on the X axis and Chirp on the Y axis.

 This feedback is similar to the BC2 feedback (above) in 2 ways: It's use of 2 yellow arrows representing phases of Suboosters in LI27, LI28 and their associated klystrons and secondly, the amplitude information is not used in this feedback to regulate beam energy, given the setpoint. Meaning, the energy is regulated by phases in LI27 and LI28 only, as is the energy in BC2 by 24-1 and 24-2 phases. All stations in LI27 are phased coherently with their subooster as are the stations in LI28 however, oppositely phased from one sector to the other. This allows for the feedback to add energy to the beam using both sectors while compensating for energy spread induced in LI27 with LI28.  The blue vector is the resultant vector of the 2 yellow arrows representing energy gain and the cyan is the phase difference, as shown here, no phase difference exists which can be interpreted as energy gain with no induced energy spread. The scale from 0 to 4000 Mev is the amount of energy that can and is given to the beam. Here it is shown as a net energy gain of 2000Mev. A RED vector implies there is no more headroom for the actuators to feedback on the measurements made, given the desired states.