November 16, 2016 - 4-Laser/LLRF Installation Meeting
1. (Joe) Winter SAD Schedule
2. (Tomasz, Rama, Dave, Scott) - LLRF status and installation plan for January
3. (Michele) HLAPP to switch 250/499 MHz - media:161012_4Laser4LLRF.docx
4. (Mike) LLAPP to set amplifiers by current instead of power
5. (John, Joe, Reza) Checkout of laser and electron beams
We seem to be on track with plans for 4 laser ops Jan 20, 2017. Here are meeting minutes from today, please correct my errors
A group effort involving Tomasz, Trent, Rama, Curt, Dave and maybe Chad (?) will enable installation of stand alone 4 laser rf system by January 20, although it will be a challenge to meet the deadline. The only way to meet this deadline is to install a simplified system, so-called Tone Mode Only. It will give John Hansknecht 4 rf signals, -10 dBm at 249.5 or 499 MHz, with independent phase control. 2 ns phase shift at 499 MHz and 4 ns phase shift at 249.5 MHz.
How does the simplified Tone Mode Only system differ from system originally proposed? It will not include hooks that would allow the monitoring of laser phase in tunnel, which would permit the possibility of laser phase feedback. But since we have never used laser phase feedback in the past, we believe Tone Mode Only will suffice.
The new 4 laser system will be installed, while maintaining complete functionality of today's 3 laser system. So should be easy to test four laser system and return to three laser system if necessary.
Scott needs to work with rf guys to better appreciate the scope of software job. But optimistic software can be ready. John and Michael want to modify laser software to operate in constant current mode. This can happen during winter sshutdown. Michelle Joyce needs time to check out high level apps software, before passing system to users. She will submit atlis and work with John H. to define suitable test. I believe this relates to switching rf rep rates, and making sure amps are in safe mode.
We discussed the problem of inadvertent 180 degree phase shifts that can occur when rf systems are powered off. An unanticipated 180 degree phase shift might result in beam going to the wrong place. We've encountered this before. Typically, the error is quickly discovered, for example, a BLM trips OFF beam. Ops then revisits injector phasing. This problem extends beyond laser rf phasing. In a CEBAF with 249.5 MHz lasers and 750 MHz separators, a global solution is warranted. Trent suggests modifications to boards that could eliminate one source of phase jump, but consensus was, we can't implement his recommended modification and still meet Jan20 deadline. We believe there is adequate machine protection today, such that if there is a 180 degree phase jump, we won't damage the machine or hurt anyone.
Joe Grames was given homework, in his absence. He will define the beamtest to be conducted in January, once the system ready for use. The beamtest will happen at injector. Sometime later, in the spring or whenever, we can consider using passing two beams through one chopper slit.