Plan For Tests of PA/tube at 2 nd Harmonic Frequencies Robyn Madrak C. Y. Tan

Goal We will most likely be using the Y567b tetrode since it is the tube which is used everywhere else at the lab: Booster, Main Injector, Recycler (previously, MainRing and Tevatron) According to the data sheet it can produce 220 kW up to 110 MHz…Until now it’s been run mainly around 53 MHz and below We need to test the tube at higher frequency – both to see if it can produce the needed output, and to be sure that we have enough drive power in the solid state drive amplifiers that we will order. John Reid recommended testing at 106 MHz, then we know we will be fine below that (but mid range might be OK)

We can reuse various things block diagram: Reuse Solid state driver (several kW) anode cathode Modulator (DC for tube anode) LC filter (blocks RF) choke (blocks RF) Cathode resonator Anode resonator Coupling capacitor tube The cathode resonator and tube form the the PA (power amp) The anode resonator is a quarter wave resonator which takes the place of the cavity during testing – want to tap it at 50 ohm point and attach a 50 ohm water cooled load

More Details Modulator – can borrow MI/Booster LC filter and choke– need to make new ones since these are tuned at a different frequency Solid state driver – need to buy prototype Tube – can use one on hand Cathode resonator: can modify (cut) booster prototype if we still have the parts. This is typically tuned to the lowest frequency (38 MHz) but has a low Q so can run up to 53 MHz. (Same for our range) Coupling capacitor: standard, on hand from existing PAs Anode resonator: Current test stand will not work, even if we try to modify it. It will be too short. Plus we would never be able to get to the 50 ohm tap point. Need to build a 3 /4 resonator

Cathode resonator tube Anode attaches to anode resonator Or cavity through coupling/blocking capacitor

Cathode resonator Tube, Goes in here Anode resonator Anode resonator Center conductor Shorted at bottom These are pictures of the TeV/RR PA and resonator. Similar idea to the Booster. I have pics of this one but not of the Booster one

Cathode Resonator – /4 resonator with some lumped elements We are pretty confident that we can model this as a transmission line with some lumped elements correctly. Following Tim Berenc’s note on the Booster SS drive and cathode resonator, we were able reproduce his results, and predict how much we would need to cut away to get to 76 MHz. Booster cathode resonator; shorted at one end. Model as 3 transmission lines. To get to 76 MHz, need to cut long section from ~9” to ~1”.

Transmission line model of cathode resonator For f=76 MHz instead of 38 MHz, change this length from 8.7” to 1.3”

Results of Model Fundamental: Down by 0.3 dB at 53 MHz, Compared to 38 MHz Modified:Down by 1.1 dB at 106 MHz, Compared to 75 MHz

Tube = 60 pF To ground Contact point between anode and coupling capacitor Ceramic of coupling capacitor (1000 pF) inner conductor Tev Anode Resonator: Model as Shorted transmission line One 1000 pF cap One 60 pF cap Tap point is not 50 ohms. Would also have to be moved for our test. On the Tevatron Test Station version of this, the tap point is much lower.

Modeling Anode resonator; See if we can model existing, so we can make a new one Initially tried to model as a resonator with l = l(center) This did not work, f ~69 MHz instead of 53 Q way too high L_center

Modeling Anode resonator Changed so L=L(outer). Not entirely correct but Joe said it’s worked in the past Frequency OK, had to add losses (in tan delta in last section) to get the correct Q. Where are the losses? Still, the tap point when using the dimensions of the test station anode resonator is not 50 ohms…

Questions/Concerns Exactly what do we have available to modify (this is not exactly all spelled out yet) Concerns about modelling anode resonator correctly/50 ohm tap point