Plan For Tests of PA/tube at 2nd

Harmonic FrequenciesRobyn 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)

Cathoderesonator

Anoderesonator

Couplingcapacitor

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 3l/4 resonator

Cathoderesonator

tube

Anode attaches to anode resonatorOr cavity through coupling/blocking capacitor

Cathoderesonator

Tube,Goes in here

Anode resonator

Anode resonator Center conductorShorted 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 – l/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 MHzinstead of 38 MHz,change this length from8.7” to 1.3”

Results of ModelFundamental: 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 pFTo 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