### Minutes & Slides from Proton Driver RF Meeting -- October 12, 2004

*(G.W. Foster)*

SUBJECT: Circulator Tests, Phase Shifter Status, 325 MHz Collaboration
Plans

Attendees: Ding Sun, Milorad Popovic, Iouri Terechkine, Dave Wildman,
Victor Yarba, Timergali Khabibouline, Gennady Romanov, Giorgio
Apolinari, Fernanda Garcia, Pierre Bauer, Bill Foster

AGENDA:

1\) Tests of 325 MHz stripline circulator prototypes (Ding Sun)

2\) 1300 MHz high-power waveguide phase shifter status (Iouri
Terechkine)

3\) High-powered Coax Tuner test plans (D. Wildman)

4\) 325 MHz front-end linac collaboration plans with ANL, KEK,... (G.
Romanov)

**[MINUTES]{.underline}**

1\) **[Test results on a prototype 325 MHz circulator]{.underline}**
were reported by Ding Sun of AD. The design targets use in a \"strip
line circuit board\" which will contain all parts for a medium-power I/Q
modulator module: i.e. circulator/isolator, branch-line-hybrid, and YIG
ferrite tuning stubs. This module will provide independent RF phase and
amplitude control for one SCRF cavity in a front end linac powered by a
single Klystron. The prototypes use G-510 YIG ferrite rings from Dave
Wildman\'s coax tuners 3\" OD x 1/2\" ID x 1/2\" width. Bias fields of
\~400 Gauss are provided by George Krafczyk\'s Main Injector corrector
magnet.

Ding has achieved good results both with a \"standard\" circulator
design, and also a novel one which places a conductive post in the
center of the circulator disk. The center post has advantages for heat
removal from the ferrite, and also drops the operating frequency by
10-20% resulting in a more compact circulator.

Typical results (see figure) include:

a\) Isolation of -30dB to -50dB at center frequency (top plot)

b\) Insertion loss of \~0.1 dB (or \~2% power loss) (2nd plot)

c\) Matching loss of -25-35 dB (3^rd^ plot)

These numbers are about as good as you can get with a store-bought
circulator, and better than we need for the SCRF cavity I/Q modulator
application. The 3\" diameter disks yields best operating frequencies in
the range of 350-500 MHz (depending on bias field and stripline port
geometry) so the disk OD will have to be increased to 3.5\"-4\" diameter
for 325 MHz operation.

Ding does have a variant which works acceptably at the 352 MHz RF
available from the Klystron test stand at the Argonne APS. So we should
be able to do peak & average power testing at this frequency. This will
require upgrading the connectors on the circulator to 7/8\" coax or
similar. These circulator tests could be folded into Dave Wildman\'s
planned expedition to ANL for high power testing of the coax tuners at
352 MHz.

![](media/image1.png){width="5.998611111111111in"
height="7.886111111111111in"}

Ding Sun's measurements of his prototype circulator (representative
results, in this case biased for 500 MHz operation and including the
metal center post through the ferrite).

Top Plot: Isolation, in this case --49dB.

2^nd^ from top: insertion loss = 0.12dB or about 3% power loss.

3^rd^ and 4^th^ plots: Matching reflection loss, in this case --27dB

![](media/image2.jpeg){width="6.367361111111111in" height="4.7875in"}

Ding Sun's circulator prototype.

2\) An **Update on the high-powered 1300 MHz waveguide style YIG tuner**
stubs was given by Iouri Terechkine. The ferrite (finally) arrived, the
coils are done & tested, the steel magnet yoke is complete, and the
waveguide has undergoing its final brazing to fix up some bad corners.
The power supply that Dave Wildman has been using at A0 should be
adequate to drive the bias coils inder slow (DC) conditions. A faster,
higher-voltage supply and a ferrite return yoke will be needed for
high-speed operation of the phase shifter. There still options under
discussion on how to best trim the YIG bricks before gluing them into
the waveguide.

![](media/image3.jpeg){width="5.993055555555555in"
height="4.495138888888889in"}

Water-cooled waveguide for high-powered 1300 MHz YIG tuner

![](media/image4.jpeg){width="5.618055555555555in"
height="4.2131944444444445in"}

Bias coils for waveguide tuners.

![](media/image5.jpeg){width="5.618055555555555in" height="4.21875in"}

Flux Return for waveguide tuner

3\) Dave Wildman reported that **tests of the \"fast\" version of the
Coax tuner are** still waiting for the 300V / 100A power supply from
Steve Hays. He believes that he has all the rest of the parts for the
test ready to go.

![](media/image6.jpeg){width="6.0in" height="4.5in"}

High-speed version of the Coax phase shifter

4\) Gennady Romanov described plans and potential collaboration on the
325 MHz front end linac which feeds the SCRF spoke resonators.
Collaboration plans are in flux, but some possible elements include

a\) Doug Moehs is investigating the best H- source design to
beg/borrow/steal/copy for the 325 MHz linac. Candidates designs include
TRIUMF, SNS, DESY, & JPARC.

b\) The RF Quadrupole from the KEK/JPARC joint project (30 mA, 3 MeV,
2.5% duty factor, 324 MHz tunable to 325MHz) looks ideal for this
project. Initial contacts with KEK have yielded a positive response, and
discussions should continue next week at the HB2004 conference in
Germany.

c\) There are a number of possibilities for the \"first DTL Tank\",
including copying the KEK DTL, independent copper resonators, or going
straight to SCRF.

Gennady's slides are at

<http://tdserver1.fnal.gov/8gevlinacpapers/meeting_minutes/RF/Romanov_325MHz_Collab_Oct12_04.ppt>