### Minutes & Slides from Proton Driver RF Meeting March 30, 2004

*(G.W. Foster)*

Subject: the 805 MHz fast phase shifter and related topics.

Attendees: Steve Hays, V. Kashikhin, Dave Wildman, Pierre Bauer, Al
Moretti, Markus Huening, Brian Chase, Ding Sun, GW Foster, Milorad
Popovic, Bob Kephart.

**\*\*NO MEETING NEXT WEEK\*\* (TESLA Collaboration meeting)**

**\*\* Next Meeting April 13^th\ \*\*^**

**[MINUTES]{.underline}**

1)  Dave Wildman presented results on loss (Q) measurements of the
    existing YIG tuner. The tuner contains 3 rings of the same
    (Trans-Tech G510?) YIG material ordered for our real tuners. It was
    was originally built as a shorted stub for a 159 MHz cavity tuner.
    When operated as a shorted-stub quarter-wave resonator, its
    frequency varies from 400-500 MHz depending on magnetic bias field
    (see data on next pages). Dave's feeling (agreed to by those
    present) was that this pretty much replicated the field pattern
    expected in the 805MHz shorted stub tuner, so the Q measured in this
    tuner could be used to estimate the losses in one stub of the E-H
    tuner. The Q increased rapidly as the bias field was increased, and
    Q was above 2,000 for H\>600 Gauss. \[We plan to operate in the
    range 900 \< H \< 1500 Gauss\]. Since an all-copper cavity of these
    dimensions would also be expected to have a Q of a few thousand,
    this indicates that the YIG losses were of the same order of
    magnitude, which is extremely good news. Dave's quick estimate was
    that this translated to \<25W of average power dissipation in the
    YIG in our final tuner design. This should not be a problem either
    RF efficiency or for heat removal. By next week we could have some
    simulation results on what fraction of the cavity Q could be
    attributed to copper vs. ferrite.

2)  Vladimir Kashikhin presented a status report of his investigation of
    bias coils and flux return shapes. He was able to achieve a 5% field
    uniformity in the YIG by covering the end of the shorted stub
    completely with a flux return cap plate made of Bsat=0.4T soft
    ferrite, putting a ferrite flux return tube around the solenoid, and
    extending the solenoid a few inches in front of the beginning of the
    YIG ferrite. A representative coil design (see his attached slides)
    requires 14kA-turns and consumes \~25W average. Removing the flux
    return tube still provides reasonable field quality but requires
    17kA-turns. If the field quality spec is relaxed, the coil could be
    shortened and the Amp-turns and power reduced.

> The question of whether a solid conductor for the coil will be
> sufficient depends on the drive waveform. If the waveform is a simple
> pulsed ramp, solid conductor should be OK. However if the tuner
> feedback loop is thrashing around continuously every few microseconds,
> the skin losses will increase and this might argue for some sort of
> Rutherford cable or Litz wire or similar. Vladimir is looking into
> whether he can get his hands on leftover copper Rutherford cable used
> for a pulsed magnet in the Tevatron.
>
> So it appears that we are looking at roughly:

(25W in the YIG) + (25W in the drive coil) = 50W per stub or 100W per
tuner,

for a coil with Bmax\~1.5kG and a slew rate of 3 Gauss/microsecond in
the YIG.

3)  Steve Hays indicated that a +/-250V 100A pulsed mode could basically
    be provided with existing equipment, albeit with uncomfortably small
    operating margins. Vladimir has also worked out a +/-100V 250A coil
    design which might be preferable. The closed loop response would be
    limited by the 40KHz switching frequency of the existing supply
    module. Faster versions using FETS in place of IGBTs could
    eventually be considered.

4)  No Meeting Next Week (see note at top). On thing to think about in
    the interim is what test procedures (and any new equipment?) are
    necessary to make the test-stand measurements needed to convince
    ourselves that both the stub and the tuner is doing what we need it
    to do. How about a pair of high-quality high-power adjustable-length
    coax shorting stubs that we could drop in place of the coax tuners
    for a reference?

ATTACHMENTS:

1)  Dave Wildman's Q Measurements (appended below)

2)  Vladimir Kashikhin's magnetic field analysis (separate file)

![](media/image1.png){width="5.995833333333334in"
height="5.121527777777778in"}

Dave's measurements of Q vs. bias field for existing YIG tuner. Above
550A the power supply regulated badly and no useful linewidth
measurements were possible.

![](media/image2.png){width="5.997222222222222in"
height="5.398611111111111in"}

RESONANCE AT 340 Amps (476 Gauss) Freq = 385 MHz, Q=102.4

![](media/image3.png){width="5.979861111111111in"
height="5.033333333333333in"}

RESONANCE AT 550 Amps (770 Gauss) Freq = 488 MHz, Q=2650

Solenoid Geometry and Parameters

V.S.Kashikhin, March 30, 2004

![](media/image4.png){width="5.376388888888889in"
height="3.7090277777777776in"}

Fig. 1. Bias field homogeneity in YIG ferrite. Total current 17 kA.
Energy 7.9 J.

![](media/image5.png){width="5.376388888888889in"
height="3.7180555555555554in"}

Fig. 2. Bias field homogeneity along Z axis at inner radius in YIG
ferrite

![](media/image6.png){width="5.6305555555555555in"
height="3.8847222222222224in"}

Fig. 3. Bias field homogeneity in YIG ferrite. Total current 17 kA.
Energy 7.8 J

![](media/image7.png){width="5.991666666666666in" height="4.14375in"}

Fig. 4. Bias field homogeneity along Z axis at inner radius in YIG
ferrite

![](media/image8.png){width="5.991666666666666in" height="4.14375in"}

Fig. 5. Bias field homogeneity in YIG ferrite. Total current 17 kA.
Energy 6.6 J

![](media/image9.png){width="5.991666666666666in" height="4.14375in"}

Fig. 6. Bias field homogeneity along Z axis at inner radius in YIG
ferrite

![](media/image10.png){width="5.991666666666666in" height="4.14375in"}

Fig. 7. Bias field homogeneity in YIG ferrite. Total current 17 kA.
Energy 6.5 J

![](media/image11.png){width="5.991666666666666in" height="4.14375in"}

Fig. 6. Bias field homogeneity along Z axis at inner radius in YIG
ferrite

**Solenoid parameters (without flux return)**

Bias field 0.15 T

Inductance 0.14 mH

Total ampere-turns 17320 A-t (no flux return)

( \~14000 A-t with flux return)

Current 321 A (no flux return)

(\~260A with flux return)

Resistance DC 16 mOhm

Resistive voltage 5 V

Conductor copper 28 strands of 1 mm diameter

Conductror copper area 22 ­mm^2^

Number of turns 54

Number of layers 6 or 1 depending on technique

Inductive voltage for dB/dt=3 gauss/usec in YIG 90 V

Power losses 25 W

(at 1.5% duty cycle)

![](media/image12.wmf)

**Summary**

The solenoid can be wound from Rutherford type of copper cable produced
on TD cabling machine. No changes of tuning are needed. Such cable was
used for the Tevatron air core pulsed quadrupole. Strands are insulated
to eliminate eddy currents. After winding the coil should be vacuum
impregnated together with the outer stainless steel cooling pipe forming
rigid mechanical structure. Only small diameter hole needed in the
ferrite end plate to organize the longitudinal cooling channel for YIG
ferrite.

Solenoid calculated to generate 0.15 T field without outer ferrite core.
During experiments the ferrite core can be added to compare both
options.