# Presentation: 612771

## High Pressure Cavity Calibration and MeasurementMCTF MeetingAl Moretti11/06/08

## εps

***ε*****ps**

***ε*****ps = Maxium Electric  Surface location**

## The program then Calculates the        Qos, εps, Surface Electric Field, EStored energy, Zo Shunt impedance, PLS rf power to produce the above and other factors.

- SuperFish Program used for the Calibration:
- The geometry is inputted to the program.
- The program then Calculates the        **Q****os, *****ε*****ps, Surface Electric Field, ****E****Stored energy, ****Z****o Shunt impedance, ****P****LS rf power to produce the above and other factors.**
**The peak surface field at Breakdown**** *****ε******pB is *****then given after the Qo****meas**, **Coupling Factor  and all attenuation factors of connecting cables are measured on a calibrated network analyzer** by:               ***ε******pB/ ******ε*****ps = *****√*****(****P****LB****/** **P****LS****)  Where ** **P****LB ****by          ** **P****LB **** = (AF) Attenuation Factor***** x***** V****p****2/****100 in a 50 Ohm system.****  **
**One way of looking at this, SuperFish gives****   *****ε*****ps ****for 1 kW disapation on the cavity surfaces and it takes about 250 kW to reach breakdown.**
**  **

-  ***ε******ps***

## The cable measurements are used to determine the attenuation factor of each cable (CA)

- A

- B

- 15/8” Power Coupler

- 3.6 mm Coax Pick-up probe

**First a Cal. NW Analyzer measurement  is made of the Coupling factor (CF) between Terminal A-B, Then a measurement is made of the Attenuation Factor of the three  cables to the Control room Terminals A’-C. The 3 cables are combined in 3 combinations, 2 at a time. These cables are then connected to the scope for **** V****p, Forward and Reverse RF Power.**

**1⁄2” Heliax, 100m long**

**20 DB Pad**

**Filter**

- A’

- C

- D

- The cable measurements are used to determine the attenuation factor of each cable (C**A**)

- Breakdown cone Surface

##           β = ((R1 + (R3 + R4)/2))/50

**3**

**LogS****11**

- Smith Chart S11

- The graphs show the resonance of  a Pill-Box cavity on a log and Smith Cart of **S****11**. The points 3 and 4 on the Log plot represent half of the insertion loss (IL) of the RF power coupler from B-D
- The point 1 on the Smith Chart represents the impedance of the cavity at resonance and at the Detuned short position.
- The points 3 and 4 represent the impedance of the cavity off resonance on the High and low frequency side of the cavity. These are used to determine  **Q****omeas **from the formula on side #2:
-           β = ((R**1 ****+ (R****3**** + R****4****)/2))/50**

**1**

**4**

## Cal. NW Analyzer Measurement of S21 of QLmeas and CF

- Cal. NW Analyzer Measurement of **S****21 ****of ****Q****Lmeas ****and CF**

- In this case the Cal NW analyzer, in the Q measurement mode is used to determine **QLmeas and CF**

##                                   εpB/ εps = √(PLB/ PLS)

**                                 ****AF= CF + **C**A –IL/2 in Log****10 ****format.**
**                                 ****P****LB  ****= Anti Log(AF) *****x***** Vp2/100**
**                                 **** **β = ((R**1 + (R3 + R4)/2))/50                            **
**                                  ****Q****omeas =**** Q****L****meas** (1 +  β )
-                                   ***ε******pB/ ******ε*****ps = *****√*****(PLB/** **PLS)**

## Slide 8

## Slide 9

## Slide 10

## This represents the calibration runs of  IL (insertion loss) for the cavity RF power coupler  for the 3 materials under test. The data was taken at the start of each test with a NW analyzer By pressurizing the cavity with N2 gas to span the frequency range of the final high power high pressure testing.

**This represents the calibration runs of  IL (insertion loss) for the cavity RF power coupler  for the 3 materials under test. The data was taken at the start of each test with a NW analyzer By pressurizing the cavity with ****N****2 gas to span the frequency range of the final high power high pressure testing.**
**It is very probable that none of the test frequencies correspond to the test points on the graph.**
**Worst case error is 0.56dB/2 or  **
**                                         ****+/- 3.3 %.**

- Some Error Analysis on IL

## Summary of  Errors 

- _Summary of  Errors__ _

- This graph represents the combined Qomeas for Al and Sn. Assuming that the electrical conductivity of the Al and Sn sample surfaces were the same, this will give a worst case error estimate for Qomeas  of +/- 1%.
- Similar analysis of R3 and R4,  error +/- 1 %
- Similar analysis of CA, error of +/- 0.5%
-                               CF error of +/- 0.5 %
-                                 IL error of +/- 3.3 %
-               NW Analyzer error of +/- 1.0%
-                         Scope error  of +/- 2 %
-                    SuperFish error of  +/-0.2%

## Possible breakdown gradient over “Breakdown Cone Surface”

- SurperFish normalized breakdown gradient relative to the “Breakdown Cone Surface” radius. Spark damage has been seen on most samples out to about 5 mm. This says that the width of the breakdown curves in out graphs should have width of about 5 %.