# Presentation: 690489

## Recent 201 MHz cavity test in magnetic field: X-ray radiation

- Dazhang Huang, IIT

- D. Huang NFMCC Friday meeting

- 2008-9-5

## New observations & results

- The modulator of the 201 MHz tube limits the accelerating gradient less than 12.75 -13.6 MV/m (15 -16 V on scope)
- No sparks observed at lower magnetic field, i.e., 0, 0.15 T, 0.30 T, 0.45 T, 0.60 T, 0.75 T, 0.90 T.
- Sparks tripped the RF down as B > 0.90 T, i.e., 1.05 T, 1.20 T, 1.275 T, 1.35 T
- Multipacting observed as E < 3.4 MV/m (4 V on scope)
- X-ray background radiation behaves interestingly:
-  A peak at 0.093 T (14.25 A solenoid current), may be due to multipacting.
-  Slope of the radiation curve varies a lot as magnetic field increases
-  At 0 and 0.15 T, the radiation first goes down, reaches a minimal  and then raises up as magnetic field goes higher
- NaI crystal detector was saturated very quickly as B > 0.15 T
- Therefore, it seems more complicated than that of the 805 MHz cavity

- D. Huang NFMCC Friday meeting

- 2008-9-5

## Detector layout and procedures

-    Measure X-ray background with PMT and chipmunk detectors
-    Scan accelerating gradient from 4 up to 16 Volts on oscilloscope and measure X-ray radiation at 0, 0.15, 0.3, 0.45, 0.6, 0.75, 0.9, 1.05, 1.2, 1.275, 1.3 Tesla magnetic field in the center of the 201 MHz cavity. The magnetic field is provided by the supercond. solenoids.
-    Rep. rate of 201 MHz RF is 2
-    Data acquisition in 500 sec.
-     Total X-ray counts of PMT detectors are indicated on visual scalers

- D. Huang NFMCC Friday meeting

- 2008-9-5

## Results-in-plots with cosmic background subtracted

-    Horizontal axis: accelerating gradient (V/m)  in log. scale
-    Vertical axis on the left: PMT detector counts in 500 sec in log. scale
-    Vertical axis on the right in green: chipmunk detector RD 26 in linear scale
-     Magnetic field uses the value at the center of the 201 MHz cavity
-    blue: NaI crystal
-    pink: small scint. paddle upstream
-    red: small scint. paddle downstream
-    green: chipmunk RD 26
-    black: power-law fit to the downstream small scint. paddle data at higher accelerating gradient

**Y=2********10****-7****E****10.4**

**Y=1********10****-14****E****16.6**

- D. Huang NFMCC Friday meeting

- 2008-9-5

## Y=710-6E8.6

**Y=7********10****-6****E****8.6**

**Y=8********10****-4****E****6.8**

**Y=2********10****-8****E****11.2**

- D. Huang NFMCC Friday meeting

- 2008-9-5

## Y=0.8E4.2

**Y=0.8E****4.2**

**Y=4********10****-4****E****7.4**

**Y=0.6E****3.9**

**Y=0.5E****4.0**

- D. Huang NFMCC Friday meeting

- 2008-9-5

##     After the power-law fit to the radiation curve of the downstream scintillator detector at higher accelerating gradient, the power index also shows interesting behavior: It fluctuates dramatically and the tendency seems following the exponential decay.

-     As well-known, the power index is determined by the work function and local electric field, and the X-ray radiation level is proportional the field emission current. Therefore this curve may imply that the field emission also varies very much as magnetic field grows up.

**Y=12.9exp********0.256B**

- D. Huang NFMCC Friday meeting

- 2008-9-5