Cold RF Gun - The Cockcroft Institute · Ir Maximum stable gradient as a function of the Young's modulus for different materials. RF frequency 805 MHz, Hydrogen pressure ~ 100 bar

Cold RF Gun

Vladimir VogelKlaus FloettmannSiegfried Schreiber

Materials and gradient

Some properties of pure metals in low temperature region

Cold RF GUN design

Vladimir Vogel | DESY | Ultra Bright Electron Sources Workshop .June 29, 2011|

Cold Linac (SC)

Normal temperature Gun

≠

RFcavityTRGP **~

#

2

low emittance -> high gradient

Dissipated power - low temperature

Gradient – new materials, (we have only one RF GUN !!!)

Motivation

2


Breakdown mechanisms

Breakdown & Pulsed Surface Heating Studies: Thermal Fatigue behavior versus Grain Orientationby Markus AICHELER (Ruhr-Universitaet Bochum)

3


Breakdown study, pulse DC

4


DC dark current

DC, 1 nA dark current

SS Cu Ti Mo

Fie

ld g

radi

ent (

Mv/

m)

0

20

40

60

80

100

120

gap 1 mm, F. Le Pimpec and al., NIM A 574 gap 0.5 mm, F. Furuta and al. NIM A 538

5


Gradient in the pressurized cavity.

Young modulus (10-10*N/m2)

10 20 30 40 50 60

E (

MV

/m)

40

50

60

70

80

90

100

110

Cu W Mo Be Ir

Maximum stable gradient as a function of the Young's modulus for different materials. RF frequency 805 MHz, Hydrogen pressure ~ 100 bar. (data from #) for Iridium, the approximation)

# ) R. Sah, A. Dudas and al., “RF Breakdown Studies Using Pressurized Cavities”PAC 2011, MOP046, NY, USA (2011)

6


Some property of pure metals in normal temperature

C Al Cu W Ta Nb Mo Cr Co V Ti SS Ir0

100

200

300

400

500

Thermal conduct. (W/m*K): --


102030405060

Yonngs module (10-10 * N/m^2): --


20

40

60

80

Resistivity (108*OHm*m): --


5

10

15

20

25

expansion (106 *1/K): --

7


Ranking materials: RF, high gradient

Temperature ~ 300 K

C Al Cu W Ta Nb Mo Cr Co V Ti SS Ir

10-1

9 (A

/m)*

(N/m

2 )

0

20

40

60

80

100

120

140

Ey*(llll/arararar)0.5

8


Temperature (K)

0 20 40 60 80 100

c p (

J/g*

K)

0.0001

0.001

0.01

0.1

1

Cu Mo

Thermal expansion

Temperature (K)

0 20 40 60 80 100

α *1

06 (

1/K

)

0

2

4

6

8

10

12

Mo Nb Cu

Thermal conductivity

Temperature (K)

0 20 40 60 80 100

λ (W

/m*K

)

0

100

200

300

400

500

Mo Nb Cu 0.1*(W/m*K)

L.A. Novickiy, I G. Kozhevnikov“Thermo physical properties ofmaterials in the low temperature region”Moscow 1975. In Russian

(Au, Ag, Ir, W, Pt…)

Helium 4.22 KHydrogen 20.3 KNeon 27 K

Some properties of pure metals in low temperature

9


Cupper, thermal conductivity

10


Electrical resistivity of Copper and Molybdenum

11


T

(K)

ρρρρ

(Ohm*m)

Cp

(J/kg*K)

λλλλ

(W/m*K)

δδδδ

(m)

Lt

(m)∆∆∆∆Ts ( K)

60 MV/m

P (W/m2)

60 MV/m

Cu

300 1.72*10-8 385 384 1.83*10-6 3.3*10-4 46.2 4.7*107

20~ 5*10-11

RRR~400~ 7 ~6000 9.8*10-8 9.8*10-3 4.6 2.5*106

Mo 20~ 8*10-11

RRR~600~ 3.5 ~360 29.2*10-8 3.2*10-3 32 3.2*106

W 20~ 1.2*10-10

RRR~450~ 2 ~ 1600 15.2*10-8 6.5*10-3 18 3.9*106

Ir 20~ 1.0*10-10

RRR~450~ 3 ~ 1900 13.9*10-8 5.3*10-3 11.3 3.5*106

DESY RF GUN5 (V. Paramonov, K. Floettmann,..)f =1300 MHz, Trf = 1 mS, Hpmax= ~ 100kA/m

Lt=(λ∗τ/(γ∗Cp))1/21/21/21/2

∆Ts=(τ*ρ*f*µ/γ∗λ∗Cp)1/2*(Hp)2

- FreyIr, Haefar “Tieftemperatur technologie” 1981, p. 5.1.1-1(11/74) - Л.А. Новицкий, И.Г.Кожевников “Теплофизические свойстваматериалов при низких температурах”, Moscow 1975.

Thermophysical properties of matter, IFI/PLENUM, NEW YORK-Washington 1970

Not included anomalous skin effect !!!

12

Thermal losses in the Gun for different materials


Anomalous skin effect

f*0πµρδ =

3/13/22

3/1

)8(3

πρ ∗∗∗∗=Λne

h

d/Ld/Ld/Ld/L, T=300 K

1.3 GHz

d/Ld/Ld/Ld/L, T=20 K

1.3 GHz

d/Ld/Ld/Ld/L

T=300 K

11.4 GHz

d/Ld/Ld/Ld/L

T=20 K

11.4 GHz

Q20/Q300

11.4GHz

Q20/Q300

1.3GHz

Cu 27 2.4*10-3 16 0.81*10-3 4.4 (exp)~ 6.2

(estim)

Mo 47 2.3*10-3 ~ 6

DESY GUN 560 MV/m ~ 6.18 MW

Cold GUN60 MV/m - ~ 1 MW

)()()(~ 3/1

2

NgRff

cR

an⋅⋅

⋅⋅Λ⋅= −

βρ

R ~ reflection factor for electronsN ~ RRR

dd dd300

300

300

300

LLLL300300300300

LLLL20202020

dd dd20

20

20

20

13


Conditioning of pure metals in pulse DC mode

14


Mo T=20 K

0

3

20

30020

≥

⋅≈

dT

dλλλ

0

1.0

20

30020

≥

⋅=

dT

dc

cc

p

pp

0

61

04.0

20

30020

30020

≈

⋅≈

⋅=

dT

dRs

RsRs

αα

No reason for the breakdown in standard BD model.

Temperature (K)

0 20 40 60 80 100

λ (W

/m*K

)

0

100

200

300

400

500

Working point Condition point~0.3 MHz Cu~0.15 MHz Nb~0.1 MHz Mo

Cold GUN, regimes for conditions and for the normal operation

15


Oversize cavity:

1. No tangential current for TM020, slot for cathodechanging, damp for HOMs

Example:TM020 in first half cellTM010 in second cell

2. More spaces for inputcouplers.

3. No cathode holder,direct Cs2Te film to thereplaceable part of cavity.

4.Cathode part of cavity canbe made from the othermaterial

RF GUN cavity design

16


Conclusion

The uncommon values of the thermal conductivity of some metals, such as Cu, Mo, W and Ir in the range of temperatures of approximately 20 degrees of Kelvin, will allow us to increase the accelerating gradient in the RF GUN and to decrease heat losses and dark current.

Conclusion

Thank you for attention!

17

Documents

Cold RF Gun - The Cockcroft Institute · Ir Maximum stable gradient as a function of the Young's modulus for different materials. RF frequency 805 MHz, Hydrogen pressure ~ 100 bar