Axial Power Input in Photocathode Electron Guns

Radiation Source ELBE

Mitglied der Leibniz-GemeinschaftDietmar Janssen

Axial Power Input in Photocathode Electron Guns

D. Janssen, FZR, Germany, V. Volkov, BINP, Novosibirsk, Russia,



Cathode

RF cavity

Beam tube

In normal and superconductingRF guns the cathode can be separeted by avacuum gap from the surrounding cavity

Idea: This gap can be used for coaxial input of RF power

Advantages: - No additional RF input coupler necessary- No emittance growth by nonsymmetric RF fields in the coupler plane- No RF losses by the coaxial line around the cathode- Optimal arrangement of magnetic coils in the normal conducting case is possible- Easy to make the RF input variable by a quarter wave filter in the superconducting case

Vacuum gap

Power input in RF guns



(1) Niobium Cavity(2) Choke Flange Filter(3) Cooling Insert (4) Liquid Nitrogen Tube

(5) Ceramic Insulation(6) Thermal Insulation(7) 3 Stage Coaxial Filter(8) Cathode Stem

Beamline Preparation Chamber

68 7

1 2 3 4

5

First operation of a SRF gun

D.Janssen et al., NIM-A, Vol. 507(2003)p314-317

T = 4.2K, Q = 2.5*108, Ezmax= 22MV/mE = 900keV, I = 520μA

RF powerinput



New SRF Gun – Cavity design

He-vessel

power coupler

HOM filter

gun half-cell

choke filter

cathode

cathode cooler

LN2 reservoir

Cathode transfer rod

PosterWPAP007



Main coupler flange

Pic-up flange

HOM coupler

HOM coupler

Coupler plane of the cavity



Beam tube with higher order mode – and main coupler

HOM coupler(TESLA design)

Main couplerMax. power 10kWDesign M.ChampionDevelopment of HEPL, Stanford



RF power input around the cathode

Power input

Power input

Warm RF window

LN2 cooling

Tube for cathode exchange

Cold RF window

cavity

cathode

Bellows for adjustment of Qext and heat isolation

End of the cryostat

Quarter wave choke

L

Δz



External quality factor and heat load of a cathode-RF coupler

3.6 3.8 4.0 4.2 4.4

0

10

20

30

40

50

60

70

80

90

100

1103.6 3.8 4.0 4.2 4.4

106

107

108

109 Heat load of the cathode Beam power

Hea

t loa

d of

the

cath

ode

[W],

beam

pow

er [k

W]

Width z of the choke cell [mm]

Ext

erna

l qua

lity

fact

or

External quality factor

Field parameters for Eacc = 25MV/mEzmax(r=0) = 50MV/m, Urmax= 6.5kV

Esmax= 43.6MV/m, Bsmax= 0.11T



Summary

In RF electron guns a coaxial gap between cathodeand cavity can be used for RF power input.

This special input coupler-is easy adjustable,-create no additional emittance growth and-produce in the superconducting case a small heat load even at large RF power

Axial Power Input in Photocathode Electron Guns

Documents

Transcript of Axial Power Input in Photocathode Electron Guns