Cell-Coupled Drift Tube Linac

Cell-Coupled Drift Tube Linac

M. Pasini, CERN AB-RF

LINAC4 Machine Advisory Committee 1st meeting CERN January 29-30, 2008

Contents• CCDTL concept and design• Beam parameters• Layout • Test and measurements of the CERN pre-

prototype• Test and measurements of the ISTC prototype• Summary


CCDTL concept and design CCDTL = Cell Coupled Drift Tube Linac

• • •

bl bl bl bl3/2 bl

•Accelerating gap and Drift Tubes do not change within the single tank•Quads are placed between the tanks not inside the DTs•Intertank spacing is constant (250 mm)

The resonating mode is π/2


250 mm

CCDTL mechanical design (1/2)


CCDTL mechanical design (2/2) Each accelerating tank is split in two halves The CCDTL half-tanks are made out of copper-

plated stainless steel, with cooling channels directly machined in the external part of the tank cylinder

Each half-tank contains a drift tube made in copper and cooled via the supporting stem

Vacuum seals and RF joints between half tanks and coupling cell are provided by “Helicoflex” type of gasket


Mechanical details


Beam Parameters

Particle H-

Initial energy 40 to 50 MeVFinal energy 90 to 102.5 MeVBeam Intensity 40 mA Duty Cycle SPL 5 %Duty Cycle LINAC 4 0.1 %Frequency 352.2 MHzFocusing Channel F0D0Synchronous phase -20 deg


CCDTL layout


CCDTL module

CCDTL Layout 50-102.5 MeVKlystron

[#]Cav/Kly

[#]Gradient[MV/m]

Energy[MeV]

Pow/Kly[MW]

Max Kilp.[#]

1 3 4 56.7 0.806 1.72 3 4.1 63.7 0.869 1.73 3 4.2 71.2 0.935 1.74 3 4.3 79.0 1.003 1.75 3 4.23 86.9 1.005 1.76 3 4.16 94.7 1.005 1.67 3 4.1 102.5 1.005 1.6

Average gradient 4.16 MV/m

Total length (including beam diagnostic)

24.96 m



N. Cav#

Cavity length[mm]

Drift tube length[mm]

Nose cone[mm]

Gap length[mm]

1 695.0 205.7 45.4 64.3

2 712.7 207.9 47.5 67.2

3 731.9 210.0 50.4 70.4

4 749.1 211.9 52.3 73.4

5 768.8 214.1 55.2 76.8

6 785.4 216.1 56.7 79.9

7 804.7 217.9 59.6 83.3

8 821.3 219.7 61.1 86.5

9 840.7 221.4 64.0 90.0

10 856.1 223.1 65.2 93.2

11 875.9 224.6 68.3 96.8

12 890.9 226.3 69.2 100.0

13 910.1 227.5 72.3 103.5

14 924.2 229.1 72.9 106.7

15 942.6 230.2 75.8 110.2

16 956.3 231.6 76.6 113.3

17 974.1 232.6 79.5 116.7

18 986.8 233.9 80.0 119.7

19 1004.5 234.8 82.8 123.1

20 1015.9 236.1 83.0 125.9

21 1033.4 236.8 86.0 129.3

Geometry details

Coupling factors – field stability Measured coupling factors from the prototypes at low

energy (40 MeV) k = 0.89% (simulated was 0.88%) Simulated coupling factors at high beta (100 MeV)

k = 0.52%50 kHz tuning error in 5 resonating cell


1 fixed tuner per half tank and 2 per coupling cell

1 moving tuner at low energy to compensate for temperature drift

2 moving tuners at high energy to compensate for temperature drift

∆T of 10 degrees should give a frequency variation of about 40 kHz (estimate)

Tuning requirements


CERN pre-prototype


Measurements resultsRa 1.2 µm

Q-value 27281k (coupling factor) 0.88%Field flatness error <1%


Q0=27281 which is 79% of Superfish (the plating is only in one half of the Helicoflex joint groove)

Spectrum Measurements


High power test area


Started with vacuum level of 10-8 mbar

Conditioning lasted less then 2 days

Max field achieved is 34.2 MV/m on the drift tube

Kp = 1.72 E0 = 4 MV/m

High Power Measurements


y = 1.0017xR2 = 0.9994

0

100

200

300

400

0 100 200 300 400

Pfw (kW)

Pcav

(kW

) The temperature on the cavity was monitored: at 0.1% duty cycle the

temperature was stabilized at around 30 deg with a minimum of 5 l/min water flow only in the drift tube. 7 kHz shift was observed in the resonance frequency

At SPL duty cycle temperature reached 58, 76 and 80 degrees in the drift tube holder, coupling iris and plunger tuner. In particular the temperature rise in the coupling iris is due to the over-coupled matching between waveguide and cavity; the resonant frequency decreased by 128 kHz from cold to hot condition.

Status of the ISTC prototype

BINP, Novosibirsk

RFNC-VNIITF, Snezhinsk


Measurements resultsRa 1.3 µm

Q-value 36700k (coupling factor) 0.9%Field flatness error <1%

Comparison of the field profile measurements done at CERN and at BINP (green)


Alignment checks


2

Alignment shaft

Alignment flange

Waveguide coupling measurements



Installation in the bunker and final tuning

Frequency: 0-mode 350.974 MHz π/2-mode 352.060 MHz π-mode 353.219 MHz k = 0.9%The frequency change of the π/2-mode after vacuum was +84 kHz. Q0=36700 which is 84% of Superfish value.

High power measurementsConditioning of the cavity lasted about 1 week. (An increased pumping capacity with an automatic conditioning routine will probably decrease the time for conditioning)After the conditioning we could easily put power inside the cavity in excess of 330kW at both Linac4 duty cycle (0.1%) and SPL duty cycle (5%). Nominal gradient requires 310 kW.The power was limited by the high voltage power supply (60kV instead of 100kV)The temperature on the cavity was monitored: at 5% duty cycle the temperature on the external part of the drift tube raised by 40 degrees, while tuners in the accelerating cells went up to 100 deg. C. The resonant frequency decreased about 80 kHz.


Summary A new layout of the CCDTL has been optimized Test and measurements of the CERN pre-

prototype and ISTC prototype are completed. The cavities didn’t show any limitation in reaching the nominal field and beyond.

For the LINAC4 duty cycle a limited amount of cooling water (~5l/m) is required for the drift tubes

For the SPL duty cycle additional cooling must be added in the tuners


Cell-Coupled Drift Tube Linac

Documents

Transcript of Cell-Coupled Drift Tube Linac