Status of X-band standing wave structure studies at SLAC

Question

1. What are the contributions in "Status of x-band standing wave structure studies at slac" ?

2. What is the effect of detuning the dipole modes within the structure?

3. How many MV/m of a SW structure can be used?

4. What are the main design requirements for a linear collider accelerator?

Accepted Answer

This paper discusses design considerations related to high power performance, wakefield suppression and results of high power tests of prototype standing wave structures.. Paper presented at the 2003 Particle Accelerator Conference ( PAC 03 ) Portland, Oregon, USA, May 12 16, 2003 Work supported by the U. S. Department of Energy contract DE-AC03-76SF00515.

Accepted Answer

Longrange wakefield suppression is achieved by detuning the dipole modes within the superstructure and damping them using azimuthially symmetric cells with fundamental mode chokes and internal loads.

Accepted Answer

It is desirable for the structures to be able to operate at unloaded gradients as high as 100 MV/m, to accommodate an NLC/JLC energy upgrade above 1 TeV using the same tunnel.

Accepted Answer

There are three main design requirements for a linear collider accelerator structure: the ability to sustain the working gradient, acceptable short-range wakefields, and suppressed long-range wakefields.

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Two of the structure types have elliptical iris tips to reduce the ratio of accelerating gradient Eacc to peak surface electric fields Epeak .

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The pair was conditioned with 2000 breakdowns in three days up 55 MV/m, 400 ns, where it ran with less then breakdown per hour for 150 hours.

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A typical operational gradient for standing wave (SW) structures of a medical linear accelerator is 30 MV/m, with surface electric fields of 130 MV/m [2] at a pulse width of several microseconds (longer than the working pulse width for SLAC TW structures).

Accepted Answer

Other requirements for the NLC/JLC accelerating structures include: operation at 120 Hz with a 270 ns flat top pulse (after the structure is filled with rf energy); no degradation of performance during decades of operation; andThis work was supported by the U.S. Department of Energy contract DE-AC03-76SF00515.less than one breakdown per 106 pulses per meter of structure [6, 7].

Accepted Answer

Single bunch wakefield effects limit the minimum average iris radius (a) of the structures to 4.7 mm, which is 18% of the X-band wavelength ( = 2.62 cm).

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The structures were aggressively processed and then run at the loaded NLC/JLC gradient (at that time 55 MV/m) with a 400 ns pulse widths (150 ns structure filling plus 250 ns flat top) at the NLCTA pulse repetition rate of 60 Hz.

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The mechanism of the surface heating also needs verification, since other effects, like single surface multipactordischarge in strong rf magnetic fields could also increase surface the temperature.

Accepted Answer

With such a connection the rf power reflected from the structures is directed to a high power load (during filling and decay time).

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Operational tests of these structures showed irreversible damage at an input power levels of 70 MW and an average gradient of about 45 MV/m (250 ns) [4].

Accepted Answer

These breakdowns may be related to the high rf magnetic and moderate rf electric fields on the sharp edges at the waveguide-to-coupler cell opening.

Accepted Answer

They will likely have a lower breakdown rate and less breakdown damage due to their reduced maximum surface electric fields and lower rf power absorbed per breakdown than TW structures at the same loaded gradient.

Accepted Answer

The experience gained with the first pair prompted us to reduce the field (both magnetic and electric) in the coupler cell (relative to the field in the rest of the cells) by 15%.

Status of X-band standing wave structure studies at SLAC

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Most frequently asked questions

1. What are the contributions in "Status of x-band standing wave structure studies at slac" ?

2. What is the effect of detuning the dipole modes within the structure?

3. How many MV/m of a SW structure can be used?

4. What are the main design requirements for a linear collider accelerator?

5. What are the design parameters of the structures?

6. How many breakdowns did the pair have?

7. What is the average operating gradient for a slac rf gun?

8. What is the rf energy required to operate a synchronous accelerating structure?

9. What is the maximum iris radius of the structures?

10. What is the iris radii of the first SW structure?

11. What is the mechanism of the surface heating?

12. What is the rf power reflected from the structures?

13. What is the average accelerating gradient of a linac?

14. What is the reason for the breakdowns?

15. What is the difference between the two structures?

16. How much field did the first pair reduce?

Figures

Citations

RF Breakdown in Normal Conducting Single-Cell Structures

Recent Studies of RF Breakdown Physics in Normal Conducting Cavities

Travelling wave and standing wave single cell high gradient tests

Travelling wave and standing wave single cell high gradient tests

Investigations on the multi-sector hard X-Band Structures

References

Medical Electron Accelerators

RF pulsed heating

2001 Report on the Next Linear Collider

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