# Presentation: 274051

## E853 Crystal Extraction at the Tevatron

- CERN mini-workshop on  crystal collimation
- March  7-8 , 2005
- Dick Carrigan

- see Carrigan, Mokhov, et al., Phys. Rev. ST Accel. Beams AB 1, 022801 (1998) 	_[http://prstab.aps.org/abstract/PRSTAB/v1/i2/e022801](http://prstab.aps.org/abstract/PRSTAB/v1/i2/e022801)_
- Carrigan, Mokhov, et al., Phys. Rev. ST. Accel.  Beams, AB **5**, 043501 (2002)
- 	_[http://prst-ab.aps.org/abstract/PRSTAB/v5/i4/e043501](http://prst-ab.aps.org/abstract/PRSTAB/v5/i4/e043501)_
- (see these for collaborators)

- E853-Crystal Extraction   January, 2000

**Notes:**
Abstract: Luminosity-driven channeling extraction was observed for the first time in a 900 GeV study at the Fermilab Tevatron carried out in the 1995-1996 period. This experiment, Fermilab E853, demonstrated that useful TeV level beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors. Multipass extraction was found to increase the efficiency of the process significantly. The beam extraction efficiency was about 25%. The history of the experiment will be reviewed. Special attention will be paid to results related to collimation.

## E853 history and goals

- History – In early 1990s, proposal for an SSC fixed target B flavor experiment. Crystal proposed for extraction. E853 given $100K to test at Tevatron. Used existing C0 dump – not needed at 900 GeV. A location with more dispersion would have helped longitudinal noise excitation

- Goals
- Extract 106 protons/s with 1012 circulating
- Study extraction efficiency
- Show luminosity lifetime not affected
- Investigate background at CDF and D0

- E853-Crystal Extraction   January, 2000

**Notes:**
In the early 1990’s a fixed target experiment was proposed for the Superconducting Super Collider to study heavy‐flavor physics using a tiny fraction of the 20 TeV circulating beam extracted with bent crystal channeling. Conventional methods of beam extraction at such high energies posed problems with no obvious cost‐effective solutions. Since the new extraction scheme proposed for the SSC was not a proven technique, E853 at Fermilab was designed to study the feasibility of this approach. E853 was given $100K to test extraction at the Tevatron. 
The goals of E853 were to extract one million 900 GeV/c protons/second with 1012 protons circulating in the Tevatron, to study the extraction efficiency, to show that the luminosity lifetime of the circulating beam was not adversely affected, and to investigate the backgrounds created at the two Tevatron collider experiments. Losses at these major collider experiments, CDF (one sixth of the ring upstream for protons) and D0 (one sixth of the ring downstream), had to be kept to a tolerable level. A central concern for E853 operation was that losses be minimized so that the superconducting Tevatron magnets were not quenched. 

## E853 Successes

- Extracted significant beams from the Tevatron
- 	parasitic, kicked and RF stimulated
- First ever luminosity-driven extraction
- Highest energy channeling ever
- Useful collimation studies
- Extensive information on
- 	time-dependent behavior
- Very robust

- E853-Crystal Extraction   January, 2000

**Notes:**
Parenthetically, this could well have been the most successful and effective experiment of the entire ill-fated SSC program. Some of the E853 successes included extracting significant beams from the Tevatron in parasitic, kicked, and RF-stimulated modes. The experiment made the first-ever and actually only observation of luminosity-driven extraction. This was the highest energy channeling ever observed. Useful collimation studies were carried out and extensive information was developed on time-dependent behavior. All-in all the operation of the crystal septum was very robust. 
There were significant constraints on where an inexpensive, parasitic extraction test could be placed in the Tevatron lattice. Any modification of the Tevatron vacuum system is expensive and requires rigorous attention to maintaining a very high vacuum. The C0 long straight section was chosen for E853 because it contained an existing 900 GeV abort system with an associated extraction line and dump that was not to be used in the 1994-1996 running period except at 150 GeV during collider injection tests. In addition there was free space along the abort beam line for instrumentation and cabling to a portakamp complex above ground for electronics and data acquisition. While this choice turned out to be quite successful it did have a problem. It would have been interesting to have more dispersion at the crystal so that longitudinal noise excitation studies could have been carried out.

## Topics

- E853 – the Fermilab-SSC crystal extraction experiment
- Extraction
- kick mode
- luminosity-driven
- rf driven
- fiber-driven
- Collimation

- E853-Crystal Extraction   January, 2000

**Notes:**
The topics covered below include the details of crystal extraction experiment. In addition the results for kick mode, luminosity-driven, RF-driven, and fiber-driven extraction will be reviewed. Information bearing on collimation will be discussed. Most of the information on channeling and time dependent effects will be omitted.Fix references

## Tevatron complex

- D17 scraper

- E853-Crystal Extraction   January, 2000

**Notes:**
Figure 1 shows the devices used for the E853 test in the Tevatron complex. E853 was at C0. Note the two colliding detectors CDF and D0. Loss monitors at these detectors were continuously monitored. There were scrapers at A0 and D17. A set of flying wires at E0 and E17 measured the beam size but also were used for fiber extraction. The damper at F1 was used for RF extraction. The E17 kicker provided a fast extraction device. 

## C0 at the time of E853

- U counters

- E853-Crystal Extraction   January, 2000

**Notes:**
Figure 2 shows the layout near C0. The abort magnet string replaced by the E853 crystal consisted of four 1.8 m long kicker modules with peak fields of 3.7 kG giving a vertical deflection of 640 μrad. Removal of the upstream kicker module provided sufficient space for the crystal goniometer. The bent crystal was on the outside of the ring and deflected protons up through the quadrupoles (Q) into the field-free region of the Lambertson magnets. Extraction consisted of two parts: a vertical kick into the field-free region of a Lambertson magnet string and horizontal separation of the circulating beam from the extracted beam by the Lambertsons. After the Lambertson magnets the extracted beam traversed two instrumented air gaps approximately 100 meters downstream of the crystal and then entered a beam dump. Air gaps, separated by 40 meters, were instrumented with several scintillators. Thin movable counters could scan the beam profile. A fluorescent screen coupled to a CCD camera in the first air gap also provided a digital readout of the beam‐profile for run‐time diagnostics. There was already a segmented‐wire ion chamber (SWIC) in the second air gap as well as a toroid to measure beam current.

## First crystal extraction at the Tevatron C0 straight section June 6, 1995 (kick mode)

- E853-Crystal Extraction   January, 2000

**Notes:**
Kick mode was employed in the initial sessions of E853. The basic technique was to move the crystal in to a predetermined horizontal location close to the beam (4.5 to 6 x from the beam center). The beam was then kicked horizontally a number of times by a fast kicker at E17 (see Fig. 1). At this distance from the crystal, the beam density was so small that no beam was observed to interact with the crystal on the first few kicks. However, after several hundred turns following a kick, the beam had grown in size as non-linearities in the machine gradually spread the beam to fill much of the phase space mapped out by the betatron oscillations. After about six such kicks, the beam size had grown by a factor 1.7 in the horizontal plane and a factor 1.2 in the vertical plane (resulting from the horizontal/vertical coupling in the Tevatron). 
The next figure shows fluorescent screen images of the extracted beam for the very first extraction using kick mode. Theta V was swept up through a 230 μrad scan, from 130 μrad below the peak to 100 μrad above the peak. The length of the dechanneling tail grows in the successive panels because the beam spot moves up and the Lambertson magnet aperture eclipses less of it. For scale, the width of the dechanneling tail is 3 mm.

## Luminosity-driven extraction

- Mechanism - colliding bunches produce scattering that drives particles from the core out into the halo. Normally scraped by collimators.
- Early on we noticed extraction rate higher when colliding for crystal at same distance from beam.

- E853-Crystal Extraction   January, 2000

**Notes:**
The second extraction technique was called “diffusion mode”, relying on either natural or stimulated diffusion during proton-only stores andpp collisions parasitic to collider operations. This diffusion was due to such effects as beam-gas scattering, beam-beam scattering and tune shift effects, magnetic field ripple, and imposed RF noise. In this mode, the crystal was slowly moved into the tail of the beam halo. Movement of the crystal was halted when an extraction rate adequate for the studies had been achieved. When operating parasitic to collider operations, this mode did not seriously affect the circulating proton beam lifetime.
Luminosity-driven extraction
Early in the E853 runs we noticed that the extraction rate was higher when the beams were colliding for the crystal at same distance from beam. This was the first evidence for luminosity-driven extraction. This occurs because the colliding bunches produce scattering that drives protons from the beam core out into the halo. During collider runs this is normally scraped by the collimators. Indeed, it is the largest source of beam related background at a collider detector.

## Technique for luminosity-driven extraction

- Would like equivalent of target in-out
- Tried cogging, displacement of anti-proton beam, or missing anti-proton bucket
- used missing pbar buckets
- 36 proton bunches of which 6 collided with 3 pbar
- Looked with two variable delay gates covering colliding or non-colliding buckets.
- Typically O(50*109 /bucket)
- Recorded bunch charge, size, some D0 luminosities

- E853-Crystal Extraction   January, 2000

**Notes:**
Since several factors such as beam-gas scattering influenced the extracted beam rate it was interesting to isolate luminosity from other effects. The equivalent in a fixed target experiment would be a target in-target out measurement. Several approaches were considered; 1) changing the arrival times of the proton and antiproton bunches at the interaction points so they did not collide (cogging), 2) displacing the antiproton beam at the interactions points, and 3) eliminating some of the antiproton bunches and thereby removing the “target”. All of these required semi-dedicated running. Cogging was tried several times and led to ambiguous results because the proton beam invariably moved transversely at some point during the exercise due to lattice dispersion. No opportunity arose to try displacing the antiproton beam, but it might not have worked for the same reason cogging did not work. The approach which worked was to run with a special store with 36 proton bunches of which only six were colliding with three antiproton bunches. Note that there were two separate sets, one with CDF and D0 buckets combines, later done separately. Steady drop required moving in by 300 microns for second set.

## Yield vs bunch

- Abscissa: time in microsec
- Histograms are measured
- Dots are calculations

- Session 1

- Session 2

- E853-Crystal Extraction   January, 2000

**Notes:**
The extraction rate was also studied as a function of luminosity. Only 6 of the proton bunches were colliding with antiprotons. Colliding and non-colliding proton bunches were observed during the same counting interval by employing two gates triggered on different bunches. With a typical bunch luminosity of 0.4•1030 cm-2s-1 and typical circulating proton and anti-proton bunch intensities of 4 to 6•1010 the extracted beam rate increased by factors of 4 to 8 for proton bunches that were colliding. The extraction rates resulting from collisions at CDF and at D0 were about the same. 
Two sets of measurements were taken. In the first set an effective gate consisted of three windows each of 470 ns spaced evenly over a turn. Two such independent gates were used. Typically one of the two gates was set on a colliding bunch and the other on a non-colliding bunch. With this arrangement collisions were detected that resulted from both the B0 and D0 interaction regions (set 1). Halfway through the measurements a different arrangement was adopted with only one window (rather than three equally spaced ones) to see the individual effects of D0 and CDF (set 2).
The count rate difference between colliding and non-colliding buckets is illustrated in the figure. The measured count rates are compared to calculated rates based on luminosity plus an averaged background. Measured count rates are shown as histograms with the widths of the gates. Colliding cases are shown as solid histograms while proton-only cases are dashed. The difference between colliding and non-colliding buckets is clearly visible. It is clear that luminous bunches produce substantially more extracted beam.ote that there is a non-luminosity background, as expected. Measured count rates are histograms. Dots are predictions based on individual bunch luminosities. Make point that luminous bunches are substantially higher.

## Results

- Colliding bucket yield is 4 times larger on average
- Increasing by factor of 4 equivalent to moving crystal in by 0.4 mm or 0.7 σx
- This is the flux a crystal collimator must address

- E853-Crystal Extraction   January, 2000

**Notes:**
Luminous bunches increased the rate to give a luminosity on/off ratio of 4.1. One way to quantify the luminosity on-off ratio is to ask how far the crystal would have had to be moved in to match a non-luminous bunch to the original luminous rate. Increasing the non-luminous count rate by a factor of 4 at xg = 2.5 mm was equivalent to decreasing xg by 0.4 mm or 0.7 sigmax.

Typically 1012 protons were circulating in six bunches in the luminosity-driven stores. The extraction rate was roughly 150 kHz. In this mode the limitation was the impact of particles scattered from the crystal in creating backgrounds for the operating collider experiments. Although the CDF experiment upstream of the crystal received no measurable background from the crystal, the D0 “lost proton” monitor was sensitive to scattering from the crystal. D0 was usually already running at 80% of the conservative upper limit set by that experiment before the crystal was moved close to the beam and reached the limit when the extraction rate was between 50 and 150 kHz. However for a special end of store with D0 not taking data and 3•1012 protons circulating an extraction rate of 900 kHz was achieved. The D0 lost proton monitor exceeded its upper limit by a factor of 1.5 before the crystal was inserted, and exceeded the limit by a factor of two after the crystal was inserted.
Note that the luminosity driven extraction is directly related to the principal collimation problem at the Tevatron and LHC.Note that increase as a function of luminosity

## RF driven extraction

- Technique
- transverse white noise RF using horizontal damper at F11.
- Very powerful effect
- used special 84 bunch train
- small finger counters to cut accidentals and saturation.

- E853-Crystal Extraction   January, 2000

**Notes:**
A horizontal damper located at F11 was also used in two E853 sessions to introduce RF noise in transverse phase space and thereby stimulate diffusion and increase the extraction rate. This characteristically decreased the beam lifetime substantially although it was still long enough for a typical study session. Significantly higher extraction rates were observed with the noise on. This approach could not be used for parasitic extraction owing to its destructive effect on the circulating beam. 
The effect of turning the RF on or off was almost immediate and had a significant effect on the extracted beam. It was so significant that these tests were complicated by saturation problems in the larger principal counters even in a special proton-only store with 84 rather than 6 circulating bunches. However the small finger counters showed little or no evidence of saturation and also had a low background rate with noise off. Use only one slide and combine with fiber, etc.

## Results

- Rate was proportional to V2
- expected from equations of motion in action angle variables (John Marriner)
- Rise time O(2-3 s), decay time O(10 s)
- Compared to luminosity case:
- factor of 4 from proton only to luminosity at 0.5*1030cm-2s-1 requires RF voltage of 2.1 V.

- E853-Crystal Extraction   January, 2000

**Notes:**
The rate was proportional to V2 as expected from the equations of motion in action angle variables (John Marriner). Typically the rise time was on the order of 2-3 s and the decay time was of order 10 s after the beam was turned off.
It is interesting to compare luminosity and RF-driven extraction. This can be done by comparing the ratio of the rate with the driver on to the rate with no driver under the same conditions. As noted in the last paragraph this ratio was 4.1 for Lpa = 0.5•1030 cm-2s-1. In the RF-driven case discussed in section VIII the rate for the finger counter coincidence is R = 15.2•Vrf2+22. A ratio of 4 is obtained for Vrf = 2.1 V. 

## Fiber-driven extraction

- Asseev concept-use fiber at edge of beam to multiply scatter halo out to the crystal.
- Demonstrated at Serpukhov
- E853 saw a substantial signal in the crystal extracted beam from the 30 micron C flying wires at E11 and E17.
- This is not Asseev concept since there is both edge and core scattering. However did see the edges of the beam so could establish the process was practical.

- E853-Crystal Extraction   January, 2000

**Notes:**
At Serpukhov Asseev demonstrated the use of a fiber at the edge of beam to multiply scatter halo out to the crystal. In E853 we saw a substantial fast signal in the crystal extracted beam from the 30 micron carbon flying wires at E11 and E17. This is not the Asseev process since there is both beam edge and core scattering. However we did see the edges of the beam so that we could establish the process was practical in the Tevatron.

## Mechanism

- Fiber perturbs beam in two ways
- multiple scattering-small
- nuclear interactions (about one in 105)
- 1 in 300-angle small enough to stay in Tevatron
- With a flying wire - have nuclear scatters, unlike Asseev concept where multiple scattering over many collisions grows the beam.
- The rate was consistent with efficiency observed in other parts of E853.

- E853-Crystal Extraction   January, 2000

**Notes:**
The fiber perturbs the beam in two ways. There is normal multiple scattering. There are also nuclear interactions at the level of about one in 105 passes. About 1 in 300 of these nuclear scatterings are at an angle small enough to stay in Tevatron. For the Tevatron flying wires it is these nuclear scatters that give rise to the early extraction signal, unlike the Asseev concept where multiple scattering over many collisions grows the beam. The flying wire extraction rates were consistent with the efficiency observed in other parts of E853.

## Beam halo effects

- Number of kicks to move beam out
- 5-7 kicks for beam to crystal distance of 3.5 mm, 10 kicks for 4.5 mm
- Moving crystals or collimators gives information on halo
- retracting crystal 200 microns cut signal by 4. In 2 minutes recovered somewhat.
- moving in-initial spurt for several minutes followed by 1/e decays of 0.5 to 5 hours

- E853-Crystal Extraction   January, 2000

**Notes:**
In E853 moving the crystal or the collimators gave information on the beam halo and an insight into how effective crystal collimation might be. Characteristically it took 5-7 kicks to produce extracted beam for a crystal to beam separation of 3.5 mm. When the crystal was retracted 200 microns the signal was typically cut by 4. The extraction rate recovered in several minutes. There was an immediate rise when the crystal moved in followed by 1/e decays of 0.5 to 5 hours.

## Collimation

- Extraction rate depended on shadowing of crystal by collimator
- 5 mm retraction to behind collimators  precipitously cut rate
- Characteristically the D0 proton loss rate rose by 5% to 20% as the collimators were opened.

- E853-Crystal Extraction   January, 2000

**Notes:**
We also studied collimation effects. Positioning of the three scraper collimators at D17 and A0 used to protect the collider experiments from beam halo was clearly interwoven with crystal position. When the crystal was effectively closer to the beam than the collimators the situation was different than when the crystal was shadowed by the collimators and diffusing beam was mostly lost on the collimators. For example a 5 mm retraction of the crystal (to well outside the collimators) lowered the rate precipitously, and even after 20 minutes there was no sign of increase.
In three study sessions the collimators were retracted almost simultaneously in small steps (typically 100 μm) near the end of the sessions by total amounts that varied from 0.5 to 1.2 mm. The figure illustrates the results for one of these sessions. In all cases the extraction rate rose, but the rate of rise as a function of collimator position varied. This may have been a result of the fact that the collimators did not have the same initial settings in the three sessions. For example in sessions with crystal-beam separations of 5.3 and 5.5 mm the rate of rise per mm was in the 1-1.5 per mm range. Characteristically the D0 proton loss rate rose by 5% to 20% as the collimators were opened.
Studies of the time to reach equilibrium after a collimator move were complicated by relatively quick collimator changes with few measurements taken between adjustments. The time required to adjust the three collimators (on the order of 10 s) was also a limitation. Fast time plots and counting rate information indicated an initial fast rise of the count rate in less than 30 s, and perhaps much less. Information is available on only one relatively long quiescent period after a collimator move. Twenty minutes after completing a collimator moving session that had lasted 13 minutes the rate had risen by 30% (four times the estimated standard deviation of the measurement).

## Fermilab E853 Summary

- 0.12 MHz parasitic luminosity-driven extraction demonstrated
- 5-10 MHz parasitic beam possible during TeV Run II
- RF and fiber-driven extraction seen
- Useful collimation information

- E853-Crystal Extraction   January, 2000

**Notes:**
E853 produced results in a number of areas. Parasitic luminosity-driven extraction was demonstrated and produced extraction rates in the 100 kHz range without unduly disturbing the collider detectors. For the same conditions this could potentially produce a 5-10 MHz parasitic extracted beam for TeV II conditions. RF and fiber-driven extraction were also investigated. Useful collimation information was developed.

## E853 Experience

- Bad:
- Interaction counters very sensitive to beam motion
- Beams in the 108 - 109 regime need special instrumentation
- Beam halo behavior is often non-linear
- Lattice location important (RHIC – difficult, Tevatron better but imperfect)

- Good:
- Crystal extraction works well, robust
- Extraction in diffusion modes means crystal collimation can work
- Multiple pass works, can take bigger goniometer steps

- Neutral:
- Large variety of time dependent behavior

- E853-Crystal Extraction   January, 2000

## Thank you

- E853-Crystal Extraction   January, 2000